Trilobite Evolutionary Faunas
1University of Iowa
Evolutionary faunas were defined by Sepkoski as "sets of higher taxa...that have similar histories of diversification and together dominate the biota for an extended period of geologic time." Trilobite evolutionary faunas were first explored (in 1998 and 2004) using intervals of the Ordovician, with families as units of analysis and genus occurrence by interval as data. This resulted in the proposal of the Whiterock and Ibex faunas. It is now possible to explore evolutionary faunas at the species level across the group's entire history. A taxonomic database compiled from the primary literature, with ongoing systematic revision, indicates that 21,889 valid trilobite species have been proposed, distributed among 4,025 genera and 165 families. Multivariate analyses using families as units, 37 temporal intervals from Early Cambrian to end-Permian as variables, and species diversity by interval as data, indicate that all known trilobites belong to one of six evolutionary faunas. Three that had previously been detected using Ordovician data (previously termed the Whiterock Fauna, and the Ibex Fauna I and II) are confirmed by the new analyses; three others, not previously recognized, are apparent in the Cambrian. Three of the faunas originated in the wake of significant mass extinction events.
Life at the end of the Boring Billion: microfossil record from the ca. 1 Ga Bylot Supergroup, Arctic Canada
1University of California Santa Barbara, USA
2McGill University, Canada
3Stanford University, USA
4Australian Resources Research Centre, Australia
The Mesoproterozoic–Neoproterozoic transition marked the end of environmental and evolutionary stability of the “Boring Billion”. This interval was characterised by gradual oxygenation of shallow marine environments, assembly of Rodinia, and appearance of crown-group eukaryotes. However, the number of studied stratigraphic units of this age is limited. High-resolution micropalaeontological and palaeoenvironmental analyses were conducted on the Bylot Supergroup (Borden Basin, Arctic Canada) to evaluate eukaryotic diversity in this poorly studied interval. Well-preserved organic-walled microfossils occur throughout siliciclastic sediments of Arctic Bay and Iqqittuq formations that are constrained by Re-Os geochronology to ~1.05 Ga. The recovered microfossils include diverse prokaryotes and eukaryotes, including Culcitulisphaera revelata, Fabiformis baffinensis, Microlepidopalla mira, Satka favosa, Squamosphaera colonialica, and 3 new taxa with striated vesicle wall. Stratigraphic range of the late Tonian C.revelata–M.mira association is extended to late Mesoproterozoic. Moderate diversity was recorded within the restricted basin facies of the Arctic Bay Formation. The transitional, shallower facies of the Iqqittuq Formation host the most diverse assemblage. The nadir of microfossil diversity co-occurs with a positive δ13Ccarb excursion (-4 to +3‰). This new biostratigraphic record indicates that several characteristic Tonian taxa appear 200 myr earlier, and eukaryotes were more diverse around 1 Ga than previously known.
The contrasted early evolution of taxonomic richness and morphological disparity of the Ammonoidea: The Devonian record from Morocco
1Univ. Lille, CNRS, UMR 8198 – Evo-Eco-Paleo
Within the Anti-Atlas of Morocco the Devonian ammonoids are particularly abundant and well preserved. These rich faunas are well documented in the literature, and this fossil record can help to constraint the palaeobiodiversity fluctuations that characterize the macroevolution of the early Ammonoidea during the Devonian period. With the aim to better understand the response of these organisms to the environmental perturbations identified during the Devonian (e.g. anoxic events), a database was constructed to analyze both, the taxonomic diversity and the morphological disparity of these organisms. Diversity can be measured in different ways and for any taxonomic rank. For this study, the taxonomic richness (species and genus) was investigated, and several standard indices based on incidence data were calculated to quantify this signal of diversity. The morphological disparity was analyzed considering three modules (the shell geometry, the aperture outline and the suture line shape), which were quantified by standard linear measurements and by geometric morphometrics. Finally, this study compares, at the substage level, the taxonomic richness and the morphological disparity patterns observed for the Moroccan ammonoids, through the Devonian time interval.
Evolutionary adaptation to aquatic lifestyle can lead to systemic alteration of bone structure
1Humboldt Universität zu Berlin
2Muséum national d'Histoire naturelle (MNHN, CNRS, UPMC, Sorbonne Université)
Bone inner structure in tetrapods is marked by lifestyle adaptations. Those of shallow-diving taxa are the best understood, and associated with postcranial bone mass increase (BMI). However, the potential implications of these adaptations on the cranial anatomy are not known. Here we show that the Mio-Pliocene (semi)aquatic sloth Thalassocnus was affected by systemic BMI, which leaded to changes in cranial structures as aberrant as dramatically thickened turbinates (usually paper-thin bones of the nasal cavity). We used micro-computed tomography to compare endocranial structure among the species of Thalassocnus, including early T. natans (postcranium with incipient BMI), middle T. littoralis (postcranium with intermediate BMI), and late T. carolomartini (postcranium with strong BMI). In the late species, the whole skull is osteosclerotic (denser), notably involving the infilling of frontal sinuses with solid bone. A gain of fitness from pachyostotic turbinates being implausible, they likely are a secondary consequence of the systemic BMI. In addition to leading to a systemic modification of bone structure, we thus suggest that such an evolutionary adaptation can involve evolutionary byproducts. An understanding of the whole skeleton’s structural adaptations should be acquired before drawing (paleo)biological interpretations related to the structure of some skeletal elements.
A mineralogical signature for Burgess Shale-type preservation
1All Souls College, University of Oxford
2Department of Earth Sciences, University of Oxford
3Department of Geology and Geophysics, Yale University
4Geology Department, Pomona College
5Peabody Museum of Natural History, Yale University
Burgess Shale-type (BST) fossils provide essential evidence of the early evolution of complex life, as they include organic remains that usually decay. Despite its importance, the factors contributing to BST fossilization remain controversial. Sediment composition—in particular clay mineralogy—has been one of the hypotheses championed. We provide the first major data set exploring the association of clay mineral assemblages with BST fossils based on X-ray diffraction data from 213 Cambrian shales over 19 successions on four different continents. Samples containing BST fossils have a constrained clay mineralogy compared to those containing only mineralized fossils. Logistic regression and classification tree methods show that BST fossils are associated with sediments containing higher abundances of berthierine/chamosite and lower amounts of celadonite and illite, likely reflecting a high kaolinite/smectite ratio in the original sediment combined with high iron concentrations during early diagenesis. BST preservation was influenced by a combination of unusual diagenetic conditions as well as palaeogeographic/climatic factors. Statistical methods using clay mineralogy can predict which lithologies will preserve BST fossils with ~80% accuracy, providing a potential tool for narrowing the search for carbonaceous fossils on Earth and possibly Mars.
A new chroniosuchian (non-amniotic tetrapod) from Laos revealed by micro-CT scan: anatomy and palaeobiology.
1CNRS - MNHN
2University of Washington
Chroniosuchians, a clade of non-amniotic tetrapods similar in overall body shape to modern crocodiles, are known in Germany, Kyrgyzstan, Russia and China, from the middle Permian to Late Triassic. The rarity of complete or articulated specimens implies that relatively little is known on this group in terms of anatomy, paleobiology, or evolutionary history.
A new genus and species of chroniosuchian is described based on a nearly complete skull and articulated left hemimandible, from rocks preserving the PT boundary of the Luang-Prabang Basin of Laos. This specimen is one of the best-preserved chroniosuchian skulls and the first fossil amphibian discovered in Laos. Its discovery reveals an unexpected geographic extension of the group in southeastern Pangea, and provides new insights about chroniosuchian paleobiology and paleoecology.
In particular, CT scan data reveal internals canals observed in the skull roof and the hemimandible with two morphologies: 1) simple canals interpreted as internalized sulci belonging to the lateral system; 2) ramified canals may be involved in the detection of surface waves generated by prey moving in water. Our interpretation of these canals suggests an amphibious life style for the Laotian chroniosuchian.
PUNCTUALISTIC DISPARITY PATTERNS AND STEP-WISE BODY PLAN CANALIZATION IN EUARTHROPODS
1Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, Ontario M5S3B2, Canada
2Department of Natural History (Palaeobiology Section), Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario, M5S2C6, Canada
3Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, 39, East Beijing road, 210008 Nanjing, China
Reconstructing patterns of macroevolution has become a central endeavor in palaeobiology, as it offers to comprehend evolutionary models shaping the history of life. As the most diverse and abundant animals since the Cambrian period, arthropods constitute ideal data to elucidate the emergence of body plans in metazoan lineages, but this effort has so far been impeded by the uncertain role of fossils in the structuration of the underlying morphological patterns. Using a current cladogram including fossil and extant taxa and its corresponding morphological matrix, I here describe disparity patterns in Euarthropoda, in light of exceptionally fast evolutionary rates known to characterize the base of extant clades. Quantified morphology shows that extant euarthropods evolved from a trilobitomorph supercluster by successively reduced punctualistic events, forming more constrained morphogroups, with the exception of malacostracans. A change in the mode of disparity is also consistent with the expectations of mosaic evolution. Such patterns suggest that extant euarthropod body plans arose during the Cambrian through large displacements of adaptive landscape optima, accompanied by relatively increasing—but not irreversible—developmental canalization. This would explain the great stability of extant euarthropod body plans over the Phanerozoic, in contrast to shorter-lived stem lineages with sub-optimal relative fitness.
The Middle Devonian Kačák Event: its identification and effects in Northern Spain
1University of Sheffield
The Kačák is an extinction event at the base of the Givetian Stage (Middle Devonian) associated with marine transgressions and benthic anoxia. It is best documented in central Europe and the Americas but is believed to be of worldwide distribution. Here we identify the Kačák Event in Northern Spain, document its effects and consider its cause. The Devonian sequence of Northern Spain accumulated in a relatively isolated setting in Peri-Gondwana. It is extensive, relatively complete and entirely marine. The coeval Naranco, Huergas and Gustalapiedra formations of Asturias, Léon and Palencia are Eifelian-Givetian in age and span the Kačák Event. Palynological analysis has yielded an extensive record of marine (acritarchs, chitinozoans, scolecodonts) and land-derived (spores) palynomorphs. Their biostratigraphy, allied with sedimentological and palaeoenvironmental analysis, suggests a period of acute environmental change. This is represented by rapid, cyclical sand and silt deposition, temporarily supplanting the background limestone deposition. The disruption immediately follows the Kačák Event, suggesting a close link between the extinction event and the palaeoenvironmental upheaval taking place in Northern Spain. These findings support an existing hypothesis postulating that the Kačák Event represents the creation of a monsoonal climate, which greatly increased terrigenous input to the oceans, devastating marine communities.
Assessing changes in leaf morphology in Ginkgo biloba and their suitability to act as a palaeo-climate proxy
1University of Leeds
2University of Exeter
Ginkgo biloba has a long evolutionary history, with leaves of a strikingly similar morphology to those of the modern plant found in sediments over 100 million years old and well-preserved representatives of the family identified in the Early Triassic. This makes the sole survivor of this once diverse clade of significant interest to palaeobotany and palaeoecology. G. biloba is known for its fan-shaped leaves and noted for the variety of shapes that these leave can produce. A survey of G. biloba trees growing in 15 cities in Great Britain and Ireland was conducted to sample leaf shape and leaf trait variation along a relatively mild climate gradient. Twenty leaves were collected from each tree and between one and three trees were sampled at each location, with one to three locations per city. Analysis of these leaves has shown a strong leaf shape variation with temperature – leaves growing in the warmer, southern locations (e.g. Exeter, London) had significantly (p < 0.5) rounder and larger leaves than those growing in more northern locations (e.g. Aberdeen). This analysis suggests that leaf shape in G. biloba is correlated to mean annual temperature and may provide a useful palaeo-temperature proxy.
Biomineralisation of Palaeozoic sponges and aragonite-calcite seas
5University of Sterling
6University of Glasgow
Many Palaeozoic reef environments were dominated by stromatoporoids and it has been proposed that skeletal mineralogy of such hypercalcifying reef builders mirrors the mineralogy of non-skeletal CaCO3 through time. However, the original skeletal composition of stromatoporoids is not well understood, with different authors arguing for an original composition of aragonite or high-Mg calcite (HMC). The skeletal composition and underlying biomineralization of stromatoporoids was reassessed using electron backscatter diffraction of stromatoporoids from the Silurian and Devonian. In addition, a chaetetid sponge from the Carboniferous Buckhorn Asphalt, a deposit renowned for its preservation of calcareous microstructures, was studied. The analysis shows that the main building blocks of the stromatoporoid and chaetetid skeletons were bundles of single-crystal fibres of HMC. The preservation is characterised by a distinct microporosity and micro-dolomite inclusions that is interpreted to reflect the disintegration of inclusions of hydrated amorphous calcium carbonate during early diagenesis. Using these new insights, we analysed Palaeozoic sponge-dominated reefs in the PaleoReef Database and find that they correlate closely with the marine Mg:Ca ratio but, unlike inorganic CaCO3 precipitation, appear to not be influenced by temperature variation.
A DICHOTOMOUS KEY FOR THE MORPHOLOGICAL IDENTIFICATION OF COPROLITES
1Universidad Autónoma de Madrid
2Instituto Geológico y Minero de España (museo geominero)
Las Hoyas is an upper Barremian continental Konservat-Lagerstätte located in Cuenca (Spain), with an abundant body fossil, as well as a diverse ichnologic record. Trace fossils correspond to Mermia ichnofacies that nonetheless do not contain coprolite data. The study of a representative number of coprolites (N=433) have resulted in twelve different morphotypes: spiral, circular, irregular, elongated, rosary, ellipsoidal, cylinder, bump-head lace, Christmas-tree, cone, straight lace and thin lace coprolites. A morphological key was built, and the variation and utility of the different features used to describe the morphotypes have been tested. The size, matrix colour and content density are not useful features because they are not morphotype-specific, whereas the overall shape, outlines, shape of the ends, constrictions and the increase of the diameter of the coprolites are optimal characters to build the dichotomous key. This key is precise and meaningful because: (1) just a few coprolites among the 433 studied differ slightly from the combination of characters proposed; (2) with few features all the morphological variation is comprised, and (3) it can be used as a base to identify and compare coprolites from other Mesozoic fossil sites.
Experimental modelling of sedimentary processes for the Burgess Shale: implications for the transport and preservation of soft-bodied organisms.
1University of Portsmouth
2University of Southampton
3University of Saskatchewan
Understanding if soft-bodied organisms within fossil assemblages could have been transported, or not, is fundamental to the study of palaeoecology. In regards to the Burgess Shale Lagerstätte, a fundamental debate remains as to whether these animals were living within or close to the environment of deposition, or could they have been transported from one environment to another? Experimentation allows us to place constraints on this problem. In a two-factorial design using an annular flume tank, experiments were conducted to explore the effect of both pre-transport decay (up to 48 hours) and transport duration (equating to distances ranging from less than 1 km to 21.6 km) on the overall completeness and preservation potential of the polychaete, Alitta virens. Fieldwork and laboratory analysis of material from the Walcott Quarry of the Burgess Shale was used to feed directly into the experimental design to replicate Burgess Shale flow conditions. The flow consisted of 11% volume of kaolinite at 0.4 ms-1 to create quasi-laminar to upper transitional plug flow conditions.
The results of these experiments are used make direct comparisons to the preservation state of Burgessochaeta and Canadia from the Burgess Shale. The implications are discussed for the palaeoecology of Cambrian marine communities.
Patterns of morphological evolution in Pelagia (Teleostei: Acanthomorpha) consistent with ancient adaptive radiation
1University of Oxford
2Natural History Museum, London
3University of Michigan
Pelagia is an anatomically disparate clade of open-ocean fishes that appears to have originated near the Cretaceous-Paleogene boundary. This differs from model ‘adaptive radiations’ (cichlid fishes, Anolis lizards) in age and geographic scale, but corresponds to the pattern for which the concept was first defined: Cenozoic mammals. We collected computed tomographic data for the crania of 73 extant species of Pelagia, sampling all 15 extant families and a third of living species, and used three-dimensional geometric morphometrics to generate a shape space for the clade. Cranial anatomy separates families, paralleling differences in body shape. Divergent examples include gempylids (snake mackerels) and trichiurids (scabbardfishes), with elongate skulls, and deep-sea chiasmodontids (black swallowers) with reduced opercular series, posteriorly directed suspensoria, and long gapes. We constructed a morphological dataset for scombrids (tunas and mackerels) and combined this with existing molecular phylogenies to place a diverse series of early fossil scombroids into this phylogenetic framework. A disparity-through-time analysis tested for deviations from a Brownian motion model of phenotypic evolution, finding substantially lower-than-expected levels of subtree disparity early in the history of the clade, providing quantitative support for an adaptive radiation in Pelagia early in the Cenozoic.
Brachiomatic: automated measurement of brachiopod size using new museum collections digitisation protocols.
1Natural History Museum, London
Brachiopods are useful for understanding how biota have responded to environmental changes in deep time. Museums are increasingly digitising collections, using high-throughput workflows based on rapidly imaging material. We are interested in whether these images can be used to collect standardised morphological data more efficiently to document changes in size across intervals of past environmental change. Using a collection of fossil brachiopods spanning the Early Toarcian hyperthermal event, we aim to test whether body size measurements generated automatically from images of specimens are more accurate, more precise and quicker to generate than measurements made by hand of the physical specimens. We completed a pilot study of a collection of 1200 brachiopods from the Jurassic of Spain. The results show that image quality and specimen orientation are important for the automated extraction of size data. Precision varies between taxa: automated measurements from those which are harder to orientate (smaller specimens) or which are harder to balance (lateral and anterior) are less precise. Precision of measurements using callipers also varies between individual researchers. Overall, length and width are more precise than depth using both methods. An additional benefit of the automated approach is better reproducibility compared to manual measurements.
First virtual endocasts of fossil Aplodontidae and their relevance in understanding the relationship between brain evolution and locomotion
1University of Toronto Scarborough
Previous studies suggest that the burrowing adaptations of the living mountain beaver, Aplodontia rufa, are derived, and that basal members of Aplodontidae were more arboreal, similar to Sciuridae (squirrels), their closest relative. This evolution of adaptations for fossoriality has never been studied from the perspective of brain evolution. We describe the first virtual endocasts of Aplodontia rufa and of two fossil aplodontids, Prosciurus relictus (Early Oligocene), and Mesogaulus paniensis (late Miocene). Our results show that the endocast of Prosciurus is more similar to the early arboreal squirrels Protosciurus and Cedromus than to the younger aplodontids in being relatively larger (higher EQ), with larger paraflocculi and a more ventrally positioned orbitotemporal canal, associated with a larger neocortex. These endocranial features have been tied to better vision and the development of arboreality in squirrels, and their presence in Prosciurus may be related to more arboreal habits. The smaller paraflocculi and smaller neocortices of the younger Aplodontia and Mesogaulus could reflect their burrowing adaptations. These results are consistent with previous observations that brain size and shape vary as a function of locomotion in rodents, and provide a rare example of apparent relative brain size decrease through time in the fossil record.
Dietary ecology of pterosaurs from quantitative 3D textural analysis of tooth microwear
1University of Leicester
2University of Birmingham
3Royal Tyrrell Museum
Pterosaurs were a successful group of Mesozoic flying reptiles. For 150 million years they were integral components of terrestrial and coastal ecosystems, yet their feeding ecology remains poorly constrained. Postulated pterosaur diets include insectivory, piscivory and/or carnivory, but many dietary hypotheses are little more than speculation based on scant evidence. We have developed a more robust approach based on quantitative analysis of the micron-scale 3D textures of worn pterosaur tooth surfaces – dental microwear texture analysis – never before applied to pterosaurs. Microwear is produced as scratches and chips generated by food items create characteristic surface textures on teeth that vary according to diet.
We compared microwear from non-occlusal tooth surfaces of 11 species of pterosaur with data from extant organisms with known diets, (bats, monitor lizards and crocodilians, including insectivorous, piscivorous and carnivorous species). This allowed for robust testing of previous pterosaur dietary hypotheses. Microwear from Dimorphodon for example, previously hypothesised as a piscivore, indicates a diet of vertebrates and invertebrates. Microwear from basal monofenestratans, previously hypothesised as carnivores, provides evidence of piscivory in these pterosaurs. Dietary evidence from microwear therefore provides novel insights into the ecological roles of respective pterosaurs and pterosaur dietary evolution.
Integrating genomic and fossil evidence to date the tree of life
1University of Bristol
2University of Bath
Establishing a timescale for the tree of life is a task that has long been approached via a literal interpretation of the fossil record. However, fossils come with caveats such as difficulties in establishing biogenicity, establishing a correct age constraint, and assigning affinities. We chose to approach the question with a combined molecular clock analysis, attempting a reappraisal of the fossil material and integrating it with molecular sequences to estimate a timescale for the tree of life. Our timescale is robust to parameter variations within the analysis and finds that the last universal common ancestor originated prior to the late heavy bombardment. The major clades diverged some time later: crown Archaeabacteria ~3178 Ma; crown Eubacteria ~3454 Ma; and crown Eukarya ~1524 Ma. These dates place the earliest potential fossils into the bracket of total life, with crown group domains not appearing until around the Strelley Pool formation. In our timescale, crown group cyanobacteria originate significantly after the Great Oxidation Event, rejecting the view that they were its primary driver. Additionally, we show a concurrent evolution of the alphaproteobacteria and the crown eukaryotes both of which originate in the Mesoproterozoic, suggesting a symbiotic acquisition of the mitochondria between 1579-1209 Ma.
Insights into the taphonomy of Weichselia reticulata
1Universidad Autónoma de Madrid
2Université Lyon 1 (Claude Bernard)
The tree fern Weichselia reticulata (Stokes et Webb) Fontaine had a wide palaeogeographic distribution in Laurasia and Gondwana during the Jurassic and Cretaceous periods. In particular, leaf fragments of a few centimetres are very abundant from the upper Barremian of Las Hoyas (Cuenca, Spain) and the Barremian of Beare Green Pit (Surrey, England). Both localities are interpreted as freshwater habitats. The plant fossils are mostly charred (i.e., preserved as charcoals), and more rarely consist of impressions and permineralizations covered by calcite or iron oxide. The maximum length of a total of 1381 fragments of W. reticulata were measured. Our results show that: (1) the mean size of impressions is larger than that of compressions and permineralizations; (2) the mean size of the fragments from Beare Green Pit is smaller (8 mm) than those from Las Hoyas (26 mm); and (3) when the remains are found associated in the same layer, the Beare Green Pit fossils show less variation in size. These differences may be explained by differences in the necrobiosis (e.g., higher fragmentation during burning) and biostratinomy (e.g., higher selection during water transportation).
The end-Ordovician Anji Biota (Zhejiang, China) and a wider Hirnantian sponge mega-community
1Nanjing Institute of Geology, 39 East Beijing Road, Nanjing 210008, China
2Department of Natural Sciences, Amgueddfa Cymru – National Museum Wales, Cathays Park, Cardiff CF10 3LP, UK
3School of Geosciences and Info-Physics, Central-South University, Changsha 410083, China
The recently-discovered Anji Biota of Zhejiang preserves an unprecedented deep-water Hirnantian fossil assemblage, preserved by pyritisation in black mudstone of the post-extinction Metabolograptus persculptus Biozone. The community was dominated by a hyper-diverse assemblage of sponges, representing both early-branching and modern groups, and preserved with detailed skeletal remains and soft tissues. Aside from abundant graptolites, associated fossils are limited to occasional orthocone nautiloids, and rare examples of other exceptionally preserved taxa such as echinoderms, eurypterids and other arthropods. One site also shows a depth transect from a shallow-water Aegiromenella Fauna into the sponge community, with an intermediate-depth assemblage between them.
Additional collections have increased the sponge diversity to over 100 species, with many new taxa expected from further collecting. Additional work elsewhere in South China has revealed similar diverse, abundant sponge faunas from the M. persculptus Biozone in several provinces, across 2000 km, despite differences in the sedimentary successions. The preservation of the sponges appears to be related to an interval of rapid suspended sediment input during transgression. We encourage investigations of Ordovician–Silurian boundary sections globally to assess whether the offshore sponge proliferation in South China was a global phenomenon, and what its implications might be for post-extinction recovery.
Geobiology and Palaeogenomics: Genes That Make Rocks
1University of Southern California
The combination of geobiology and palaeogenomic studies is a powerful approach which leads to a more fundamental understanding of how Earth and life have changed through time in building the sedimentary rock record. For example, linking palaeogenomic studies of biomineralization genes for modern organisms and when they first evolved in the Cambrian with geobiological studies of the impact this had on the production of carbonate sedimentary facies and the development of the Neritan ocean provides a unique perspective on how genes have shaped formation of the sedimentary record. Another component of the Cambrian explosion, the evolution of vertical bioturbation at the start of the Cambrian, has had significant effects on biogeochemical cycling and sediment production, and provides an inviting target for future genomic studies. The remaining Phanerozoic includes a broad variety of evolutionary innovations which within a joint geobiological and palaeogenomic context can also be profitably studied. These include evolution of the coccolithophore exoskeleton as they have strongly contributed to widespread deposition of carbonate sediment in deep settings and development in the Mesozoic of the Cretan ocean. Such work will ultimately provide a history of how genomic changes shaped the development of the sedimentary rock record.
Accounting for differences in species frequency distributions when calculating beta diversity in the fossil record.
1Museum für Naturkunde Berlin
2University of the Witwatersrand
3Humboldt-Universität zu Berlin
Beta diversity is a measure of the taxonomic differentiation between habitats/localities within an assemblage, and is normally calculated as a set of pairwise taxonomic “distances”. It has long been understood that, due to the incompleteness of the fossil record, beta diversity estimates for fossil assemblages will always be higher than the true value. However, the difference between the observed and true distances will vary greatly depending on differences in the shape of the relative abundance distribution. Using simulations, it is shown that incomplete sampling of a homogenous fauna with more even relative abundances of taxa produces higher beta diversity than one with very few extremely common taxa. A new procedure is proposed for calculating beta diversity in the fossil record, whereby the observed distances are compared to the distances obtained by making random samplings from a homogenous fauna with the same abundance distribution. This method is applied to an empirical dataset: Permian-Triassic tetrapods from the Karoo Supergroup of South Africa. A homogenous fauna is observed in the Guadalupian, but during the Lopingian increased provinciality is observed. No change is found across the Permian-Triassic boundary, but during the Middle Triassic beta diversity again decreases.
Scotland’s Jurassic Park: New Dinosaurs, Crocodylomorphs, Pterosaurs, and Fishes from the Middle Jurassic of Skye
1University of Edinburgh
2National Museums Scotland
3The Hunterian, University of Glasgow
The Isle of Skye is one of the rare localities worldwide that preserves vertebrate fossils from the Middle Jurassic (ca. 174-163 million years ago), a critical time when several major dinosaur groups were diversifying and more modern-style mammals, lizards, and amphibians radiated. The PalAlba consortium of Scottish-based palaeontologists has launched several expeditions to Skye over the last five years to collect Middle Jurassic fossils in the lagoonal and fluvial rocks of the Great Estuarine Group, and we report our key findings here. Several new dinosaur tracksites—including the first sauropod tracks and first ornithopod trackway from Scotland—indicate that sauropods preferred nearshore lagoonal settings while other dinosaurs preferentially left their tracks on mudflats. New crocodylomorph material reveals a high diversity of dog-sized species, the recent discovery of a pterosaur skeleton demonstrates the presence of a rhamphorhynchoid-grade taxon that may fill an important gap in pterosaur evolution, and a bounty of new fish beds contains a diversity of pycnodont species with intriguing biogeographic affinities to Gondwanan forms. These and other finds provide a unique window into whole ecosystems of the Middle Jurassic, and suggest that much remains to be discovered on Skye.
The "push of the past": an important bias in the fossil record
2University of Leeds
Homogeneous “birth-death” models for speciation and extinction may be used to model patterns of diversification, but survivorship biases can create remarkable and counter-intuitive effects through time. Here we consider the “push of the past”, the effect that occurs by imposing the condition that clades survive until the present (which of course, some have). Such clades tend to begin with high bursts of diversification and an early origin of the first crown group, an effect that becomes more pronounced as extinction rates increase: similar effects occur after mass extinctions. An extra effect increasing rates in early lineages is also seen in very large living clades. These effects are also likely to affect rates of phenotypic change and may even distort molecular clock estimates of clade origins. Understanding this and other biases that emerge from the “null hypothesis” of clade diversification is thus essential before causal mechanisms for major macroevolutionary patterns are sought. It may be that many traditional major features of the fossil record turn out to be the inevitable consequence of our own perspective – looking back in time from within a large clade that has survived over half a billion years.
Evolution or revolution at the J/K boundary: The case of the Ammonoidea
1NARG - SEES - University of Manchester
2University of Bristol
The original conception of the Tithonian and Berriasian Stages was entirely ammonite based, and ammonite biostratigraphy still has much to contribute to the definition of a J/K boundary. The database of Ammonoidea occurrences is substantial with reference sections in SE France, SE Spain, Bulgaria, Ukraine (Crimea), Turkmenistan, Irak, the Himalayas, Yemen, Morocco, Tunisia, Mexico, Argentina, the United Kingdom and Russia (Volga Region and Siberia).
Over the past 10 years these faunas have been re-investigated as part of a team study of the Berriasian Working Group (ISCS/IUGS). New primary data on the taxonomy, stratigraphic ranges and palaeobiogeographic distributions were obtained.
Besides the reappraisal of the high endemism of the faunas, the new picture of the ammonoid evolution accross the J/K boundary points outlines salient issues regarding the tempo of the “so-called” turnovers that affect the ammonite faunas during the Late Tithonian and Early Berriasian. All new evidences strongly suggest that the picture formerly obtained from the Ammonitico Rosso successions of SE Spain is oversimplistic.
Decoupled morphological and phylogenetic diversification during the rise of the ruling reptiles and their kin
1University of Birmingham
2CONICET−Sección Paleontología de Vertebrados, Museo Argentino de Ciencias Naturales, Buenos Aires, Argentina
One of the key faunal transitions in terrestrial ecosystems occurred after the Permo-Triassic mass extinction (PTME; ~252.2 Ma), when the previously obscure archosauromorphs (crocodylians, dinosaurs, birds, pterosaurs and stem-species) become the dominant terrestrial vertebrates. This transition set the scene for the dinosaur-dominated ecosystems of the Jurassic and Cretaceous, but its pattern and processes remain poorly understood. Here, we place all known late Permian–early Late Triassic archosauromorph species into an explicit phylogenetic context, and use this dataset and topology to quantify changes in species richness, disparity and evolutionary rates through this interval. Our results indicate the following sequence of diversification: (1) a morphologically conservative and globally distributed post-extinction ‘disaster fauna’ in the earliest Early Triassic; (2) a major phylogenetic diversification with significantly elevated evolutionary rates in the later Early Triassic; and (3) a marked increase in species richness, abundance, and disparity occurring around the Early–Middle Triassic boundary. This final diversification phase is contemporaneous with global ecosystem stabilization, as indicated by the end of intense carbon perturbations, a global cooling event, and the return of conifer-dominated forests. Our results show the fundamental role of the PTME in reshaping terrestrial ecosystems, and its far-reaching impact on Mesozoic and modern faunas.
Phylogenomic analysis of Brachiopoda and Phoronida: implications for morphological evolution, biomineralization, and the Cambrian radiation.
3University of California, Davis
Brachiopods are among the first appearing biomineralised Cambrian metazoans and represent a major component of the early animal fossil record. While their fossil record is ultimately key to determining character homology and polarity during evolution of the brachiopod body plan, reading this pattern has been clouded by phylogenetic uncertainty among the crown clades. Specifically, monophyly of brachiopods with respect to phoronids, and the relationships of the calcitic to phosphatic brachiopods. Much of this phylogenetic uncertainty stems from difficulties in rooting the tree of brachiopods within Lophotrochozoa. Phylogenomics—the analysis of hundreds to thousands of orthologous genes—has been instrumental in resolving difficult phylogenetic relationships in diverse metazoan clades through reduction of random error in combination with careful evolutionary model selection. We have conducted the first extensive phylogenomic investigation of Brachiopoda/Phoronida with analyses that combine novel sequence data with all publicly available transcriptomes and a broad range of protostome outgroups. Analyses were run under best fitting evolutionary models (LG and gamma) utilising a published 106-gene lophotrochozoan ortholog set. Preliminary results strongly support a monophyletic Brachiopoda with Phoronida as sister group within Lophotrochozoa, with weak support found for Inarticulata, thus constraining possible scenarios for the evolution of brachiopod biomineralisation.
The first functional analysis of the lateral line system in fossil fish.
1University of Edinburgh
The lateral line is a mechanosensory system used by fish for predator evasion, prey detection, shoaling and navigating their environment. Fish display an extremely diverse range of lateral line morphologies ranging from simple grooves on the surface of the body to elaborate and complex ramifying tubes enclosed in dermal tissue and bone. Whereas the lateral line has been recognised in fossil fish for well over a centrury, the function of the lateral line is only recently beginning to be understood in modern taxa. Recent work has demonstrated that the degree of complexity of ramifying lateral line tubes may behave as a signal filter, the effects of which are dependent on the dimensions of the canal system. Here we employ a simple fluid mechanics model using Hagen–Poiseuille flow to calculate the mean flow and pressure inside lateral line canal segments for a given pressure acting on the pore openings in a fossil lateral line system. The solution describes the pressure and velocity that motion-sensitive neuromast cells within the canal experience. The technique offers great potential for investigating functional of fish lineages in different environments and how sensory systems diversify and change during key evolutionary events.
A Total-Evidence Approach to Resolving Pancrustacean Phylogeny
1University of Bath
2University of Bristol
3University of Manchester
Many aspects of arthropod biology are intently researched, and their phylogenetic interrelationships are no exception. Recent studies have converged in favor of the Pancrustacea hypothesis of arthropod phylogeny, which describes a topology in which taxa traditionally grouped together as “crustaceans” form a paraphyletic group with respect to hexapods (insects and their close relatives). However, the relationships within Pancrustacea are more controversial, especially regarding the affinities of Hexapoda to other pancrustaceans. In an effort to resolve the remaining uncertainties in pancrustacean phylogeny, the present study uses a total-evidence framework, incorporating both molecular and morphological characters for inference of phylogenetic topology. A phylogenetic matrix was assembled including 753 morphological characters and 56,504 amino acid positions scored for a total of 259 crown-arthropod taxa, of which 86 were fossil taxa, and analyzed under both Bayesian and maximum likelihood models. This matrix then underwent several modifications that were intended to improve phylogenetic resolution. Excepting the positions of a few fossil taxa, preliminary results were largely congruent with each other and with previous research on pancrustacean phylogeny. The best-resolved iterations of the analysis had highly reduced taxon sampling including only extant taxa coded for both molecular and morphological data, as well as fossil taxa.
Helcionelloid molluscs from Cambrian Series 2, Stages 3-4 of East Antarctica and outline morphometric approaches to problematic taxonomy
3Stockholm Museum of Natural History
New problematic helcionelloid molluscs from the Shackleton Limestone (Cambrian Series 2, Stage 3-4) outcropping in the Transantarctic Mountains can be reliably identified to the new Dailyatia odyssei Zone of South Australia. Keystone taxa such as the Zone’s eponym, Pojetaia runnegari and Mackinnonia rostrata also allow for increased correlation of East Antarctica to other rock units in East Gondwana as well as Laurentia. Most taxa are represented by relatively poorly preserved steinkerns (internal moulds), reflected in their open nomenclature.
Presented are results of elliptical Fourier analysis of the outlines of steinkerns of Mackinnonia rostrata from the Shackleton Limestone and Ajax limestone (Cambrian Series 2, Stages 3-4, South Australia) and Mackinnonia taconica from the Bastion Limestone (Cambrian Series 2, Stages 3-4, North-East Greenland). Principal component analysis of the protoconchs and supra-apical field is capable of reliably (p<0.05) distinguishing the three groups. The intraspecific variation uncovered between the M. rostrata assemblages is interpreted as incipient speciation.
Problems with helcionelloid identification and taxonomy which hinder reliable biostratigraphy may be solved by techniques such as elliptical Fourier analysis which is sensitive to subtle morphological variation.
Sampling biases constrain interpretation of the fossil records of non-marine lepidosaurs and turtles
1Natural History Museum, UK
Fossil record quality is a popular topic, with many studies on a variety of vertebrates and invertebrates. Particularly prominent are attempts to ‘correct’ curves of taxic diversity through time via the use of subsampling techniques, in order to eliminate biases caused by under- or oversampling of the record in space or time. I used Shareholder Quorum Subsampling (SQS) to estimate non-marine lepidosaur and turtle diversity for the Triassic–Paleogene (252–23 myr). In addition, generalized least-squares regressions (GLS) were used to examine the relationships between diversity and varied combinations of sampling and environmental proxies. The lepidosaur record is more poorly sampled than the turtle record, but both reveal a similar pattern of under-sampling in the southern hemisphere, affecting observed ‘global’ patterns. At the K–Pg boundary, global lepidosaur diversity decreases, whereas in turtles the transition is negligible. The diversity of both groups fluctuates similarly in response to changing Paleogene climates, and undergoes a global decrease across the Eocene-Oligocene boundary during the Grande Coupure. GLS analyses compared using Akaike weights indicate sampling biases (particularly collection counts per bin) best explain long-term diversity fluctuations. More work must be done to alleviate geographic sampling biases in both records.
Rotten livers, muscles and guts: controls on exceptional preservation of internal organs.
1Uni of Leicester
Exceptionally preserved soft tissues are found in many Lagerstätten and are invaluable in reconstructing ancient life. The most important control on the replacement of organics by authigenic minerals is the generation of suitable geochemical conditions, especially pH, during decay. Studies based on fossil material have concluded that localised organ specific ‘microenvironments’ must occur within a carcass during decay for exceptional preservation to occur.
Experiments investigating this phenomenon have relied on external conditions around a carcass as a proxy for whether internal conditions are suitable for mineral precipitation. We have designed a novel experiment to investigate the formation of microenvironments inside a carcass in real time. Our experiments demonstrate that (i) internal chemical gradients are more pronounced than immediately around the carcass, (ii) microenvironments are predominantly controlled by the body cavity and not individual organs, and (iii) decaying organs, such as the stomach, have little influence on surrounding tissues and do not cause ‘pH-cascades’ during integrity failure. Our data also indicates that organ histology is the dominate factor in preferential preservation, explaining the biases seen throughout the fossil record.
Naked chancelloriids from the lower Cambrian of China: evidence for sponge-type growth
1School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester, LE1 7RH, UK
2Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming 650091, China
3Department of Earth Sciences, The Natural History Museum, Cromwell Road, London SW7 5BD, UK
4Earth Collections, Oxford University Museum of Natural History, Parks Road, Oxford OX1 3PW, UK
5Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3PR, UK
Fossils with extinct character combinations can help reconstruct the origins of modern body plans. Some Cambrian animals, however, have defied phylogenetic placement because of their seemingly irreconcilable anatomies. Chancelloriids are an extinct group of animals with an overall sponge-like habit, but with sclerites that suggest a close relationship to halkieriids and other motile bilaterians, posing a phylogenetic conundrum. Here, we describe new chancelloriid specimens from the lower Cambrian (Stage 3) Chengjiang Lagerstätte that are notable for their weak or even absent spination. A single apical orifice leads to a simple body cavity, in keeping with their sponge-like external anatomy, and the apex bears a tuft of differentiated sclerites, in common with recently described chancelloriids from the Burgess Shale. By considering the microstructure of the sclerites and their distribution across the body, we propose a new model of chancelloriid growth featuring a sub-apical growth zone. Among comparably shaped organisms, this mechanism is shared with particular calcarean sponges. We suggest that chancelloriids are most parsimoniously interpreted as sponges, albeit with convergent spicule-like structures and an unusually robust epidermis. Chancelloriids could therefore shed light on the disparity, development and tissue complexity of early sponges, which occupy a pivotal position in the metazoan tree.
Asymmetry of paired endites on frontal appendages in Amplectobeluidae (Radiodonta: stem Euarthropoda) and its taxonomic significance
1The Natural History Museum
3University of Lausanne
The frontal appendage is the main feeding structure and the most well-known part of radiodontans, and thus has been used as the main source of characters in the classification of these putative stem-group euarthropods. The endites (or ventral/inner spines), normally considered as paired on each podomere, are of particular value in taxonomy and autecology. Here we show that, in all known taxa of Amplecotobeluidae, the paired endites on each podomere are conspicuously different in size, contradicting the traditional idea that they are always of the same size. Such asymmetry between the paired endites suggests that the frontal appendage might have had the ability to rotate to some degree. We further argue that the paired endites were particularly differentiated in most taxa of Hurdiidae, forming one row of comb-like endites and one row of ‘lateral spines’. This is in contrast to Anomalocarididae, where paired endites were ventral, symmetrical, and equal in shape and size. This differentiation in the size of paired endites in different clades indicates divergence of feeding strategy in early radiodontans, which was accompanied by the differentiation of other feeding structures (such as mouthparts and gnathobase-like structures). Such discoveries offer new characters for discerning the main clades of radiodontans.
Faunal response to sea level and environmental change in the Jurassic Sundance Seaway, western United States: a stratigraphic palaeobiological approach
1Plymouth University, UK
2University of Georgia, USA
A stratigraphic palaeobiological approach is essential to understand how regional ecosystems respond to sea level and environmental perturbations, a main challenge in palaeoecology. Here we use quantitative abundance estimates, integrated within a sequence stratigraphic and environmental framework, to reconstruct benthic community changes through the 13 myr history of the Jurassic Sundance Seaway. We observe a turnover event at the Middle–Upper Jurassic transition, which coincided with a shift from carbonate to siliciclastic deposition. Turnover was not uniform across the onshore–offshore gradient, but was higher in offshore environments in both carbonate and siliciclastic settings. The higher resilience of onshore communities to third-order sea-level fluctuations and to the change from a carbonate to a siliciclastic system was driven by a few abundant eurytopic species that persisted from the opening to the closing of the Seaway and were not restricted to single depositional environments or sequences. Lower stability in offshore facies was instead controlled by the presence of more volatile stenotopic species. This pattern is consistent with previous observations that shallow-water settings are dominated by abundant, geographically widespread, and environmentally tolerant species. Numerical models suggest that such selection is caused by wide variations in the area of shallow-marine habitat during sea-level change.
The evolution of acellular bone in teleosts: structure-function relationship in fish bone histology
1University of Oxford
2Muséum national d'Histoire naturelle, France
3Université de Poitiers, France
4University of Michigan Museum of Paleontology, USA
The skeleton of most teleost fishes shows a peculiar type of acellular bone, in which the main bone cells (osteocytes) are missing entirely. In the literature, acellular bone is considered to be a character of the highly-diverse clade Neoteleostei. However, it is also found in other teleosts, such as pikes (Esocidae), while some neoteleosts such as tunas (Scombridae) have cellular bone. The evolutionary history of the character is therefore complex. We address two main questions: 1) What is the phylogenetic distribution of acellular bone in deep time? 2) Is there a functional explanation to this distribution? We use a dataset of more than 500 fossil and extant taxa, mapped on a time-calibrated tree built from recent molecular topologies to reconstruct the history of acellular bone in teleosts. Acellular bone appeared several times independently, with a main occurrence in Euteleostei (including Neoteleostei). Tunas are confirmed to have reacquired cellular bone secondarily, possibly due to their endothermic metabolism. We study bone histology for the first time in the opah, another endothermic teleost. It also shows secondary cellularity, with features strikingly similar to those of tuna bone. Thus, functional parameters such as endothermy appear to be linked with histological features in teleost fishes.
The search for physical sedimentary-stratigraphic signatures of ancient life
1University of Cambridge
Animal, plant and microbial life all influence modern geomorphological landforms through the mediation of rates and scales of processes such as erosion, deposition and sediment transport. The known preservation of relict landforms, translated into the sedimentary-stratigraphic archive as particular combinations of sediment type, bedforms and stratal architecture, implies that there may be a long-term sedimentological record of such interactions, which extends beyond the body or trace fossil record. Here we systematically consider the extent to which the evolution of major groups of organisms may have manifested influences on landscapes throughout Earth history. Particular emphasis is placed on alluvial settings, where the internal stratigraphic architecture of particular geomorphic features is better understood, and frequently occurs at scales that are readily recognised in geological outcrops. The paucity of unmistakably ‘biotic’ landscape components at this scale presents challenges to the identification of indirect life signatures from individual examples, but is sometimes possible. A more holistic view of the long-term geologic record has the potential to elucidate signatures of life, recorded as the frequency distribution and scale of certain sedimentary associations wax and wane in close stratigraphic synchrony with the evolutionary history of different organism groups.
New insights on the correlation of Permo-Triassic terrestrial faunas of South Africa with those of European Russia
1University of the Witwatersrand
2Borissiak Paleontological Institute
The mid-Permian to the mid-Triassic is a fascinating period in tetrapod evolution, witnessing the transition from primitive to modern ecological structures and the rise of archosaurs following the apogee of Palaeozoic therapsid faunas. It also encompasses two major extinction events, of differing magnitude, that are evident in both terrestrial and marine environments. This time period is best known from the fossiliferous sequences of the South African Main Karoo Basin and the sedimentary basins of European Russia. Palaeontological studies over the past 15 years have resulted in numerous discoveries that have refined the biostratigraphic framework of both regions, and independent dating methods have been employed that have further clarified the relationship of the two faunal successions. We present a new regional correlation between the faunal assemblages of these high latitude regions, incorporating this new data. Both are defined by mid-Permian faunas dominated by dinocephalian therapsids, after which tetrapods of Gondwanan origin enter Eurasia in the aftermath of the Capitanian mass extinction event, particularly dicynodonts and theriodont therapsids. Following the end-Permian mass extinction temnospondyls diversified in both regions and archosaurs became more common but, by the mid-Triassic, cynodonts were evolving complex postcanine occlusion in Gondwana but had become extirpated from European Russia.
A chondrichthyan-like shoulder girdle in an “acanthodian” helps tease apart early chondrichthyan relationships.
1Imperial College London
2University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, Netherlands
3Geosciences, Queensland Museum, 122 Gerler Rd, Hendra, Brisbane, Queensland 4011, Australia
435 Millside Road, Peterculter, Aberdeen, AB14 0WG, United Kingdom
5Vine Lodge, Vine Road, Johnston, Haverfordwest, Pembrokeshire SA62 3NZ, UK
There is a growing consensus that acanthodians – a collection of prodigiously fin-spined, Palaeozoic fishes – are in fact some of the very earliest relatives of living chondrichthyans (sharks, rays, and elephant sharks). This places acanthodian anatomy in a uniquely important position to inform our understanding of jawed vertebrate evolution. While this phylogenetic status is now well supported, uncertainty about stem-chondrichthyan intrarelationships leave questions of stepwise character evolution poorly resolved. Here we present new information on the Lochkovian (Early Devonian) acanthodian Vernicomacanthus uncinatus. We show that the shoulder girdle of V. uncinatus is unique among acanthodians in the possession of a prominent posterolateral angle—a character previously known only in Palaeozoic “sharks”. Alongside this are a number of chondrichthyan and gyracanth-like aspects of the dermal anatomy. Using this information, as well as novel information on the shoulder girdles of the acanthodians Ptomacanthus and Diplacanthus, we reassess the morphology of the acanthodian shoulder girdle and build a new phylogenetic dataset spanning the chondrichthyan total-group. Using this we test possible schemes of relationships amongst stem-chondrichthyans and assess the resulting implications for stepwise character evolution in chondrichthyans.
A model for marine reptile taphonomy in the Late Jurassic Slottsmøya Member Lagerstätte
1Natural History Museum, University of Oslo
2University of Alaska Museum
3Department of Geosciences, University of Alaska Fairbanks
4University of Southampton
The completeness of the fossil record has received renewed interest in the last years, with amongst others large-scale models for dinosaur and marine reptile diversity and preservation through the Mesozoic. To make these globally applied algorithms more accurate, the preservation and biases of the fossil record need to be addressed also on a local scale: How can the preservation of each specimen be explained and how does taphonomical history vary through time? How is the vertebrate record coupled to the preservation potential of remainders of the ecosystem?
To do so, excavations needs to be undertaken with detailed stratigraphic control and a holistic approach. In the Late Jurassic Slottsmøya Member Lagerstätte, Spitsbergen, the taphonomy and ecosystem evolution can be studied through 12 million years in one site. 60 plesiosaurian and ichthyosaur specimens are described with respect to articulation, landing mode, preservation, predation and scavenging. Their stratigraphic distribution is analyzed and a correlation is found between high TOC, low oxygen levels, low benthic invertebrate density and optimal skeletal preservation. Marine reptile elements are broken and brittled, but surprisingly three-dimensional for the known compaction rate. In the proposed taphonomical model the thoroughly described methane seep communities is one key factor for this result
Differences in extinction rates explain contrasting regional diversity patterns in modern tropical bryozoans
1Natural History Museum London
2Smithsonian Institution Washington DC
Marine biodiversity surrounding the Indonesian Archipelago is several times higher than anywhere else but why this is true is unknown because of poor historical data. To address this, we compared the fossil records of cheilostome bryozoans from Indonesia versus the Caribbean, regions that differ several-fold in species richness today. Cheilostome diversity was strikingly similar in the two regions until the end of the Miocene 5.3 Ma, so that the modern disparity must have developed more recently. However, the Miocene faunas were ecologically very different, with a greater proportion of erect and free-living species in the Caribbean. Our results support the hypothesis that modern differences in diversity arose primarily from differential extinction of Caribbean erect and free-living species due to oceanographic changes associated with uplift of the Isthmus of Panama, rather than exceptional rates of diversification in the Indo-Pacific.
Long-term mammalian stable isotope record across the Great American Biotic Interchange
1Universidad Complutense de Madrid, Spain
2Instituto de Geociencias (CSIC, UCM), Spain
3University of California Santa Cruz, USA
4Universidad Nebrija, Spain
5INGEOSUR-CONICET. Universidad Nacional del Sur, Argentina
6Universidad Nacional de La Pampa, Argentina
The South American late Cenozoic fossil record provides a unique natural laboratory for the study of mammalian paleoecology in the context of changing biotic and abiotic forces. South America remained largely isolated from other continents for more than 50 Ma. First, the presence of emerging land and then, the permanent establishment of the Isthmus of Panama (~3.1–2.7 Ma) triggered an interchange of terrestrial taxa with North America, an event known as Great American Biotic Interchange (GABI). We investigate resource use through stable isotope analysis of mammals from a long-term fossil record from the Pampean Region (La Pampa and Buenos Aires provinces, Argentina) spanning from ~9 Ma to ~12 Ka. Our analyses point to a major shift in resource use by most of endemic herbivorous taxa, as they switched from a pure C3 diet to a mixed C3-C4 diet at the Late Miocene-Early Pliocene. Carnivorous taxa mirrored this shift, with endemic Sparassodonta consuming prey from pure C3 environments, whereas immigrant Felidae preferred prey from mixed C3-C4 areas. Flexible dietary behavior (e.g., gomphotheres, equids), as indicated by our stable isotope data, may have facilitated the successful settlement of some immigrant groups in the Pampean area.
Skull development and biomechanics in the coelacanth Latimeria; implication for fossil coelacanths and fossil lobe-finned fishes
1University of Hull
The coelacanth Latimeria is the only living vertebrate that retains an intracranial joint (IJ), which enhances the biting force during feeding. In adults, the brain represents 1% of the endocranial volume (EV), and lies posterior to the IJ. By contrast, the brain spans the IJ in younger individuals and represents a more substantial EV. We investigated whether the dramatic changes in the position and relative size of the brain during Latimeria growth allow for protecting the brain from higher loadings generated by the IJ during biting in adults. We simulated muscle activity and joint-reaction forces during biting using Multibody Dynamics Analysis, and calculated the stresses and strains in the skull and brain with Finite Element Analysis (FEA). Stresses and strains are low in the adult brain, but clearly higher when it is replaced by the juvenile brain that has been scaled to the EV of the adult, and spans the IJ. Our results hence suggest that the evolution of a biting-enhancing mechanism involving the IJ in fossil coelacanths, and potentially in other sarcopterygian “fishes”, could have imposed major constraints on brain evolution.
An enigmatic amphibian from the Early Cretaceous of Japan
1University College London
2Kanagawa Prefectural Museum of Natural History, Japan
Albanerpetontids are small enigmatic salamander-like amphibians with a fossil record extending from the Middle Jurassic to the Pleistocene. Although there are a few articulated (but crushed) specimens from the Early Cretaceous of Spain and Italy, most of the record is based on 3-D microfossils representing a few characteristic elements. Consequently the anatomy, and thus phylogenetic position, of these amphibians remains poorly understood, as does their palaeobiogeographic history. The first and last records are from Europe, but albanerpetontids are a consistent presence in North American microvertebrate deposits from the latest Early Cretaceous until the Palaeocene. Given their apparent absence in Asia prior to the Late Cretaceous, it has been suggested that albanerpetontids dispersed from North America into Asia with the opening of the Bering land bridge.
New material from the Early Cretaceous Kuwajima Formation of Japan offers new perspectives. High resolution micro-CT scanning of a key specimen has revealed an association of exquisitely preserved skull and postcranial elements, many of which were previously unknown. Moreover, phylogenetic analysis places the Japanese taxon as a relatively derived albanerpetontid. Its presence in Asia in the Early Cretaceous, prior to the first appearance of the group in North America, falsifies the America-first hypothesis.
Mosiacism, Development, and the Early Evolution of Birds
1University College London
2The Natural History Museum
The discovery of Archeopteryx, the first bird, inspired the term “mosaic evolution,” describing the presence of ancestral and derived characteristics within a single organism. This requires that traits evolve semi-independently, responding to selection at different rates. Mosaic evolution has been influential in shaping avian evolution. For example, the early adaptive radiation of birds has been attributed to the dissociation of the forelimb, hind limb, and tail, which allowed for independent ecomorphological specialization of each of these regions. Here, we use high-dimensional geometric morphometric data examine the degree to which the avian skull can be divided into semi-autonomous regions (modules) and the tempo and mode of evolution in each module. We show that that the skull is highly modular and that each module exhibits unique punctuated bursts of evolution occurring in different lineages. Evolutionary rate and disparity in each cranial module is found to be associated with embryonic development: modules with complex developmental origins (multiple cell populations) have higher rates and disparity. Finally, we reconstruct a 3D model of the cranial phenotype at the root of crown birds, generating a hypothesis of ancestor of all modern birds. These results demonstrate the importance of intrinsic factors in shaping large-scale evolutionary patterns.
Newly discovered complete skull of Ichthyornis reveals unforeseen mosaicism late in the dinosaur-bird transition
1University of Bath
The Late Cretaceous toothed avialan Ichthyornis dispar represents one of the closest Mesozoic relatives to crown-group birds, and since its initial description in 1872 has provided critical information on the biology of birds preceding the evolutionary radiation of crown clade Aves. Despite continued work affirming its evolutionary importance, no substantial new cranial material of I. dispar has been reported since the 19th Century. Furthermore, Jurassic and Cretaceous lagerstätten that have yielded the most evolutionarily informative Mesozoic bird fossils typically preserve crushed and distorted skulls, severely limiting our understanding of non-avian ornithuromorph cranial morphology. Here we report four new specimens of I. dispar bearing cranial remains, including a new, extraordinarily complete skull and two previously unrecognized elements from the holotype. We found that I. dispar exhibited a transitional beak – small, lacking a palatal shelf, and restricted to the tip of the jaws – coupled with a crown-like kinetic system. The brain was relatively modern but the temporal region, poorly known in most non-avian avialans, was surprisingly archaic and deinonychosaur-like, bearing a large adductor chamber bounded dorsally by substantial bony remnants of the upper temporal fenestra. The far-crownward persistence of this temporal configuration demonstrates unforeseen complexity during the modernization of the avian skull.
A new ray-finned fish from the late Devonian: fresh insights into the rise of actinopterygians
1University of Oxford
3University of Michigan
Actinopterygians comprise 50% of living vertebrate diversity, with an evolutionary history extending back nearly half a billion years. However, fundamental issues preclude a robust understanding of their early history. Specifically, issues abound regarding the origin of the living radiations, as well as the effects of the end-Devonian mass extinction on the group as a whole. Here we present a new articulated actinopterygian from the Late Devonian ‘Chemung facies’ of Warren, Pennsylvania, USA. First reported by Eastman as Rhadinichthys sp. in the early 20th century, this small (ca. 60 mm total length) individual is largely complete, but critical anatomical details, especially of the head, remain obscured by matrix. MicroCT scanning reveals suprising anatomical detail, including a nearly intact cranium. This taxon displays surprisingly derived features for a Devonian actinopterygian, including an unfused dermohyal, multiple suborbitals and an opening in the aortic canal along its ventral midline. Phylogenetic analysis places the Warren actinopterygian among post-Devonian forms, and implies the divergence of many lineages prior to the Devonian-Carboniferous boundary. These results have important implications for patterns of evolution early in actinopterygian history, and the impact of the Hangenberg mass extinction on ray-finned fishes.
The positive influence of continuous characters and extended implied weighting on phylogenetic reconstruction: a crocodylian case study
1University College London
2Natural History Museum, London
Morphological characters have traditionally been coded into discrete categories for phylogenetic reconstruction. Recently, however, the use of continuous characters such as ratios and angular measurements has become more prevalent, although it remains rare. Here we used the crocodylomorph clade Neosuchia to test the impact of continuous data on fossil and extant phylogenies. With their complex evolutionary history and widespread homoplasy in several longirostrine (long-snouted) groups, neosuchians offer an excellent opportunity for studying the influence of new characters on phylogenetic reconstruction. We created a new data set of 84 continuous and 487 discrete characters scored for 106 neosuchian and outgroup taxa, which was analysed using Maximum Likelihood with and without extended implied weighting (EIW) in TNT and Bayesian Inference in MrBayes for a rediscretised data set. Both methods exhibited no notable differences when using rediscretised data without EIW, providing lower overall tree resolution than continuous character analyses and no separation of longirostrine clades. In contrast, our results show that use of continuous data and EIW successfully separates longirostrine clades in Neosuchia, improving overall tree resolution. This study demonstrates the usefulness of continuous data and EIW not only in phylogenetic reconstruction but also in successfully dealing with rampant convergence in morphological evolution.
Oxygen minimum zones in the early Cambrian ocean
2University of Cambridge
3University of Leeds
4University of Leicester
5The Australian National University
The relationship between the evolution of early animal communities and oceanic oxygen levels remains unclear. In particular, uncertainty persists in reconstructions of redox conditions during the pivotal early Cambrian (541-510 million years ago, Ma), where conflicting datasets from deeper marine settings suggest either ocean anoxia or fully oxygenated conditions. By coupling geochemical palaeoredox proxies with a record of organic-walled fossils from exceptionally well-defined successions of the early Cambrian Baltic Basin, we provide evidence for the early establishment of modern-type oxygen minimum zones (OMZs). Both inner- and outer-shelf environments were pervasively oxygenated, whereas mid-depth settings were characterized by spatially oscillating anoxia, within zones of higher productivity and correspondingly higher oxygen demand. This picture of a spatially restricted anoxic wedge contrasts with prevailing models of globally stratified oceans, offering a more nuanced and realistic account of the Proterozoic-Phanerozoic ocean transition, which bears importantly on models of early Earth oxygenation.
Jurassic onychites (arm hooks from squid-like cephalopods) associated with the statolith occurrences in the Wessex Basin, southern England
1Natural History Museum
2School of Geography, Earth and Environmental Sciences, Plymouth University
Modern coleoid (squid-like) cephalopods have arms that carry arrays of both suckers and hardened, organic hooks. Fossil arm hooks have been known since the work of Sternberg in 1823, but it was Kulicki & Szaniawski in1972 who described 22 hook parataxa from the Jurassic of Poland. Exceptional soft-bodied preservation of species such as Belemnotheutis antiquus from the Callovian-Oxfordian of the United Kingdom has allowed the identification of the host animal of some parataxa, though the majority remain un-attributable. In the Christian Malford lagerstätte (Upper Callovian) of Wiltshire large numbers of hooks (including forms described as Acanthuncus, Arites, Deinuncus, Falcuncus, Longuncus and Paraglycerites) are found associated with an abundance of statoliths (cephalopod ‘ear bones’) and macrofossil evidence of both belemnites and teuthids, some of which includes exceptional soft-bodied preservation. Using reference material in various museum collections it is possible to document the variation in hooks in both single species and between species, and this has enabled isolated hooks found in microfossil residues to be used to determine the presence of species in the absence of body fossils.
Kulicki, C. & Szaniawski, H. 1972. Cephalopod arm hooks from the Jurassic of Poland. Acta Palaeontologica Polonica, 17, 379–419.
The Downton Bonebed: insights into a lost world.
1University of Portsmouth
The Downton Bonebed is a multitaxic Fossil Concentration-Lagerstätte located in the Platyschisma Shale Member of the Downton Castle Sandstone Formation c. 1.5 m above the Ludlow Bonebed. The Downton Bonebed has received little direct study since its discovery over a century ago. The aims of this study were to catalogue for the first time the fossil contents of the Downton Bonebed, and to look at the sedimentology to define the depositional environment that the bonebed formed in, as well as its wider global context. The bonebed is rich in fossils with a broad diversity of vertebrates, invertebrates, plants and allies, however with each group the diversity is low suggesting that the Downton Bonebed was formed in a restricted environment. The sedimentology reveals evidence of two energy conditions shifting between quiet low energy setting with trace fossils present and periods of rapid burial in which all of the other fossils are found associated with swaley and hummocky cross laminations suggesting large storms. The environmental setting for the Downton Bonebed is a quiet hyposaline inlet/lagoon in close proximity to a terrestrial freshwater source, cut off from the Downton Sea by a barrier or barrier beach.
Coupling palaeoclimate data and numerical climate models to constrain Cambrian palaeogeography
1University of Leicester
2British Geological Survey
3Aix Marseille Université, CNRS
The Proterozoic/Phanerozoic transition was characterised by major biological changes, including increasing metazoan mineralization and mobility, with profound consequences for geochemical cycles and the physical environment. However, our understanding of the co-evolution of the environment and the biosphere throughout the Cambrian radiation is hampered by loose constraints on the global palaeogeographic context. Here we couple palaeoclimate models and proxy data to evaluate the viability of contrasting Cambrian continental reconstructions proposed in the literature. We focus on two configurations that may be considered ‘end-members’ on the spectrum of Cambrian palaeogeographies, with Gondwana either spanning the full range of Southern palaeolatitudes or lying along the equator. We simulate potential climatic conditions associated with each reconstruction by running a general circulation model under a wide range of greenhouse gas levels and orbital configurations. We compare model outputs to a new database of early Cambrian palaeoenvironmental data. Scoring of the model agreement with geological data allows us to determine which continental configuration most plausibly represents the Cambrian world, and also identify regions where improvements to palaeogeographic reconstructions or model simulations are needed. This study reaffirms the coupling between numerical climate models and geological climatic data as a fundamental tool to refine deep time palaeogeographic reconstructions.
What were the Ediacaran biota? Answers from the Chengjiang Lagerstätte
1Tokyo Institute of Technology
2University of Cambridge
Since the Lower Cambrian, frondose fossil Stromatoveris psygmoglena was described from eight specimens (Shu, Conway Morris and Han 2006), more than two hundred new fossils have been discovered from the Chengjiang Lagerstätte by researchers at Northwest University, China. These specimens reveal exceptionally preserved anatomical details, which enable phylogenetic reconstruction of the relationships between Stromatoveris, iconic Ediacaran taxa and the extant phyla. Further to this, chemical analysis of exceptionally preserved Stromatoveris body tissue forms an independent line of evidence on original composition, affinities and modes of preservation. These results provide insights into the nature of hitherto enigmatic Ediacaran macro-biota, linking them to the more familiar taxa and ecology of the Cambrian.
An Early Ordovician somasteroid from Morocco reveals the origin of crown-group Echinodermata
1University of Cambridge
The early evolution of asterozoans remains uncertain given the difficulty of comparing the ossicle organization of the endoskeleton in diverse groups of Lower Palaeozoic ancestors. The Extraxial-Axial Theory proposes the homology of the biserial ambulacral ossicles based on embryonic and ontogenetic data, but its broader implications for informing the deep origin of crown-group Echinodermata have not been tested under a comprehensive phylogenetic framework. We describe an early asterozoan from the Ordovician Fezouata biota, Morocco. Despite the presence of typical somasteroid features, such as offset ambulacrals, a virgal series composed of simple ossicles, it is unique in the absence of an axially-oriented ossicle series along the body margins. Bayesian and parsimony-based phylogenetic analyses resolve this specimen in a basal position within total-group Asterozoa, illuminating the ancestral morphology of this clade. Somasteroids comprise a paraphyletic grade with stem-group Asteroidea, whereas stenuroids are paraphyletic within stem-group Ophiuroidea. Asterozoa and Crinoidea are united by the synapomorphic extension of the body wall into the free appendages. These findings clarify the contentious phylogenetic relationships between crown-group Echinodermata and its Cambrian stem lineage, which includes sessile forms with incipient pentarradial symmetry. Pelmatozoan monophyly is not supported and instead blastozoans represent the most likely sister-taxon to crown-group Echinodermata.
The murky history of Cenozoic coral reefs in the Coral Triangle
1Natural History Museum
The Coral Triangle region of Southeast Asia contains the most diverse marine ecosystems on Earth. To date most of the mechanisms proposed to explain this hotspot remain untested due to a lack of paleontological data. However, new large-scale studies of Late Cenozoic reef corals from Eastern Borneo that reveal that the first coral assemblages that occurred in the region were mainly low-relief patch reefs that developed in environmental conditions of low light and high sediment inputs. These shallow turbid habitats hosted a high coral diversity with 100 species of 55 genera in the Oligocene and 234 species of 79 genera in the Miocene. We found no significant faunal turnover at generic level within the studied time interval as 85% of extant genera were already present by the early Miocene. Preliminary comparisons of coral faunas from ancient turbid reefs with analogous modern habitats of Eastern Borneo show similarities. Our observations suggest that turbid reefs have played an important role during the origination and maintenance of coral diversity in the Coral Triangle. Most importantly, there is increasing evidence that these so-called ‘marginal’ habitats may act as crucial ecological refugia as Coral Triangle ecosystems respond to ongoing anthropogenic environmental change.
Phylogenetic position of a new Late Cretaceous duck-billed dinosaur (Hadrosauroidea) from the Dorotea Formation, Chilean Southern Patagonia
1Institut für Geographie und Geoökologie, Karlsruher Institut für Technologie (KIT), Kaiserstrasse 12, 76131 Karlsruhe, Germany
2Red Paleontológica U-Chile, Laboratorio de Ontogenia y Filogenia, Universidad de Chile, Las Palmeras 3425, Ñuñoa, Santiago, Chile
3Staatliches Museum für Naturkunde Karlsruhe (SMNK), Karlsruhe, Germany
4Institut für Geowissenschaften, Ruprecht-Karls-Universität Heidelberg, Im Neunheimer Feld 234, 69120 Heidelberg, Germany
5Laboratorio de Paleobiología de Antártica y Patagonia, Instituto Antártico Chileno, Lautaro Navarro 1245, Punta Arenas, Chile
6Área de Paleontología, Museo Nacional de Historia Natural, Casilla 787, Santiago, Chile
7Laboratorio de Zoología de Vertebrados, Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras 3425, Santiago, Chile
8Institut für Zoologie, Universität zu Köln, Zuelpicher Str. 47b, D-50674, Cologne, Germany
9Instituto de Investigación en Paleobiología y Geología (CONICET-UNRN), Avenida Roca 1242, 8332 General Roca, Río Negro, Argentina
10Área de Patrimonio Natural, Consejo de Monumentos Nacionales, Av. Vicuña Mackenna 84, Santiago, Chile
A new species of a hadrosauroid dinosaur has been discovered in the Dorotea Formation (Maastrichtian) in Southern Chile, representing the first non-Argentinian hadrosauroid. In order to establish its phylogenetic relationships we use the matrix of Xing et al (2014) for the Parsimony and Bayesian Inference analyses. The new taxon is unique in having (1) a prominent mediolaterally extended sacral ridge, projecting medioventrally from the medial face of the preacetabular process, extending across the entire dorsal margin of the iliac plate and covering the entire medial face of the preacetabular process. It reaches a maximum depth of approximately half the height of the ilium, level with the transition from the preacetabular process to the iliac plate. (2) craniolaterally a strongly deflected preacetabular process is, reaching an angle of 62° with the longitudinal axis of the supraacetabular process. The phylogenetic results suggest that the new species is a hadrosauroid no-hadrosaurid, increasing the diversity of South American hadrosauroids and it is the southernmost record for this group in South America. The specimen represents one the latest occurrences of hadrosaurian dinosaurs in South America and provides additional evidence for the discussion of the paleobiogeographical events that explain the existence of contemporary hadrosaurs in Antarctica.
Is parsimony dead? Bayesian and parsimony phylogenies tested using both empirical and simulated morphological data
1University of Manchester
2Imperial College London
All evolutionary inferences require reliable phylogenies. Morphological data has traditionally been analysed using parsimony methods, whilst likelihood methods are more commonly applied to molecular data. Recent simulation studies have suggested, however, that the Bayesian Mk-model is more accurate for morphology analyses. This is potentially problematic as very different trees can be derived using these methods. Here we simulate data under two distinct models. The first uses the fossilised birth-death process to build trees and matrices. The second uses selection of digital organisms in a mutating fitness landscape. In addition to these simulated data, 31 independent empirical datasets were used to compare trees derived from molecular data (using a priori specified models) with trees derived from morphological data through Bayesian and parsimony searches (including both equal and implied weighting). For all comparisons we used both Robinson-Foulds and SPR tree distance metrics. The results of these independent analyses are in conflict: simulation studies suggest that parsimony outperforms Bayesian, whereas empirical data finds higher congruence between molecules and morphology analysed under Bayesian inference. How these results are applied to tests of evolutionary hypotheses depends upon the confidence placed in the realism of simulations versus the reliability of empirical molecular data.
Three-dimensional priapulid trace fossils from the early Cambrian (Series 2, Stage 4) of Sweden
2Universidad de Extremadura
Of the few occasions that Cambrian ecosystems can be reconstructed with a certain amount of fidelity, fossil scalidophoran worms have constituted a dominant component. Their role is widely recognized as key actors in these ecosystems as prolific burrower-bioturbators and predators. The lower Cambrian Mickwitzia Sandstone Member from southern Sweden contains one of the most diverse and well preserved Cambrian (Stage 4) shallow marine ichnofacies representing a diverse faunal assemblage. The fine scale fidelity of preservation of traces in these rocks is of considerable significance often recording sub-millimetre scale impressions of the producer’s external anatomy and burrowing toolkit. Moulded impressions of worms found in outcrops of the Mickwitzia Sandstone that preserve a remarkable amount of anatomical detail of the producer permit assignment of traces to much lower taxonomic ranks. Comparisons with the morphology and architecture of extinct priapulids, as well as the locomotory and burrowing behaviour of extant priapulids demonstrates that these traces are assignable to stem-priapulid, or at least scalidophoran producers. This indicates that priapulids where ubiquitous in Cambrian marine environments and present in diverse ecosystems. They occupied a variety of niches including well oxygenated subtidal ecosystems and were only later displaced to their current range possibly through competition.
Evidence for a rapid recovery of snakes following the Cretaceous-Paleogene mass extinction
1Department of Biology & Biochemistry, and Milner Centre for Evolution, University of Bath
2School of Biological Sciences, and School of Earth Sciences, University of Bristol
The Cretaceous-Paleogene (K-Pg) mass extinction event saw the demise of non-avian dinosaurs, pterosaurs, and mosasaurs, amongst numerous other groups, but its aftermath also stimulated major radiations in multiple vertebrate clades. Rapid post-extinction radiations have been documented in mammals, birds, frogs, and teleosts, however the influence of the K-Pg on the evolution of snakes is poorly understood. We investigated this using a molecular clock approach, and demonstrate that all snakes descend from five boundary-crossing lineages, and Alethinophidia, the clade comprising the majority of modern snake diversity and disparity, underwent a rapid diversification in the early Paleogene. We used a novel supermatrix representing 169 species coded for up to 52 loci, with numerous outgroup taxa included to control for rate heterogeneity within the ingroup. Divergence time analyses were performed under a variety of parameterisations, outgroup topologies, and calibration sets, using both Bayesian and Maximum Likelihood methods. Our inferred association between the K-Pg event and the subsequent diversification of Alethinophidia provides evidence of the importance of this mass extinction in shaping Earth’s modern vertebrate faunas. Additional analyses of the disparity of Cretaceous and Paleogene snakes, and ancestral state reconstructions, suggest that fossoriality and small size contributed to snake survival across the K-Pg boundary.
Breathing life into an extinct sea scorpion: revealing the gill structure of a three-dimensionally preserved eurypterid through MicroCT scanning
1West Virginia University
2University of Leicester
3American Museum of Natural History
Exceptionally preserved fossils provide unique windows into the lives of extinct organisms, revealing interactions between species, behaviours frozen in time, and parts of animals that were previously unseen. These fossils allow us to reconstruct long-dead animals as living creatures and place them on the tree of life. Eurypterids were important members of Palaeozoic ecosystems, filling a wide variety of ecological roles. While the external morphology of eurypterids is well-understood, we know very little about their internal anatomy, largely due to the fact that most specimens are compressed into flattened impressions. We use MicroCT to reconstruct the internal structures of an exceptional eurypterid fossil from the Hunterian Museum in Glasgow, preserved inside a concretion, and showing unique three-dimensional preservation of internal structures. Most notably, the Glasgow specimen preserves the gills, which can provide information about whether eurypterids were active predators like scorpions or scavengers like modern horseshoe crabs. The gills may also hold the key to discovering whether eurypterids are more closely related to horseshoe crabs or arachnids. Our preliminary results indicate that eurypterids had horizontally oriented book gills similar to xiphosurans and that their gills had a surface area equivalent to that of modern active marine organisms.
Re-evaluating the Function of Cephalopod Septa
1BCUBE Center for Moleculer Bioengineering
Ammonoids are an extinct group of cephalopods whose shells have been used to reconstruct palaeoecology, macroevolutionary trends, and interpret geochemical data. However some fundamental aspects of their palaeobiology, such as habitat depth and mode of life, are poorly understood. One traditional method to estimate habitat depth is using the complex morphology of the highly curved, multi-lobate septa. Hypotheses state the increased complexity of these structures increase the resistance of the shell to implosion from hydrostatic pressure, thus forms with more complex sutures inhabit deeper waters. Evidence of this mechanical function is limited to theoretical mechanical models, the results of which directly have contradicted each other. We circumvent these problems by combining high-resolution computed tomography and finite element analysis to test different septal morphologies against a constant hydrostatic pressure. Based on the tested morphologies, septal complexity does not strengthen the shell against water pressure; furthermore, increasing the amplitude of septal folds increases the stress developed within the septa rather than decreasing it. More complex septa do show decreased stress under point loading compared to simpler septa. These results challenge the traditional interpretation of the function of septal complexity in ammonoids and the indices developed to calculate habitat depth from septal geometry.
A 3.77 (or possibly 4.28) billion year history of microbial communities associated with marine hydrothermal vents
1University of Leeds
Modern hydrothermal vents provide diverse environments for microorganisms. Here there is a large phylogenetic and physiological diversity of bacteria and archaea, occurring in a wide range habitats. An assumption is that similar communities of microorganisms have been present on Earth for an extremely long time, given that there is direct evidence of marine hydrothermal activity going back to the Archaean eon (which began 4 billion years ago), and the hypothesis that life may have originated in these environments. In this presentation I will review the fossil record of microorganisms at hydrothermal vents, which comes from two different rock types: volcanogenic massive sulfides (VMS), which formed at high temperature vents, and jaspers (iron-silica rocks), which formed at low-temperature, sulfide-poor vents. Occurrences of microorganisms in VMS go back to the Paleo-archaean era (3.235 billion years ago) and in jaspers to the Eo-archaean (3.770, or possibly 4.280, billion years ago), with the latter being the oldest organisms yet discovered on Earth. These very dates suggest that life may have been possible on Mars during its equivalent aged warmer period, and that life may be found at putative hydrothermal sites on the icy moons with liquid oceans (e.g. Europa and Enceladus).
Colonies, clones and modularity: a new view of Ediacaran fronds
1University of Cambridge
2University of Bristol
3British Geological Survey
4Memorial University of Newfoundland
The Rangeomorpha and Arboreomorpha include some of the oldest large, macroscopic organisms in the fossil record, with specimens capable of attaining lengths approaching two metres. The seemingly rapid acquisition of large size in these groups has been widely assumed to stem from an underlying morphogenetic simplicity. However, the detailed morphology of many of these organisms remains poorly constrained, rendering assumptions about morphogenesis and phylogenetic placement premature.
We here present morphological, morphogenetic and palaeoecological evidence to suggest that Ediacaran frondose taxa may variously have had modular, colonial and, perhaps, clonal body plans. Reassessment of Arborea from South Australia reveals a distinctive arrangement of internal anatomical structures that connect individual external branch units to the interior of the organism, consistent with a colonial construction. Filamentous structures amongst frond-bearing fossil assemblages worldwide reveal that rangeomorphs could be physically interconnected to other individuals of the same species by enduring stolon-like structures, over distances of tens of centimetres to metres. Furthermore, new morphogenetic data from several multifoliate rangeomorphs reveal potential evidence for biological modularity. Taken together, this information enables us to offer an alternative colonial hypothesis to explain the rapid transition to large body size in the middle Ediacaran.
HIGH DIVERSITY OF SMALL DINOSAURS PRECEDING THE CRETACEOUS- PALEOGENE (K-PG) MASS EXTINCTION
1University of Bath
Dinosaurs dominated terrestrial ecosystems for over 100 million years, before disappearing at the end of the Cretaceous. It is thought that latest Cretaceous faunas were low in diversity and dominated by large species, suggesting a decline in dinosaur diversity preceding the K-Pg boundary. However, small dinosaurs are undersampled and understudied, and so their apparent low diversity could be an artefact of sampling and study biases. Here, it is shown that alongside the giant T. rex and Triceratops, a diverse fauna of small dinosaurs thrived in the Maastrichtian, including previously unrecognized taxa of Dromaeosauridae, Troodontidae, Caenagnathidae, Alvarezsauridae, Thescelosauridae and Leptoceratopsidae. Total diversity includes roughly 40 species ranging from 2 kg to 50,000 kg, occupying carnivorous, herbivorous, insectivorous, and piscivorous niches. An analysis of functional diversity shows that ecological niche occupation increased rather than decreased from the Late Campanian to the Late Maastrichtian in the Western Interior, driven by the immigration of new taxa such as alvarezsaurids and titanosaurians. These patterns reject a diversity decline, and suggest that dinosaurs remained ecologically diverse until the end of the Cretaceous. These findings are consistent with a catastrophic extinction at the end of the Maastrichtian coinciding with, and driven by, the Chicxulub asteroid impact.
Molecular clocks on Chelicerata recover monophyly of mites and arachnids and suggest an early colonization of land
1University of Bristol, School of Biological Sciences
2University of Bristol, School of Earth Sciences
3The Natural History Museum, Department of Earth Sciences
Animal life have marine origins, with only few phyla completing their entire life cycle outside water. The process through which organisms adapt to life on land is known as terrestrialisation, and it is one of the most extreme cases of adaptation. The chelicerates (pycnogonids, horseshoe crabs, spiders) are an ancient group of arthropods, with an astonishing fossil record dating back to Cambrian, and includes the second largest clade of fully terrestrial organisms, the arachnids. Whereas morphological phylogenies support a single land colonization, phylogenomic studies support multiples by nesting marine horseshoe crabs within terrestrial arachnids.
Here, we present a timescale for Chelicerata aiming to test how many times and when arachnids adapted to life on land. We used an expanded multigene dataset covering most chelicerate diversity and the largest set of fossil calibrations to date. Our results recover monophyly of Chelicerata, Euchelicerata and Arachnida, suggesting a single terrestrialization event. Furthermore, we found Acari as monophyletic (Parasitiformes+Acariformes) and recover Tetrapulmonata (Araneae+Pedipalpi) in alliance to Scorpiones (Arachnopulmonata) or allied to a clade composed by Scorpiones+Pseudoscorpiones. Our results reconcile previous results based on morphology and molecular evidence, and suggest a Cambrian-Ordovician colonization of land by arachnids, substantially predating trace or body fossil evidence.
Increased disparity in Therapsida coincides with emergence of novel ecologies, Cistecephalidae (Therapsida:Anomodontia) as a case study
1University of Chicago
2Field Museum of Natural History
Synapsid evolution can be characterized by three successive radiations: the Permo-Carboniferous pelycosaurs, the Permo-Triassic Therapsida, and finally the Late Triassic Mammaliaformes. While descriptive studies suggest increased morphological disparity concurrent with the rise of therapsids, no work has compared disparity across the entire interval. We present detailed analysis of shape disparity in synapsid humeral elements of the majority of pelycosaur and therapsid groups, and a selection of Triassic cynodonts. Clades were analyzed for Procrustes variance, in 5 million year time bins from 305 - 235 Mya (Carboniferous - Triassic). We found that pelycosaurs show lower disparity than therapsids, and increased disparity coincides with the emergence of Therapsida. Macroevolutionary changes observed in Therapsida have historically been associated with ecological diversification. To confirm associations between clade-wide dynamics and novel ecomorphologies, we conducted comparative geometric and linear morphometric analyses on pelycosaurs, therapsids, and extant tetrapods, with emphasis on the therapsid family Cistecephalidae - small arguably fossorial dicynodonts. We found that Cistecephalidae morphospace is unoccupied by any known pelycosaur group, and the expansion of therapsid morphospace is associated with novel synapsid ecomorphologies such as that of Cistecephalidae. This provides evidence that increased disparity associated with novel ecomorphologies may have been critical to the evolutionary success of early Synapsida.
The Earliest Evidence of Metazoan Symbiosis
1Natural History Museum
3University of Leicester
4University of Oxford
The Cambrian Explosion represents a major metazoan radiation event, which is reflected in the dramatic increase of both taxonomic and ecological diversity. In light of recent fossil discoveries from exceptionally preserved Cambrian lagerstätten, the ecological complexity and trophic structures of these Cambrian marine communities has been further revealed. Here we will present the newly discovered worm species, Inquicus fellatus gen. et sp. nov, which infested the Cambrian scalidophoran worms Cricocosmia and Mafangscolex, representing the earliest examples of aggregate infestation, host specificity and host shift in metazoans. The exact taxonomic affinity of I. fellatus and the nature of its symbiotic relationship with Cricocosmia and Mafangscolex will be further discussed. Other examples of metazoan symbiosis from Cambrian communities and their ecological and evolutionary implications will also be further explored.
The ‘pliable’ nature of the phylogenetic relationships within early ornithopods
1Institute of Paleobiology, Polish Academy of Sciences, Twarda 51/55, PL-00-818 Warsaw, Poland
2North Dakota Geological Survey, Bismarck, North Dakota, United States
Neornithischians were a major clade of herbivorous dinosaurs that existed from the earliest Jurassic to the latest Maastrichtian. During their long evolutionary history, neornithischians diverged into several highly distinctive clades, including ceratopsians, pachycephalosaurs, and hadrosaurids. However, the origin and the early evolution of Neornithischia, and the phylogenetic relationships of the taxa situated near the base of the clade, remain somewhat elusive. This especially applies for those taxa traditionally placed at the base of Ornithopoda. Recent recognition of a new basal ornithopod from the Cenomanian of the Czech Republic prompted to reevaluation of the phylogenetic relationships among neornithischians situated outside of Marginocephalia and Ankylopollexia. A phylogenetic analysis reconstructed a diverse Elasmaria as a basal clade within Ornithopoda. At the same time, it inferred Hypsilophodon foxii outside of Ornithopoda as the sister taxon to Cerapoda. These results continue an ongoing trend of the removal of subsets of taxa traditionally dubbed as ‘hypsilophodontids’ from the base of the ornithopod branch of the Neornithischia to outside of Cerapoda. However, the position of these former ‘hypsilophodontids’ remains highly pliable between analyses depending on the data sampling, and the tree-search strategies used. Therefore, the changing positions should be viewed cautiously until a consensus is reached.
Sporadic sampling not climatic forcing drives early hominin diversity
1University College London
2Birkbeck, University of London
The role of climate in the origin and diversification of early hominins is hotly debated. Much of this debate has centred on whether change in the early hominin fossil record is continuous or pulsed, and whether diversification is causally linked to directional shifts in climate or climatic instability. Yet, in all previous studies, fluctuations in the number of hominin taxa are accepted as genuine changes in diversity, even though it is possible that such fluctuations reflect changes in the quality of their fossil record. We present a detailed examination of early hominin diversity dynamics through time, including both taxic and phylogenetically corrected diversity estimates, and compare these estimates to sampling metrics for rock availability and collection effort. Taxic diversity, primate-bearing formations, and collection effort strongly correlate, suggesting some features of hominin diversity may represent sampling biases rather than a genuine evolutionary signal. Peak diversity at 1.8 Ma is a sampling artefact, reflecting maximal rock availability and collection effort. Phylogenetic diversity estimates imply peak diversity at 2.4 Ma, and show little relation to sampling. We find no evidence of pulsed turnover in the early hominin fossil record and conclude that the appearance of pulsed change is an artefact of uneven sampling.
Stomata, carbon isotopes and past CO2 reconstruction: A critical comparison of fossil plant based CO2 proxy models and methods
1Trinity College Dublin, the University of Dublin
2University College Dublin, Ireland
3University College Dublin, Ireland
4University College Dublin, Ireland
5University of California, Davis, USA
Over the past decade new stomatal proxy methods and models have been developed to estimate palaeo-amospheric carbon dioxide concentration (pCO2) from fossil plants. These include mechanistic models which are founded on existing knowledge of plant photosynthetic and stomatal conductance responses to pCO2 and empirical models of plant stable carbon isotope discrimination and pCO2 derived from experimentation with the model angiosperm taxon Arabidopsis. Few experimental tests have been conducted on the efficacy of these novel pCO2 proxy methods using multiple species of varied phylogenetic origin. Fewer still have undertaken cross comparison studies through the application of multiple CO2 proxy methods to the same experimental plant material growing in known CO2 concentrations. This presentation will briefly review all new stomatal and plant stable carbon isotope based proxy CO2 methods and present new results on a cross comparison test of their accuracy when applied to 10 different plant taxa that are representatives from the four major vascular plant groups (lycophyte, monilophytes, gymnosperms and angiosperms) growing in controlled elevated CO2 chambers. The impact of exposure to varying oxygen and carbon dioxide levels on model accuracy will also be assessed.
The central nervous system of Trilobitomorpha – taphonomy, morphology and evolutionary implications
1UNIVERSITY OF CAMBRIDGE
The discovery of exceptionally preserved neurological tissues in early and middle Cambrian total-group euarthropods has clarified major controversies regarding the segmental origin of specific cephalic appendages, and illuminated the evolution of the central nervous system (CNS) in the evolutionary context of Panarthropoda. Different aspects of the CNS, such as the condensed dorsal brain and the ventral nerve cord, have so far been reported for radiodontans, fuxianhuiids, megacheirans, and bivalved euarthropods. However, data on the neurological organization of Trilobitomorpha – a diverse clade of Palaeozoic euarthropods that includes trilobites as its most familiar representatives – remains more elusive. New investigations of the Burgess Shale mollisoniid Houghtonites gracilis (Walcott) reveal details of the CNS in exceptional detail, including optic nerves, putative optic neuropils, a condensed dorsal brain, and the entire ventral nerve cord; the latter consists of condensed ganglia with segmental nerves, linked together by longitudinal connectives throughout the body. Elemental analyses reveal that the CNS of Houghtonites is replicated in graphitized organic carbon films, and thus is in agreement with the classical model of Burgess Shale-type preservation. In a broader context, Houghtonites provides new insights on the CNS of Trilobitomorpha, and casts new light on the ancestral neurological organization of crown-group Euarthropoda.
A bizarre early tetrapod from the Early Permian of Kansas, USA, provides further support for radical polyphyly of ‘lepospondyls’
1University of Calgary
2University of Pennsylvania
Two decades of phylogenetic analyses have supported a monophyletic Lepospondyli, but this was recently challenged by a study that placed two groups, the Recumbirostra and Aïstopoda, in distinct parts of the tetrapod tree. Other lepospondyl groups, such as Nectridea, remain untested. We report a new nectridean-like lepospondyl from the Permian of Manhattan, Kansas, preserving 3D morphology of the posterior skull, anterior axial skeleton, pectoral girdle, and limbs. The specimen possesses a mosaic of derived nectridean (holospondylous vertebrae with elongate transverse processes) and primitive features similar to colosteid and ‘whatcheeriid’ stem tetrapods. Cervical and anterior thoracic ribs flare distally, with the distal edge of the first thoracic rib articulating directly with the scapulocoracoid, which is low, broad, and fully-ossified with a flat, posteriorly-directed glenoid. The humerus is short and robust, with a straplike humeral head and a well-developed preaxial plate. Phylogenetic analysis resolves Urocordylidae, comprised here of the Manhattan lepospondyl plus Urocordylus and Crossotelos, as the sister taxon of the colosteid Greererpeton, well within the tetrapod stem but distinct from aïstopods, further eroding support for a traditional Lepospondyli. ‘Lepospondyli’ may represent diverse experiments in ecomorphology throughout early tetrapod phylogeny, in which case early tetrapod evolvability may be underestimated.
Get low: The evolution of the baleen whale auditory pathway
1Natural History Museum
Living baleen whales (Cetacea: Mysticeti) are the largest animals to have ever lived, using baleen to filter vast amounts of small prey in a single feeding event. They also hear the lowest frequency sounds of any mammal. This is achieved using bone conduction, where skull vibrations are transmitted to the inner ear (cochlea), which is adapted for detecting low-frequency sounds. Conversely, the earliest mysticetes were small-bodied animals that possessed teeth and fed raptorially or via suction. Whether these toothed mysticetes possessed similar auditory abilities to their leviathan descendants is one of the least-explored aspects of cetacean evolution.
Here, we detail how the mysticete auditory pathway has evolved, resulting in extant mysticetes detecting infrasonic sounds. Stem mysticetes retain the plesiomorphic basicranial morphology seen in basilosaurids with sounds entering via acoustic fat pads in the mandibles. In contrast, crown mysticetes display substantial changes indicative of the skull becoming the entry point of the auditory pathway and the use of bone conduction. Cochlear morphology is essentially unchanged, with the exception of an increase in absolute dimensions. These data suggest that although toothed mysticetes were specialised for hearing low frequencies, it was not until the appearance of crown mysticetes that infrasonic hearing became possible.
The Estuary Effect and the Origin of Lake Faunas: Critical Linkages Between Global Tectonic, Sea Level and Biodiversity
1University of Connecticut
3University of Cork
The timing and mechanisms of how faunas established themselves on land is critical to our understanding of clade origination, radiation and derivation through time. In addition, determining the conditions and physiological traits necessary for clades to invade continents allows us to better characterize the nature of these invasions and understand the requirements for survival in non-marine environments as well as informing on the possible cause of diversity disparity across the tree of life.
The early history of lake faunas is one of opportunity and amelioration. Feedback loops created by the establishment of vascular land plants altered the terrestrial nutrient cycle and impacted lacustrine regimes by increasing the nutrient availability and loading, allowing more complex trophic interactions to develop.
Clades invading the continents via the “estuary effect” did so numerous times via the episodic establishment of marine-freshwater connections along continental margins. The invasion occurrences and subsequent diversification demonstrates a dramatically different diversification pattern on continents than in the marine realm. The global tectonic and geochemical cycling that has occurred throughout the Phanerozoic may have influenced continental colonization and subsequent diversification of those clades through time.
Burgess Shale fossils reveal the ancestral state of annelid nervous systems
1University of Bristol
2Royal Ontario Museum
Despite the expectation that nervous tissues have limited preservation potential, rare occurrences of nerve cords and brains have been documented from Cambrian Burgess Shale-type Lagerstätten. Nervous tissues have been reported from euarthropods and early chordates, but are yet to be described in fossil spiralians. We report the brain, palp nerves, circumoral nerve ring, segmental ganglia and parapodial nerves of the stem group annelid Canadia spinosa, an iconic polychaete from the Burgess Shale. The nervous system of extant annelids is a highly variable organ system, ranging from ganglionated and cephalised in errant animals to the total loss of discrete segmental ganglia in sessile taxa. The earliest diverging annelids are Oweniidae and Magelonidae according to phylogenomics, which is controversial, but congruent with some morphological characters. In these animals the nervous system is simply organized and lacks ganglia with the brain possibly consisting of a simple loop. As a result of their deeply branching position and simple morphology, these taxa have been argued to possess nervous system morphologies that are annelid plesiomorphies. Canadia reveals that a complex nervous system was present in the annelid stem group and that annelid evolution is punctuated by multiple independent losses of complexity in this important organ system.
Diversity and disparity of USA Radiodonta
1University of Oxford
2University of Lausanne
Radiodonta, large Cambrian pelagic predators, are often preserved as disarticulated elements of their body plan: frontal appendages, circular mouthparts made of radial plates, lateral flaps, or carapace elements, although they are rarely found as complete specimens. These animals are best known from the Chengjiang, Haiku, Emu Bay Shale and Burgess Shale Lagerstätten. A study of radiodontan material from Cambrian deposits from the Great Basin (Utah, Nevada, and California) and Kinzers Formation (Pennsylvania) offered the opportunity to study the evolution and distribution of radiodontans at a local and regional level and at high temporal resolution, and also increased our knowledge of radiodontan diversity. Here we report the oldest Amplectobelua from Laurentia, the youngest representatives of Stanleycaris, Caryosyntrips and Tamisiocaris worldwide, and a new genus of hurdiid – all only known from USA deposits.
The frontal appendages of radiodontans were used in feeding, with different morphologies indicating different feeding styles. The disparity of frontal appendage morphologies was quantified using a character-based morphospace, separating radiodontan frontal appendages into 5 major groups: two-appendage durophages, one-appendage durophages, filter feeders, sediment sifters and raptorial predators. USA Lagerstätten contain radiodontans with the full range of radiodontan ecologies, and rival more famous Cambrian Lagerstätten in radiodontan disparity and diversity.
The ecological consequences of extinctions: from giant sharks to small mollusks
1Museum fur Naturkunde
3University of Gothenburg
4Smithsonian Tropical Research Institute
The end of the Pliocene marked the beginning of a period of great climatic variability and sea-level oscillations. Although it has been proposed that these environmental changes triggered the extinction of benthic communities in the Caribbean, large marine vertebrates are usually assumed to have remained globally resistant. We overturn this assumption by reporting a previously unrecognized extinction event in the Pliocene, in which 36% of the marine megafauna genera were lost. We used a functional diversity approach to evaluate the potential impacts of this extinction for ecosystem functioning, and found that seven out of 49 (14%) functional groups (unique trait combinations) disappeared, along with 17% of functional richness (volume of the functional space). This contrasts with previous studies that have reported negligible functional changes after the extinction of marine invertebrates. We further compared the functional diversity loss after the newly reported marine megafauna extinction and the well-known Caribbean mollusks extinction. We found that small, speciose mollusks are functionally redundant (large number of taxa filling functional groups), and consequently resilient, whereas large megafaunal taxa are functionally unique and their communities highly vulnerable. Our results suggest that functional redundancy is a key determinant of the consequences of extinctions for marine ecosystems.
The multiple origins of powered flight among paravian theropod dinosaurs: constraints from new phylogenetic, aerodynamic and anatomical data
1Vertebrate Palaeontology Laboratory, Department of Earth Sciences, University of Hong Kong, Pokfulam, Hong Kong.
2Unidad Ejecutora Lillo, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Tucumán, Argentina.
3Natural Sciences Division, University of Pittsburgh Johnstown, Johnstown, Pennsylvania, 15904, U.S.A.
4Division of Paleontology, American Museum of Natural History, New York, New York, 10024, USA.
5Foundation for Scientific Advancement, Sierra Vista, Arizona, 85650, U.S.A.
6Redpath Museum, McGill University, Quebec, H3A 0C4, Canada.
7Keck School of Medicine, University of Southern California, Los Angeles, California, 90033, U.S.A.
8School of Geosciences, University of Edinburgh, Edinburgh, EH9 3FE, U.K.
9Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology & Paleoanthropology, Chinese Academy of Sciences, Beijing, 100044, China.
The evolution of birds (Avialae) from paravian theropods is a textbook evolutionary radiation. Our understanding of this transition has been frustrated, however, by lack of consensus on the relationships between birds and their closest relatives. This lack of consensus has made it difficult to understand the timing and sequence of evolutionary changes along the line of descent to modern birds, particularly those involved with flight. We have addressed this issue through a larger, more resolved evolutionary hypothesis produced by analysing a revised dataset using an automated pipeline of analysis tailored to large morphological datasets. The grouping of dromaeosaurids and troodontids (Deinonychosauria) as the sister taxon to birds is corroborated, and we recover the Chinese ‘Jianchang’ paravians (e.g. Anchiornis) as the basalmost avialans, instead of troodontids. Wing loading and specific lift (theoretical and in vivo based criteria devised to discern volant from flightless avians) calculated for taxa with vanned feathers and interpreted in the context of the improved phylogeny provide upper and lower bounds for flapping-based locomotor evolution, especially powered flight. Powered flight appears to be limited to paravians and originated multiple times, with the strongest non-avialan candidates for this behaviour being the dromaeosaurids Microraptor and Rahonavis.
Gymnosperm–insect pollination relationships in Early Cretaceous amber from Spain
1Oxford University Museum of Natural History
2Universitat Jaume I
4Institututo Geológico y Minero de España
5Universitat de Barcelona
6American Museum of Natural History
7National Museum of Natural History, Smithsonian Institution
8University of Maryland
9Capital Normal University
10Muséum National d’Histoire Naturelle
Amber from Spain, ca. 105 Ma in age, currently provides the soundest evidence for insect pollination during the Early Cretaceous, with three known instances of insects vectoring gymnosperm pollen. The three modes of pollination are: (1) two melanthripid thrips species with bodily attached pollen clusters of cycadalean or ginkgoalean affinity; (2) a zhangsolvid long-proboscid fly with a clump of abdominally adherent bennettitalean pollen; and (3) an oedemerid beetle with several bennettitalean or cycadalean pollen grains clinging to its body, followed by a trail of additional grains resulting from insect movement before complete resin entombment. Each of these gymnosperm-pollinating lineages spotlights a distinctive evolutionary-ecological pathway, respectively. First, there were lineages that survived to the present that still pollinate gymnosperms; second, other lineages became extinct; and third, some lineages shifted to angiosperm hosts. Curiously, Cretaceous records of insects vectoring angiosperm pollen are lacking. Current evidence suggests that insect pollination was generalised among Early Cretaceous gymnosperms, specifically during the Albian–Aptian interval when angiosperm lineages were rapidly proliferating. During that time, there was considerable lineage extinction, origination, and host-plant shifts. Nevertheless, the role of insect pollination during the early evolution and radiation of angiosperms requires further assessment.
Evaluating bite marks and predation of fossil jawless fish during the rise of jawed vertebrates
1University of Manchester
The extinction of diverse clades of armoured jawless vertebrates (ostracoderms) during the radiation of jawed vertebrates in the Devonian is a major evolutionary event. Here we use fossil evidence to directly test the hypothesis that the demise of jawless vertebrates was a result of predation by jawed vertebrates. A survey of heterostracan ostracoderm fossils finds predation traces in 37 specimens. They are interpreted as predation traces due to their 1) regular geometric shape, 2) complementary traces on both sides of the animal, 3) a distinct pattern, and 4) evidence of sub-lethal (repair) attacks. Occurrences of these attacks dramatically rise during the Early Devonian (Emsian), which coincides with an increase in jawed vertebrate diversity. Our results demonstrate that the occurrence of no single jawed vertebrate group correlates with predation trace occurrences, but faunal assemblages containing predation traces were found to contain significantly different jawed vertebrate fauna to those without any predation evidence. Results therefore indicate that specific jawed taxa were likely predators in Silurian and Devonian vertebrate assemblages, but that predation did not increase through time.
The influence of cranial biomechanics on the evolution of the mammalian jaw joint and definitive mammalian middle ear
1University of Bristol
2University of Birmingham
3Natural History Museum
4University of Chicago
5University of Hull
The evolution of the mammalian dentary-squamosal jaw joint and the corresponding definite mammalian middle ear is a key event in vertebrate evolutionary history. Fossils spanning the cynodont-crown Mammalia transition document osteological modifications to the jaw and cranial bones. Theoretical biomechanical models have postulated that these osteological changes result in a shift in adductor muscle orientation, reducing load at the jaw hinge and concurrently amplifying bite force production, coupled with consolidation of cranial bones and supposed reduction in feeding-induced stress. Despite persisting in the literature for many years, these ideas remain to be tested. Here we assemble six digital reconstructions of key fossil taxa across the transition. Using multibody dynamics analysis (MDA) and finite element analysis (FEA) we test the proposed biomechanical hypotheses. Despite a slight decrease in cranial stress and strain we find no evidence for an increase in cranial strength across the transition. There is no reduction in load at the jaw hinge or increase in bite magnitude. Our results suggest that modification to load regime did not trigger the emergence of a novel jaw joint. We propose that miniaturization provided a small-size, low load environment where modifications to auditory and feeding function were possible without compromising cranial performance.
The Tournaisian Recovery of Terrestrial Vegetation Following the End Devonian Mass Extinction
1University of Southampton
2University of Leicester
3British Geological Survey (Scotland)
4University of Cambridge
To understand how terrestrial vegetation was impacted by and recovered from the End Devonian Mass Extinction, a quantitative record of Tournaisian plant spores has been acquired from a 500 m borehole through the Ballagan Formation and related outcrop sections in the Scottish Borders. This is part of the NERC TW:eed project – an integrated study of the earliest Carboniferous tetrapods and their world. The immediate post-extinction vegetation was simple and then progressively increased in diversity, including inceptions and the return of some Devonian plant groups. After this initial reestablishment, the creeping lycopod Oxroadia (Anaplanisporites baccatus with its abundant megaspore Lagenicula subpilosa) became dominant, forming dense thickets on the floodplain. These thickets were repeatedly interspersed, on the tens of meters scale, by Prolycospora claytonii-dominated assemblages. Although not known in situ, a strong association with fragments of Genomosperma kidstoni indicates a seed plant affinity. Additionally, a marked increase in abundance of Spelaeotriletes crustatus in the late Tournaisian suggests an increasing abundance of ?progymnosperms. Quantitative abundance of selected spores correlates with palaeosol distribution, highlighting repeated climatic fluctuations between wetter and drier episodes. CONISS analysis reveals eight distinct assemblages that can be mapped onto long Milankovitch cycles, identified in marginal marine sections.
Get across the wood: exceptional preservation of Cretaceous soft-bodied xylophagous mollusks
1CR2P UMR 7207 Sorbonne Universités, Muséum national d'Histoire naturelle, Université Pierre et Marie Curie, CNRS, Paris, France.
2ISYEB UMR 7205 CNRS, Muséum national d'Histoire naturelle, Université Pierre et Marie Curie, EPHE, Paris, France.
3IPHEP UMR 7262 CNRS INEE, Poitiers, France.
4IMPMC UMR 7590 CNRS, Université Pierre et Marie Curie, IRD, Muséum national d'Histoire naturelle, Paris, France.
6Palaios association, Valdivienne, France.
Teredinidae are obligate xylophagous bivalves colonizing drifted woods and displaying a specialized anatomy with a shell highly reduced in size, so that the vast majority of their anatomy consists in soft-tissues. Therefore, their fossil occurrences mostly correspond to burrows, isolated shell valves or small terminal aragonitic structures called “pallets”. Here, we report exceptionally preserved shipworms from the Late Cretaceous of the Envigne Valley (Vienne, France) with soft-parts which are frozen by silicification emerging out of the wood. This preservation led us to investigate the inner content of the inhabited wood pieces using computed tomography to document the anatomical preservation of the animals and their organisation inside the wood. The 3D-reconstructions evidence that rare and fragile soft-tissues are preserved inside (mantle, respiratory siphons) but also surprisingly that the mineralized pallets, which are a key-feature of the Teredinidae anatomy, are here absent. On the basis of this finding, we analyzed the different tissue mineralogy to conclude on the evolutive of taphonomic absence of these structures and further suggest an explanation to their up to date variable fossil record. The selection of the colonized woody pieces and the local environment of the Envigne Valley are also inferred from the study of these shipworms.
Tooth replacement and tooth resorption mechanisms in Osteichthyes
1Naturalis Biodiversity Center
2University of Bristol
Mechanisms of tooth replacement are characterized in Chondrichthyes with tooth families resembling a conveyor belt and intraosseus tooth replacement in Tetrapoda. Tooth replacement in Osteichthyes is linked with resorption before shedding, whereas in Chondrichthyes teeth are shed without resorption. Basal conditions and the origin of tooth replacement and resorption in Osteichthyes are debated. Comparative data on tooth replacement and resorption of fossil and recent taxa are rare.
We use digital, non-destructive Synchrotron microscopy (SRXTM) to identify lines of arrested growth and resorption lines as evidence to reconstruct sclerochronology. Detailed 3D segmentation in submicron scale of articulated undebated jaws and teeth of recent and fossil osteichthyans allows an identification of replacement mechanisms in teeth and oral denticle morphotypes.
Resorption lines in Polypterus and Moythomasia are continuous proximal to the replacement teeth and can erode deeply, erasing parts of initial teeth completely or only partially. Oral denticles e.g. in Moythomasia are not replaced, but added appositionally. Although dental morphologies in Moythomasia are different their replacement and resorption are similar in contrast to oral denticles that differ in morphology and replacement. These results facilitate an interpretation of mechanisms in fragmentary material and evolution of tooth resorption in Osteichthyes.
Approaching sexual dimorphism in non-avian dinosaurs and other extinct taxa
1University of Bristol
2Institut des Sciences de l’Évolution de Montpellier
3University of Bath
Sexual dimorphism, exhibited in most extant vertebrates, including Aves, has been proposed for various extinct taxa. Such claims in non-avian dinosaurs have been received skeptically, with rates of dimorphism claims underrepresented compared to other fossil groups. Alternative explanations regarding dinosaur ornaments/armaments either misrepresent sexual selection theory (e.g., ‘species recognition hypothesis’) or ascribe relatively rare socio-sexual systems broadly across Dinosauria (e.g., ‘mutual sexual selection hypothesis’). We propose a different approach to testing for dimorphism in extinct taxa. Under game theory, the null hypothesis for anisogamic species is that dimorphism is present. Previous studies rely on low-power statistical approaches and fail to test for the actual signal of dimorphism (demonstrated here through statistical modeling). Contrary to how these studies frame the problem, the goal should be to constrain the plausible range of the magnitude of sexual dimorphism. Rather than testing for two distinct morphs, our approach looks for divergence in a trait through growth combined with testing specific alternate hypotheses (e.g., ontogenetic, interspecific, non-sex-based individual variation) using histological and taphonomic methods and focusing on traits typically involved in sexual selection (e.g., body mass, coloration, ornaments/armaments). Many dinosaur taxa show patterns in bizarre structures consistent with sexual selection and are therefore likely dimorphic.
The Other Old Red Continent: Ichnological Signatures of Arthropod Terrestrialization Throughout the Silurian of Australia
1University of Cambridge
The terrestrialization of arthropods is a key event in the history of Earth; its timing, estimated through ichnological evidence, suggests Cambro-Ordovician excursions were followed by Siluro-Devonian colonization of fully non-marine habitats. Much of this evidence comes from Euramerica, leading to potential bias in our understanding of terrestrialization towards the ‘Old Red Continent’.
Here we present field results of an holistic ichnological survey across much of the Silurian-Devonian sedimentary record of Australia (Grampians Group, VIC, Mereenie Sandstone, NT, Tumblagooda Sandstone, WA). We find high ichnological diversity in the shallow marine record of the Grampians Group, but fluvial parts of the succession are barren. This contrasts to the classic aeolian deposits of the Mereenie Sandstone, where a limited ichnofauna is dominated by Diplichnites and Polarichnus. Both areas differ from the high ichnodiversity Tumblagooda Sandstone, from which we present new sedimentological evidence demonstrating tidal deposition, rather than a fluvial-aeolian setting as previously interpreted.
Australian ichnological data is compared with Euramerican data to show that, worldwide, Silurian non-marine environments appear to have had limited ichnodiversity, suggesting this interval records the initial phases of full colonization.
Closing the gap between palaeontological and neontological speciation and extinction rate estimates
2University of Gothenburg
3University of Lausanne
4Swiss Institute of Bioinformatics
Speciation and extinction drive changes in biodiversity, therefore defining and quantifying the rates of species origination and extinction has wide-reaching implications in macroevolution. Neontologists use phylogenies of extant species to estimate diversification rates, while palaeontologists infer them using the fossil record. Although living and extinct species are samples of the same underlying evolutionary process, large discrepancies between speciation and extinction rates inferred using fossils and phylogenies have been widely documented for empirical data, but the theoretical reasons for this discrepancy remain unknown. Here, we demonstrate that the discrepancies are driven by differences in implicit assumptions about the process of speciation in neontological and palaeontological models. We present the birth-death "chronospecies" model that clarifies the definition of diversification rates in a joint palaeontological and phylogenetic framework. Using simulations and empirical datasets, we show that the model can explain much of the apparent incongruences between rates estimated using fossils versus phylogenies. Our new model will play an important role in the future integration of palaeontology and phylogenetics.
Incorporating inapplicable data in phylogenetic analysis
2Imperial College, London
Morphological cladistic analysis is a central tool in bringing palaeontological data to bear on biological and evolutionary questions. One impediment to reliable phylogenetic analysis arises where morphological observations are translated into discrete, computer-readable characters. There is presently no satisfactory way to account for ‘ontogenetically dependent’ characters that are cannot logically be applied to all taxa: for example, ‘tail colour’ where some taxa lack a tail.
Existing algorithms treat such ‘inapplicable’ data points as either ambiguous (‘missing’) data, or as an extra state. Both of these approaches introduce systemic error in tree length calculations, causing suboptimal trees to be recognized as the shortest and thus jeopardizing phylogenetic conclusions.
We resolve this issue with a new approach that enumerates occurrences of homoplasy, rather than transformations between character states. A modified four-pass version of the Fitch algorithm generates accurate length counts for all character configurations, which allows the safe inclusion of inapplicable data without the introduction of bias.
Inapplicable data are particularly common in larger datasets, and ‘combined’ datasets incorporating observations from multiple taxa. Our new method enables robust phylogenetic analysis of datasets with broader taxonomic scope.
Towards more accurate inference of phylogeny from morphology: a case study in extant crocodilians
1Museum für Naturkunde, Berlin
DNA is generally used to infer phylogeny for modern taxa, and its use is increasingly reliable, but for fossils we must rely on morphology. For groups where phylogenies have been inferred using DNA and morphology separately, the two often disagree. There are grounds to consider DNA-based phylogenies to be more reliable, including biogeographic consistency and lower homoplasy, indicating that morphology-based phylogenies for fossils may be far from correct. Better ways to to infer phylogenies from morphology must be developed. In order to begin to address this, the consistency of a matrix of morphological characters with a DNA-based phylogeny for modern crocodilians is assessed. Groups of characters are compared used a Mann-Witney U test and three consistency indices, and all characters were reassessed first hand and documented. Postcranial characters were significantly more homoplastic ( p < 0.05) than cranial characters, perhaps due to the lower functional load and greater complexity of the cranium. Characters which were clearly homologous within each state and where state delimitation was clear were significantly less homoplastic (p < 0.05) than other characters. Focus on character quality, rather than quantity and/or skeletal coverage is thus tentatively recommended, but further work examining different methodologies and taxa is required.
A minimum population extinction time driven by stochastic environmental forcing
1California Institute of Technology
2University of Michigan
3Massachusetts Institute of Technology
The number of individuals within a population, or number of species within a lineage, changes with time in an inherently stochastic manner. Fluctuations within such a stochastic trajectory have long been recognized as a pathway by which extinction occurs, particularly within small populations. However, it is less well understood how external sources of stochastic forcing, such as environmental variability, interact with a population's intrinsic stochasticity. In this work, we develop a model from which the typical time to extinction of a population is computed, subject to forcing from an environment that switches randomly between two states with differing death rates. We find that there exists a frequency of environmental fluctuations that minimizes the mean time to extinction. This “worst” switching rate scales with the population’s generation turnover timescale, indicating that extinction risk varies across species with differing per capita birth rates. We discuss the implications of this timescale-sensitivity for extinction selectivity during past extinction events within the geological record. Furthermore, we show that the rate of evolution may be dependent critically upon the timescale of environmental perturbations.
The environmental context of early animal evolution
2Trinity College Dublin
Animals originated and evolved during one of the most unique times in Earth history—the Neoproterozoic Era. A large dataset of >10,000 Neoproterozoic-Paleozoic shale samples compiled by the Sedimentary Geochemistry and Paleoenvironments Project is interrogated here to better understand the landscape early animals inhabited. Using a space-for-time translation, animal ecosystems along modern natural gradients of oxygen and primary productivity are then used to conceptualize Neoproterozoic ecosystems. Analyses of redox-sensitive trace metals demonstrate that animals evolved in a relatively low-oxygen ocean, although perhaps not considerably less oxygenated than the Paleozoic. Anoxic water columns were generally ferruginous (iron-rich) rather than euxinic (sulfide-rich, as in the modern ocean), and sulfide stress was likely limited. Habitats suitable for chemosymbiotic lifestyles based on sulfide oxidation were also likely rare. Analyses of sedimentary total organic carbon suggest that early animals lived in an ocean with lower primary productivity compared to the preceding Mesoproterozoic or following Paleozoic. Combined with an inability to inhabit productive regions in this low-oxygen ocean—where aerobic respiration would quickly draw down oxygen to lethal levels— Neoproterozoic animal communities would have likely been more food limited than generally appreciated, leading to important impacts on ecosystem structure and organismal behavior.
Fossil plant cuticles may track SO2 pollution during LIP volcanisms - implications for understanding mass extinctions
1Swedish Museum of Natural History
2University College Dublin
3University of Leeds
Flood basalt volcanism and large igneous provinces (LIP) have been implicated in several of the major Phanerozoic mass extinctions, principally through global warming caused by highly elevated pCO2. The Triassic-Jurassic boundary (Tr-J) and the associated end-Triassic mass extinction, is one such event. However, the patterns of Tr-J biodiversity loss observed are sometimes difficult to reconcile with the effects of global warming alone. Recently attention has therefore turned to additional volcanic products as potentially aggravating factors - in particular sulfur dioxide (SO2), but so far it has been difficult to detect SO2 in the geological record. Here, we present new data showing that fossil plant cuticles may indicate the presence of SO2 at the Tr-J. Plant cuticles are highly resistant, often persisting as fragments in sediments even when macrofossils are not available. We show that damaged and distorted cuticle surfaces across the Tr-J are consistent with modern and experimental SO2-caused cuticle damage and with leaf-shape changes across Tr-J, providing more detailed information about the Tr-J environmental degradation and ecosystem response. These results identify fossil cuticle distortion as a useful proxy for past SO2 emissions and with it the potential to improve our understanding of the Earth system.
Climate change and rates of crocodylomorph body size evolution
1University of Bristol
The Crocodylomorpha are an extremely ancient group, but unlike other vertebrate groups of similar antiquity they have an extensive crown-group. The Crocodylomorpha have therefore been subjected to dramatic environmental changes and multiple extinction events throughout their history. The Crocodylomorpha frequently exhibit an aquatic mode of life, robust skeletons and tough osteoderms, improving their preservation potential. As such, the Crocodylomorpha have a good fossil record relative to other vertebrate clades. Their long history and good preservation makes them excellent subjects for studying the effects of environmental change on vertebrate evolution. Here we present a study of crocodylomorph body size evolution using comparative phylogenetic approaches. Rates of crocodylomorph body size evolution is highly heterogeneous, with generally low rates interrupted by brief periods of rapid diversification. Crocodylomorph diversity, body size and rate of body size evolution is found to be strongly correlated with temperature. Diversity is constrained by cooling, but can recover quickly in periods of climate stability. Body size and rates of body size evolution increase with cooling. Punctuational evolution and sensitivity to temperature lends support to the Court Jester hypothesis. A relationship between body size and temperature has is a cause for concern in the light of anthropogenic climate change.
The importance of microenvironment in determining the roles of early diverging fungi in early terrestrial ecosystems
1Natural History Museum
Fungi are thought to have been important in early terrestrial ecosystems as saprotrophs, mutualists and parasites of plants and animals. Fossil fungi are abundant, but determining their roles can be difficult. Environmental context is important, so we are investigating fungal diversity in different microenvironments using high resolution photographic mapping of substrates in thin sections to plot fungal distribution in relation to organic matter. Fossils of interest are targeted for more detailed study using Confocal Laser Scanning Microscopy. We examined a thin section of the 407-million-year-old Rhynie Chert (Scotland). We observed layering of the vegetation and corresponding variation in preservation on a millimetre scale, which reflects fossilisation in a time series under different environmental conditions. Colonization of plants by fungi varies significantly through the section in terms of abundance. Taken together the environmental context, state of preservation of the plants and the morphology of the fungal bodies indicate predominantly saprotrophic interactions by early diverging fungi operating in litter vegetation under drying conditions. This approach, which considers the microenvironment of the fossils, is essential to developing a deeper understanding of the roles of fungi in early terrestrial ecosystems.
Species discovery and changing taxon concepts in Cenozoic molluscs - after 50+ years what does revision of a popular handbook tell us?
1Natural History Museum, London
Over the past 30 years it’s been established that many common and widespread (‘traditional’) morphologically-based species of benthic marine invertebrates fall into more narrowly distributed allopatric and genotypic clusters. These DNA clusters typically correspond with more narrowly defined morphological species – so-called cryptic species - that are considered by almost all taxonomists to be species. Because invertebrate palaeontology pays little attention to species concepts, does this mean that that species (=taxon) concepts are diverging between zoological and palaeontological communities? Until now this has not been examined.
Updating a handbook of common British Cenozoic fossils for a new 2017 edition involved fully revising identification, taxonomy and stratigraphic range data for 266 molluscan species. This small but highly vetted data set allows insight to whether taxon inclusiveness has changed over the past 56 years since the first edition. I will examine how current views of the morphological inclusiveness of species has changed in response to; improved taxonomy and nomenclature, increased sampling, improved stratigraphic resolution, and novel discoveries. I will examine how these changes have led to stratigraphic or geographic range changes and how newly established species durations compare to data derived from other taxonomic and geographic studies of Cenozoic molluscs.
Carbon characterization in the Sirius Passet Biota and a geothermal gradient through Cambrian Lagerstätten
2University of Bologna
3University of Johannesburg
Mechanisms that delay the degradation or destruction of organisms are viewed as one of the most important taphonomic factors that lead to the exquisite preservation seen in Lagerstätten deposits. However, perhaps of equal importance, yet rarely explored, is the subsequent metamorphic history and peak thermal paleotemperature of Lagerstätten deposits. Raman spectroscopy is a non-destructive technique that allows the investigation of the organic and inorganic chemical structure of samples. The structure and the degree of disorder of the organic matter in that sample can then also be used to estimate peak metamorphic temperature. Here we investigate the structure of the carbonaceous matter in the exceptionally preserved early Cambrian Sirius Passet Lagerstätte using Raman spectroscopy. The spectral characteristics are indicative of moderately ordered kerogenous matter and indicate that the transitional Buen Formation that hosts the Sirius Passet biota was thermally altered at a peak temperature of 409 °C (±50°C). How does this palaeotemperature compare with other prominent Cambrian Lagerstätten (such as the Burgess Shale) and is there a relationship between the morphological fidelity of fossils in Lagerstätten deposits and the thermal maturity of the host strata?
A ‘reptilian’ mode of reproduction in pterosaurs and its implications for pterosaur palaeobiology
1University of Leicester
Determining the biology of pterosaurs has proven challenging and key aspects such as their reproductive biology are still much debated. Over the last decade a spectacular series of fossil finds, including eggs, embryos, neonates and several complete postnatal growth series have provided critical new evidence. Interpreted using current knowledge of reproduction in extant amniotes these fossils present a remarkably detailed picture of pterosaur reproduction. Females had paired ovaries and laid relatively small, oval, pliable-shelled eggs that were incubated at ambient temperatures in vegetation or a loose substrate. Neonates were well developed with extensive flight membranes and likely superprecocial, able to fly at, or soon after, hatching. Young pterosaurs required little or no parental care and grew slowly at rates a magnitude lower than that of extant birds or bats. This reproductive mode, which is strikingly different from that of extant fliers, but fully compatible with that of basal amniotes, has important implications for other aspects of pterosaur biology. Embryonic development at ambient temperatures is more consistent with heterothermy than homeothermy which, in turn, is consistent with relatively slow post-natal growth rates. The ability to grow and fly may help explain pterosaur gigantism and also has profound implications for pterosaur ecology.
Reconciling the commonality of long-term stasis in the fossil record and the rare detectability of stabilizing selection in extant biota
1CNRS, Univ. Lille, UMR 8198 Evo-Eco-Paleo, Lille, France
2Limnology Unit, Department of Biology, Ghent University, Ghent, Belgium
Rapid evolutionary changes are common in many extant species, whereas fossil species regularly display morphological stasis for millions of years. Hence, evolutionary biologists from different disciplines can carry drastically different expectations on rates of evolutionary change. Here I dissect these apparent discrepancies in expectations by constructing models of expected trait change under various micro-evolutionary processes (genetic drift, directional and stabilizing selection) and by comparing these models with observed morphological change in a fossil species lineage that displayed stasis in all examined traits for over 5,000 years, and that was sampled at a resolution bridging ecological and evolutionary timescales. On ecological timescales the expected magnitude of trait change is very similar for all models of micro-evolutionary processes, and observed magnitudes of trait change broadly overlap with all of these models. Stasis-associated rates of morphological change in the fossil species lineage fall largely, but not exclusively, within the range of genetic drift. On evolutionary timescales, however, change is more constrained than predicted by neutral evolution. In short, the absence of evidence for stabilizing selection from studies of morphological changes over ecological periods even applies to high-resolution studies of paleontological stasis and it does not imply that the process is rare in extant natural populations.
Cambrian weird wonders and the origin of ctenophores
1University of Bristol
2Yunnan Key Laboratory
3Natural History Museum, London
Ctenophores have in the last decade figured in a sometime acrimonious debate regarding their systematic position in the metazoan tree—are they the sister group to all other animals, or are they immediately stemward of bilaterians, perhaps together with cnidarians? Molecular phylogenetic studies have recovered both and a wide consensus is still lacking. Here we describe a remarkable new specimen of Dinomischus from Chengjiang, China. It preserves rows of compound cilia on tentacles, resembling comb row structures, that together with a number of other Cambrian fossils demonstrate an evolutionary origin of ctenophores from a sessile polyp-like suspension feeder. Dinomischus furthermore preserves internal mesenteries, like cnidarians. Morphological phylogenetics firmly recovers cnidarians and ctenophores as a clade (Coelenterata) based in part on this new evidence, together with several anatomical and embryological features. Furthermore, the development of ctenophores is echoed by the Cambrian stem groups introduced here, including the scleroctenophores, Siphusauctum (the “tulip animal”), and Xianguangia, which shifts from the cnidarian stem to the ctenophore stem. Our findings simplify some aspects of the early evolution of metazoan body plans compared to the “ctenophores first” scenario.
High-dimensional geometric morphometric approach to understanding skull shape evolution in squamates
1University College London
2Natural History Museum U.K.
3University of Texas, Austin
4Museum für Naturkunde, Berlin
5Muséum national d'Histoire naturelle, Paris
Squamata, with ~10,000 extant species, exhibits remarkable diversity in cranial morphology that mirrors its incredible range in ecological modes. With such wide variation, elucidating how and why certain skull configurations evolved in squamates has enormous potential to formulate general principles underlying skull evolution. Achieving this task, however, requires a systematic and robust characterization of cranial morphology and a comprehensive taxonomic sampling of extant and fossil groups. Here, we harness 3-D reconstructions from micro-CT and surface scans of ~150 taxa to generate a dense geometric morphometric characterization of skull morphology. With a suite of computational tools, we test the tempo, mode, pattern of modularity, and potential drivers of cranial shape evolution. The dataset, capturing the morphological and ecological breadth of squamates, shows a strong ecological signal, namely among fossorial groups, elevated disparity and morphological evolutionary rates in the early history of the clade, and distinct highly modular rostral and integrated posterior parts of the skull. As phenomic data accumulate rapidly in paleontology, this study demonstrates an emerging class of evolutionary analyses that synthesizes high-dimensional phenotypic data with a deep time perspective—one with incredible potential for understanding the morphological evolution of major vertebrate clades.
Tracking genome size variation in a 407 milion year old plant.
1Department of Palaeontology and Stratigraphy, Faculty of Earth Sciences, University of Silesia, Poland
2Department of Earth Sciences, The Natural History Museum, London, UK
Asteroxylon mackiei is a 407 Ma clubmoss from the Rhynie Chert, but its exceptional preservation creates an opportunity to study a phenomenon important for all living plants – changes in genome size (GS). Changes in GS played a major role in plant evolution with evidence from comparative genomics of repeated cycles of ancient whole genome duplication followed by diploidization. Because GS is related to stomata guard cell length (GCL) it can be investigated in fossils (GCL is greater in plants with bigger genomes). Previous research based on small samples of published GCL values concluded that early land plants possessed exceptionally large genomes. A. mackiei stomata were measured directly from slides in the collections of The Natural History Museum (London), The Hunterian (Glasgow) and The University of Münster (Germany). These were compared to GCL of living clubmosses of known GS. GCL of A. mackiei falls within the larger range of modern Lycopodiaceae, indicating that its GS is not exceptionally large but comparable to that of living Huperzia selago. These fossils also showed a very broad range of GCL values (39-92 µm), which we interpret as providing the earliest direct evidence of genome size variation in plants at the species level.
High-resolution virtual histology in 3D for understanding development in living and fossil birds
1University of Southampton
2University of Debrecen
Determination of developmental age and life history traits of fossils is crucial for accurate taxonomy and understanding evolution and biology of extinct animals. However, the exceptionally rapid growth of extant birds means ageing methods based on incremental growth lines (e.g. LAGs), used in other vertebrates, are largely inapplicable and robust alternative ageing methods remain to be established.
Analysis of avian intracortical bone microstructure provides a promising approach but, to date, most microstructural studies in avian bone are qualitative, 2D, involving a limited range of living species, and applying destructive thin-section-based histology. We aim to use minimally-destructive high-resolution 3D imaging to identify and quantify microstructural phenotypes in extant species to help estimate developmental age and life history in fossil birds.
We assessed the 3D microstructure of cortical bone from the midshaft of the femur, tibiotarsus, and humerus in a growth series of domestic ducks (Anas platyrhynchos) using high-resolution synchrotron-based computed tomography and found qualitative changes in pore diameter and heterogeneity throughout development. While volumetric bone measures allow distinguishing juvenile from adult birds, further analysis is ongoing to interpret age more specifically. Future work will test how variation in microstructure relates to body mass, life history, and phylogeny, by comparing extant species.
Hidden diversity of small theropods from the Bathonian (Middle Jurassic) of the UK
1Department of Earth Sciences, Natural History Museum, London
2Department of Earth and Planetary Sciences, Birkbeck, University of London
Theropod dinosaurs are well represented in the British Middle Jurassic. The record is dominated by large-bodied tetanuran theropods including: Magnosaurus nethercombensis and Duriavenator hesperis from the Bajocian Inferior Oolite of Dorset; the historically important taxon Megalosaurus bucklandii from the Taynton Limestone Formation of Oxfordshire; Cruxicheiros newmanorum from Cross Hands Quarry, Warwickshire; and Eustreptospondylus oxoniensis from the Oxford Clay of Oxfordshire. With the exception of Proceratosaurus bradleyi and other fragmentary remains, small-bodied taxa are less well known. In order to investigate the diversity of these small-bodied taxa more thoroughly, a dataset was built on the basis of 250 small theropod teeth recovered from microvertebrate sites throughout the UK Bathonian. Tooth shape was quantified and analysed using multivariate statistical methods, including Principle Component Analysis and Pairwise Discriminant Function Analysis to test if these isolated teeth overlap with, or are quantifiably distinct from, the morphologies of approximately coeval taxa from similar geographic areas. Results demonstrate that there are at least four quantifiably distinct theropod tooth morphotypes that do not overlap those of named taxa. The Bathonian record of the UK therefore contains a much higher theropod diversity than previously recognised, with these new records including a dromaeosaurid-like taxon and an early troodontid.
New record of an abundant ammonite assemblage from the latest Cretaceous Corsicana Formation, Brazos River, Texas. Implications for the Cretaceous–Paleogene (K–Pg) mass extinction event in the Gulf of Mexico.
1Division of Paleontology (Invertebrates), American Museum of Natural History, New York, USA
2Earth and Environmental Sciences, Brooklyn College, Brooklyn, New York, USA
3Department of Geography & Geology, University of Copenhagen, Copenhagen, Denmark
4Geology Department, Amherst College, Amherst, Massachusetts, USA
5Earth Sciences, University of Southern California, Los Angeles, California, USA
6Department of Geology & Geophysics, Texas A&M University, College Station, Texas, USA
Outcrops along the Brazos River, Texas, containing the Cretaceous-Paleogene (K–Pg) boundary provide critical insight into the timing and nature of the mass extinction event 66 million years ago. Investigations of the Corsicana Formation at two sites (Darting Minnow and Cottonmouth Creek) have resulted in the discovery of an abundant ammonite assemblage directly below the K–Pg boundary. Findings of Discoscaphites iris confirm the presence of the highest Maastrichtian ammonite range zone in North America, corroborated by dating from calcareous nannofossil biostratigraphy. The Brazos ammonite fauna is characterized by high abundance but low diversity, dominated by the genera Eubaculites and Discoscaphites, with rare Sphenodiscus and gaudryceratids – first record of this group in the Maastrichtian of the United States. Jaws and juvenile specimens are present, indicating a living community. Well-preserved shell material allows for determination of water temperatures during the latest Cretaceous, which can be compared with sedimentary geochemistry to explore climate trends and the effects of volcanism leading up to the mass extinction and Chicxulub bolide impact. Ammonites thrived during the latest Maastrichtian in the western Gulf Coast, contradicting hypotheses for an early disappearance of the group at low latitudes prior to the K–Pg extinction.
Evolution of complex life: Late Neoproterozoic co-divergence of bilaterians and their gut microbiota
1Massachusetts Institute of Technology
The seemingly simultaneous appearance of animal crown group fossils in the early Cambrian, while reliable Neoproterozoic fossils remain limited, is known as Darwin’s Dilemma. Recent work has combined geological age data with molecular sequences from living species to establish a timescale for the Tree of Life, with increasing evidence for bilaterian divergence in the Cryogenian and/or Ediacaran periods. Meanwhile, microbiota associated with animals play a pivotal role in their development (e.g. nutrient processing, immune system activation), but bacteria lack a fossil record entirely. Here I show that bacterial clades significant to the animal gut microbiota have estimated divergence times during the Cryogenian-Ediacaran, coincident with the inferred evolution of bilaterian gut morphology. New strategies are introduced to constrain bacterial divergences, including the horizontal transfer of genes into fossiliferous clades, and the cospeciation of bacterial symbionts with their fossiliferous animal hosts. 18 calibrations are derived from fossils which meet phylogenetic and straigraphic criteria comparable to the level of scrutiny in high-quality divergence time analyses of animals. Prior calibrations do not circularly invoke the Neoproterozoic, implying this result is genuine. I suggest that bacterial diversification was sparked by the opening of new niches in the form of bilaterian tissue differentiation.
Substrate relationships and biomineralisation of an Ediacaran encrusting poriferan
1University of Edinburgh
Benthic metazoans encrust in order to secure and maintain growth on a substrate, a key competitive innovation. Here we describe the substrate relationships, mode of biomineralisation and possible affinity of Namapoikia rietoogensis, a large (<1 m), robustly skeletal, and modular Ediacaran metazoan which colonised the walls of synsedimentary fissures within microbial-metazoan reefs.
Namapoikia had an internal structure of open tubules and transverse elements, and a non-deterministic growth form which could encrust both lithified, and living microbial substrates, the latter via modified skeletal holdfasts. Namapoikia shows growth interactions and substrate competition with contemporary living microbial mats, including the production of plate-like dissepiments which elevated living tissue above the microbial surface. Namapoikia could also recover from partial mortality caused by microbial overgrowth.
We infer that initial skeletal growth involved the rapid formation of an organic scaffold via a basal pinacoderm prior to calcification. This may be an ancient mode of biomineralisation similar to the living calcified demosponge Vaceletia. Possible skeletal growth banding, combined with large size, also implies individual longevity. The open tubular internal structure, non-deterministic skeletal organisation, and inferred biomineralisation style of Namapoikia suggest affinity within total-group poriferans.
A Triassic-Jurassic window into the early evolution of Lepidoptera
3Hessisches Landesmuseum Darmstadt
4Staatliches Museum für Naturkunde Stuttgart
Based on an assemblage of fossilized wing scales encountered in latest Triassic and earliest Jurassic sediments from northern Germany, we here present the so far earliest evidence for Lepidoptera (moths and butterflies). The diverse scales confirm a (late) Triassic radiation of lepidopteran lineages, including the divergence of the Glossata, the clade that comprises the vast multitude of extant moths and butterflies that have a sucking proboscis. The microfossils extend the minimum calibrated age of glossatan moths by ca. 70 million years, refuting ancestral association of the group with flowering plants. Development of the proboscis may be regarded as an adaptive innovation to sucking free liquids for maintaining the insect’s water balance under arid conditions. Pollination drops secreted by a variety of Mesozoic gymnosperms may have been non-mutualistically exploited as a high-energy liquid source. The early evolution of the Lepidoptera was probably not severely interrupted by the end-Triassic biotic crisis.