The origins of colour patterns in fossil insects: insights from trace element chemistry
*Nidia Alvarez Armada1, Maria E. McNamara1, Sam Webb2 and Fiona L. Gill3
1University College Cork, Ireland
2Stanford Synchrotron Radiation Lightsource, USA
3University of Leeds, UK
Insects are the most diverse group of animals known and are adapted to live in almost all terrestrial, and some aquatic, biomes. The most striking adaptations of insects include colour patterns on their cuticle, which are produced primarily by pigments such as melanin. Many fossil insects also exhibit patterns on their cuticles, but which pigments are responsible for generating the patterns is unknown. We resolve these issues using synchrotron X-ray fluorescence (XRF) to characterise the spatial distributions of trace elements in patterned cuticles of fossil and modern insects. Principal component analysis (PCA) of the concentrations of these elements reveals a strong taxonomic signal: representatives of individual insect families show similar concentrations of trace elements. In at least some families, this taxonomic signal is overprinted by a pigment-related signal, whereby cuticle regions of different colours differ in trace element chemistry. Understanding pigment- and taxon-specific variation in trace element chemistry will greatly enhance our ability to interpret the original pigmentary colours of fossil insects, thus informing models of the evolution of colour and its ecological functions in insects through deep time.
Mineralogical insights into the tissues of Burgess Shale animals
*Ross P. Anderson1, Nicholas J. Tosca2, Stuart L. Kearns3 and Derek E. G. Briggs1
1Yale University, USA
2University of Oxford, UK
3University of Bristol, UK
Burgess Shale-type fossils are crucial to our understanding of the diversification of animals during the Cambrian explosion. There has been a substantial effort to understand their taphonomy since it is vital to biological interpretations. Clay minerals have been implicated in preservation, templating soft tissues during decay and early diagenesis. Differences in elemental abundances (and, by inference, clays) across fossil anatomy were previously attributed to contrasts in the decaying tissues. However, subsequent work suggested that the clays formed much later, with differences reflecting volatization of tissues during different stages of metamorphism. In either case, the clays could reflect the nature of tissue chemistry, but clearly linking specific clay minerals with different tissues remains a challenge. Here we utilize selected area X-ray diffraction to identify clays non-destructively across the anatomical features of multiple specimens of Marrella from the Burgess Shale. These analyses revealed that the stomach and cephalic canals, and occasionally the gut trace, are differentiated from the remainder of the fossil and matrix by the presence of kaolinite. Identifying mineral phases provides more information on their formation than elemental mapping alone and may allow us to differentiate the chemistry of the original tissues on which they precipitated, thereby revealing new biological information.
Cambrian bivalved arthropods and the origin of mandibulates
*Cedric Aria1 and Jean-Bernard Caron1,2
1University of Toronto, Canada
2Royal Ontario Museum, Canada
Although they were first believed to be related to crustaceans, a number of iconic Cambrian taxa with bivalved carapaces (such as Canadaspis, Odaraia, Branchiocaris) have, in the last decade, been more commonly presented as early, or even earliest, euarthropods. This view was based heavily on a lack of information on the cephalic configuration of these animals, translated into minimalist heads with one or two segments. Extraordinarily well-preserved specimens of a new branchiocarid arthropod from Marble Canyon (Burgess Shale, Kootenay National Park) and a critical reevaluation of Branchiocaris material from Utah and the Burgess Shale show that these animals had a mandibulate head configuration, with intercalary segment, mandibles, maxillae and maxillipeds. Canadaspis and Odaraia are also arguably part of the same clade, characterised by multisegmented, enditic basipods. This new evidence reshapes the phylogeny of panarthropods and constitutes a major step forward in unifying hypotheses of mandibulate limb evolution, notably those of Müller and Walossek, and Boxshall, with developmental studies and molecular phylogenies. Our new topology also sheds light on the significance of larval morphotypes in the Cambrian, suggesting that heterochrony played a major role in the emergence of crown features and the apparent large disparity of early arthropod body plans.
Vision in fossil polychelidan lobsters
Denis Audo1,3, Joachim T. Haug2, Carolin Haug2, Sylvain Charbonnier3, Günter Schweigert4, Carsten H. G. Müller5 and Steffen Harzsch5
1Université de Rennes, France
2LMU Munich, Germany
3CNRS UMR 7207, Muséum National d’Histoire Naturelle and Sorbonne Universités, France
4Staatliches Museum für Naturkunde Stuttgart, Germany
5Erst-Moritz-Arndt-Universität Greifswald, Germany
Compound eyes are fascinating structures which undoubtedly play a critical role in the evolution of crustaceans. Several types of compound eyes exist: apposition eyes, with a superior resolution; three superposition eye subtypes, which trade-off resolution for sensitivity. Decapod crustaceans are probably the group with the greatest eye type diversity. The study of their visual system is complicated by the occurrence of groups in which extant species have reduced eyes, such as polychelidan lobsters, sister-group of all lobsters and crabs (Eureptantia). Our study is the first to focus on this problem by studying the eyes of Jurassic fossil polychelidan from Europe. Our results reveal that fossil polychelidans had functional eyes. Most of these were reflective superposition eyes, easily identified by their squared facets. However, for Rosenfeldia oppeli facets were hexagonal. Rosenfeldia oppeli eyes probably correspond to apposition type. We searched for variations in the size of eyes. Our results show a weak but significant taxonomic effect. Surprisingly, no significant environmental effect was detected. More samples are now required to further our statistical analysis; these efforts have already allowed the identification of two unusual specimens: small adult Voulteryon parvulus with both squared and hexagonal facets.
How good are your palaeodiversity measurements?
Abel Barral1, Bernard Gomez1, Juan M. Zorrilla2, José M. Serrano2, Johan Yans3, Véronique Daviero-Gomez1 and Christophe Lécuyer1
1CNRS UMR 5276, Université de Lyon and Ecole Normale Supérieure de Lyon, France
2Complutense University of Madrid, Spain
3Université de Namur, Belgium
One of the main concerns in palaeontology is how large a sample should be in order to assess the diversity of a fossil assemblage. Sampling effort analyses are used in neoecology to evaluate diversity representativeness, by minimizing the bias in data acquisition and adjusting the effort needed to obtain reliable results. These methods can be very useful in palaeoecological studies, in which exhaustive sampling is usually carried out. The Clench model is a useful method as it allows for the monitoring of several parameters to examine the accuracy and reliability of diversity estimates during data acquisition: 1) a value of collected richness, associated with 2) a value of stability for the estimates produced by the model, 3) an estimate of the total richness held in the sample, and 4) a prediction of the sampling effort required to reach a given proportion of total richness. Thus, the Clench equation allows the evaluation of the trade-off between the loss of information and the amount of work required to reach the information for the whole sample. The application of the Clench equation to palaeodiversity studies gives us a great opportunity to enhance the performance of data acquisition and to provide a quality test for the resulting taxonomic inventories.
The enigmatic archosaurs Mandasuchus and Teleocrater from the Middle Triassic of Tanzania and their implications for archosaur evolution
Paul M. Barrett1, Sterling J. Nesbitt2, Alan J. Charig1 and Richard J. Butler3
1Natural History Museum, London, UK
2Virginia Polytechnic Institute and State University, USA
3University of Birmingham, UK
The Lifua Member of the Manda Beds (Middle Triassic: Anisian) crops out in the Ruhuhu Valley, Tanzania, and has yielded a diverse fauna of terrestrial vertebrates. This fauna has had major impacts on our understanding of the establishment of clades that subsequently dominated the Mesozoic landscape. Rhynchosaur and synapsid remains are the most abundant, but archosaurs are represented by multiple specimens and taxa. Here we provide the first evaluations of two archosaur taxa that have been frequently mentioned in the literature, but never formally described, which both have important ramifications for understanding the early evolution of the clade. ‘Mandasuchus’ and ‘Teleocrater’ were named in an unpublished thesis 60 years ago and are each represented by several partial skeletons and isolated referred remains. This material provides a good overview of their postcranial anatomy, but cranial material is scarce. Both taxa can be diagnosed on the basis of autapomorphies and unique character combinations. Phylogenetic analysis reveals that ‘Mandasuchus’ is referable to Crurotarsi, as an early-diverging member of Loricata, whereas ‘Teleocrater’ is recovered within Avemetatarsalia. ‘Teleocrater’ forms a clade with several other previously engimatic archosaurs from South America, India and Russia, substantially altering our knowledge of early avemetatarsalian evolution prior to the pterosaur/dinosaur split.
Testing turbulent waters: palaeoecological implications of the durability and preservation potential of soft-bodied organisms in sediment-density flows
*Orla Bath Enright1, Nicholas J. Minter1 and Esther J. Sumner2
1University of Portsmouth, UK
2University of Southampton, UK
Experiments in an annular flume tank explored the durability and preservation potential of the polychaete Alitta virens when transported by fast and turbulent sediment-laden flows. Understanding whether soft-bodied organisms within fossil assemblages could have been transported or not is fundamental to the study of palaeoecology. Experiments can allow us to place constraints on interpretations of transport distances from life environments. In a three-factorial experimental design, we generated fully turbulent sandy flows and tested the effects of transport duration, sediment concentration, and grain angularity on the states of bodily damage experienced by freshly euthanized Alitta virens. Results identified statistically significant effects of transport duration and grain angularity. Increasing sediment concentration had a significant effect with angular sediment but not with rounded sediment. Our experiments demonstrate that if soft-bodied organisms such as polychaetes were alive and then killed by a flow they would have been capable of enduring prolonged transport with little damage. Dependent upon flow conditions, specimens were capable of remaining intact over extended transport durations and distances. This has significant palaeoecological implications for fossil Lagerstätten deriving from sediment-density flows, because the organisms present may have been transported over substantial distances and thus will not represent true palaeocommunities.
A new fossil Bramoides from the Eocene London Clay, re-aligned with the enigmatic modern genus Gasterochisma (Teleostei: Scombridae)
Hermione T. Beckett1, Zerina Johanson2, Mark Graham2 and Matt Friedman3
1University of Oxford, UK
2Natural History Museum, London, UK
3University of Michigan, USA
The London Clay Formation (Ypresian) yields a rich fauna documenting an important stage in the radiation of modern spiny-rayed teleosts. Many London Clay species show clear affinity with modern lineages, but placement of others remains uncertain. Among these is Bramoides, known only from isolated braincases. We recently located an unprepared, articulated skull in the Natural History Museum, London, representing the most complete Bramoides known. Mechanical preparation and computed tomography revealed distinctive features of the genus: high sagittal crest with a supraoccipital contribution extending anterior to the eyes, ‘box-like’ profile of the braincase in posterior view, wide vomer, and expansion of the exoccipitals into large articular facets for the vertebral column. Additionally, the specimen revealed the presence of beak-like, non-protrusible upper jaws and large cycloid scales. This distinctive combination of features is otherwise only known in Gasterochisma, which represents the earliest diverging branch of Scombridae but has no fossil record. Separation of Bramoides and Gasterochisma seems merited, as several features of the Eocene taxon are less specialized than the modern form. Placement of Bramoides in Gasterochismatinae expands the diverse assemblage of London Clay scombroids, providing further evidence for the rapid radiation of this group in the early Palaeogene.
The pattern of ecological radiation of mammals across the K-Pg boundary
*Gemma L. Benevento1, Matt Friedman2 and Roger B. J. Benson1
1University of Oxford, UK
2University of Michigan, USA
The apparent adaptive radiation of mammals following the Cretaceous–Palaeogene (K-Pg) extinction has long attracted the interest of palaeontologists. Despite this prominence, some aspects of mammalian diversification remain unclear. To date, quantitative work has either focused on mammalian subgroups (e.g. eutherians or multituberculates), examined comparatively short time intervals (e.g. Late Cretaceous–Paleocene), or explored limited trait data (e.g. body mass alone), making it difficult to assess the timing and magnitude of possible changes in ecomorphological diversity across the Mesozoic and Cenozoic. Continuous character traits were collected from direct examination of specimens and from the primary literature, with measurements selected to capture key mechanical properties. We find little increase in the morphological diversity of jaws immediately post-K-Pg, but from the Tiffanian (60 Ma) onward mammalian mandibular disparity increases in a stepwise fashion until the end of our study interval. Our results indicate that the increase in disparity was principally concentrated in larger mammals rather than in species comparable in size to those of the Mesozoic. This may suggest that the previously observed increase in mammalian upper body mass allowed Palaeogene mammals to explore novel feeding ecologies unavailable to smaller Mesozoic species, consistent with the hypothesis of ecological release following the extinction of the dinosaurs.
Reappraisal of Compsognathus longipes (Saurischia; Theropoda) skull anatomy and endocast shape by synchrotron imaging and virtual reconstruction.
Vincent Beyrand1,2, Paul Tafforeau2, Stanislav Bureš1 and Oliver W. M. Rauhut3
1Palacký University, Olomouc, Czech Republic
2European Synchrotron Radiation Facility, France
3Bayerische Staatssammlung für Paläontologie und Geologie, Germany
Compsognathidae is a small, basal coelurosaurian theropod with a wide distribution during the Late Jurassic and Early Cretaceous. The name-bearing taxon of the group, Compsognathus longipes, is based on a specimen found in the nineteenth century in the Kimmeridgian/Tithonian lithographic limestones of southern Germany. As the specimen is preserved in a slab, only the bones on the surface can be described, leading to incomplete knowledge of bone morphology and skull shape. C. longipes has been scanned using the ID19 and BM05 beamlines of the ESRF (France) using propagation phase contrast microtomography. This method, currently the most powerful one to investigate internal structures in such fossils non-destructively, helped us to look at more details of the bone anatomy in the skull of C. longipes. Detailed segmentation allowed us to perform a virtual reconstruction of the skull and to access the endocranial anatomy of this specimen. The virtual endocast shows a rather short and wide cerebrum and unusual conformation of the olfactory tracts and cerebellum compared to most theropod dinosaurs.
Mass extinctions: towards an understanding of how, why and when ecosystems collapse
David P. G. Bond
University of Hull, UK
Advances in our understanding of mass extinctions have resulted from greater resolution in the fossil record, better dating, and improved proxies for palaeoenvironmental change, but we still do not know what drives extinctions. The realization that Earth is again facing stresses implicated in its past crises (global warming, anoxia, ocean acidification) has intensified research on the ultimate cause(s) of extinctions (e.g., large igneous provinces and bolide impacts). There is growing evidence that volcanic eruptions might be the driver of proximal kill mechanisms, but the links between these are not well understood. Likewise, the temporal relationship between bolide impact and the Cretaceous extinction implies a causal relationship, but the mechanics of biotic losses remain unclear. This talk evaluates environmental factors implicated in major episodes of species extinctions and explores the links between killers and ultimate drivers. Experimental biology, by examining responses of species to change, is helping us understand how extinctions happen. Reduced pH, for instance, alters the efficacy of fishes’ chemical receptors, leaving them less equipped to detect prey, predators and mates – invoking ‘death-by-celibacy’ scenarios. Experimental geobiologists and Earth scientists could together unravel the causes of past extinctions, and better inform understanding of the modern crisis.
The death of dinosaurs and rise of mammals in the San Juan Basin of New Mexico, USA
Stephen L. Brusatte1,2, Thomas E. Williamson2, Matthew T. Heizler3, Daniel J. Peppe4, Ross Secord5, Adam Davis4, C. Will Fenley4, Andrew Flynn4, Caitlin Leslie4 and Sarah L. Shelley1
1University of Edinburgh, UK
2New Mexico Museum of Natural History and Science, USA
3New Mexico Bureau of Geology and Mineral Resources, USA
4Baylor University, USA
5University of Nebraska, USA
The end-Cretaceous extinction (66 Ma) was a turning point in Earth history, as the dinosaur-dominated world of the Cretaceous gave way to complex mammalian faunas in the Palaeogene. The alluvial foreland basin deposits of the San Juan Basin (New Mexico, USA) document this transition in remarkable detail, particularly the early Palaeogene radiation of mammals. A new geochronology of the basin based on radioisotopic dates and magnetostratigraphy indicates that diverse dinosaur communities persisted into the last 300,000 years of the Cretaceous and the first highly diverse mammalian faunas (Puercan 2 biozone) were established within 350,000 years of the extinction, the result of extremely high rates of evolution. Analysis of over 15,000 fossils, collected over the past 40 years and spanning c. 4 million years of the Puercan and Torrejonian biozones of the early Palaeogene, shows that mammal richness, originations and extinctions fluctuated dramatically over this time. Peak local diversity was achieved early in the Torrejonian, approximately 3 million years after the extinction, and high turnover rates and shifts in body size towards the end of the Torrejonian may have been related to climate or environmental perturbations, possibly including two short-term transient warming events (‘hyperthermals’) that were precursors to the Paleocene–Eocene Thermal Maximum.
Palaeoecology of an Upper Ordovician submarine cave-dwelling fauna in northern Kentucky, USA
Caroline J. Buttler1 and Mark A. Wilson2
1Amgueddfa Cymru – National Museum Wales, UK
2College of Wooster, USA
A bryozoan-dominated fauna that inhabited small caves underneath a carbonate hardground is here described from the Grant Lake Formation (Upper Ordovician, Katian) of Kentucky. The dominant bryozoan, Stigmatella personata, is found growing upwards in presumably well-lit waters on the exposed hardground surface and downwards from the ceilings in the gloomy caves. The cave-dwelling forms in some cases have longer zooecial tubes than its exposed equivalent. In both conditions the bryozoans formed mounds of multiple overgrowing colonies, sometimes showing changes in growth direction controlled by microenvironmental effects. The large colonies have multiple layers formed by self-overgrowth. The overgrowths are marked by thin layers of sediment infilling the upper zooecial chambers. We suggest that biofilms developed on patches of the colony where the zooids had died. Sediment adhered to these surfaces and the colony then grew on top. The bryozoan skeletons and the carbonate hardground are extensively bored by two forms of the cylindrical ichnogenus Trypanites. Both types preferentially penetrated along zooecial walls, suggesting that the bryozoan skeletons were not yet infilled with calcite cement. This fauna is one of few submarine examples known from the Palaeozoic, supporting the hypothesis that early cave-dwelling organisms were little differentiated from their exposed counterparts.
Mass extinctions as drivers of increased faunal cosmopolitanism on the supercontinent Pangaea
David J. Button1, Richard J. Butler1, Graeme T. Lloyd2 and Martin D. Ezcurra3
1University of Birmingham, UK
2Macquarie University, Australia
3Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Argentina
Mass extinctions have had a profound impact on the evolution of life, not only by reducing taxonomic diversity but also through influencing faunal distribution. In particular, they have been widely considered to drive increased biogeographic cosmopolitanism. The overlap between contemporaneous faunas can be quantified as the biogeographic connectedness, i.e. the density of links in a taxon-locality network. We quantify faunal cosmopolitanism for a global dataset of 891 terrestrial amniote species spanning the Late Permian–Early Jurassic, using a novel phylogenetic modification of biogeographic connectedness that weights the links between taxa according to the phylogenetic distance between them. We apply our analysis to eight time bins and ten biogeographic areas, the latter defined using K-means clustering of palaeocoordinates. This interval is of key biogeographic importance, and includes the onset of fragmentation of the supercontinent Pangaea, the origins of many modern amniote groups, and both the end-Permian and end-Triassic mass extinctions. Results demonstrate an overall decline in cosmopolitanism through this interval, but significant increases occur after both mass extinction events, leading to relatively homogeneous global ‘disaster faunas’ dominated by groups that radiated in the immediate aftermath of the extinction events. These shared patterns suggest that mass extinctions have predictable influences on animal distribution.
Phylogenetic analysis implies early diversification of tetrapods in the Tournaisian
Jennifer A. Clack1, Marcello Ruta2 and Timothy R. Smithson1
1University of Cambridge, UK
2University of Lincoln, UK
Five new tetrapods from the Tournaisian of Scotland are sufficiently well preserved to be diagnosed and cladistically analysed. Some include anatomical information available only from micro-CT scan data. Several other new taxa are represented by an array of further specimens. Not sufficiently complete to be included in the analysis, these are nevertheless distinct and informative. The five new tetrapods represent new species and are spread across the tetrapod stem and into the crown group. They show no close relationship to each other and exhibit different combinations of plesiomorphic and derived characters. Some taxa cluster with Devonian forms, suggesting a possible relict fauna, whereas others appear more crownward, even clustering near the base of the crown group. They imply an early radiation of tetrapods during the Tournaisian, with an early Carboniferous date for the crown group split. These new forms also suggest a blurring of the Devonian–Carboniferous boundary in respect of tetrapod evolution, a feature also noted in tetrapod remains from Nova Scotia. The appearance of large forms about a million years later than the Devonian–Carboniferous boundary suggests rapid recovery from the extinction event, and that large size was achieved quickly rather than slowly as some recent studies have indicated.
Is a ‘one size fits all’ taphonomic model appropriate for Mazon Creek?
*Thomas Clements, Mark A. Purnell and Sarah E. Gabbott
University of Leicester, UK
The Late Carboniferous Mazon Creek Lagerstätte (Illinois, USA) is a world-renowned fossil deposit with a large diversity of both flora and fauna. Constraining a ‘one-size fits all’ taphonomic model for the Mazon Creek Lagerstätte is difficult because of our poor understanding of sideritic concretionary preservation, the large geographical area, the influences of fresh, brackish and saline waters during burial, and the subsequent complicated diagenetic processes. To determine whether Mazon Creek fossil organisms have undergone similar preservational pathways, we have compiled fossil morphological character data sets for three polychaete taxa: Esconites zelus, Didontogaster cordylina and Astreptoscolex anasillosus. We then used these data to test for variation in mode of preservation between taxa and between specific tissue types – suites of morphological characters. We also compared fossil datasets to experimental decay data to constrain the impact of decay prior to fossilization. Our analysis indicates that there are variations in preservation potential of specific characters shared by polychaete taxa; modes of preservation, however, are consistent across all three taxa. This quantitative approach is being utilised as part of a larger ongoing investigation to elucidate the mode and timing of the preservation of ‘complex’ organisms preserved in the Mazon Creek deposit. This will lead to better understanding of taphonomic biases operating in this Lagerstätte.
Appendicular nature of gnathobase-like structures in Cambrian radiodontans
Peiyun Cong1,2, Allison C. Daley3, Gregory D. Edgecombe1 and Xianguang Hou2
1Natural History Museum, London, UK
2Yunnan University, China
3University of Lausanne, Switzerland
The morphology and homology of limbs in the euarthropod stem lineage is vital to understanding the early evolution of this megadiverse phylum. Whether limbs additional to the paired frontal appendages are present in radiodontans (anomalocaridids) is a contentious issue. Here we document at least two pairs of gnathobase-like structures in Amplectobelua symbrachiata, the most abundant radiodontan in the Chengjiang biota, and in two unnamed radiodontan taxa from the same Konservat-Lagerstätte. The appendicular nature of these gnathobase-like structures is inferred from their paired presence, dentate morphology, and topological position relative to the frontal appendages and other cephalic structures. The superficial similarity between the gnathobase-like structures and the mandibles of some crustaceans and jaws of onychophorans indicates that their likely function was to tear and mince food captured by the frontal appendage. This observation reinforces the case that most radiodontans were predators. The discovery of these gnathal structures also explains the absence of isolated Peytoia-like oral cones in Chengjiang, compared to their abundance in the Burgess Shale. This new mouthpart morphology is in line with the great diversity of oral structures seen within Radiodonta, including a variety of oral cones or the complete absence of mouth plates (Lyrarapax).
Palaeopsychrospheric ostracods during the Late Palaeozoic–Middle Triassic: the key to surviving mass extinction events?
Sylvie Crasquin1, David J. Hone2 and Marie-Béatrice Forel1
1CNRS UMR 7207, Muséum National d’Histoire Naturelle and Sorbonne Universités, France
2Queen Mary University of London, UK
The Late Palaeozoic palaeopsychrospheric ostracod fauna was established in the Early Devonian and survived the Frasnian–Famennian boundary crisis (Kellwasser Event) that wiped out 75% of ostracod species but affected mainly neritic taxa. Palaeopsychrospheric ostracods then diversified in the late Famennian and were abundant during the Early Carboniferous in deep basins throughout the Palaeo–Tethys realm, but data from younger strata are scarce. Our reconsideration of the Devonian faunas and their palaeoenvironmental settings leads us to suggest that, rather than being oxygen-deficient, deep waters were well-ventilated and provided extensive benthonic refugia during the shallow-water crises that caused mass extinction. The misconception that the formation of deep, cold water masses requires the existence of polar ice must also be corrected; the sinking of cool surface waters can occur at temperatures <10°C at a normal marine salinity, so the formation of sea ice is not a prerequisite, although it enhances the process. Some isolated discoveries show that the palaeopsychrospheric ostracod fauna persisted in the Late Carboniferous and during the Permian. The fact that Triassic palaeopsychrospheric faunas with Permian affinities have been described from the Anisian and Ladinian leads us to speculate that deep, cold, well-oxygenated refugia played an important role in the survival of podocopid ostracods during the end-Permian crisis when almost all palaeocopids became extinct.
Fossilized nuclei from the Ediacaran Weng’an Biota (Doushantuo Formation, South China)
John A. Cunningham1, Zongjun Yin2, Kelly Vargas1, Stefan Bengtson3 and Philip C. J. Donoghue1
1University of Bristol, UK
2Nanjing Institute of Geology and Palaeontology, CAS, China
3Swedish Museum of Natural History, Sweden
The interpretation of animal-embryo-like microfossils from the Ediacaran Weng’an Biota (c. 600 Ma) has proven contentious because they are among the oldest plausible claims of animals in the fossil record, but also because they preserve little more than simple geometric arrangements of cells. However, fossilization frequently extends beyond the cellular to preserve subcellular structures, including contentious large intracellular structures (LISs) that have been alternately interpreted as nuclei, other organelles, degraded cytoplasmic remains, or abiological structures. Our decay experiments demonstrate the feasability of a fossil record of nuclei. Nuclei can survive decay over a period compatible with soft tissue mineralization and can be mineralized in taphonomy experiments. New tomographic data on LISs in Weng’an fossils include specimens that lack late-stage void-filling mineralization and therefore allow us to test between the competing interpretations. All the lines of evidence, including consistency in the number, shape, position, and relative size (LIS-to-cell ratio) of the LISs, as well as presence of internal structures and their occurrence within preserved cytoplasm, support their interpretation as cell nuclei. Together our findings reject the commonly expressed view that nuclei cannot be fossilized, improving the potential for interpreting the fossil record of early eukaryote evolution.
The Capitanian biodiversity crisis among tetrapods
Michael O. Day
University of the Witwatersrand, South Africa
The Capitanian biodiversity crisis has been variously considered as one of the Phanerozoic’s greatest mass extinction events, as an ecological crisis with only moderate taxonomic losses, or as simply a decline in originations. For tetrapods, the Capitanian–Wuchiapingian transition certainly involved high taxonomic turnover and, with this, the extinction of the most successful group of Guadalupian therapsids, the dinocephalians, paving the way for the Lopingian diversification of dicynodonts, gorgonopsians and therocephalians. Although these latter clades were already present within the Main Karoo Basin, many basal and/or stem genera were lost. The extinction is marked by a low diversity interval followed by the appearance of Lopingian taxa representing the early recovery. In Russia a similar series of events is recorded, albeit with the immigration of groups originating in Gondwana after the extinction of dinocephalians. CA-TIMS U-Pb ages from syndepositional ash-fall tuffs allow the extinction peak to be constrained to just before 260 Ma, which suggests links with Emeishan volcanism. Cooling is now widely accepted in the Capitanian but there is as yet no direct evidence linking the tetrapod extinction event to any one cause. Nevertheless, the close temporal coincidence with the onset of Emeishan volcanism is compelling.
Preferential origin of calcitic cephalopod shell structures during calcite seas
Kenneth De Baets and Munnecke Axel
Friedrich-Alexander University of Erlangen-Nuremberg, Germany
Based on the aragonite composition of extant cephalopods and exceptionally preserved fossil cephalopods going back to the Palaeozoic, it is commonly assumed that externally shelled cephalopods had an aragonitic shell wall. Here we present evidence that at least two lineages of orthoconic nautiloids in the Silurian and Devonian calcite seas had an original biphasic mineralogy, which developed convergently with gastropods and bivalves. If we quantitatively analyse the timing of the evolutionary origin of these and other reliably dated carbonitic cephalopods structures in relationships with calcite or aragonite seas, we find support for a preferential origin of calcitic structures during calcite seas, particularly in the Palaeozoic. This further corroborates the hypothesis that seawater chemistry at the time a particular mineralized structure was first acquired within a lineage was particularly crucial for its mineralogy – even in pelagic organisms like cephalopods. These finds also highlight the need to verify the shell composition of exceptionally-preserved cephalopods more comprehensively – even at sites where aragonite has typically been dissolved or replaced.
Reconstructing anomalocaridid feeding appendage dexterity sheds light on radiodontan ecology
Giacinto De Vivo, Stephan Lautenschlager and Jakob Vinther
University of Bristol, UK
Anomalocaridids were one of the most successful animal groups in the Early Palaeozoic. They are particularly renowned for their pair of large feeding appendages used to capture and detain prey. Since the early stages of their evolution, anomalocaridids have evolved different feeding appendage morphologies, indicating an adaptive radiation into distinct niches early in their history. Here, to test different likely anomalocaridid feeding modes, their appendages have been reconstructed in 3-D and their range of movement explored. Our results indicate that Anomalocaris canadensis was able to catch small, agile prey, while Hurdia victoria and Peytoia nathorsti preyed upon relatively larger benthic animals. Anomalocaris briggsi from the Emu Bay Shale is here recognized as a filter feeder similar to Tamisiocaris borealis. The appendages of the Early Ordovician anomalocaridid Aegirocassis benmoulai show higher dexterity than previously thought, which allowed them to create a basket-like or fan-like structure. The inferred anomalocaridid prey size corresponds to the diameter of the mouth, suggesting that the prey was ingested whole. This indicates that the oral opening was able to dilate, probably by mouth eversion and expansion of the oral cavity, offering new clues to feeding mechanics in stem arthropods.
Contributions to the ongoing work on the international chronostratigraphy of the Cambrian: preliminary data from the Terreneuvian of Iran and Series 2 of Mexico
Léa Devaere1, Sébastien Clausen2, Dieter Korn1, Abbas Ghaderi3, Ulrich Struck1, Juan J. Palafox-Reyes4, Blanca E. Buitrón-Sanchez5 and Daniel Vachard2
1Museum für Naturkunde, Germany
2CNRS UMR 8198, Université de Lille 1, France
3Ferdowsi University of Mashhad, Iran
4Universidad de Sonora, Mexico
5Universidad Nacional Autónoma de México, Mexico
After several decades of intense research, the topic of the Cambrian explosion has fed an abundant literature focusing on its biodiversity and phylogenetic patterns. Our understanding of this is, however, limited by the lack of accurate dating of the fossil radiation and abiotic changes. Although efforts have been made to develop a refined timescale, the Cambrian remains one of the last systems for which series and stage boundaries have not yet been accurately defined. This can be ascribed in part to the paucity of comprehensive litho-, bio-, and chemostratigraphic studies of early-mid Cambrian successions from key regions, such as Sonora (Mexico) and Iran. Data from Sonora are essential for establishing the still incomplete although fundamental Cambrian chronostratigraphy of Laurentia, whereas Iranian Cambrian successions represent the best opportunity for correlations between the western Gondwana margin and the Yangtze Platform in South China. This study presents preliminary stratigraphic data from Sonora and Iran. Special attention has been given to the range of the abundant and widely-distributed polyphyletic small shelly fossils (SSFs) due to their high potential for the subdivision of the early Cambrian.
Freshly-moulted trilobites from the Fezouata Lagerstätte of Morocco
*Harriet B. Drage1, Thijs R. A. Vandenbroucke2, Peter Van Roy2,3 and Allison C. Daley1,4
1University of Oxford, UK
2Ghent University, Belgium
3Yale University, USA
4University of Lausanne, Switzerland
Trilobites, as arthropods, must periodically moult their protective hardened exoskeleton for growth, development, and repair. This complex process involves disassociating the epidermis and internal systems from the exoskeletal cuticle, secretion of new cuticle, and ecdysis of the old exoskeleton. Immediately post-moulting the new exoskeleton is soft and compressed (i.e., the ’soft-shell stage’). This stage must necessarily be short-lived, as the individual is extremely vulnerable to predation at this time. The brevity of the stage is reflected in the paucity of soft-shelled specimens in the fossil record, accentuated by their reduced preservation potential. The few soft-shell post-moult trilobites described to date were identified based on the co-occurrence of wrinkling and flattening (indicating compressed, soft cuticle). However, preservational or tectonic deformation may also be responsible, and therefore freshly-moulted trilobites must be considered in context. We describe a rare example of soft-shell trilobite preservation from the exceptional Burgess Shale-type Lower Ordovician Fezouata Lagerstätte of Morocco. Nileid specimens illustrate the complete moult sequence, with a putative moulted exoskeleton, several fully-hardened carcasses, and specimens showing varying degrees of the soft-shell stage. The latter show a progression in exoskeletal hardening by decreasing longitudinal wrinkling and flattening. Comparison with co-occurring arthropods excludes preservational bias. This assemblage likely represents the first described preserved-in-the-act trilobite mass moult.
The Chronicles of Charnia: developmental biology and phylogenetic inference from an Ediacaran rangeomorph
*Frankie Dunn1,2, Philip R. Wilby2, Philip C.J. Donoghue1 and Alexander G. Liu1,3
1University of Bristol, UK
2British Geological Survey, UK
3University of Cambridge, UK
The late Ediacaran Period (580–541 Ma) witnessed the emergence of the first complex, macroscopic organisms – the Ediacaran macrobiota – which are commonly considered to include antecedents to modern animal groups. Definitive evidence tying these organisms to the Metazoa, however, has not been convincingly demonstrated, and consequently multiple non-metazoan hypotheses of affinity have been proposed for the biota. We have investigated growth and development in an attempt to identify constraints on the phylogenetic affinity of the iconic Ediacaran macro-organism Charnia masoni. Previous work has considered ontogeny in Charnia to be irreconcilable with its most morphologically similar metazoan clade, the Pennatulacea. Our analysis of Charnia masoni reveals hitherto unrecorded ontogenetic characters, including a second polar growth zone, indicating that it was a bipolar organism and challenging phylogenetic interpretations that assume Charnia was unipolar. This and other new characters allow us to refute close phylogenetic relationships to several non-metazoan groups which do not grow in this way, and, crucially, reconcile Charnia as a member of total-group Metazoa. As such, the rangeomorphs inform debate surrounding the establishment of animal body plans, specifically the evolution of the principal body axes and the making and breaking of axial symmetries in Metazoa.
Modelling enrolment mechanisms in Ordovician trilobites
Jorge Esteve1, Juan-Carlos Gutierrez-Marco2, Pedro Rubio3 and Isabel Rabano4
1Complutense University of Madrid, Spain
2Instituto de Geociencias (CSIC UCM), Spain
3Burashi S.L., Spain
4Museo Geominero, Spain
Enrolment represents one of the most iconic behaviours described in the fossil record. Cambrian trilobites displayed very simple enrolment type and most of them simply flexed the second half of the trunk in order to cover the ventral side of the head and the anterior part of the trunk. Enrolment in trilobites was a behaviour that required high complexity, coordination and synchronization among different trunk tergites. Middle and Late Cambrian trilobites developed new ways to enrol, but Ordovician trilobites were the first to develop novel structures to close their body in a more efficient way. However, despite the complexity of enrolment some Ordovician trilobites had similar body patterns. For instance, Neseuretus and Placoparia display an ‘unrolled spiral’ and ‘inverted spiral’ respectively, but both genera had a very similar body pattern. The outstanding preservation of some Ordovician trilobites from Spain allows precise 3D reconstructions using a structured light scanner. These scanners form the basis of computer models of enrolment. These models shed light on the functional morphology and kinetics of this behaviour, with implications for the evolutionary history of different enrolment type causes that forced the trilobites to develop different ways to close the body.
Burgess Shale-type fossil in the Middle Ordovician of the Barrandian area (Czech Republic)
Charles University Prague, Czech Republic
Re-examination of the putative green alga Krejciella putzkeri Obrhel, 1968 shows no morphological difference from Margaretia dorus Walcott 1931, a fossil recently interpreted as an organic tube produced and inhabited by the enteropneust worm Oesia disjuncta Walcott, 1911. Margaretia, originally described from the mid-Cambrian Burgess Shale, has been reported from several Early to mid-Cambrian Lagerstätten in Laurentia (e.g. Latham, Kinzers, Marjum, USA), Siberia (as Aldanophyton in the Sinsk Lagerstätte, Russia), and East Gondwana (Guashan Lagerstätte, China). Geographic distribution of Margaretia indicates a possible latitudinal control, as all occurrences are obviously restricted to tropical to subtropical belts. The herein reported occurrence of Krejciella in the Barrandian area extends the record of organic tubes supposedly produced by enteropneusts to the Middle Ordovician cold-water areas of West Gondwana. Krejciella represents the first Burgess Shale-type fossil in the Middle Ordovician of the Barrandian area.
Diets of giants: the nutritional value of herbivorous dinosaur diet during the Mesozoic
Fiona L. Gill1, Juergen Hummel2, A. Reza Sharifi2, Alexandra P. Lee3 and Barry H. Lomax3
1University of Leeds, UK
2Georg-August University Goettingen, Germany
3University of Nottingham, UK
A major uncertainty in estimating energy budgets and population densities of extinct animals is the carrying capacity of their ecosystems, constrained by net primary productivity (NPP) and digestible energy content of that NPP. The hypothesis that increases in NPP of land plants due to elevated atmospheric CO2 contributed to the unparalleled size of the sauropods, the largest ever land animals, has recently been rejected based on modern studies on herbivorous insects. However, the nutritional value of plants grown under elevated CO2 levels might be very different for vertebrate megaherbivores with more complex digestive systems and different protein:energy requirements than insects. Here we show that the metabolisable energy value of five species of potential dinosaur food plants does not decline consistently with increasing CO2 growth concentrations, with maxima observed at 1,200 ppm CO2. Our data potentially rebut the hypothesis that CO2 levels were constraints on herbivore diet quality in the Mesozoic.
The early aquatic angiosperm Montsechia from the Barremian of Spain
Bernard Gomez1, Véronique Daviero-Gomez1, Clément Coiffard2, Abel Barral1,
Carles Martin-Closas3 and David L. Dilcher4
1CNRS UMR 5276, Université de Lyon and Ecole Normale Supérieure de Lyon, France
2Museum für Naturkunde, Germany
3Universitat Barcelona, Spain
4Indiana University, USA
Montsechia vidalii (Zeiller) Teixeira has been reported in several localities from the Barremian of Spain. The vegetative parts are of two types: one has relatively long, opposite-decussate leaves, and the second has tiny, spirally-arranged leaves. The two types are never connected and are without roots. Besides being more frequent in the second, both types bear pairs of fruits at the top of leafed stems. Fruits are closed, even when found dispersed on rock slabs, except for a tiny rounded hole at the tip, and contain a single orthotropous pendant seed. Palaeontological and sedimentological evidence suggest that it grew in freshwater lakes or ponds. Its closest phylogenetically affinity is with Ceratophyllum. Together with its palaeoecology, Montsechia is the youngest early aquatic angiosperm known so far. Plant fossils, such as Archaefructus and Montsechia, open the possibility that aquatic plants were locally common at a very early stage of angiosperm evolution and that aquatic habitats may have played a major role in the diversification of some early angiosperm lineages.
Synchrotron X-ray spectroscopy reveals burial conditions and fossilization in a Cretaceous freshwater Lagerstätte
CNRS USR 3461 and SOLEIL Synchrotron, France
The Cenomanian (~95 Ma) Djebel-Oum-Tkout Lagerstätte comprises a unique freshwater fauna of molluscs, insects, crustaceans and fish. The fossils exhibit finely mineralized soft-tissues and are found in association with microbial mats, suggesting microbially induced phosphatization. Synchrotron micro-X-ray spectroscopy techniques have provided unexpected information regarding the chemistry of the burial environment, allowing the precise reconstruction of a taphonomic scenario in agreement with recent decay experiments. X-ray fluorescence provides semi-quantitative concentrations of rare earth elements, and therefore an indirect assessment of the redox conditions through the ‘cerium anomaly’, X-ray absorption allows direct access to the oxidation state of the redox-sensitive Ce and Fe, and X-ray diffraction allows us to identify the minerals that compose the fossils. While anaerobic conditions were previously shown to rapidly establish in decaying carcasses, our analyses reveal the presence of oxidized Ce(III) and Fe(III), pointing to slightly oxidative burial conditions at Djebel-Oum-Tkout. Instead of an anaerobic, reducing environment, an oxidizing microenvironment attributed to microbial activity was formed inside the carcasses. This is consistent with recent decay experiments that showed that the microenvironments generated by microbial mats turn oxic after initial anaerobic conditions. Non-invasive synchrotron X-ray spectroscopy shows great promise for characterizing burial conditions in different fossilization contexts.
Feeding in chelicerate arthropods – diverse and far from ‘primitive’
LMU Munich, Germany
Euarthropods include two main modern lineages. On the one side are insects, myriapods and other crustaceans, such as shrimps, crabs and their smaller relatives. On the other side are chelicerates, including spiders, scorpions, mites and such like. Chelicerates are often considered to be the ‘primitive’ part of the family tree. It has even been suggested that they somehow failed to evolve proper mouthparts. I will present examples of different fossil representatives of chelicerates and reconstruct the evolution of the feeding apparatus within chelicerates. This reconstruction demonstrates that feeding mechanisms within chelicerates are, in fact, highly diverse and strongly derived from the euarthropod condition. Feeding in chelicerates can therefore in no way be considered ‘primitive’. Instead, the entire body of chelicerates has become highly modified in conjunction with changes of the feeding apparatus. Crustaceans and their relatives on the other hand have retained numerous ancestral (plesiomorphic) traits that have been lost in chelicerates. Hence, chelicerates are a prime example of the restrictions of typological thinking. Only with detailed studies of morphology interpreted in an evolutionary phylogenetic framework can we overcome simplified views on character transformation and avoid unscientific labels such as ‘primitive’.
Why we are looking at the wrong phase of life – palaeontology beyond the adult paradigm
Joachim T. Haug
LMU Munich, Germany
It has been recognized in recent years that modern biology is adult-centred. This is even more relevant to palaeontology. Taxonomy, systematics, but also ecological interpretation is largely based on adults. The presence of an adult at a specific time slice is therefore immediately translated into the presence of a specific larva. I will present examples that demonstrate why the general adult-centered view is more than a simple misunderstanding; it represents a significant oversimplification that causes severe artefacts in any kind of reconstructions of the past. Most simply, the modern biosphere is dominated by non-adults concerning both number of individuals and biomass. Modern seas are full of planktic larval forms of which only very few individuals will survive long enough to become adult. Terrestrial ecosystems are dominated by insects, which live for many moults, of which only the final one is the adult. Many insect larvae persist for months or years, while the adults live for only a few weeks or as little as a single day. I discuss how modern palaeontology can overcome the adult paradigm and recognize fossil species as once-living organisms. This includes accepting the fact that the immature is the normal condition while being adult is something special.
Can phosphatic microfossils constrain Cambrian climates?
*Thomas W. Hearing1, Thomas H. P. Harvey1, Mark Williams1, Sarah E. Gabbott1, Philip R. Wilby2 and Melanie J. Leng2
1University of Leicester, UK
2British Geological Survey, UK
Exceptional fossil discoveries have thrown considerable light on the biological changes throughout the Cambrian metazoan radiation. However, quantitative constraints are needed to understand possible environmental causes and consequences of this dramatic radiation. There is a particular dearth of sea temperature data, which are important for constraining oceanographic and palaeoenvironmental reconstructions. We aim to begin quantifying Cambrian sea temperatures by combining the long-established stable oxygen isotope (δ18O) palaeothermometer with novel taxa. We examined phosphatic small shelly fossils (SSFs) from the Lower Comley Limestone (Cambrian Stage 4/5, Shropshire, UK), deposited in shallow seas approximately 60°S. To minimize the influence of ecology on preserved environmental signals only taxa with well-constrained benthic lifestyles and/or modern analogues were selected, including Rhombocorniculum, Torellella and various linguliformean brachiopods. By subjecting selected specimens to a rigorous assessment of preservation using optical and scanning electron microscopy along with in situ chemical analyses, we found both biogenic and diagenetic microstructures and chemistries, and could distinguish a subset of well-preserved SSFs. Preliminary δ18O data provide plausible temperatures that support geological evidence for warm Cambrian climates. Carefully selected well-preserved SSFs could help fill the 50-million-year absence of quantitative palaeoenvironmental constraints in the earliest Phanerozoic Eon.
Macroevolution of Mesozoic lepidosaurs
*Jorge A. Herrera Flores, Michael J. Benton and Thomas L. Stubbs
University of Bristol, UK
Lepidosauria is a group of reptiles that originated in the Early or Middle Triassic, and this group is currently divided into two orders, the Squamata and the Rhynchocephalia. Extant squamates (lizards, snakes and amphisbaenians) are well known for their high diversity that today reaches over 9,000 species, but in contrast rhynchocephalians are only represented by a single living species, the tuatara from New Zealand. Nevertheless, the fossil record shows that in the Mesozoic these relative proportions were quite different. We used geometric morphometrics in order to explore changes in morphospaces and possible evidence of competition of both orders through the Mesozoic by using a database of 2D images of lower jaws from 93 genera. Our results show that Jurassic rhynchocephalians occupied a wide morphospace while squamates formed a tight cluster. On the other hand, Cretaceous rhynchocephalians showed a considerable decrease in morphospace, while squamates had a huge expansion that overlaps most of the rhynchocephalian morphospace. Our work provides some quantifiable evidence to support the suggestion that the radiation of Cretaceous squamates was the possible cause of the decline of rhynchocephalians in the late Mesozoic.
The diversification of early Asterozoa: resolving a palaeontological quandary
Aaron W. Hunter
Curtin University, Australia
Our understanding of the evolution of the earliest asterozoan echinoderms has until recently been hampered by a lack of well-preserved taxa and uncertainty of the homology between the four major groups. Although the nature of the sudden appearance of primitive Asterozoa in the Ordovician remains a mystery, our understanding of their diversification has now advanced considerably in light of new discoveries from exceptionally preserved specimens from the Early Ordovician of Morocco and France, significantly increasing the scope of morphological data available for study. Exceptionally preserved ‘bat-stars’ from the late Tremadocian Fezouata Shale, Anti-Atlas Morocco, one of the oldest discovered asterozoan assemblages, represent at least three distinct somasteroid morphotypes. These inhabit a diverse community containing elements of Cambrian and Ordovician faunas. We have found that these communities, along with those of comparable age taxa of Australia (Tasmania) and North America (Utah), were dominated by primitive somasteroids and stenuroids, with other more derived asterozoan taxa being absent. The late Tremadocian of France (Montagne Noire), however, preserves the oldest recorded proto-ophiuroids and asteroids as a minor component of this ‘somasteroid-world’, and by the Floian, proto-ophiuroids and somasteroids are seen to have been replaced by ‘true’ archaic ophiuroids, which persisted to the mid-Permian.
Prospects and limitations of ecological studies of a fossil reef community (Aferdou el Mrakib, Middle Devonian, Morocco) based on fore-reef talus
Michał Jakubowicz1, Jan J. Król1, Mikołaj K. Zapalski2 and Blazej Berkowski1
1Adam Mickiewicz University in Poznań, Poland
2University of Warsaw, Poland
Many fossil reef communities are preserved mainly in the form of fore-reef debris deposits, with the actual reefs either not preserved at all, or affected by advanced diagenesis. This is the case for Aferdou el Mrakib (Givetian, eastern Anti-Atlas, Morocco), the largest Devonian reef of northwestern Gondwana. The core of the reef has been pervasively dolomitized, and few portions of well-preserved reef facies can be observed. The best preserved fossils are found in the talus strata and include large, platy to massive colonies of rugose and tabulate corals, domical stromatoporoids, and numerous smaller tabulates, solitary rugosans, brachiopods, amphiporids, crinoids and some algae-derived structures. Reef-derived components mix with autochtonous, off-reef fauna, composed of solitary rugosans, some branching tabulates, and brachiopods. In addition, the off-reef debris succession contains locally large blocks of the original reefal material, most likely transported by means of debris flow-type mass flows initiated by storm- or seismic-related events. The palaeontological and sedimentological data combine to give a picture of a rich, diverse palaeoecosystem that at least at some stage reached very shallow depths, challenging previous interpretations of the reef as situated below the range of the euphotic zone.
Looking snappy: quantifying convergence in cranial morphology between phytosaurs and crocodylomorphs
*Andrew Jones, Pedro L. Godoy and Richard J. Butler
University of Birmingham, UK
Phytosaurs were a widespread group of carnivorous archosauriform reptiles in Late Triassic ecosystems (c. 230–201 Ma), with their abundant remains demonstrating a cosmopolitan global range and ecological importance. Functional similarities between phytosaurs and crocodylomorphs have been proposed qualitatively on the basis of gross morphological similarities between the two clades, but this convergence has not yet been quantified. Here we present results from comparative shape analyses using geometric morphometrics to tease apart and quantify subtle variation in the many known phytosaur and crocodylomorph skull morphologies to aid further functional investigation. These analyses explore dorsal and lateral variation in a broad range of morphologies representative of Phytosauria and Crocodylomorpha. We use a combination of semilandmark curves and traditional landmarks to allow the accurate digitization of evolutionarily convergent features which lack directly homologous points. Results indicate that phytosaurs do overlap with crocodylomorphs in morphospace, though only with a small subset of total crocodylomorph diversity. When compared only with longirostrine crocodylomorphs, more nuanced skull variation sets phytosaurs apart from most crocodylomorphs. This variation, mainly pertaining to the supratemporal fenestra, may suggest differences in biting capability and feeding biomechanics.
Early Cambrian ostracoderms and the trials and tribulations of total evidence dating
*Joseph N. Keating1,2, Richard Dearden1,3 and Philip C. J. Donoghue1
1University of Bristol, UK
2University of Manchester, UK
3Imperial College London, UK
The origin of jawed vertebrates is a formative episode in evolutionary history. Key to understanding this important interval are the armoured jawless ‘ostracoderms’, the relationships among which have previously been considered either in terms of clade intrarelations, or interrelations among clade exemplars. Thus, the monophyly of the putative ostracoderm plesions have yet to be adequately tested, principally because of computational limitations surmounted in the last decade. We constructed a supermatrix of 560 characters and 240 taxa, which we analysed using the MK likelihood model. The ensuing trees were compared using Bayes factors. Our results support the majority of ostracoderm clades, but resolve galeaspids and heterostracans as paraphyletic grades of stem-gnathostomes, and stem-vertebrates, respectively. Finally, we considered the role of time in topology estimation, using the fossilized birth-death model (FBD). This approach resolved heterostracans, thelodonts and anaspids as a single clade, while suggesting that ostracoderms evolved in the earliest Cambrian. This result conflicts strongly with the fossil record, suggesting that the FBD method may incorrectly estimate divergences of extinct taxa. Taken together, these results suggest that the consensus of early vertebrate relations, underpinned by the last 40 years of cladistics, does not stand up to deeper scrutiny afforded by likelihood-based phylogenetics.
The palaeobiology of Ediacaran rangeomorphs: reproduction, environmental sensitivity and ecological succession
Charlotte G. Kenchington1,2 and Philip R. Wilby2
1Memorial University of Newfoundland, Canada
2British Geological Survey, UK
The Earth has supported life for most of its 4.5-billion-year history, but the first macroscopic organisms appeared only in the Ediacaran (c. 600 Ma). Many aspects of their biology and ecology remain a mystery. Late Ediacaran fossil assemblages of Avalonia (Charnwood Forest, UK and Newfoundland, Canada) are among the oldest evidence for complex macroscopic life, and are dominated by rangeomorphs (a group characterised by ‘fractal’ branching). We resolve key aspects of rangeomorph palaeoecology by combining detailed petrographic analysis with multivariate statistical techniques. We demonstrate that higher taxonomic diversity is correlated with low–intermediate physical disturbance and that upright taxa (e.g. Charnia) and flat-lying forms (e.g. Fractofusus) preferentially occur on surfaces with high and low sediment input, respectively. The population demographics of several taxa show multimodality, caused by culling part of an incumbent population and by non-continuous/pulsed reproduction. Disturbance demonstrably influenced community succession: early-colonising taxa dominated horizons with low levels of disturbance, while those able to survive disturbance events dominated horizons with higher levels of disturbance, and also post-disturbance recovery populations. Based on the life history traits and environmental preferences identified for different rangeomorphs, we propose a model of ecological succession for Avalonian rangeomorph communities.
Arms race or feeding competition? The mid-Palaeozoic origins of cephalopod and vertebrate jaws
Christian Klug1, Linda Frey1, Dieter Korn2, Romain Jattiot1 and Martin Rücklin3
1University of Zurich, Switzerland
2Museum für Naturkunde, Germany
3Naturalis Biodiversity Center, Netherlands
The oldest known cephalopod feeding structures are documented by radulae from the Ordovician, questionable opercula from the Silurian, and Late Devonian ammonoid mandibles. Based on new discoveries of latest Devonian buccal apparatuses in three different ammonoid clades, we revise the origin of mandibles in ammonoids. Their presence in four major clades argues for chitinous mandibles as a plesiomorphic character for the Ammonoidea. This hypothesis finds support in early Carboniferous Coleoidea with homologous mandibles. Accordingly, we further hypothesize the presence of mandibles in the last common ancestor of coleoids, ammonoids and recent nautilids, i.e. in some orthocerids, likely in the Silurian. Jawed vertebrates may have evolved as early as the late Ordovician, but certainly in the early Silurian with an initial diversification in the late Silurian, which intensified in the Devonian. The phylogenetic evidence for pre-Devonian cephalopod mandibles and synchronous diversification of jawed vertebrates in the Siluro–Devonian might have been linked ecologically. The increasing abundance of defensive structures in invertebrates may have caused a positive selection for reinforced mouthparts of invertebrate and vertebrate predators during that time.
On the agglutinated nature of Ediacaran palaeopascichnids from northern Siberia
*Anton V. Kolesnikov1,2
1Trofimuk Institute of Petroleum Geology and Geophysics, RAS, Russia
2CNRS UMR 8198, Université de Lille 1, France
The Khatyspyt Formation of the Khorbusuonka Group of northern Siberia contains one of the most fascinating Ediacaran fossils. The unique mode of fossil preservation in carbonate rocks allows us to discover new morphological features, palaeoecology and environments of preservation of problematic Ediacara-like biota. This study focuses on the problematic group Palaeopascichnida. Abundant palaeontological material from the Khatyspyt Formation gives us the opportunity to study these fossils in the finest detail and test hypotheses about the origin of Ediacaran organisms. Detailed morphological observations, conducted on thin sections with the help of both petrographic and scanning electron microscopes, revealed evidence of possible wall agglutination around the globular chambers of Palaeopascichnida. Thus, we can consider the Palaeopascichnida group as one of the oldest known macroorganisms with an agglutinated skeleton. The presence of an agglutinated skeleton places emphasis on these organisms and encourages the re‑examination of other palaeopaschnid-like fossils, as well as the stratigraphic correlation of Ediacaran sequences; it also contributes to our improved understanding of the evolution and survival of the Ediacaran biota in the aftermath of the Kotlinian Crisis.
Ecological fitting within sheet-forming skeletal metazoans and the Ordovician rise of reef ecosystems
Björn Kröger1, André Desrochers2 and Andrej Ernst3
1University of Helsinki, Finnish Museum of Natural History, Finland
2University of Ottawa, Canada
3University Hamburg, Germany
Sheet-forming skeletal, colonial metazoans, such as bryozoans, tabulate corals, and stromatoporoid sponges, diversified simultaneously during the Early–Middle Ordovician period and became globally the dominant Ordovician reef-builders. Based on studies from reefs of the Middle Ordovician Chazy and Mingan formations (USA and Canada), and of the Late Ordovician Vasalemma and Ärina formations (Estonia), we demonstrate that sheet-forming skeletal, colonial metazoans formed a specific type of cluster–frame reefs with a micrite-rich matrix. The accretion mechanism of these reefs is reconstructed as a combination of metazoan biomineralization and microbially-mediated organomineralization. The diversification of sheet-forming skeletal, colonial metazoans clearly lagged behind the first appearance of their respective skeletal ancestors and can be best interpreted as an ecological shift or habitat expansion of encrusters from cryptic and/or very shallow marine hard substrates onto soft-substrate and toward microbial-metazoan consortia. Their habitat expansion can be exemplified as a case of simultaneous ecological fitting, i.e., the independently evolved shared traits of encrusting metazoans simultaneously were co-opted and became advantageous under globally different environmental conditions.
Comparison of the postembryonic development in the family Paradoxididae (Trilobita)
* Lukáš Laibl1, Jorge Esteve2 and Oldřich Fatka1
1Charles University Prague, Czech Republic
2Complutense University of Madrid, Spain
We reinvestigate early postembryonic stages of the Cambrian paradoxidid trilobites Paradoxides gracilis, Acadoparadoxides pinus, Eccaparadoxides pusillus, E. pradoanus, and Hydrocephalus carens. The protaspid and early meraspid stages of these taxa show considerable variability in morphology and dimensions. In Paradoxides and Acadoparadoxides these stages have a rather narrow glabella with quite distinct medial and lateral furrows. In Eccaparadoxides they share sub-elliptical glabellae with the medial furrow, and in the case of E. pusillus also with the lateral furrows. Early postembryonic stages of Hydrocephalus are characterised by a large sub-circular and effaced glabella. The earliest known stages of Acadoparadoxides, Paradoxides and Eccaparadoxides are around 0.9 mm long, while the earliest stages of Hydrocephalus reach almost 2 mm. The late meraspid development of all of these taxa includes a change in the glabellar morphology, disappearance of intergenal spines, shortening of the preglabellar field, and successive degeneration of thoracic macrospines. The variability of size, morphology and other developmental trends suggest that the earliest postembryonic stages of different taxa within Paradoxididae were influenced by different selection pressures.
The Weeks Formation Fauna (Utah, USA) and the evolution of marine animal communities during the late Cambrian
Rudy Lerosey-Aubril1, Robert R. Gaines2, Thomas A. Hegna3, Bertrand Lefebvre4, Javier Ortega-Hernández5, Peter Van Roy6, Carlo Kier7 and Enrico Bonino7
1University of New England, Australia
2Pomona College, USA
3Western Illinois University, USA
4CNRS UMR 5276, Université de Lyon and Ecole Normale Supérieure de Lyon, France
5University of Cambridge, UK
6Ghent University, Belgium
7Back to the Past Museum, Mexico
Exceptionally preserved fossil assemblages have proved critical to our understanding of the Cambrian explosion. Thanks to recently discovered Konservat-Lagerstätten, similarly detailed data on Ordovician marine animal communities are increasingly available. By contrast, the late Cambrian fossil record of ‘soft’-bodied metazoans remains particularly scarce, with only a single diverse macroscopic fauna of that kind: the late Guzhangian Weeks Formation. Recent field investigations have greatly improved our understanding of this remarkable fauna and the environment it inhabited. Microfacies analyses revealed that intervals with exceptional preservation were deposited in a quiet, oxygen-depleted environment on a distal carbonate ramp below storm-wave base, a setting much like that of most Cambrian Lagerstätten. The biota comprises c. 80 species, belonging to nine phyla, and is dominated by arthropods, sponges and brachiopods, which is similar to older exceptionally preserved faunas. Analysis of the intra-phylum composition reveals a more complex picture. Cnidarians, hyolithidids, priapulids or sponges are all represented by taxa known from older strata. Some arthropods are also more typical of Early–Middle Cambrian times. However, other components of the fauna (e.g. aglaspidids, solutes), including newcomers of uncertain affinities, suggest the onset of a restructuring of marine animal communities in the early late Cambrian.
Phylogenetic diversity as a palaeobiodiversity metric: new evidence for a Cretaceous decline in Mesozoic dinosaurs
Graeme T. Lloyd1,2, David W. Bapst3,4, Matt Friedman5,6 and Katie E. Davis7
1University of Leeds, UK
2Macquarie University, Australia
3University of California, Davis, USA
4South Dakota School of Mines and Technology, USA
5University of Michigan, USA
6University of Oxford, UK
7University of York, UK
Phylogenetic diversity (PD) – the sum of the branch lengths of the subtree connecting a set of taxa – is a common biodiversity metric for extant taxa, but has not been used to explore temporal changes due to the lack of sufficiently large phylogenetic hypotheses. Here we explore how PD changes over deep time using a set of simple birth–death models (BDMs) and an empirical case study: a meta-analytically derived and probabilistically time-scaled set of phylogenetic hypotheses for 960 taxa of Mesozoic dinosaur. We show that under all of our BDMs PD will continually increase over time. For most models this follows an exponential curve, although for a diversity-dependent model (carrying capacity of 50 species) a clear inflection point is seen. Empirical curves for Dinosauria and the three major subclades (Ornithischia, Sauropodmorpha, Theropoda) show much greater variation, and a general pattern of a rise to a mid-Cretaceous peak followed by a decline towards the K-Pg boundary. However, subsampling suggests this decline is largely artefactual, except in the case of the Ornithischia. Overall, PD captures aspects of diversity that richness cannot, including the selectivity of extinction, which is most apparent in the removal of ‘prosauropods’ and the subsequent re-rooting of the sauropodomorph tree.
Environmental partitioning and differential growth in species of the thyreophoran dinosaur Stegosaurus in the Upper Jurassic Morrison Formation, USA
Susannah C. R. Maidment1, D. Cary Woodruff2 and John R. Horner3
1University of Brighton, UK
2University of Toronto, Canada
3Burke Museum of Natural History and Culture, USA
Two species of Stegosaurus are considered valid: Stegosaurus stenops, from Colorado, Utah and Wyoming, and Stegosaurus mjosi, known only from Wyoming. In 2015, a small specimen of Stegosaurus mjosi was excavated near Livingston, Montana. Histological examination suggests that the animal was still growing at time of death. Individuals of Stegosaurus stenops of a similar level of osteological maturity are larger in size, and small stature appears to be a feature common to Stegosaurus mjosi. The distribution of all individuals of Stegosaurus contemporaneous with the Livingston specimen was examined. The ranges of Stegosaurus mjosi and Stegosaurus stenops did not overlap during the time interval in which the Livingston specimen is found. Stegosaurus stenops occupied the southern part of the Morrison basin, while Stegosaurus mjosi occupied the northern part. The southern part of the basin was more arid than the northern part, and thus segregation of the two species may have been environmental. Large body size has been suggested as an adaptation to aridity among living megaherbivores, and it is possible that the larger size displayed by Stegosaurus stenops may have been an adaptation to prevailing conditions in the south of the Morrison basin.
Exploring the morphological diversity and hydrodynamic performance of extinct jawless vertebrates
Carlos Martinez Perez1,2, Humberto G. Ferron1, Imran A. Rahman3, Victor Selles de Lucas4, Philip C. J. Donoghue2 and Hector Botella1
1University of Valencia, Spain
2University of Bristol, UK
3Oxford University Museum of Natural History, UK
4University of Hull, UK
Most extinct jawless vertebrates are characterised by the presence of a heavy cephalic shield, which has traditionally been related with poor swimming capabilities and a bottom-dwelling lifestyle. However, the huge morphological diversity of the cephalic shields suggests that these groups could be more ecologically diverse than previously thought. Interestingly, galeaspids and osteostracans show a similar range of forms, which were acquired independently in each lineage in different geographical regions. Thus, the study of such taxa provides a great opportunity to analyse whether this morphological convergence was the result of equivalent functional adaptations to similar aquatic environments. With this aim, we have created a morphospace for 70 species of galeaspids and osteostracans using geometric morphometrics and tested the hydrodynamic performance of the most extreme forms using computational fluid dynamics. Our results show that both groups occupy broadly the same areas of morphospace. In addition, comparison of their hydrodynamic performance (i.e. drag and lift forces and their coefficients) allowed us to better understand variations in morphology in terms of swimming strategies and modes of life. This opens up a new opportunity to investigate the ecology of these groups of early vertebrates.
Critically accessing the depositional setting of the Ediacaran Mistaken Point Biota
*Jack J. Matthews1,2
1Memorial University of Newfoundland, Canada
2Oxford University Museum of Natural History, UK
The Mistaken Point Ecological Reserve, Newfoundland, contains some of the oldest known examples of the enigmatic Ediacaran macrobiota. The fossil assemblages, preserved on more than 100 bedding planes, provide some of the earliest evidence for both complex macroscopic eukaryotes and metazoan-style locomotion. Several depositional settings have been proposed for the strata of the Mistaken Point Formation in which many fossil taxa are found, including deep-marine and terrestrial environments. These interpretations have been used to argue against photosynthetic biological affinities, and in favour of a lichen-affinity for the biota, respectively. In this study, detailed sedimentological analysis of the Mistaken Point Formation demonstrates that the Ediacaran organisms lived and died in subaqueous, most likely deep-marine, environments. Furthermore, the use of several geochemical proxies as indicators of palaeoenvironment is questioned. These findings categorically refute a terrestrial depositional environment for this unit, and enable constraint of the possible phylogenetic affinities for organisms in the Mistaken Point assemblages, specifically refuting the possibility that these organisms could have been lichens.
Variable preservation of fruit flies in Pinus and Wollemia resin
*Victoria E. McCoy1, Carmen Soriano2, Arnoud Boom1 and Sarah E. Gabbott1
1University of Leicester, UK
2Advanced Photon Source, Argonne National Laboratory, USA
Fossilization in amber is highly variable, ranging from exceptional examples including minute details and internal soft tissues to empty moulds. Resin (the modern precursor to amber) chemistry is also highly variable, leading to the hypothesis that these variations may contribute to different preservation in the amber inclusions. Here we use actualistic taphonomic experiments to compare decay and preservation in two different modern resins. Fruit flies (Drosophila melanogaster) were embedded in modern resin from either a Scots pine (Pinus sylvestris) or a Wollemi pine (Wollemia nobilis), left to decay for six months, and then external and internal morphological decay were assessed through propagation phase-contrast synchrotron microtomography. The volatile and semi-volatile components of each resin were assessed using gas chromatography. Synchrotron tomographic analysis revealed that the flies entombed in Wollemia resin were well-preserved, and still had most of their internal soft tissues, and external cuticle. The flies entombed in Pinus resin, in contrast, had very little preserved internal soft tissue and poorly preserved external cuticle which had been breached by the resin in many places. The differential preservation may be due to the different chemical composition of the two resins.
Ultrastructure and chemistry of integumentary structures in an ornithischian dinosaur
Maria E. McNamara1*, Pascal Godefroit2, Danielle Dhouailly3, Michael J. Benton4, Sofia M. Sinitsa5, Yuri L. Bolotsky6, Alexander V. Sizov7 and Paul Spagna2
1University College Cork, Ireland
2Royal Belgian Institute of Natural Sciences, Belgium
3Université Joseph Fourier, France
4University of Bristol, UK
5Institute of Natural Resources, Ecology and Cryology, RAS, Russia
6Institute of Geology and Nature Management, RAS, Russia
7Institute of the Earth’s Crust, RAS, Russia
Research into the evolutionary origins of feathers has been stimulated over the last twenty years by discoveries of feather-like structures in non-avian theropod dinosaurs from the Middle Jurassic to Early Cretaceous of China. Despite such intensive research, many aspects of feather evolution remain poorly understood, including the nature and significance of filamentous integumentary structures and aberrant feather types. Previous studies of these tissues have lacked insights from tissue ultrastructure and chemistry. Here we report the preservation of diagnostic tissue structures and evidence of original biochemistry in diverse integumentary structures in the neornithischian dinosaur Kulindadromeus zabaikalicu, a basal neornithischian dinosaur from the Jurassic of Siberia. We analysed diverse integumentary structures, including scales, monofilaments, and compound feather-like structures, using scanning- and transmission electron microscopy, time-of-flight secondary ion mass spectrometry, and synchrotron X-ray absorption spectroscopy. The results reveal the widespread preservation of tissue ultrastructure, including keratinous tissue layers and melanosomes, in feathers and scales. Different tissue types can be discriminated on the basis of the geometry and trace element and sulfur speciation chemistry of melanosomes. Our data provide a new mechanism to determine the nature of evolutionarily important tissue types in feathered dinosaurs and will help constrain scenarios for the evolution of feathers.
Identifying patterns and drivers of coral diversity in the Central Indo-Pacific marine biodiversity hotspot
Morana Mihaljevic1, Chelsea Korpanty1, Willem Renema2 and John M. Pandolfi1
1University of Queensland, Australia
2Naturalis Biodiversity Center, Netherlands
Biodiversity hotspots are recognized as areas of high taxonomic and functional diversity. These hotspots are dynamic and shift geographically over time in response to environmental change. To identify drivers of the origin, evolution, and persistence of diversity hotspots, we investigated the diversity patterns of scleractinians in the Central Indo-Pacific, a marine biodiversity hotspot for the last 25 million years. We used the scleractinian fossil record (based on literature and a new fossil collection) to examine the taxonomic and functional diversity of corals from the Eocene–Pliocene, which we correlated with known environmental changes. Increases in taxonomic diversity, high origination rates, and changes in abundance of functional character states indicate that the origin of the Central Indo-Pacific hotspot occurred during the Oligocene, initially through proliferation of pre-existing taxa and then by origination of new taxa. In contrast to taxonomic diversity, overall functional diversity of Central Indo-Pacific scleractinians remained constant from the Eocene–Pliocene. Global sea level was identified as a main driver of diversity increase that, together with local tectonics, regulates availability of suitable habitats. Moreover, our results show that the marine biodiversity hotspot developed from both the accumulation of taxa from older biodiversity hotspots and the origination of new taxa.
Testing niche versus neutral models of Ediacaran community assembly
*Emily G. Mitchell1, Charlotte G. Kenchington2, Alexander G. Liu1, Simon J. Harris3, Philip R. Wilby3 and Nicholas J. Butterfield1
1University of Cambridge, UK
2Memorial University of Newfoundland, Canada
3British Geological Survey, UK
Spatial analysis of in situ Ediacaran macrofossils can reveal key insights into the ecological dynamics of these early communities. The full potential of this approach, however, has been limited by the slow acquisition rate of large quantities of accurate data, and a focus on only a small number of bedding surfaces. Using a high-resolution tripod-mounted laser line probe, we have overcome these logistical issues, and comprehensively mapped six of the most diverse and abundant Avalonian communities to a resolution of 50 µm. These include the Mistaken Point ‘E’ Surface, Spaniard’s Bay and two previously undocumented surfaces from Newfoundland, Canada, and the North Quarry and Memorial Crags surfaces in Charnwood Forest, UK. For each community, we analysed taxa spatial distributions using pair correlation functions (PCF) and have compared the patterns with different models of known biological and habitat interactions. Preliminary analyses suggest that Avalonian communities were predominately dominated by dispersal, with only weak habitat interactions. This result stands in stark contrast to modern sessile communities where habitat or ‘niche’ processes dominate over dispersal or ‘neutral’ models of community assembly. Rapid data acquisition enables the comparison of inter-regional ecological dynamics, enabling the broader ecological patterns of the Ediacaran–Cambrian transition to be uncovered.
A new Burgess Shale polychaete from Marble Canyon (British Columbia)
*Karma Nanglu1,2 and Jean-Bernard Caron2
1University of Toronto, Canada
2Royal Ontario Museum, Canada
Most of our direct evidence regarding early annelid evolution comes from the ‘middle’ Cambrian Burgess Shale, which contains five out of eight of the currently known Cambrian species. Here we describe the first new Burgess Shale species in over 40 years, based on hundreds of exceptionally well-preserved specimens recently discovered from Marble Canyon (Kootenay National Park, British Columbia). The new polychaete reaches up to 25 mm in length (c. 25 segments) and 2 mm in width (trunk only). The biramous parapodia are large, up to half the width of their associated trunk segment, and harbor c. 16 notochaetae and c. 12 neurochaetae. The chaetae are straight, thin (approximately 10–30 µm wide), and long, about four times the width of their chaetiger. There is no evidence of aciculae. The head bears a pair of elongate sensory palps, up to half the total body length, and a medial antenna suggesting a level of sensory complexity previously unknown in a Cambrian polychaete. Details of internal anatomy include a gut and possible neural and cardiovascular tissues. This new species helps refine our understanding of the early evolution of annelids, in particular regarding the morphology of the head and acquisition of sensory structures.
Revision of the imbricate eocrinoid Vyscystis from the mid Cambrian of the Barrandian area (Czech Republic)
Martina Nohejlová1, Oldřich Fatka1 and Elise Nardin2
1Charles University Prague, Czech Republic
2CNRS UMR 5563/ IRD UR 234, Université de Toulouse, France
Echinoderms are abundant in the Cambrian of the Czech Republic. They are preserved mostly as disarticulated remains and occasionally as fully articulated specimens. Among them, the lepidocystid genus Vyscystis is currently known from less than five fairly complete specimens. The Jince Formation (Drumian Stage, Cambrian Series 3) of the Pfont-family:ArialMT'>říbram–Jince Basin has recently yielded numerous beautifully preserved complete to weakly fragmented specimens of Vyscystis, associated with a diverse benthic fauna (e.g. felbabkacystid and eocrinid echinoderms, trilobites, agnostids, brachiopods, hyoliths). Vyscystis is characterised by a slightly domed irregularly-plated oral surface, an elongate cone-shaped aboral region, and distinctive coiled biserial brachioles. It is interpreted as an epibenthic low-level suspension feeder. The new recently collected material offers us the opportunity to reassess the morphology of the genus Vyscystis. Study material is housed in the Palaeontological Department of National Museum Prague, in the Czech Geological Survey Prague, and also in private collections. Several excellently preserved previously unstudied specimens provide new evidence depicting allometric trends and palaeoecology of the peri-Gondwanan lepidocystids, and inferring major evolutionary patterns among early blastozoans.
Palaeoecological and palaeoenvironmental significance of Brigantian Gigantoproductus brachiopod beds, Derbyshire carbonate platform, UK
*Leah Nolan1, Lucia Angiolini2, Giovanna Della Porta2, Vanessa J. Banks3, Sarah J. Davies1, Flavio Jadoul2, Melanie J. Leng3 and Michael H. Stephenson3
1Univeristy of Leicester, UK
2University of Milan, Italy
3British Geological Survey, UK
A sedimentological and palaeoecological analysis of beds dominated by species of the brachiopod genus Gigantoproductus investigates the rapid colonization and success of this taxon in the Derbyshire carbonate platform. Diversification of Gigantoproductus has been linked to a warming climate in the late Visean; during the Brigantian the genus thrived in the tropical and subtropical waters of Palaeotethys. Two key localities have been studied in Derbyshire. A shell bed at Ricklow Quarry comprises life assemblages (>72% of brachiopods in life position) and neighbourhood assemblages. They represent a low-moderate diversity community rapidly established in inner-middle ramp settings over relict Brigantian mud mounds. Brachiopod orientations indicate a south-directed palaeoflow. Once this community was established, the dominance of thick-shelled forms enabled baffling of mud and fine bioclasts, potentially providing localized shelter for larvae and nearby individuals. A shallower and higher energy inner ramp location, Once-a-Week Quarry, revealed a lower diversity community exclusively comprising neighbourhood assemblages (37% in life position) with no preferred shell orientation. High-resolution trace element and stable isotope data from well-preserved Gigantoproductus shell calcite reveal geochemical heterogeneity, potentially reflecting environmental or climatic changes. These data enable evaluation of data quality and preservation potential of palaeoenvironmental signals in deep-time specimens.
What can spores and pollen tell us about taphonomic bias at the Permian–Triassic boundary in the Eastern and Southern Alps?
*Hendrik Nowak1, Evelyn Kustatscher1,2, Guido Roghi3, Massimo Bernardi4,5 and Karl Krainer6
1Naturmuseum Südtirol, Italy
2Bayerische Staatssammlung für Paläontologie und Geologie, Germany
3Institute of Geosciences and Earth Resources, Italy
4Museo delle Scienze di Trento, Italy
5University of Bristol, UK
6Universität Innsbruck, Austria
The mass extinction at the Permian–Triassic boundary is famous for being the most severe extinction event of both marine and terrestrial faunas and one of only two mass extinctions among plants. In order to determine the importance of taphonomic bias for the observed extinction and recovery patterns, an interdisciplinary project has started to study the boundary interval in the Eastern and Southern Alps. This region contains numerous outcrops documenting coeval marine and terrestrial palaeoenvironments. Here we present the first palynological results from sections at Tesero, Bulla/Pufels and the Laurinwand. Most of the samples from the Upper Permian Bellerophon Formation yielded a rich sporomorph assemblage dominated by bisaccate taeniate and non-taeniate pollen, which were produced by conifers and seed ferns (pteridosperms). Spores of lycopsids and ferns mostly occur only sporadically. Possible algae (or fungi) of the genus Reduviasporonites comprise almost the entire assemblage in samples from the Tesero Member (uppermost Permian to lowermost Triassic) of the Werfen Formation at the Tesero section. Further work will be aimed at finding differences in assemblages between different depositional environments, the identification of possible biases and the reconstruction of terrestrial ecosystems over time.
The influence of taphonomic bias on Bayesian estimation of clade ages using morphological data
Joseph O’Reilly and Philip C. J. Donoghue
University of Bristol, UK
Total-evidence divergence time estimation methods have expanded the utility of fossil data when estimating evolutionary timescales. In classic divergence-time analyses fossil data are reduced down to purely chronological data, with discrete characters being discarded. New methodology now allows for the inclusion of these data, allowing fossil morphology to refine our understanding of evolutionary history. Yet fossil morphological data are relatively incomplete, with a decidedly non-random distribution of missing data. This distribution is constrained by taphonomic processes, with soft characters likely to be poorly represented while harder, more easily fossilized characters dominate matrices. Such a bias may lead to the inaccurate estimation of divergence time estimates. We apply a series of taphonomic filters to simulate the effects of different stages of fossilization on a large and highly complete matrix. Divergence times estimated using this matrix then allow us to demonstrate the relative influence of different stages of the process of fossilization on the accuracy of divergence time estimates. We show that the loss of soft characters poses little threat to the accuracy of divergence time estimates, but that the concomitant loss of characters from different assemblages attributable to particular anatomical categories may increase age estimate error.
Recent new discoveries from the upper Ediacaran of western Mongolia
Tatsuo Oji1, Stephen Q. Dornbos2, Hitoshi Hasegawa1, Sersmaa Gonchigdorj3, Keigo Yada1, Akihiro Kanayama1, Takafumi Mochizuki4, Hideko Takayanagi5 and Yasufumi Iryu5
1Nagoya University, Japan
2University of Wisconsin-Milwaukee, USA
3Mongolian University of Science and Technology, Mongolia
4Iwate Prefectural Museum, Japan
5Tohoku University, Japan
We have surveyed the upper Ediacaran to the lowest Cambrian of Govi-Altai and Zavkhan provinces, western Mongolia, for several years, and we have obtained interesting palaeontological data hitherto unknown from other Ediacaran sections, or not known at least from Mongolia. We will present two topics from the upper Ediacaran of these provinces. One is the existence of U-shaped burrows, possibly assignable to the ichnogenus Arenicolites, from the uppermost part of the Ediacaran of Bayan Gol, Govi-Altai Province. These ichnofossils occur in more than 10 horizons, and the diameter of some of their openings reach more than 1 cm. This discovery strongly suggests that bilaterians already existed by the end of the Ediacaran. The other is the occurrence of two species of algae (Chinggiskhaania bifurcata and Zuunartsphyton delicatum) from thinly laminated shale of the Ediacaran of Zuun Arts, Zavkhan Province. The shale containing these algae is considered to be a Burgess Shale-type deposit and further excavation at this site may lead to new discoveries of fossils including metazoans.
Within-guild niche partitioning in sympatric species: how ecologically sensitive is texture analysis of tooth microwear?
Mark A. Purnell1, Christopher Nedza1 and Leszek Rychlik2
1University of Leicester, UK
2Adam Mickiewicz University in Poznafont-family:Arial-ItalicMT'>ń, Poland
Recent work shows that tooth microwear analysis can be applied further back in time and deeper into the phylogenetic history of vertebrate clades than previously thought (e.g. niche partitioning in early Jurassic insectivorous mammals; Gill et al. 2014, Nature). Furthermore, quantitative approaches to analysis based on parameterization of surface roughness are increasing the robustness and repeatability of this widely used dietary proxy. Discriminating between taxa within dietary guilds has the potential to significantly increase our ability to determine resource use and partitioning in fossil vertebrates, but how sensitive is the technique? To address this question we analysed tooth microwear texture in sympatric populations of shrew species (Neomys fodiens, Neomys anomalus, Sorex araneus, Sorex minutus) from Białowieza Forest, Poland. These populations are known to exhibit varying degrees of niche partitioning (Churchfield and Rychlik 2006, J. Zool.) with the greatest overlap between the Neomys species. Sorex araneus also exhibits some niche overlap with N. anomalus, while S. minutus is the most specialized. Multivariate analysis based only on tooth microwear textures recovers the same pattern of niche partitioning. Our results also suggest that tooth textures track seasonal differences in diet. Microwear analysis clearly has the potential for very subtle dietary discrimination in fossil insectivores.
Exploring the drivers of ecological and evolutionary turnover in the Caribbean
Paola G. Rachello-Dolmen1,2, Ethan L. Grossman2, Kenneth G. Johnson3, Jonathan A. Todd3 and Aaron O’Dea1
1Smithsonian Research Institute, Panama
2Texas A&M University, USA
3Natural History Museum, London, UK
The Caribbean experienced a massive regional extinction in the Plio-Pleistocene that led to a loss of over 50% of marine species. Extinction was strongly selective against taxa better adapted to nutrient-rich environments, thus the extinction has been attributed to declining planktic nutrients in the Caribbean due to isolation from the Pacific during closure of the Isthmus of Panama. However, while nutrients declined between 4 Ma and 3 Ma the extinction occurred 1-2 million years later. In this study we dissect the ecological and environmental dynamics of this turnover. Our data include more than 500,000 specimens of molluscs, bryozoans, fish otoliths and corals from before, during and after the extinction. We measure environmental change using >4,000 stable isotope analyses from profiles of gastropod shells and explore relative abundances and co-occurrences of taxa and functional traits of organisms through this time and across space. Preliminary data suggest that functional traits provide a better predictor of turnover than taxonomic affinity. We observe that taxa that eventually go extinct tend to aggregate irrespective of taxonomic affinity, suggesting that refugia allowed doomed taxa to persist.
Using melanosomes to discriminate between tissues in vertebrate eyes
*Christopher S. Rogers and Maria E. McNamara
University College Cork, Ireland
The vertebrate eye contains three tissue sources of melanosomes: the retinal pigment epithelium (RPE), the choroid and the iris. These melanosome populations can be discriminated in part by their morphology. The presence of layers of melanosomes of different morphologies in the eyes of fossils has been used as evidence of the RPE and thus a vertebrate affinity. However, whether melanosomes from different tissue sources in the eye consistently differ in geometry across a range of vertebrate taxa has yet to be demonstrated. We confirm that melanosomes from different ocular tissues differ significantly in geometry both within and among taxa. Importantly, our data show that the preservation of melanosomes organized into size-specific layers could result from the superposition of melanosomes from other tissues in the eye or elsewhere in the head. Further investigation into the geometry and chemistry of melanosomes in the vertebrate eye will help constrain the extent to which the vertebrate eye can be used for phylogenetic studies.
Preservation and phylogeny of Cambrian ecdysozoans tested by experimental decay of Priapulus
University of Manchester, UK
The exceptionally preserved Cambrian fossil record provides unique insight into the early evolutionary history of animals. Understanding of the mechanisms of exceptional soft tissue preservation frames all interpretations of the fauna and its evolutionary significance. This is especially true for recent interpretations of preserved nervous tissues in fossil ecdysozoans. However, models of soft tissue preservation lack empirical support from actualistic studies. Here experimental decay of the priapulid Priapulus reveals consistent bias towards rapid loss of internal non-cuticular anatomy compared with recalcitrant cuticular anatomy. This is consistent with models of Burgess Shale-type preservation and indicates that internal tissues are unlikely to be preserved with fidelity if organically preserved. This pattern, along with extreme body margin distortion, is consistent with onychophoran decay, and is therefore resolved as general for early ecdysozoans. Application of these patterns to phylogenetic data finds scalidophoran taxa to be very sensitive to taphonomically informed character coding, but not panarthropodan taxa. Priapulid decay also has unexpected relevance for interpretation of myomeres in fossil chordates. The decay data presented serve not only as a test of models of preservation, but also a framework with which to interpret ecdysozoan fossil anatomies and the subsequent evolutionary inferences drawn from them.
The (incomplete) Phanerozoic fossil record of major phytoplankton lineages
Thomas Servais1 and Ronald E. Martin2
1CNRS UMR 8198, Université de Lille, France
2University of Delaware, USA
The Phanerozoic fossil record of marine biodiversity remains an enigma. A broad range of physical and biological factors have been proposed to explain the record but none, singly or in combination, satisfactorily explain the basic patterns. One factor which has received relatively little attention with regard to the Phanerozoic fossil record is that of food. We suggest that the quantity (primary productivity) and quality (stoichiometry) of food at the base of food pyramids, i.e. the phytoplankton, was critical to biodiversification. Cambrian and Palaeozoic faunas are paralleled by nutrient-poor (high carbon:phosphorus ratios, ‘green’) lineages, whereas the modern fauna is paralleled by nutrient-rich (low carbon:phosphorus ratios, ‘red’) lineages. Based on studies of trophic cascades of lacustrine ecosystems, Palaeozoic macrofauna would have had to expend energy up front to ‘burn off’ excess carbon to obtain phosphorus (an essential macronutrient) of ‘green’ phytoplankton, leaving less energy for reproduction. The converse holds for modern macrofauna and ‘red’ lineages. However, the fossil record of phytoplankton is dramatically incomplete. A major problem in understanding the base of marine food chains is the total absence in the fossil record of the picophytoplankton (< 5 µm) that represents over 50 % of modern marine biomass.
Where to find the Carboniferous terrestrial fauna: recent discoveries in Romer’s Gap point the way
Timothy R. Smithson1, Carys E. Bennett2, Jennifer A. Clack1, Neil D. L. Clark3, Sarah J. Davies2, Gregory D. Edgecombe4, Timothy I. Kearsey5, John E. A. Marshall6, David Millward5, Andrew J. Ross7 and Janet E. Sherwin2
1University of Cambridge, UK
2University of Leicester, UK
3University of Glasgow, UK
4Natural History Museum, London, UK
5British Geological Survey, UK
6University of Southampton, UK
7National Museums Scotland, UK
Recent exploration of the Ballagan Formation (Tournaisian) in the Tweed Basin, Scottish Borders, has revealed numerous new beds containing tetrapods and terrestrial arthropods. The most common lithology preserving this fauna is sandy siltstone. These beds usually overlie palaeosols and were deposited in seasonal flooding events as cohesive flows. This taphofacies contains the most abundant and rich fossil deposits in the early Carboniferous. It includes a diverse variety of vertebrates, bivalves, ostracods, millipedes, scorpions and other arthropods, and abundant plant remains. During the early Carboniferous the Tweed Basin was a low-lying coastal flood plain traversed by large rivers, and housed permanent and temporary freshwater lakes. Overbank flooding and periodic high rainfall provided sediment deposition in which the fauna and flora were preserved. During times of flooding, proximity to land provided refuge for the terrestrial fauna. These conditions were an ideal environment for the evolution of terrestrial ecosystems and in northern Britain were fairly stable over millions of years. Similar conditions must have prevailed throughout the Carboniferous, and basins adjacent to upland areas in which wetland palaeosols form a significant component of the succession are where we should be looking for new tetrapod and terrestrial arthropod sites.
Modern brains and their Cambrian antecedents: evolutionary stability, genealogical correspondence and evolved loss
Nicholas J. Strausfeld1, Xiaoya Ma2 and Gregory D. Edgecombe2
1University of Arizona, USA
2Natural History Museum, London, UK
The evolutionary exuberance of euarthropods is reflected in their variety of forms, behaviours and habitats. Such profusion of shapes and functions might be expected to reflect corresponding diversity of brains and nervous systems. However, contemporary studies suggest that brain and nervous system organization is constrained to a set of divergent motifs, called ‘ground patterns’. Although arthropod brains comprise a rich variety of neural arrangements in defined centres, each ground pattern today typifies one of the major arthropod clades. Here we review the interpretation of discoveries deriving from exceptionally preserved fossils from China’s Chengjiang and Xiaoshiba and Canada’s Burgess Shale fauna that resolve these neural ground patterns as very ancient, spanning a range of about 518–505 million years. The overarching view of the panarthropod central nervous system is thus one of evolutionary stability. Four types of brain and three ventral nervous systems found in fossils correspond to the four ground patterns of four clades of extant panarthropods. Current understanding of phylogeny and time of origin of panarthropod lineages allows allocation of divergent brain centres to each ground pattern identified in Cambrian fossils. Those times of origin tell us when transformations of sensory/motor centres are likely to have occurred.
The effect of climate on equatorial late Palaeozoic floral transitions in the limnic Muse and the paralic Mengkarang Formations. Two sides of the same coin?
Isabel M. Van Waveren1, Menno Booi1, Christopher J. Cleal2, Mike J. Crow3, Fauzie Hasibuan4, Pierre Pellenard5, Mark D. Schmitz6 and Ellen Stolle7
1Naturalis Biodiversity Center, Netherlands
2Amgueddfa Cymru – National Museum Wales, UK
4Pusat Survei Geologi, Indonesia
5CNRS UMR 6282, Université de Bourgogne Franche Comté, France
6Boise State University, USA
7*EP Research, Germany
Two newly described uninterrupted sections from the Late Palaeozoic equatorial belt indicate apparent inverse developments of the palaeoflora. Detailed analysis of the limnic beds from the Muse Formation (Autun Basin, France) indicates a transition from peltasperm to cordaite and marattialean dominated vegetation, while the paralic Mengkarang Formation (Sumatra) displays a transition from cordaite and marattialean to peltasperm dominated vegetation. New isotopic age measurements for both formations shows their respective duration is comparable. The top and central ash bands from the Muse beds indicate 850,000 years of deposition for the metre of bituminous shales they enclose, while the top and base of the 500-metre-thick section through the paralic Mengkarang Formation indicates a duration of 630 million years. Comparison with the global eustatic sea level curve shows that the early Asselian Muse beds represent a transition from a low to a high eustatic sea level, while the middle Asselian Sumatra section shows the inverse transition. As Late Palaeozoic eustatic sea level fluctuations are related to Gondwanan glaciations, it appears that the peltasperm vegetation reflects the low eustatic sea level conditions of a glaciation while the cordaite and marattialean reflect the high eustatic sea level of global warm conditions.
Biostratigraphic assessment of the uppermost Ordovician in the central Anti‑Atlas (Morocco)
Enrique Villas1, Jorge Colmenar2, Juan C. Gutiérrez-Marco3, Sofia Pereira4, José-Javier Álvaro3, Diego García-Bellido5 and Saturnino Lorenzo6
1University of Zaragoza, Spain
2University of Copenhagen, Denmark
3Instituto de Geociencias (CSIC UCM), Spain
4University of Lisboa, Portugal
5University of Adelaide, Australia
6University of Castilla-La Mancha, Spain
We have revisited the stratotype area of the Lower Formation of the Second Bani Group, west of Tagounite in the Moroccan Anti-Atlas, and sampled brachiopods and trilobites from its uppermost quartzitic horizons. In addition to those brachiopods listed in previous papers on the region, we have found Plectothyrella sp. and Kinnella sp. Both genera are exclusive of the pandemic Hirnantia fauna, which allows confirmation of a Hirnantian age for the upper member of the Lower Second Bani Formation. By contrast, the lower member of the same unit has yielded Katian brachiopods and trilobites, such as Eostropheodonta intermedia, Destombesium sp., Hirnantia sp. (species other than H. sagittifera), Actinopeltis aff. insocialis, Mucronaspis termieri and Cekovia aff. perplexa. According to the lithostratigraphic framework, the Katian/Hirnantian boundary lies within the Lower Formation of the Second Bani Group and lithostratigraphically correlative horizons, such as those reported in Bou Ingarf. The latter were mainly dated as a result of lithostratigraphic and sequential correlations and, based on correlation with the Tagounite area, are in need of revision. The age of the lower part of the chitinozoan Tanuchinita elongata Biozone should be re-evaluated, and the suggested delayed onset of the Hirnantian glaciation reconsidered.
Ammonoids from the Griesbachian (Early Triassic) of northeastern Greenland: taxonomy and biostratigraphy
David Ware and Hugo Bucher
University of Zurich, Switzerland
The Wordie Creek Formation in northeast Greenland is well known for its well-preserved and abundant Griesbachian (earliest Triassic) ammonoids. Their taxonomy is, however, still based on a very typological approach, and their biostratigraphy is based mostly on scattered occurrences and small sample size with a poor stratigraphical control. Intensive fieldwork conducted recently led to the collection of large samples collected in situ. These allow us, as a first step, to revise their taxonomy by studying their ontogeny and intraspecific variability. Based on this revised taxonomy, a more detailed and better substantiated biostratigraphical scheme for this area is established. The boundaries of the Griesbachian substage for this region as defined by Bjerager et al. (2006) are here questioned, especially concerning the Hypophiceras triviale zone and the Bukkenites rosenkrantzi zone, here considered as already Griesbachian and Dienerian in age, respectively. A new biostratigraphical scheme with nine Griesbachian zones is proposed, which clearly contrasts with the previously established five zones of Bjerager et al. (2006).
A fossilized birth–death model for the reliable estimation of speciation and extinction rates
Rachel C. M. Warnock1,2, Tracy A. Heath3 and Tanja Stadler1
1ETH Zurich, Switzerland
2Smithsonian Museum of Natural History, USA
3University of Iowa, USA
Estimating speciation and extinction rates is essential for understanding the past, present and future of biodiversity. Widespread interest in this topic has led to a divergent suite of competing approaches using stratigraphic versus phylogenetic data. The fossilized birth-death (FBD) process is a model that explicitly recognizes that the branching events in a phylogeny and the fossils sampled from the rock record were generated by the same underlying diversification process. Here we present an extension that allows the branching process to be modelled in the absence of any phylogenetic information. This eliminates the requirement for anything about the underlying phylogeny to be known, such that the model can be applied when only first and last occurrence data are available, but still allows the inherent phylogenetic structure of the data to be considered. We tested the model using simulations that incorporate non-uniform fossil preservation and compared our approach to widely implemented fossil-based alternatives. We show that our new method is both accurate and precise, but that the performance of all methods is impacted by non-uniform preservation and uncertainties in taxonomy. These represent critical areas for development among all methods that aim to recover reliable estimates of diversification rates in deep time.
The importance of fossils in dating the Tree of Life: from exceptional preservation to complete absence
Joanna M. Wolfe
Massachusetts Institute of Technology, USA
Geological age data and molecular sequences are increasingly combined to establish a timescale for the Tree of Life. In the best case scenarios, the geological dates are derived from fossils which meet a series of criteria, such as data on their phylogenetic placement and stratigraphy. Here I empirically explore one of the absolute best cases, using a morphological dataset with over 200 arthropod fossils, mainly from Cambrian localities with exceptional preservation (thus stronger phylogenetic evidence). I also explore the worst cases, dating in ‘prokaryotes’ (Bacteria and Archaea), which generally lack a fossil record, and have divergences expected prior to the Neoproterozoic. New strategies are introduced to constrain these microbial divergences, including harnessing the horizontal transfer of genes into fossiliferous clades, and the coevolution of bacterial parasites and their fossiliferous metazoan hosts. Directly or indirectly, the fossil record remains indispensable to date any branches of the tree.