A downloadable PDF version can be found here: Annual Meeting 2015 - Cardiff - Abstracts & Programme
The grapes among the apes: implications of a new fossil record of the Vitaceae from the African Miocene
*Neil F. Adams1, Margaret E. Collinson1,2, Selena Y. Smith3, Marion K. Bamford4, Félix Forest5, Panagiota Malakasi5, Federica Marone6 and Dan Sykes2
1Royal Holloway, University of London, UK
2Natural History Museum, London, UK
3University of Michigan, USA
4University of the Witwatersrand, South Africa
5Royal Botanic Gardens, Kew, UK
6Paul Scherrer Institute, Villigen, Switzerland
The early Miocene Hiwegi Formation on Rusinga Island in Kenya has yielded a rich flora and fauna, including the early hominoid Proconsul. The flora is important because it provides rare evidence for habitats directly inhabited by early hominoids in the transition between arboreal primates and later hominids, and because tropical palaeolatitude records are uncommon. A comparative study of fossil and modern seeds using micro-computed tomography (µCT) and synchrotron radiation X-ray tomographic microscopy (SRXTM) shows that some fossils belong to four new Cissus species and represent the first African fossil record of the grape family (Vitaceae). Virtual taphonomy explains how key features of the fossils were obscured during fossilization leading to previous misidentification of some specimens to the moonseed family (Menispermaceae). Phylogenetic relationships within modern Cissus were reconstructed using previously obtained DNA sequences, as well as newly generated sequences for African species. Modern species most similar to the fossils belong to at least three clades, in early diverging lineages, currently widespread across Africa and southeast Asia. The fossils are interpreted to represent moist forest and arid-adapted taxa and add previously unrecognized diversity of lianas and shrubs to a Miocene mosaic of woodland and forest habitats: the setting for early hominoid evolution.
New windows into the ecology and taphonomy of Ediacaran acanthomorphs
*Peter W. Adamson1,2 and Nicholas J. Butterfield1
1University of Cambridge, UK
2British Geological Survey, UK
The Ediacaran is marked by a distinctive assemblage of large acanthomorphic acritarchs, best known from the Doushantuo Formation in South China. These fossils offer the only reasonable prospect for biostratigraphic subdivision of the early Ediacaran, although such potential seems compromised by their restriction to localized low-energy environments, primarily chert and phosphorite facies. Our study of the interstices of a debris-flow conglomerate in the Ediacaran Biskopås Formation (Norway) substantially expands the known palaeoenvironmental and taphonomic range of Doushantuo-type acanthomorphs. In some cases the spaces were filled with fossiliferous micrite (now microsparite) – the first documented occurrence of Doushantuo-type acritarchs preserved in carbonate. Elsewhere the interstices include the remains of phosphatized, boulder-encrusting microbial mats with incorporated acanthomorphs – the first documented occurrence of Doushantuo-type phosphatization outside of South China. Given these two distinct taphonomic pathways, and the contemporaneous growth of microbial mats, it is clear that the acanthomorph-forming organisms were living in direct proximity to the actively prograding conglomerate, either within the interstices or on locally quiescent palaeosurfaces. The discovery of acanthomorphs in both high-energy environments and carbonates presents an important new search image for such fossils, and substantially increases their potential for biostratigraphically partitioning the early Ediacaran.
The Mesoproterozoic Ruyang Group, China – a hotspot of early eukaryote biodiversity
*Heda Agić1, Małgorzata Moczydłowska1 and Leiming Yin2
1Uppsala University, Sweden
2Nanjing Institute of Geology and Palaeontology, China
The Mesoproterozoic Era was a critical time for the diversification of Eukaryota and the appearance of the first complex morphologies. Earliest eukaryotic fossils with ornamentation and sculpture occur in the 1.8–1.6 Ga successions worldwide. The Ruyang Group, China, records a high diversity (26 taxa) of such organic-walled microfossils. Studied samples derive from organic-rich shale intervals through Baicaoping and Beidajian formations, deposited in shallow marine environments. Acetolysis-resistant palynomorphs were extracted from the rock via HF-maceration and studied using light and scanning microscopy. Depositional age of Ruyang successions has been constrained to 1.75–1.40 Ga via zircon U-Pb dating, extending the first appearance of complex eukaryotic characters back in the fossil record. Novel morphologies among this unicellular biota include a variety of processes, spongy membranes, and specimens with internal bodies of varying sizes, up to 87% of the vesicle diameter. Fossil diversity is highest in the middle Baicaoping and the uppermost Beidajian Formation. Key characters displayed by the Ruyang biota are consistent with reproductive structures (cysts) among modern protists. A significant degree of intracellular complexity would have been required to produce such intricate morphologies. Size, morphology and wall ultrastructure support the position of some Ruyang microfossils in the crown-group Eukarya.
Chitinozoan biozonation in the Arenig Series (Floian–lower Darriwilian stages) of Wales
*Chloé E. A. Amberg1, Thijs R. A. Vandenbroucke2, Stewart G. Molyneux3, Jean‑François Ghienne4 and Philippe Razin5
1Université Lille 1, France
2Ghent University, Belgium
3British Geological Survey, UK
4Institut de Physique du Globe de Strasbourg, France
5Université de Bordeaux, France
The Early-Middle Ordovician has long been considered a super-greenhouse world. However, emerging evidence suggests that global cooling towards the Late Ordovician glaciations may have started earlier than previously thought, perhaps even during the Early Ordovician. Our research project further investigates this hypothesis, testing the following predictions: 1) if low-stand sedimentary features (such as unconformities) in the near field (Anti Atlas of Morocco) are of glacio-eustatic origin, they ought to correlate with other, distant, indications of lowstand; and 2) if the climate changed, this ought be reflected in the distribution patterns of Early–Middle Ordovician chitinozoans. Both approaches are challenged by the lack of chitinozoan data from the Anglo-Welsh basin, needed to correlate the Moroccan sections (without graptolites) into the classic Anglo-Welsh area. Here, we present a chitinozoan biostratigraphy for the historical type Arenig Series in Wales. Our results indicate that the Avalonian chitinozoan fauna, containing assemblages of Lagenochitina aff. esthonica, differs from that of Gondwana in the lower and middle Arenig. The upper Arenig Avalonian fauna correlates with the Desmochitina bulla Biozone from Gondwana. This new framework and the absence of several key Gondwana taxa is here used to make inferences about the Early Ordovician climate.
Variations in wildfire activity driven by atmospheric oxygen changes across the Toarcian OAE
*Sarah J. Baker, Claire M. Belcher, Stephen P. Hesselbo and Tim M. Lenton
University of Exeter, UK
Oceanic anoxic events (OAEs) represent periods in Earth’s history of major disruption to the global carbon cycle. During an OAE, organic carbon burial rates increase due to abundant primary productivity within surface waters leading to anoxic bottom waters and enhanced organic preservation. Over geological timescales organic carbon burial serves as a major source of atmospheric oxygen. Small changes in atmospheric oxygen concentrations have been shown to greatly influence wildfire activity, yet no one has considered studying fossil evidence postulated changes to atmospheric oxygen driven by OAEs before. Here we show variations in charcoal abundance as a proxy for wildfire activity across the Toarcian OAE, from three sites. Our results show significant changes in wildfire activity that we suggest may be able to resolve the potential timescale over which atmospheric oxygen can change across an OAE. Increased charcoal abundance coincides with the onset of the Toarcian OAE and remains high throughout its duration, diminishing only during a negative carbon isotope excursion period due to elevated precipitation levels that likely dampened wildfire activity. Our results provide physical evidence from the fossil record that changes in atmospheric oxygen concentrations, driven by increased organic carbon burial during an OAE, were possible across this relatively short geologic timescale.
Five new Tournaisian tetrapods: their sedimentology and palaeoenvironments
*Carys E. Bennett1, Jennifer A. Clack2, Timothy Kearsey3, Sarah J. Davies4, David Millward3, Tim R. Smithson2, Marcello Ruta5, Ben Otoo2, John E. A. Marshall6, Emma Reeves6 and Andrew Ross7
1University of Leicester, UK
2University of Cambridge, UK
3British Geological Survey, UK
4University of Leicester, UK
5University of Lincoln, UK
6University of Southampton, UK
7National Museums Scotland, UK
Far from being a depauperate interval for fossil tetrapods, the Tournaisian has recently yielded an unprecedented diversity of taxa. A cladistic analysis of five new tetrapod species places three taxa below the origin of the tetrapod crown group. The remaining two taxa are part of the amphibian stem group. The fossils occur spaced through the Ballagan Formation at the Burnmouth and Willie’s Hole sites. Despite their stratigraphic and geographic separation, four of the five tetrapods occur in the same lithology, a microconglomerate: matrix-supported grey siltstones with clasts of 1-2 mm in size derived from floodplain sediments. Microconglomerates are common (140 beds in a 490 metre succession), often (71% of beds) overlying desiccation cracks, and are one of the richest fossil deposits in this formation; plant fossils and megaspores are abundant as are the remains of actinopterygians, rhizodonts, ostracods, eurypterids, myriapods and non-marine bivalves. Tetrapods, lungfish and chondrichthyans are rarer. Deposition occurred in seasonal flooding events, likely due to monsoonal rainfall. Varied palaeosols and palynology indicate a mosaic of environments including forests, scrubland, wetlands and desiccating pools. Fossil specimens are often articulated and indicate minimal transportation and rapid burial. These under-recognized deposits record early diversification of tetrapods into newly-appearing habitats.
Near-stasis in the long-term diversification of Mesozoic tetrapods
Roger B. J. Benson1, Richard J. Butler2, John Alroy3, Philip D. Mannion4, Matthew T. Carrano5 and Graeme T. Lloyd3
1University of Oxford, UK
2University of Birmingham, UK
3Monash University, Australia
4Imperial College London, UK
5Smithsonian Institution, USA
How did evolution generate the extraordinary diversity of vertebrates on land? Zero species are known prior to ~380 million years ago, and more than 30,000 are present today. The widely-held expansionist model suggests that this was achieved by large and unbounded increases, leading to substantially greater diversity in the Recent than at any time in the geological past. However, only a small amount of empirical data have been used to test this hypothesis. We quantify patterns of vertebrate standing diversity on land during the Mesozoic–early Palaeogene interval, applying sample-standardization to a global fossil dataset containing 27,260 occurrences of 4,898 non-marine tetrapod species. Our results show a highly stable pattern of Mesozoic tetrapod diversity, underpinned by a weakly positive, but near-zero, long-term net diversification rate over 190 million years. Diversity of non-flying terrestrial tetrapods less than doubled over this interval, despite the origins of exceptionally diverse extant groups within mammals, squamates, amphibians and dinosaurs. Therefore, although major groups of modern tetrapods have Mesozoic origins, rates of Mesozoic diversification inferred from the fossil record are slow. Apparently multiplicative diversity increases over the K/Pg boundary suggest that the gradualistic evolutionary diversification of tetrapods was punctuated by brief but dramatic episodes of radiation.
The Strawberry Bank Lagerstätte reveals insights into Early Jurassic life
Michael J. Benton1, Matt Williams2, Andrew Ross3 and Matt Friedman4
1University of Bristol, UK
2Bath Royal Literary and Scientific Institution, UK
3National Museums Scotland, UK
4University of Oxford, UK
The Strawberry Bank Lagerstätte from the Early Jurassic (early Toarcian) of Ilminster, Somerset, provides a rich insight into Early Jurassic marine vertebrate life, revealing exquisite anatomical detail of marine reptiles and large pachycormid fishes thanks to exceptional preservation, and especially the uncrushed, 3D nature of the fossils. The site documents a fauna of Early Jurassic nektonic marine animals (five species of fishes, one species of marine crocodilian, two species of ichthyosaurs, cephalopods and crustaceans), but also over 20 species of insects. Unlike other fossil sites of similar age, the 3D preservation at Strawberry Bank provides unique evidence on palatal and braincase structures in the fishes and reptiles. The age of the site is important, documenting a marine ecosystem during recovery from the end-Triassic mass extinction, but also exactly coincident with the height of the Toarcian oceanic anoxic event, a further time of turmoil in evolution. Initial digital reconstructions show the great potential of the site, and a new, funded project aims to extract full information from this long-forgotten Lagerstätte.
Conodont-based, high-resolution, quantitative biochronology of the end-Permian mass extinction in South China
*Morgane Brosse1, Hugo Bucher1 and Nicolas Goudemand1,2
1University of Zurich, Switzerland
2École normale supérieure de Lyon, France
The construction of a high-resolution zonation across the Permian–Triassic Boundary (PTB) is of paramount importance for elucidating the mechanisms at play before, during and after the end-Permian mass extinction because it provides a time frame for reconstructing the global sequence of abiotic and biotic events that occurred during that critical interval. We propose a new conodont-based regional biozonation of the PTB interval for the Chinese Nanpanjiang basin, including the reference-setting GSSP section of Meishan. This discrete zonation comprises six Unitary Association Zones (UAZs). UAZs are preferred to the traditional, continuous interval zones, because they enable the detection and solving of biostratigraphical contradictions, hence lead to more robust and more accurate biozonations. We standardized the high-resolution conodont data from six well-documented sections. The resulting zonation is largely compatible with the conodont data of five additional sections and enables intra-basinal correlations, including between sections displaying drastically different facies. Combining these results with published carbon isotopic data and radiometric absolute ages, we show that the deposition in South China during the earliest Triassic of microbialites lasted no more than 0.55 Ma.
On the origin of animals and biologically mediated flow
Nicholas J. Butterfield
University of Cambridge, UK
The evolution of multicellular metazoans was one of the most revolutionary transitions in the history of life on Earth. Explanations for its conspicuously-late appearance (in the mid-Neoproterozoic) have focused largely on atmospheric evolution, reasoning that multicellular organisms require fundamentally higher levels of oxygen than corresponding unicells. This isn’t true. Whereas unicells live in viscous flow regimes and exchange oxygen and CO2 solely by diffusion, the collectivized activity of flagellated cells in sponge-grade organisms gives rise to turbulent flow (advection) and, as a consequence, access to fundamentally greater levels of gas exchange. Given the presence of single-celled aerobic eukaryotes a billion years prior to the earliest estimated appearance of sponges, oxygen availability can be dismissed as a viable hypothesis for the delayed appearance of animals. By the same token, the primary impetus for multicellularity was likely to have been feeding rather than gas exchange. Even so, the invention of this new fluid dynamic technology was a prerequisite for advancing to more complex grades of organization. In turn, the increasingly sophisticated means of diploblastic and triploblastic animals to bioturbate their aqueous medium revolutionized Phanerozoic ocean structure and dynamics – with local returns to Proterozoic conditions during mass extinction.
Reconstructing Miocene neotropical palaeoenvironments: a case study from the palaeosols and ichnofossils of Cerdas, Bolivia
*Angeline M. Catena1, Daniel I. Hembree2, Beverly Z. Saylor1 and Darin A. Croft1
1Case Western Reserve University, USA
2Ohio University, USA
Bolivia is one of the few countries in South America that preserves a rich fossil record of middle Miocene Neotropical mammals. Nevertheless, little is known about the palaeoenvironments that fostered the development of this ancient mammalian diversity. Cerdas, an early Middle Miocene (16–15 Ma) locality has produced remains of 15 mammal species in seven orders and nine families. In this study, we use palaeopedology and ichnology to investigate its palaeoenvironment. The palaeosols of Cerdas are weakly to moderately developed, occur in compound profiles, and are primarily composed of red-to-brown silty sandstone. The molecular weathering ratios are characterized by low oxidation and lessivage values and moderate calcification and leaching values. The palaeosols are interpreted as eutric Inceptisols that formed proximal to braided streams. Rhizohaloes and linear to J-shaped, lined and unlined, horizontally to subvertically oriented burrows are common in the palaeosols. The rhizohaloes are interpreted as roots of small- to medium-sized plants that grew in imperfectly drained soils, and the burrows are interpreted as dwelling and feeding structures of various soil invertebrates. Based on the characteristics of the palaeosols and ichnofossils, the palaeoenvironment of Cerdas is interpreted as a humid to subhumid shrubland located proximal to an alluvial system.
The 100 million year journey to teleost supremacy
*John Clarke1, Lauren Sallan1 and Matt Friedman2
1University of Pennsylvania, USA
2University of Oxford, UK
Teleost fishes, with ~29,000 species and a bewildering array of morphologies, represent the dominant group of aquatic vertebrates today. In dramatic contrast, their holostean sister group consists of just eight species and two body plans, restricted to the freshwaters of North America. However, the pattern by which teleosts achieved this dominance is unclear. This is because a Mesozoic ‘golden age’of holostean diversity, described in classic palaeontological accounts, has not been quantified, preventing any reasoned comparison with teleosts. We quantified disparity for >350 neopterygian species across the first 150 million years of the Mesozoic. Holosteans show greater disparity than teleosts across the Triassic and Early Jurassic. Teleosts approach holostean levels of disparity in the Middle Jurassic, before achieving and maintaining higher disparity than holosteans from the Late Jurassic onwards. Although the period of teleost supremacy coincides with the origin and subsequent diversification of crown teleosts, crown taxa were not responsible for the initial teleost takeover in the Late Jurassic. Instead, it was the presence of early diverging stem teleost clades, such as Aspidorhynchids and Pycnodonts, that drove the initial teleost takeover, clades that remained important contributors to teleost disparity throughout the Lower Cretaceous, even when outnumbered by crown taxa.
An outstanding upper Katian (Upper Ordovician) fossil assemblage from Portugal (Buçaco, Central Iberian Zone): biostratigraphical and palaeobiogeographical significance
*Jorge Colmenar1, Sofia Pereira2,3,4, Artur A. Sá3,4 and Carlos M. da Silva2
1University of Copenhagen, Denmark
2Universidade de Lisboa, Portugal
3Universidade de Trás-os-Montes e Alto Douro, Portugal
4Universidade de Coimbra, Portugal
The Nicolella Community was the most typical brachiopod-dominated assemblage throughout high-latitude Gondwanan shelves during mid to late Katian times. It is widely represented in the Upper Ordovician rocks of the Porto de Santa Anna Formation (Central Iberian Zone, Portugal). The present study focuses on the rich fossiliferous silicified rocks of the upper half of this formation in the Cabeço Pedrogão locality (Espinheira, Buçaco). The fossil assemblage is dominated by echinoderms, followed by brachiopods and bryozoans, but trilobites and algae are fairly common too. The re-study of the classical fossil collections from these beds housed at the Museu Geológico (Lisbon), supplemented by several sampling campaigns, revealed the presence, among others, of previously unregistered brachiopod and trilobite taxa in Portugal: Kjaerina (Villasina) meloui, a brachiopod recorded previously only in the uppermost Rosan Formation (Armorican Massif, France); Ceraurinus? meridianus and “Bumastus” aff. commodus, trilobites only known from the Cystoid Limestone (Iberian Chains, Spain). These records are important additions to the knowledge of the Portuguese Upper Ordovician benthic marine communities, providing crucial new data to constrain the biostratigraphy of the upper half of the Porto de Santa Anna Formation and the palaeogeographical setting of this region during the Late Ordovician.
Are solemyoids and ctenodontids related?
John C. W. Cope
Amgueddfa Cymru – National Museum Wales, UK
The chemoautotrophic solemyoids are one of the most primitive living bivalve groups; they have protobranch gills and are therefore often compared with the other extant protobranch group, the nuculoids, and most authorities suggest that the solemyoids were derived from the nuculoids. Unlike most bivalves, solemyoids are distinctly elongated anteriorly, and this anterior elongation has caused them to be linked with a group of Ordovician anteriorly-elongated nuculoids, the ctenodontids, although ctenodontids possess a taxodont dentition, whilst solemyoids are edentulous. Studies have been published suggesting putative intermediate forms between the two groups. However, all this has been thrown into disarray, following the discovery of a seemingly fully-fledged solemyoid in the Early Ordovician. In spite of this, however, the latest cladistic analyses link the two groups closely. But is this suggested relationship spurious?
On the difficulty of reconstructing hybodont dentitions based on isolated teeth
*Gilles Cuny and Stanislas Rigal
University Claude Bernard Lyon 1, France
Hybodont sharks represent the sister-group of modern elasmobranchs. They appeared in the Devonian and disappeared at the end of the Cretaceous. Like for all cartilaginous fishes, complete fossils are very rare in the fossil record and these animals are known mainly through isolated teeth. However, to reconstruct the complete dentition from only isolated teeth is almost impossible, which could make their phylogenetic relationships very difficult to decipher as the following two examples demonstrate. Asteracanthus magnus, hitherto known only from isolated teeth, was considered close to A. medius, of which a complete dentition is known. However, a partial dentition of A. magnus recently found in the Middle Jurassic (Bathonian) of Normandy (France) shows that teeth usually identified as anterior of A. magnus represent in fact teeth of the first lateral file and that it possessed high-crowned anterior teeth. As a result, A. magnus appears closer to A. smithwoodwardi than to A. medius. Isanodus paladeji is a heterodont hybodont described from the Lower Cretaceous (Barremian) of Thailand. Its dentition was reconstructed using Lissodus nodosus as a proxy, but new discoveries do not fit the current reconstruction and it seems that this species could encompass teeth belonging to at least two separate genera.
The morphology and affinity of the Cambrian “muscle worm”
Allison C. Daley1, Emily M. C. Tilby1, John P. Paterson2, Diego C. Garcia-Bellido3, Gregory D. Edgecombe4 and James B. Jago5
1University of Oxford, UK
2University of New England, Australia
3University of Adelaide, Australia
4Natural History Museum, London, UK
5University of South Australia, Australia
Myoscolex is an enigmatic animal with prominent musculature from the Cambrian Emu Bay Shale in Australia. Its affinities are widely debated, having been compared to annelids, arthropods, Opabinia, and chordates. Myoscolex has some of the oldest and best-preserved phosphatised muscle tissue in the fossil record, so it is important for understanding the evolution of this morphological feature. Hundreds of recently collected specimens of Myoscolex have been examined and described to give a more complete overview of its anatomy. The elongated body is segmented and shows longitudinal and dorsal-ventral muscles, the latter arranged in opposing pairs on each segment. SEM examination reveals details on the size and arrangement of the muscle fibres. The new material shows that each body segment had a pair of rigid, rod-like structures to which setae arranged in a cross-hatch pattern were attached. The external cuticle was smooth and adorned with triangular plates along the ventral margin. There is no evidence for Opabinia-like flaps or a proboscis. A possible cephalic region consists of three round carapaces with tiny, paired sclerite structures. Identifying the affinity of Myoscolex requires careful consideration of the ontogeny and preservation of exceptionally preserved specimens of this abundant Emu Bay Shale animal.
“MISS” conceptions and misconceptions: microbial, abiotic and problematic sedimentary surface textures from the Archaean to the present
Neil S. Davies1, Alex G. Liu2 and Martin Gibling3
1University of Cambridge, UK
2University of Bristol, UK
3Dalhousie University, Canada
In recent years, an increasing number of sedimentary surface textures in the rock record have been suggested to document the presence of microbial mats, resulting in their classification as microbially induced sedimentary structures, or “MISS”. The rapid rate at which this understanding has developed has led to repeated misconceptions arising in the literature, with implications for understanding aspects of evolution and extinction in the fossil record. Commonly repeated claims include: 1) MISS are more common prior to the evolution of, or during post-extinction lulls in, bioturbation, and 2) MISS are predominantly shallow marine features produced by cyanobacteria. Combining a meta-survey of literature with original observations from multiple Precambrian and Phanerozoic formations, we demonstrate that both of these claims are unfounded. MISS are in fact more common in Phanerozoic than Precambrian strata, and have a continuous pan-environmental, post-Archaean record. The perception that they are restricted to exceptional intervals of Earth history likely arises from a sampling and publication bias. We also address the decreasing appreciation of abiotic sedimentary processes that may create morphologically similar features to MISS. By introducing the umbrella term ‘sedimentary surface textures’, of which MISS are one subset, we suggest a practical, non-sensational methodology for classifying these features.
Dinosaur biogeographic structure and Mesozoic continental fragmentation: a network-based approach
Alexander M. Dunhill1, Jordan Bestwick2, Holly Narey3 and James Sciberras3
1University of Leeds, UK
2University of Leicester, UK
3University of Bath, UK
Dinosaur macro-biogeographic structure is influenced by continental fragmentation, although some intercontinental exchange of dinosaur faunas continued up to the end of the Cretaceous. Macro-biogeographic patterns are obscured by uneven geographic sampling through time and a residual earlier Mesozoic distribution which is sustained up to the end of the Cretaceous. Here, we use a novel network-based approach to reconstruct dinosaur macro-biogeographic patterns through the Mesozoic Era and test how continental fragmentation affected dinosaur macro-biogeographic structure and evolutionary rates. Geographic connectedness declines through time, from peak aggregation in the Triassic–Jurassic to complete separation in the latest Cretaceous. Biogeographic connectedness shows no trend in the raw and novel connection networks, but decreases through time whilst showing some correlation with continental fragmentation in the first-step networks. Despite continental isolation and high sea levels, intercontinental faunal exchange continued right up to the end of the Cretaceous. Continental fragmentation and dinosaurian macro-biogeographic structure do not share a common pattern with dinosaurian evolutionary rates, although there is some evidence that increased continental isolation resulted in increased origination rates in some lineages. Spatiotemporal sampling biases and early Mesozoic establishment of family-level distribution patterns are important drivers of apparent dinosaur macro-biogeographic structure.
Silicified molluscs from the Vikinghøgda Formation, central Spitsbergen: systematic and palaeoecological significance
*William Foster1,2,3, Silvia Danise1,4 and Richard Twitchett2
1Plymouth University, UK
2Natural History Museum, London, UK
3University of Texas, USA
4University of Georgia, USA
Understanding how the marine biosphere recovered from the late Permian mass extinction event is a major question in the evolutionary history of life on Earth. The quality of the global fossil record of this interval is, however, somewhat poor, due to problems with preservation. Here we report on a new early Induan marine fauna from the Vikinghøgda Formation, Svalbard, which are all silicified and represent the oldest silicified fauna known from the Triassic. Excellent preservation of the internal characteristics of bivalve shells, gastropod apertures and protoconchs provides critical new systematic data. For its age, the assemblage is exceptionally diverse with 12 species belonging to 10 genera of bivalves and gastropods. Although this richness is due largely to the excellent preservation, the assemblage provides further evidence that the mid-palaeolatitude Boreal Ocean housed significant biodiversity during the Early Triassic. Four species are new, and several taxa are recorded in the Early Triassic for the first time. These new data support taxonomic reassignment of some of these taxa, which has important implications for their inferred palaeoecology and our understanding of the composition and function of benthic marine communities in the wake of the late Permian mass extinction.
Estimation of taxonomic richness variation through geological times: a simulation approach
*Corentin Gibert and Gilles Escarguel
Claude Bernard University Lyon 1, France
Estimating taxonomic richness and its variations through geological time is a notoriously difficult task, due to several taphonomical and methodological reasons making the reconstructed signal potentially distinct from the real (but unknown!) one. Through a simulation approach, we examine the effect of a major, while surprisingly still understudied, source of potential disturbance: the effect of time discretization through biochronological construction, generating spurious coexistences of taxa within biozones, and thus ultimately making continuous- and discrete-time taxonomic richness curves very different. Our approach relies on continuous-time simulated biodiversity curves, then time-discretized to estimate the actual loss of information generated by this manipulation. A broad spectrum of dataset parameters (e.g., average biozone duration, total number of taxa, average taxonomic longevity) are tested through sensitivity analysis, showing that the worsening effect of time-discretization on the biodiversity signal highly depends on such parameters. Based on these simulation results, we propose a simple algorithm allowing the back-transformation of a discrete-time taxonomic richness dataset as customarily constructed by palaeontologists into a virtually continuous-time dataset. We show that the new biodiversity curve obtained this way fits the original signal much more closely, even when the initial dataset conditions are particularly hostile to an accurate time-discretized reconstruction.
Earliest members of a ‘living fossil’ lineage indicate a late origin of modern ray-finned fish diversity
*Sam Giles1, Guang-Hui Xu2 and Matt Friedman1
1University of Oxford, UK
2Institute of Vertebrate Paleontology and Paleoanthropology, China
Actinopterygians account for over half of living vertebrate diversity. Difficulty lies in unravelling how modern actinopterygian lineages, particularly polypterids, emerged from a ‘haze’ of inadequately known fossil taxa, leading to problems when ascertaining the age of the living radiation. Recent cladistic analyses that incorporate extant actinopterygians in addition to a range of Palaeozoic and Mesozoic taxa typically recover a Middle Devonian age for the actinopterygian crown. This is seemingly incongruous with the Cretaceous age of the earliest known polypterid fossils and molecular evidence suggesting that the living polypterid radiation is Neogene in origin. Here we use CT scanning to describe previously unknown aspects of the braincase, jaws and gill skeleton of Fukangichthys, a scanilepid from the Triassic of China, revealing a stem-polypterid affinity for the Scanlepiformes and exposing many of the supposedly primitive features of modern polypterids as reversals. This discovery shifts all Palaeozoic and some Mesozoic taxa onto the actinopterygian stem and suggests a much younger age for the actinopterygian crown, bringing it more into line with estimates indicated by the earliest fossil members of other extant actinopterygian lineages. This fundamental shift in the age of the crown has major implications for the accuracy of current molecular clock models.
Evactinostella crucialis – another weird and wonderful bryozoan
Eckart Håkansson1, Marcus Key2 and Andrej Ernst3
1The University of Western Australia, Australia
2Dickinson College, Pennsylvania, USA
3Universität Hamburg, Germany
The Lower Permian Callytharra Formation in Western Australia has yielded a rich bryozoan fauna dominated by cystoporate and fenestrate bryozoans. Variation in the faunal composition reflects a pronounced cyclic depositional environment, with shale-carbonate para-sequences bundled into para-sequence sets. Bed planes in the homogeneous carbonate sands terminating most of the para-sequence sets are exceptional in exposing large colonies in life position, with the cystoporate E. crucialis and the fenestrate Lyroporella erkosoides as the most prominent. While L. erkosoides appears directly adapted to the shallow water, storm wave-generated deposition interpreted from the sediment supporting these colonies, the mode of life of E. crucialis remains somewhat ambiguous. Investigation of well-preserved colonies in life position – including internal as well as external colony architecture in combination with branch geometry – allows detailed interpretations regarding ‘mode of life’ of E. crucialis. These colonies typically comprise four symmetrically arranged, vertical branches reaching up to 25 cm in length, rising from a base partially submersed in the sediment surface, but not otherwise attached; evenly distributed, prominent maculae indicate the presence of well-controlled, colony-wide feeding currents. Both of these observations appear at odds with the ambient, storm wave-dominated environment.
Ontogenetic stages in the basal Gondwanan eusauropod Patagosaurus
*Femke M. Holwerda1, Oliver W. M. Rauhut1 and Diego Pol2
1Bayerische Staatssamlung für Paläontologie und Geologie, Germany
2Museo Paleontológico Egidio Feruglio, Trelew, Argentina
Patagosaurus is the best-represented eusauropod from the Middle Jurassic of South America; several specimens are known from two contemporaneous bonebeds from the Cañadón Asfálto Formation, Patagonia, Argentina. Among these are individuals representing different ontogenetic stages. The material consists mostly of axial elements, but appendicular elements such as femora and scapulae were also recovered, as well as two dentaries. Osteological redescriptions of the holotype and referable material reveal three distinct ontogenetic stages within this taxon; one juvenile, two subadults (including the holotype) and one fully-grown adult. Major morphological differences between ontogenetic stages lie mainly in the vertebrae; increasing stage of fusion between the neural arch and the vertebral body, increasing depth of the pleurocoels, expression of laminae, absence/presence of centrodiapophyseal fossae, increasing height of neural arch, diagonal/horizontal projection of transverse processes. Lastly, tooth count and dentary symphysis depth increase with ontogeny. Appendicular elements seem to grow isometrically. Apart from the North African genus Tazoudasaurus, and possibly Lapparentosaurus from Madagascar, there are no well-known Gondwanan eusauropods with ontogenetic stages preserved, leaving a gap between basal sauropodomorphs, such as Massospondylus, and more derived sauropods (mostly diplodocids). Patagosaurus thus represents an important data point in studying ontogeny in more basal sauropods.
How easy was the Ediacaran transition to large body size? Rangeomorph growth, development and complexity.
Jennifer Hoyal Cuthill
University of Cambridge, UK
The Ediacaran fossil record captures one of the most dramatic events in the history of life, the evolution of large body size. The rangeomorphs had already achieved impressive sizes of up to two metres at their first appearance (580 Ma). Yet we know little about the evolutionary-developmental mechanisms underlying this transition, or how rapidly it could have occurred. We lack direct knowledge of the genetic and developmental underpinnings of the extinct rangeomorph body plan. However, the iterative branching structure of the rangeomorph frond offers an opportunity to infer fine-scale patterns and rates of growth through ontogeny. I will present the findings of such a study and discuss the implications for the complexity and evolution of early macro-morphology.
A new use for old pollen: reconstructing past solar irradiance using pollen chemistry
Phillip E. Jardine1, Wesley T. Fraser1,2, Barry H. Lomax3 and William D. Gosling4
1The Open University, UK
2Oxford Brookes University, UK
3University of Nottingham, UK
4University of Amsterdam, The Netherlands
Despite the importance of solar irradiance as a dominant control on Earth’s energy budget, no proxy has been developed that can provide total solar irradiance (TSI) reconstructions prior to the Holocene. Here, we present a novel proxy based on the chemical composition of sporopollenin, the primary component of the outer walls of pollen and spores (sporomorphs). Sporopollenin chemistry is responsive to levels of ultraviolet-B (UV-B) radiation exposure, which offers the possibility of using fossil sporomorph chemistry as a proxy for past UV-B flux and, by extension, TSI. The high preservation potential of sporomorphs means that this new proxy has the potential to reconstruct UV-B and TSI flux over much longer timescales than has previously been possible. Furthermore, Fourier Transform Infrared (FTIR) spectroscopy allows sporopollenin chemistry to be rapidly and non-destructively assessed on small sample sizes (£10 sporomorphs/sample). We demonstrate the utility of this proxy using grass pollen chemistry data from the late Pleistocene of Ghana, and relate this to modelled TSI. This proxy provides a new approach for quantifying UV-B flux and TSI through time, and therefore offers the potential to determine how changes in solar irradiance have contributed to climatic and biotic change in the past.
Morphology of the jaw adductor complex across the cynodont–mammaliaform transition
Stephan Lautenschlager1, Pamela Gill1, Michael Fagan2 and Emily J. Rayfield1
1University of Bristol, UK
2University of Hull, UK
The evolution of the mammalian jaw is characterized by the gradual reduction of its individual bones into a single element and the incorporation of the post-dentary bones into the middle-ear complex. This osteological transformation is accompanied by a modification of the jaw adductor musculature, which is thought to have allowed the evolution of a more efficient masticatory system. Here we use digital techniques to reconstruct the jaw adductor musculature of different non-mammalian cynodonts and mammaliaforms (including Thrinaxodon, Probainognathus, Diademodon, Morganucodon, Hadrocodium). Three-dimensional digital models of the adductor muscles were created on the basis of osteological correlates, homological criteria and spatial constraints. Different hypothesized arrangements were tested, taking into account maximum muscle stretch factors and comparative data from contrast-enhanced CT scans of an extant taxon (Monodelphis). The resulting models show a trend in the arrangement of the neomorphic masseter muscle, shifting from an originally vertical position in basal taxa to an anteroposteriorly diagonal position in Morganucodon, thus avoiding interference with the post-canine teeth. At the same time, the temporalis muscle increased in absolute and relative size in mammaliaforms. These digital models confirm existing assumptions, but also provide new data and quantitative assessments on the musculoskeletal evolution of the mammalian masticatory system.
The role of framboidal pyrite and sulfur cycling in Ediacaran taphonomy
Alexander G. Liu
University of Bristol, UK
Late Ediacaran mouldic preservation of soft-bodied organisms, in diverse lithologies, contrasts markedly with the often temporally- and spatially-restricted preservation of soft tissues in Phanerozoic deposits. Preservation of Ediacaran macrofossils in coarse sandstones has been explained by the “death mask” hypothesis of Gehling (1999), whereby early diagenetic (microbially-induced) pyrite mineralization cast the exterior morphology of organisms prior to soft-tissue decay and lithification of the sediment. However, a paucity of evidence for pyrite has previously prevented extension of this taphonomic pathway to other Ediacaran facies. New petrological and compositional data from Newfoundland (Canada) demonstrate that framboidal pyrite played an integral role in macrofossil preservation in Ediacaran deep-marine settings. Pyrite framboids or their oxidation products form laterally extensive sub-millimetre-thick surface veneers on all studied fossil-bearing bedding planes, and occur in association with a variety of smothering substrates. When combined with increasing recognition of pyrite in association with macrofossils at other global Ediacaran localities, the “death mask” model is here proposed to offer a universal explanation for mouldic Ediacaran preservation. The Ediacaran taphonomic window may thus be an artefact of global marine sulfur cycling and the activity of sulfate reducers, rather than reflecting true evolutionary signals.
Conservation palaeobiology of Chesapeake Bay oysters
Rowan Lockwood1 and Kristopher M. Kusnerik2
1College of William and Mary, Virginia, USA
2Florida Museum of Natural History, University of Florida, USA
Populations of the eastern oyster (Crassostrea virginica) in Chesapeake Bay (USA) are declining precipitously due to overharvesting, sediment influx and disease. Although ecological records are limited to the past century, the Pleistocene record stretches back 500,000 years and may provide a baseline for ecological restoration. The focus of this research was to reconstruct the size distribution, growth rates and population densities of Pleistocene oyster deposits in the mid-Atlantic region. Bulk samples were collected from 10 localities, ranging from early to late Pleistocene and yielding 21 to 2,400 oysters per locality. Shell height was measured for 3,500 left valves and population density was quantified at the only intact field locality. Age was estimated by: 1) counting lines on bisected hinges; and 2) counting bumps on the medial surface of the hinge. Late Pleistocene oysters are significantly larger than colonial or modern oysters and population density for Pleistocene reefs is an order of magnitude larger than modern estimates. Aging techniques yield correlated age estimates, but additional sclerochronology is required for ground-truthing. This study suggests that, although restoration efforts focus on the raising and seeding of oyster larvae, priorities need to shift to protecting large, disease-resistant oysters.
Tetrapodophis amplectus, a four-legged snake from the Early Cretaceous of Gondwana, and implications for the origins of snakes
*Nicholas R. Longrich1, David M. Martill2 and Helmut Tischlinger3
1University of Bath, UK
2University of Portsmouth, UK
Snakes are a diverse and successful group of squamates, with over 3,000 known species, but the origins of this remarkable diversity are poorly understood. Two-legged snakes have previously been described, but four-limbed have remained unknown – until now. Tetrapodophis amplectus from the Early Cretaceous (Aptian) Crato Formation of Brazil represents the oldest definitive snake and the first with four limbs. Tetrapodophis shows numerous snake apomorphies, including hooked teeth implanting into sockets, an intramandibular joint, zygosphene-zygantrum articulations between vertebrae, >150 presacral vertebrae, and transverse belly scales. Although snake-like in most features, Tetrapodophis retains short but well-developed arms and legs. Adaptations for aquatic life are absent. Instead, Tetrapodophis exhibits burrowing specializations, consistent with a subterranean origin for snakes. Surprisingly, the limbs are not vestigial, but are specialized for grasping. Along with a highly flexible spine, here interpreted as an adaptation for constriction, recurved teeth, and the presence of a vertebrate in the gut, this suggests that early snakes were carnivores. Finally, Tetrapodophis provides insight into the geographic origin of snakes. Tetrapodophis, together with a high diversity of basal lineages from Africa and South America, both extinct and extant, indicates that crown Serpentes originated and radiated in Gondwana during the Early Cretaceous.
Unlocking the preservation pathways of Cambrian neural tissue
Xiaoya Ma1, Gregory D. Edgecombe1, Xianggang Hou2, Tomasz Goral1 and Nicholas J. Strausfeld3
1Natural History Museum, London, UK
2Yunnan University, China
3University of Arizona, USA
Exceptionally preserved Cambrian fossils provide a rich source of data regarding neural organization during the early stages of the animal radiation. Recent reports of neural structures in Cambrian panarthropods significantly contributed to our understanding of the early evolution of panarthropod nervous systems and controversies about segmental homologies. However, scarcity of fossilized neural tissue means that most studies to date are based on single specimens, hindering tests of the fidelity of those structures and the diagenetic processes that led to their exceptional preservation. This study describes newly-discovered specimens of Fuxianhuia protensa with fossilized brains revealing matching morphological profiles, which allow rigorous testing of their reproducibility. The new specimens support a recent interpretation of a tripartite brain in this species but revise the trajectory of its optic nerves as confluent with the anterior protocerebrum. Geochemical analyses provide crucial insight into neural tissue preservation, revealing that the neural tissue was initially preserved as carbonaceous film and subsequently pyritized. This mode of preservation is consistent with the taphonomic pathways of gross anatomy, indicating that no special mode is required for the fossilization of labile neural tissue. Preliminary decay experiments also support the preservation potential of neural structures and their morphological interpretation after compression.
The eldonids: cryptic éminences grises of the Palaeozoic oceans
Breandán Anraoi MacGabhann1,2,3 and John Murray3
1Edge Hill University, UK
2University of Edinburgh, UK
3National University of Ireland, Galway, Ireland
The eldonids are an extinct group of asymmetrical unmineralized discoidal organisms ranging from the early Cambrian to the late Devonian. First described in 1847, they remain little known and poorly understood, even with thousands of specimens from multiple Palaeozoic Lagerstätten including the Burgess Shale and Chengjiang. Based on a combination of newly-acquired fossil material, older curated specimens and published descriptions, the taxonomy of the entire eldonid group has been revised. At least eight genera and ten species are divided across three families, one order, and one class, placed within the deuterostome stem group Cambroernids. The eldonids remained quite anatomically conservative throughout their record. All possessed a dextrally coiled sac (containing the alimentary canal) with circumoral tentacles, and radiating bifurcating lobes within the body cavity. The proposed taxonomic groupings are distinguished on variations of these morphological features and the nature of the dorsal integument. Eldonids often occurred in large gregarious swarms, with a remarkably cosmopolitan palaeoenvironmental and palaeogeographic distribution – known from shallow- to deep-marine environments from tropics to poles. Their general restriction to Lagerstätten is essentially a taphonomic artefact, and belies the fact that they were likely a ubiquitous and significant component – the éminences grises – of the Palaeozoic oceans.
Ontogeny, preservation and systematics of Palaeoscolecida (stem-Priapulida?) – is the diversity of the group drastically overestimated?
*Emmanuel L. O. Martin1, Rudy Lerosey-Aubril2 and Peter Van Roy3
1University Lyon 1, France
2University of New England, Australia
3Ghent University, Belgium
Palaeoscolecids are a diverse group of Early Palaeozoic marine worms. First assigned to annelids, they are now regarded as phylogenetically close to priapulids (Cycloneuralia). However, their long annulated trunk is covered by (primarily?) phosphatic sclerites, which are sometimes found isolated. 61 species (45 genera) have been described from body fragments, either preserved as compression fossils (CF) or secondarily phosphatised (Orsten-type fossils; OF). CF are usually more complete, occasionally displaying the proboscis, but OF exhibit much better preservation of sclerites. In this contribution, we argue that this difference in preservational styles profoundly impacts the systematics of Palaeoscolecida. Actually, not a single genus is known from both types of materials. Besides, the maximum body width of CF species is c. 6 mm on average (occasionally >10 mm), whereas it rarely exceeds 1.5 mm in OF species (mean: 1.3 mm). This suggests that 39% of palaeoscolecid species may actually be defined on immature specimens. Using 68 CF (maximum body width 0.51–3.33 mm) of a new species from the Fezouata Shales (Lower Ordovician, Morocco), we show that growth was discontinuous in palaeoscolecids. We also demonstrate that many characters used to discriminate taxa significantly change during ontogeny, which further questions the validity of OF species.
Clay-microbe interactions and implications for exceptional preservation
1H. McMahon and D. E. G. Briggs
Yale University, USA
Exceptionally preserved fossils are produced by multifarious interactions between tissues, autolytic enzymes, minerals and other substrates, oxidants and other nutrients, and a diverse, shifting community of microorganisms. Experimental taphonomy aims to tease apart these interactions and isolate their individual significance. Our work explores the role of microbes, which mediate essential steps in the fossilization of a carcass, from initial decay to the alteration of carbonaceous compounds and replication in minerals. Clay minerals and bacteria are of similar particle size. A number of studies have shown that particular clay minerals promote or inhibit the growth of specific types of bacteria via an array of physical and chemical interactions. This has profound implications for the distribution of taphonomic biases in the fossil record. While interactions between certain clay minerals and animal tissues or enzymes have been implicated in Burgess-Shale type preservation, we suggest that clay–microbe interactions may be critical. Preliminary experimental data indicate that glauconite, for example, to a greater extent than many other clays, may inhibit the growth of specific bacteria involved in the decay of marine animals. Such results have the potential to explain relationships between marine sediment composition and exceptional preservation in the Palaeozoic record.
Cryptogamic ground covers as modern analogues of early terrestrial ecosystems
Ria L. Mitchell and Paul Kenrick
Natural History Museum, London, UK
Cryptogamic ground covers (CGCs, i.e., communities of bryophytes, lichens, algae, fungi and bacteria) are the early colonizers of fresh and potentially nutrient-poor ground surfaces. A growing body of data from both the fossil record and molecular phylogenetics indicates that comparable associations were components of the first extensive terrestrial biosphere in the Early Palaeozoic. Our goal is to understand how cryptogamic organisms contribute towards the development of soils by mineral weathering, with a view to using them as modern analogues of early soil ecosystems. We employed a variety of micro-analytical techniques to bryophyte and lichen dominated primeval volcanic substrates from Iceland and New Zealand. X-ray micro-CT imaging of substrate cores suggests complex physical interactions between the organic and mineralogical components. SEM and EDX reveals an assortment of biotic/mineral attachment methods (mucilage secretion sticking, rhizoid sticking, symbiotic fungal entwining) showing physical and chemical micro-features from a bio-weathering origin. XRD data suggest that smectite clays are also from a biological origin. These features could assist in distinguishing between biotic and chemical weathering markers in the sedimentological record, and ultimately assist in recognising ancient CGCs and their respective soils during the first substantial colonisation of the land during the Early Palaeozoic.
Latitudinal diversity gradients in Mesozoic non-marine turtles
David B. Nicholson1, Paul M. Barrett1 and Patricia A. Holroyd2
1Natural History Museum, London, UK
2UCMP Berkeley, USA
The latitudinal gradient in diversity is a first-order pattern of taxic richness today and is important in the evolutionary history of climate-sensitive ectothermic organisms like reptiles. We explore the importance of the latitudinal diversity gradient in Mesozoic turtles, which first appear in the Triassic and are represented by at least 17 families and 75 genera by the end of the Cretaceous. Recent area-corrected species richness is highest at 25°N, but area-corrected genus richness is even from 30°N to 5°S, with a notable drop in richness outside the tropics and subtropics at c. 30°N and 30°S. In the Mesozoic, raw genus richness is greatest at 30–45°N and is lowest in the tropics and above 60°N and 60°S. This is partly a reflection of sampling bias, as tropical regions are under-represented in the tetrapod fossil record. However, the absence of turtles at well-sampled high latitude tetrapod localities suggests that low richness above 60°N/S is genuine and shareholder quorum subsampled data bear out this general pattern. Comparisons between generalized least squares regression models indicate that sampling intensity is a better predictor of latitudinal genus richness in the fossil record than either palaeo-land area or sampling plus land area.
Remarkably preserved brain tissue ultrastructure in an Early Cretaceous iguanodontian dinosaur
David B. Norman1, Martin D. Brasier†, Alexander G. Liu3, Laura Cotton4, Jamie Hiscocks5, Russell Garwood6 and David Wacey7
1University of Cambridge, UK
†University of Oxford, UK (deceased)
3University of Bristol, UK
4Naturalis Biodiversity Center, Leiden, The Netherlands
6University of Manchester, UK
7The University of Western Australia, Australia
We report high-fidelity mineralization of soft tissues within a natural cranial endocast of an iguanodont dinosaur from fluvial sediments of the Wealden (Hastings Group) in Sussex. Moulding of the braincase wall and adjacent brain tissues by phosphates and carbonates allows direct examination of fossilized brain tissue, arguably for the first time in the fossil record. SEM imaging and CT-scanning reveal ultrastructural preservation of the membranes that surrounded the brain itself (meninges) and larger blood vessels are preserved in collophane (calcium phosphate), and the vessels are either lined by, or infilled with, microcrystalline siderite (iron carbonate). Meninges of the cerebellum preserved in this specimen exhibit ultrastructural similarities with those seen in living archosaurs. In addition, some of the fabric of the outer cortical layers of the brain and associated smaller blood vessels are also preserved in phosphate and carbonate. The structure of these membranes and associated tissues has some bearing on the extent to which the brain filled the endocranial cavity and therefore upon estimates of encephalization quotients (EQs) in these dinosaurs. Implied behavioural repertoires derived from functional and biological inferences drawn from trace fossils among iguanodontian ornithopods are compared and contrasted with brain volume observations based upon this new specimen.
Recent advances in lobopodian palaeobiology and evolution
University of Cambridge, UK
The lobopodians comprise more than 30 species of soft-bodied animals with a worm-like appearance that are known from several Palaeozoic Konservat-Lagerstätten, although most representatives have been described from Early and Middle Cambrian deposits worldwide. Lobopodian evolution is widely recognized as critical for understanding the deep origins of the megadiverse clade Panarthropoda, whose extant representatives include Euarthropoda (arachnids, millipedes, crustaceans, hexapods), Tardigrada (water bears) and Onychophora (velvet worms). New fossil discoveries and the input of developmental data have helped to clarify some of the more controversial issues in lobopodian evolution, such as their affinities relative to extant groups. Recent analyses indicate that armoured forms – which encompass most of lobopodian diversity – occupy a position within stem-group Onychophora, whereas forms with spinose ‘frontal appendages’ and gut diverticulae belong to stem-group Euarthropoda. The recovery of stable phylogenies also allows the study of broad evolutionary patterns, such as the recognition of bottom-heavy disparity and ecological complexity within the onychophoran stem lineage. It is now possible to tackle more contentious issues such as the enigmatic origins of tardigrades, whose depauperate fossil record and miniaturized body size in extant representatives has led to much disagreement regarding their early evolution and phylogenetic relationships with other groups.
What limits the morphological disparity of clades?
*Jack W. Oyston1, Martin Hughes2, Peter J. Wagner3, Sylvain Gerber4 and Matthew A. Wills1
1University of Bath, UK
2Natural History Museum, London, UK
3Smithsonian Institution, USA
4University of Cambridge, UK
Variation in form within clades is decoupled from estimates of diversity. Specifically, groups tend to reach maximum levels of morphological disparity relatively early in their evolutionary histories, even if diversity is low. This pattern is found in many clades of both animals and plants, suggesting it may represent a universal evolutionary phenomenon. This suggests a ‘restricted morphospace’, consistent with an observed decrease in the rate of origination of novel bodyplans and higher taxa over time. It has also been demonstrated that the rate of evolution of new character states decreases up the phylogenies of most clades. We used a sample dataset of published phylogenies of 93 clades of animals to test whether character exhaustion is widespread among animal clades. We also investigated the possibility that character exhaustion can account for early high disparity by testing whether a simple relationship exists between the level or rate of exhaustion in character states up a phylogeny and the shape of a clade’s disparity profile. The result has profound implications not only for the link between the evolution of novel characters and overall morphological disparity but also suggests that while evolution is shaped by constraint, some constraints have a greater importance than others.
A stable isotopic investigation of chemosymbiosis through geological time
*Edine Pape, Fiona L. Gill, Crispin T. S. Little and Robert J. Newton
University of Leeds, UK
Biomineralizing organisms use organic templates during shell formation, and this shell-bound organic matter (SBOM) records the isotopic composition of an animal’s diet. By analysing the isotopic signature of SBOM the nutritional strategies of fossil bivalves and brachiopods can potentially be directly reconstructed. We aim to investigate the occurrence of chemosymbiosis through geological time. Chemosymbiosis is an unusual nutritional strategy whereby invertebrate animals obtain their nutrition from symbiotic bacteria, which oxidize sulfur (thiotrophy), methane (methanotrophy) or both (dual symbiosis). This allows bivalves to thrive in inhospitable ecosystems of the deep sea (cold seeps and hydrothermal vents), but whether or not ancient seep dwellers were chemosymbiotic is unknown. In modern bivalve and brachiopod taxa, nutritional strategies can be distinguished using SBOM nitrogen, sulfur and carbon stable isotope values. SBOM has successfully been isolated from ancient cold seep specimens, and results allow positive identification of thiotrophy in fossil seep clams and seep mussels (Cretaceous–Pleistocene). Data will be presented for pre-Cretaceous fossils seeps, where we find extinct bivalve taxa and mono-specific brachiopod assemblages. This will test the possibility of chemosymbiosis in seep dwelling brachiopods, which disappeared from cold seeps after taxonomic domination in the Palaeozoic and Mesozoic.
Annelid fossil data reconcile morphological and molecular phylogenies
*Luke Parry1,2, Gregory D. Edgecombe2 and Jakob Vinther1
1University of Bristol, UK
2Natural History Museum, London, UK
Despite transcriptomic data becoming more available, hypotheses of annelid relationships based on morphological and molecular data have remained incongruent. Morphological analyses have typically recovered a monophyletic Polychaeta, with the simple-bodied polychaetes forming an early diverging clade or grade. This is in stark contrast to molecular trees, in which polychaetes are paraphyletic and include clitellates, echiurans and sipunculans. The oldest stem group annelid body fossils are complex-bodied polychaetes that possess well-developed parapodia and head appendages (palps), suggesting that the root of annelids is misplaced in morphological trees. We present a reinvestigation of the morphology of key fossil taxa and include them in a comprehensive phylogenetic analysis of annelids. Cambrian taxa present several unusual characters, including the occurrence of palps on a limb-bearing, segment-like head, which contrasts with the presegmental head of extant annelids. We present the most taxonomically inclusive phylogenetic analysis of annelid morphology to date, containing a representative sample of extant and fossil annelids from the Palaeozoic, analysed using implied weights parsimony and Bayesian inference. We find that the inclusion of fossil taxa polarizes morphological characters in a manner that is compatible with current molecular hypotheses, with echiurans and clitellates recovered within polychaetes.
Namapoikia: a modular, calcareous probable sponge from the Ediacaran
*Amelia M. Penny1, Rachel Wood1, Andrew Curtis1 and Rosalie Tostevin2
1University of Edinburgh, UK
2University College London, UK
The earliest calcified metazoans appeared during the latest Ediacaran (~550-541Ma). Of these, Namapoikia, found exclusively in the Driedoornvlagte reef complex of the Nama Group of southern Namibia (~548 – ~547Ma), is unique in having a robust, modular carbonate skeleton and attaining large diameters of up to a metre. Namapoikia was initially described as a possible cnidarian or poriferan, but here we confirm likely affinity with the Porifera and clarify growth style and strategy. Namapoikia colonised the walls of fissures in thrombolitic reefs, or occasionally open surfaces. Serial image stacks show that Namapoikia contains irregular tubular voids which range from columnar to labyrinthine in shape, and are disrupted by transverse partitions. In places, the skeleton shows synchronized banding, which may reflect episodic seasonal or annual growth. Namapoikia also shows two substrate-specific attachment strategies: encrusting onto lithified microbialite, but using arrays of holdfasts to attach to living microbial substrates. The large size and modular body plan of Namapoikia suggest that it grew over longer time periods than the co-occurring, smaller metazoans Cloudina and Namacalathus. Namapoikia may have required a stable, persistently oxygenated habitat, which was comparatively uncommon in the variable redox conditions of the Ediacaran ocean as represented by the Nama Group.
Biostratigraphical review and palaeobiogeographical remarks on the trilobite genus Lichas Dalman, 1827
*Sofia Pereira1,2,3, Artur A. Sá2,3, Miguel Pires4 and Carlos M. da Silva1
1Universidade de Lisboa, Portugal
2Universidade de Trás-os-Montes e Alto Douro, Portugal
3Universidade de Coimbra, Portugal
4Arcodere, Unipessoal Lda., Torres Novas, Portugal
The trilobite genus Lichas is currently known from Upper Ordovician (uppermost Sandbian/Katian) to Silurian (Wenlock-Ludlow? Series) sequences. Originally described from the upper Katian of Sweden, the genus presently includes 11 valid species reported from Portugal, Spain, Italy, the United Kingdom, Sweden, Morocco, UEA and probably also Japan and Mongolia. Lichas keisleyensis Reed, 1896 is considered a junior synonym of L. subpropinquus McCoy, 1851. New data from the Upper Ordovician of Portugal led to the definition of two new species from the Porto de Santa Anna Formation (Katian) of Buçaco. The presence of Lichas sp. in the Chão do Amieiral and Cabeço do Peão formations (uppermost Sandbian/Katian) of Portugal constitutes the oldest records of this genus. From a phylogenetic point of view, the occurrence of Lichas in the Portuguese Upper Ordovician and the presence of a posteromedian spine in the pygidium of the oldest known species of the genus indicate a closer relationship between the monogeneric tribe Lichini and Dicranopeltini Phleger, 1936. Biostratigraphical and palaeobiogeographical analysis suggest that Lichas originated in high-latitude Gondwana, where it has its older record and numerous Sandbian/Katian species, and not in Baltica as previously considered.
Experimental taphonomy and the role of decay and preservation in determining the anatomy and diversity of Cambrian vertebrates
Mark A. Purnell1, Sarah E. Gabbott1, Duncan J. E. Murdock1 and Peiyun Cong2
1University of Leicester, UK
2Yunnan University, China
The Lower Cambrian Chengjiang biota of China contains four genera of early vertebrates: Haikouichthys, Myllokunmingia, Zhongjianichthys and Zhongxiniscus. These are the oldest fossil vertebrates known and they play key roles in calibrating molecular clocks and informing our view of the anatomy of animals, potentially including transitional forms, close to the origin of vertebrates. Despite the evident importance of these fossils the degree to which taphonomic processes have affected their anatomical completeness has not been investigated. For example, some or all might have been affected by stemward slippage – the pattern observed in experimental decay of non-biomineralized chordates in which preferential decay of synapomorphies and retention of plesiomorphic characters would cause fossil taxa to erroneously occupy more basal positions than they should. We have expanded this analysis to include a broader range of potentially significant environmental variables and, by comparing and combining the results of different experiments from several taxa, we have identified general patterns. Applying our results to the Chengjiang vertebrates demonstrates that experimentally-derived models of phylogenetic bias are applicable to fossils. Anatomical and phylogenetic interpretations of early vertebrates that do not take these biases into account risk overestimating diversity and the evolutionary significance of differences between fossil specimens.
When fossils and living taxa agree on patterns of morphological evolution: a case study with Afrotheria
*Mark N. Puttick1 and Gavin H. Thomas2
1University of Bristol, UK
2University of Sheffield, UK
There is an ongoing debate about the limits of inferring past change based solely on extant taxa. Here we test the effects of fossil inclusion and exclusion when investigating patterns of body mass evolution in the placental clade Afrotheria – a clade that includes elephants, sea cows and elephant shrews. We find a general congruence when fossils are included and excluded from analyses: in both cases we find a small afrotherian ancestral size (~100 grams) and a rate increase on the branch leading to the larger-bodied Paenungulata and Tubulidentata. The inclusion of cladistics morphological data and fossils does change phylogenetic topology, but these differences also have little impact upon patterns of body mass evolution, and these results are congruent with the fossil record generally. Surprisingly, the largest differences between analyses result from model selection, not the addition of fossils. Models that allow for variation in rate on the phylogeny produce a ~tenfold smaller ancestral size compared to homogeneous-rate models. The inclusion of fossils will always increase confidence in reconstructed patterns even in cases where patterns agree. However, in addition to including fossils, careful selection between models is necessary when reconstructing patterns of morphological evolution.
Phylogenetic relationships of Heterostraci, agnathans on the gnathostome stem
*Emma L. Randle and Robert S. Sansom
University of Manchester, UK
Inter- and intra-evolutionary relationships of jawless fish are fundamental to our understanding of patterns of vertebrate evolution. Key amongst these are the ostracoderms, a paraphyletic group of stem gnathostomes. The largest and most diverse group, the heterostracans, are currently lacking a reliable phylogenetic framework, thus limiting understanding of ostracoderm diversification. Using the Pteraspidiformes as a case-study (47 taxa), we investigated different coding strategies incorporating continuous characters to build phylogenies within the group. This framework enabled expansion to include broader heterostracan taxa (i.e. Cyathaspididae and Psammosteidae). Here we show that some ‘classic’ clades hold true, but the Psammosteidae are well nested within the Pteraspidiformes in all iterations. Analysis with discrete and continuous characters yields the best resolved trees, whilst gap coding performs poorly given its sensitivity to missing data. The results serve as a framework to consider the intra- and inter-relationships of the group more broadly. Only once this is achieved can inferences about the early evolution of vertebrates be made, including ancestral morphotypes, character transitions and the timing and tempo of these innovations.
Hot and fiery or just hot? A global record of early Palaeogene wildfire
*Brittany E. Robson1, Margaret E. Collinson1, Walter Riegel2,3, Volker Wilde3, Andrew C. Scott1, Erica M. Crouch4, Elizabeth M. Kennedy4, J. Ian Raine4, Christian Dupuis5, Carlos Jaramillo6 and Richard D. Pancost7
1Royal Holloway, University of London, UK
2Geowissenschaftliches Zentrum Göttingen, Germany
3Senckenberg Forschungsinstitut und Naturmuseum, Germany
4GNS Science, New Zealand
5University of Mons, Belgium
6Smithsonian Tropical Research Institute, Panama
7University of Bristol, UK
Modern wildfire is predicted to increase dramatically due to global warming (Liu et al. 2010). Our documentation of higher-than-modern levels of wildfire in the early Palaeogene greenhouse at a German site supports this prediction (Robson et al. 2015). Here we examine global early Palaeogene fire activity using literature from India and China and new data on charcoal (inertinite) in lignites from Australasia, Europe, North America and South America. Typically, the latest Paleocene (Thanetian) had higher levels of wildfire activity than the Early Eocene (Ypresian). Through the latest Paleocene and much of the Early Eocene, wildfire activity was very variable both within and between sites. Within sites, charcoal can comprise 0–44% of the lignite. Examples of wildfire activity considerably higher than modern levels (c. 4.3%) are present in all sites studied. In most sites where both Thanetian and Ypresian could be compared the highest charcoal values (22–44%) occur in the Thanetian. Some Ypresian sites contain intervals characterized by low charcoal amounts similar to modern, but others contain only infrequent low values. These charcoal data from the early Palaeogene greenhouse suggest that wildfire activity may increase and become more variable in future warm climates.
Evidence for sexual dimorphism in the plated dinosaur Stegosaurus mjosi (Ornithischia, Stegosauria) from the Morrison Formation (Upper Jurassic) of Western USA
*Evan T. Saitta
University of Bristol, UK
Dimorphism in the shape of Stegosaurus mjosi dermal plates (n=40) does not result from non-sex-related individual, interspecific, or ontogenetic variation and is most likely a sexually dimorphic feature. One morph possessed wide, oval plates 45% larger in surface area than the tall, narrow plates of the other morph. Intermediate morphologies are lacking. Principal component analysis supports marked size- and shape-based dimorphism. In contrast, non-sex-related individual variations often show intermediate morphologies. A new quarry in Montana shows at least five individuals buried in a single horizon that were not brought together by water transportation. This site demonstrates co-existence, and possibly suggests sociality, between two morphs that only show dimorphism in their plates. Without evidence for niche partitioning, it is unlikely that the two morphs represent different species. Histology of the new specimens in combination with studies on previous specimens indicates that both morphs occur in fully-grown individuals. The dimorphism is not a result of ontogenetic change. The two morphs of plates do not come from different positions on the back of a single individual. Plates from all positions on the body can be classified as one of the two morphs, and previously discovered, isolated specimens possess only one morph of plates.
Differential speciation and extinction rates across space and through time: implications for the generation of latitudinal diversity gradients
Erin E. Saupe1, Huijie Qiao2, Corinne E. Myers3, Jorge M. Soberón4, A. Townsend Petersen4, Stephen J. Hunter5, Joy S. Singarayer6 and Paul J. Valdes7
1Yale University, USA
2Chinese Academy of Sciences, Beijing, China
3University of New Mexico, USA
4University of Kansas, USA
5University of Leeds, UK
6University of Reading, UK
7University of Bristol, UK
Biodiversity is unevenly distributed across the surface of the Earth. The tropics harbour greater numbers of species than temperate zones, a pattern seen in both ancient and modern times. The causal mechanism(s) responsible for these latitudinal gradients still remain debated, although centuries have passed since their initial discovery. It is still unknown whether rates of speciation and extinction directly follow a latitudinal gradient, or whether secondary dispersal contributes to higher species diversity in the tropics. We introduce a cellular automaton algorithm designed to simulate processes of extinction, allopatric speciation, and dispersal within the evolving climate system of the Pleistocene. We test whether differential rates of speciation and extinction in tropical versus temperate climates can alone produce diversity gradients. We additionally test whether the magnitude of the diversity gradient on a continental scale depends on the degree of environmental heterogeneity observed across continents through time. Preliminary results suggest that speciation rates are elevated in tropical regions and depressed at higher latitudes. Interestingly, diversity hot spots developed without invoking higher extinction rates at higher latitudes. This work provides a null model for spatial patterns of biodiversity dependent solely on the contributions of species’ physiological tolerances, dispersal, and the evolving climate system.
The Ordovician explosion in the designs of trilobite eyes
*Brigitte Schoenemann1 and Euan N. K. Clarkson2
1University of Cologne, Germany
2University of Edinburgh, UK
The eyes of Cambrian trilobites are poorly known, apart from those of the eodiscids and the Furongian to upper Ordovician Order Olenidae, though more are being discovered. Most are reniform ‘slit-eyes’ and all are holochroal. Schizochroal eyes arose in the early Ordovician by paedomorphosis from a holochroal ancestor, but in addition the ‘explosion’ in trilobite diversity during the Ordovician is matched by a striking increase in different kinds of holochroal eyes. The range in holochroal eye morphology correlates well with the habitat of the Ordovician trilobites; thus thin-shelled trilobites living in quiet conditions normally have thin biconvex lenses, while robust-bodied trilobites living in high-energy environments have thick, and sometimes prismatic lenses. The optics of trilobite eyes can be studied using tools developed for the analysis of living arthropod eyes, which facilitate an understanding of habitat. Special attention here is given to the eyes of asaphid and cheirurid trilobites, which raise some interesting problems.
Ancient spiders and salt lakes
Paul A. Selden and Matt R. Downen
University of Kansas, USA
The Green River Formation crops out over 64,000 square kilometres of Wyoming, Colorado and Utah, averages 600 m in thickness, and represents one of the world’s longest-lived Great Lakes systems, lasting approximately 17 million years. Spider fossils are abundant in some horizons but, until recently, only a single specimen (Linyphia byrami Cockerell, 1925) had been described. In the first part of this talk, a sample of spiders from the families Uloboridae, Hersiliidae, Selenopidae and Thomisidae are described. Such diversity represents a variety of life modes and habitats; it is suggested that storms and flash flooding were the likely mechanisms for transporting the spiders into the lake. In the second part of this talk, we compare the spider fauna of Green River with those of two other palaeolake deposits, and demonstrate how spider leg flexure can serve as a proxy for the palaeosalinity of ancient lakes.
How do marine microfossils get trapped in amber?
Leyla J. Seyfullah, Dennis Grabow and Alexander R. Schmidt
University of Göttingen, Germany
Amber is well-known for entrapping terrestrial organisms (inclusions), like arthropods, plants and fungi, and preserving them. Rarely, amber also preserves limnetic organisms like water beetles, together with terrestrial taxa. Marine organisms are usually only found as surface or fissure contaminants on amber found on the coast. However, three amber deposits from the Cretaceous of France (c. 100 Ma) have several amber pieces with marine inclusions (diatoms, radiolarians, sponge spicules, foraminiferans, larval echinoderm remains), alongside terrestrial ones. This implies the proximity of a resinous forest to the Atlantic coast, but the exact conditions necessary to produce amber pieces that contain terrestrial and marine inclusions are debated: were these mangrove forests or the result of rare high-energy conditions like a cyclone or tsunami flooding the low-lying forest, or the results of normal coastal conditions? We set up experiments along the highly resinous low-lying coastal Araucaria columnaris forests in New Caledonia to test this. Using fresh resin applied to slides we showed that normal coastal conditions allow some marine microorganisms to become embedded in resin, so seawater did not have to make contact with the resinous trees, but the diversity found in French amber suggests that a much more energetic event occurred.
How big is a genus?
Julia D. Sigwart1, Keith D. Bennett1 and Mark Sutton2
1Queen’s University Belfast, UK
2Imperial College London, UK
Genera are units that contain variable numbers of species, from one (monotypic) to thousands. The largest proportion of genera, usually over 30%, contain only a single species and a very small proportion contain large numbers of species. Past observations of this phenomenon have invoked taxonomic ‘splitting’, and implied this skewed distribution is in conflict with strict tree-thinking or true phylogenetic systematics. We show the predominance of monotypic genera is a strongly consistent pattern across Metazoa, so empirical evidence suggests it may be a ‘real’ result of speciation processes. We compared empirical data (real taxonomy of real organisms) with simulations that provide omniscient or ideal genus-size frequencies (simulated taxonomic sorting on simulated trees). We generated hypothetical trees using birth–death models with known and constant probabilities of speciation (birth) or extinction (death) at each generation. We imposed a taxonomic sorting on the set of species that were non-extinct after 500 generations, based on phylogenetic topology and/or character attributes of surviving lineages. Observed taxonomy of living animals in fact closely match an idealized hypothetical taxonomy of monophyletic units, especially when defined by character similarities. Monotypic genera are, as should be expected, very frequent, and large genera very rare (splitters 1, lumpers 0).
A record of small carbonaceous fossils (SCFs) from the Ediacaran–Cambrian of Baltica: expanding the Burgess Shale-type taphonomic window
*Ben J. Slater1, Thomas H. P. Harvey2, Romain Guilbaud1 and Nicholas J. Butterfield1
1University of Cambridge, UK
2University of Leicester, UK
Given the spatiotemporal rarity of Burgess Shale-type Lagerstätten, attention has recently turned to small carbonaceous fossils (SCFs) as a cosmopolitan tool for investigating early metazoan evolution. Efforts have predominantly focused on middle-late Cambrian sediments of North America. Here we push back the record into the early Cambrian and Ediacaran of the Baltoscandian Basin, sampling a continuous collection of drillcores for SCF-yielding mudstones. The basin-wide approach employed in this study is the largest-scale spatiotemporal investigation of SCF assemblages to date. A clear temporal trend has emerged; early Cambrian (Stage 4) sediments contain high metazoan diversity including exquisitely-preserved priapulid microstructures, a variety of wiwaxiid sclerites, palaeoscolecids, trilobites, fragments of arthropod cuticle and organisms previously known only from the Burgess Shale (e.g. Burgessochaeta-like annelids). Older (Stage 3–Fortunian) assemblages are characterized by lower metazoan diversity and exhibit greater regional homogeneity, principally being composed of numerous protoconodont/chaetognath grasping spines alongside assorted macroscopic algae. Ediacaran SCFs are dominated by bizarre enigmatic forms, comprising ‘vendotaenids’, tubular and sheet-like structures, but conspicuously lack recognizably metazoan-derived elements. The SCF record in Baltica reveals a previously unrecognized cryptic diversity of organic-walled Ediacaran fossils and fundamentally expands the biogeographic and temporal distribution of earliest Phanerozoic metazoans otherwise restricted to Burgess Shale-type Lagerstätten.
The monophyly of Euparkeriidae and its implications for the rise of crown Archosauria
*Roland B. Sookias1,2
1University of Birmingham, UK
2Ludwig-Maximilians-Universität München, Germany
Euparkeria capensis has been considered to approach the ancestral archosaur in its morphology, and is the sister taxon to crown Archosauria in many phylogenetic analyses. Several other taxa have been assigned to Euparkeriidae, but recent work has found only one valid taxon – Halazhaisuchus qiaoensis from China – to form a clade with Euparkeria. However, no phylogenetic analyses to date have included more than two putative euparkeriids. For the first time, a phylogenetic analysis including all putative euparkeriid taxa is undertaken, using a large matrix of stem and crown archosaurs, analysed with maximum parsimony and Bayesian methods. Using both methods, the putative Russian euparkeriid Dorosuchus neoetus is found to be the sister taxon to Archosauria+Phytosauria, whilst Euparkeria capensis forms a euparkeriid clade with Halazhaisuchus qiaoensis and the Polish taxon Osmolskina czatkowicensis, one node stemwards of Dorosuchus neoetus. Osmolskina and Halazhaisuchus are sister taxa. Support for the euparkeriid clade recovered is low, and uncertainty regarding assignment of material to Osmolskina and Dorosuchus means that conclusions remain tentative. However, the broad phylogenetic position of putative euparkeriids close to the base of Archosauria is confirmed, and the euparkeriid Bauplan can be considered the antecedent of the cursorial, upright locomotion underlying the rise of crown Archosauria.
Evolutionary rates reveal mechanisms of axial body plan evolution in Sauropterygia
*Laura C. Soul1 and Roger B. J. Benson2
1Smithsonian Institution, USA
2University of Oxford, UK
Sauropterygians were highly successful Mesozoic marine reptiles that had a broad range of body plans, including the highest cervical vertebral count and range of any clade (5 to 76). They therefore provide a model system for studying the evolution of vertebral counts and axial regionalization in tetrapods. We present a dataset of axial body plan measurements from 120 sauropterygian taxa spanning 180 million years. Using various phylogenetic comparative methods we test three explicit hypotheses about sauropterygian evolution: 1) neck length evolved via changing somitogenesis (vertebral number) and homeotic effects (axial regionalisation) rather than by differential somitic growth; 2) somitogenesis and homeotic effects were decoupled; 3) somitogenetic change was the dominant mechanism of axial body plan evolution. Our results show that differential somitic growth was not an important driver of macroevolutionary change in sauropterygian body plans, unlike in mammals. In line with previous studies of tetrapods, background patterns of somitogenetic and homeotic change were decoupled. However, the establishment of higher-level taxa with novel body plans involved rare, correlated, high-magnitude changes to both somitogenesis and homeotic effects. Our results demonstrate the importance of heterogeneous statistical models in uncovering the links between hypothesised developmental drivers of macroevolutionary change in vertebrate body plans.
TRiPS, SQS, ACE and Chaos; evaluating the accuracy and precision of species richness estimators in palaeobiology
University of Oslo, Norway
To accurately portray the dynamics of species richness in deep time using fossil data we need ways to account for the non-random deterioration of biological signals that occurs in the heterogeneous processes of fossilization, preservation, detection and publication. There are a multitude of different estimators of species richness ranging from simple and intuitive subsampling techniques to complex and computer-power-demanding models. I have recently proposed a new approach called TRiPS (True Richness estimation using a Poisson Sampling model) that not only reconstructs species richness, but also estimates the bias itself (i.e. the differential preservation and detection of fossils among geological intervals). I will here detail this new approach and compare its accuracy and precision with other richness estimators commonly used in palaeobiology, among them SQS (shareholder quorum subsampling), ACE (abundance coverage estimator), Chao1 and Chao2 using simulations. Finally, I’ll apply these richness estimators to the observations on Mesozoic dinosaurs from the Paleobiology Database and discuss drawbacks and benefits of the various estimators.
Phylogeny and macroevolution of crocodylomorphs
*Max T. Stockdale1, Michael J. Benton1, Mario Bronzati2, Marco B. de Andrade3 and Gavin T. Thomas4
1University of Bristol, UK
2Bayerische Staatssammlung für Paläontologie und Geologie, Germany
3Pontifícia Universidade Católica do Rio Grande do Sul, Brazil
4University of Sheffield, UK
The Crocodylomorpha present a unique dichotomy in their diversity and morphological disparity through time. The stem group is limited to the Mesozoic, but is represented by a highly disparate range of ecomorphologies. Conversely the crown group is limited to amphibious ambush predators, but is represented by a much greater species richness than the stem group. Despite the abundance of the crown group, the crown-group Crocodylomorpha are represented by just 23 extant species. Does this pattern represent a true decline in disparity and diversity through time, or a more complex sequence of shifts within the group? Here we present a comparison of evolutionary rates among crown- and stem-group Crocodylomorpha in relation to morphospace occupation. The phylogenetic framework of these analyses is a new phylogeny of the Crocodylomorpha assembled using the matrix representation parsimony (MRP) method. This study finds support for extreme evolutionary stasis in several crocodylomorph clades. Diversity among the Crocodylomorpha appears to be closely linked with temperature, with decreasing diversity in the Cenozoic closely matching global cooling. Additional morphospace occupation by stem-group Crocodylomorpha relative to the crown group is occupied by taxa originating from two discrete adaptive radiations in the Mesozoic, with disparity otherwise remaining constant throughout the Mesozoic and Cenozoic.
A Cambrian greening of the terrestrial landscape
Paul K. Strother
Boston College, USA
Although studies of living plants and green algae have generated a robust phylogeny that encompasses the origin of the land plants (embryophytes), the evolutionary pathway that tracks the algal–plant transition remains largely unknown. Bower originally proposed that the plant sporophyte evolved in response to selection in subaerial settings, and that spores preceded embryophytic development in evolutionary time. This general framework is supported both by extant studies in bryophyte sporogenesis and by the fossil record which shows laminated cryptospore dyads by the middle Cambrian and embryophytic spore tetrads occurring in the middle Ordovician, some 40 million years prior to the first upright axial plant mesofossils. Organic debris from shallow marine deposits from the Cambrian of Laurentia includes dispersed spores and spore dyads, spore clusters, patterned spore clusters, cuticular remains and possible protonematal remains. These spores and fragments document the remains of organic structures adapted to subaerial settings prior to the first occurrence of true land plants. They add support to Bower’s theory of the antithetic origin of the plant sporophyte. It is likely that an evolving complex of aeroterrestrial charophytic algae were contributing to a greening of the terrestrial surface well in advance of the evolutionary origin of the plant embryo.
The ecomorphological diversifications of Mesozoic marine reptiles
*Thomas L. Stubbs and Michael J. Benton
University of Bristol, UK
Mesozoic marine ecosystems were dominated by reptiles, including sauropterygians, ichthyosaurs, crocodylomorphs, turtles and mosasaurs. Previous research has shown that early marine reptiles achieved great taxonomic diversity in the Middle Triassic, as they broadly diversified into many feeding modes following the Permo–Triassic mass extinction. However, it is not known whether this initial phase of evolution was exceptional in the context of the entire Mesozoic. I explore this by quantifying trends of morphological disparity, focusing on functional variation in the jaws and dentition and skull size diversity. Results show that the Middle to early Late Triassic represented a time of pronounced phenotypic diversification in marine reptile evolution, with rapid attainment of maximum functional disparity in the jaws and dentition, and a disparate range of skull sizes. Following Late Triassic extinctions, it took over 100 million years to recover comparable variation in the Campanian and Maastrichtian. Clades that diversified during the Triassic biotic recovery, the sauropterygians and ichthyosauromorphs, show early diversifications, early high disparity and early burst trends, while less support for these trends is found in thalattosuchian crocodylomorphs and mosasaurs. Overall, the Triassic represented a special interval in marine reptile evolution, as numerous groups radiated in new adaptive zones.
Depositional and preservational environments of the Ediacara Member, Rawnsley Quartzite (South Australia): assessing the timing of ‘ferruginization’
Lidya G. Tarhan1, Noah J. Planavsky1, Mary L. Droser2 and James G. Gehling3
1Yale University, USA
2University of California, Riverside, USA
3South Australian Museum, Australia
The palaeoenvironmental setting in which the Ediacara Biota lived, died and was preserved in the eponymous Ediacara Member of the Rawnsley Quartzite of South Australia is an issue of longstanding interest and recent debate. Over the past few decades, interpretations have ranged from deep marine to shallow marine to terrestrial. We examine the evidence in support of and against various palaeoenvironmental interpretations of the fossiliferous Ediacara Member, and focus particularly upon the history of ferruginization of these rocks. Ferric oxides, previously mooted as evidence for a terrestrial palaeoenvironment, consist largely of surficial, non-bedform-parallel staining and irregular patches and thus strongly reflect late-stage processes. Moreover, uranium isotope analysis of iron oxides associated with Ediacara fossiliferous beds indicates that these oxides record recent, post-depositional oxidation. Sedimentological and geochemical evidence indicates that Ediacara iron oxides cannot be used to invoke a terrestrial palaeoenvironmental setting for the Ediacara Biota. Conversely, independent sedimentological, palaeoecological and geochemical evidence lends strong support for a shallow marine depositional environment. These findings demonstrate that careful assessment of palaeoenvironmental parameters is essential to the reconstruction of the depositional and early diagenetic history of the Ediacara Biota and the factors that led to the fossilization of these early complex ecosystems.
Using fossils and phylogenies to date the timing of key gene regulatory network innovations in echinoids
*Jeffrey R. Thompson, Elizabeth Petsios and David J. Bottjer
University of Southern California, USA
Molecular developmental biology lends the ability to understand the genetic underpinning behind the origin of evolutionary novelties through the study of Gene Regulatory networks (GRNs). GRNs are the system of genetic interactions responsible for the development and formation of body plans and morphologies. The resultant products of the interactions of GRNs are visible in the rock record in the form of fossil morphologies. Because fossils show us direct evidence for the outcome of genetic interactions taking place in GRNs, they allow us to infer the activity of portions of GRN topologies in the fossil record, and thus date the timing of these genetic evolutionary innovations. Using paired fossil data and phylogenetic analyses, we have been able to date the appearance of a novel piece of GRN circuitry essential for skeletogenesis in larval echinoids, the double-negative gate. The double-negative gate has been demonstrated to be present in a number of phylogenetically distant euechinoid echinoids; however, it is absent in their sister clade, the cidaroids. Using well-dated fossil taxa and a robust phylogeny for echinoids, we are able to date the appearance of this innovation to at least the Lower Jurassic, coincident with the first appearance of irregular echinoids in the fossil record.
Kalania pusilla, an exceptionally preserved non-calcified alga with the oldest documented gametophores from the lower Silurian (Aeronian, Llandovery) of Estonia
Oive Tinn, Viirika Mastik, Leho Ainsaar and Tonu Meidla
University of Tartu, Estonia
Dasycladacean algae are an order of unicellular organisms within the Division Chlorophyta. Having been in existence since the Cambrian period, they constitute a substantial component of algal geological history. A significant proportion of dasyclads develop a calcium carbonate skeleton, the main characteristics of the order are the radially symmetrical thallus architecture and the siphonous body plan of the cell. A working quarry in Kalana, Estonia, has revealed rich exceptionally-preserved flora and fauna of Early Silurian (Aeronian, Llandovery) age with algae, especially dasyclads, as the most diverse and abundant fossil group. Here we present a new dasycladacean species Kalania pusilla. The fossils of the siphonous unicellular algae occur as black or dark brown carbonaceous compressions on surfaces; many of them reveal three-dimensional preservation together with finely preserved details. The algal fossils are non-calcified and do not show any traces of possible carbonate skeleton. K. pusilla is characterized by a cylindrical uniaxial thallus, two orders of lateral segments – perpendicularly arranged whorls of short bulbous primary laterals, which bear clusters of ovate gametophores in their mature stage, and fine hairy secondary laterals. The reproductive structures of the fertile specimens represent the oldest documented evidence of gametophores in the fossil record.
Camouflage patterns in an ornithischian dinosaur
Jakob Vinther1, Robert Nicholls2, Stephan Lautenschlager1, Gerald Mayr3, Emily Rayfield1 and Innes Cuthill1
1University of Bristol, UK
3Senckenberg Institute, Germany
Countershading is one of the most widespread forms of camouflage. A dark dorsum and light ventrum counteract the gradient created by illumination from above, obliterating cues to 3D shape. Because the optimal countershading varies strongly with light environment, pigmentation patterns give clues to an animal’s habitat. Melanosomes are preserved in feathered dinosaurs and aspects of original colour patterns can be reconstructed from these. Here we present a study of an exceptionally well-preserved specimen of Psittacosaurus from the Chinese Jehol biota, at the Senckenberg Museum. This Psittacosaurus was countershaded with a light underbelly and tail, while the chest is relatively more pigmented. Other pigmentary patterns resemble disruptive camouflage, while the chins and lateral horns on the face appear heavily pigmented. SEM analyses show that the impressions preserve small, spheroidal melanosomes, suggesting a brownish colour to the body. We have projected the colour patterns onto an anatomically correct lifesize model of Psittacosaurus in order to assess their function experimentally. These are compared to the predicted optimal countershading from the measured radiance patterns generated on an identical grey-scale model in direct versus diffuse illumination. These studies suggest that Psittacosaurus inhabited a closed habitat such as a forested area with a relatively dense canopy.
The radiation of plankton during the Bajocian: a Mesozoic pelagic revolution
*Nickolas J. Wiggan1, James B. Riding2 and Nicholas J. Butterfield1
1University of Cambridge, UK
2British Geological Survey, UK
The Bajocian (Middle Jurassic, 170–168 Ma) was a critical interval in the evolution of modern marine plankton. Dinoflagellates underwent a major radiation, whilst coccolithophores diversified and became significantly more abundant, and planktonic foraminifera appeared for the first time. In the Early Bajocian, dinoflagellate cyst diversity was limited and dominated by species of Dissiliodinium. It was during this interval that the coccolithophore genus Watznaueria diversified and dramatically increased in abundance, which marks the transition to ecological dominance of this genus for the remainder of the Mesozoic. Cyst-forming dinoflagellates radiated rapidly through the middle to Late Bajocian, with over 50 species appearing by the earliest Bathonian. This diversification was accompanied by significant experimentation in the archaeopyle (excystment aperture) formation of cyst-forming dinoflagellates. The coincidence of this phytoplankton radiation with the appearance of planktonic foraminifera reflects a fundamental shift in contemporaneous marine plankton, with important biogeochemical, ecological and evolutionary implications. Given the coincident radiations of marine nekton, most notably ammonites, there would appear to be major innovations in pelagic ecosystems as a whole, with the connecting links provided by mesozooplankton. Viewed in this light, the primary impetus for the middle Bajocian radiation was ecological – a Mesozoic Pelagic Revolution.
Phosphatisation of soft-tissues: an integrated palaeontological and geochemical analysis of the Christian Malford Lagerstätte (Callovian, Middle Jurassic)
Phil R. Wilby1, Mark A. Woods1, Keith L. Duff2, Greg D. Price3, Mike J. Norry2, John D. Hudson2, Kevin N. Page3, Roy G. Clements2 and Malcolm B. Hart3
1British Geological Survey, UK
2University of Leicester, UK
3Plymouth University, UK
Phosphatised soft-tissues are comparatively widespread and routinely preserve sub-cellular details. Thus, they constitute the richest source of data available to palaeobiologists. Nevertheless, the fundamental depositional drivers remain unclear. Phosphatised soft-tissues are abundantly preserved in a variety of organisms (fish, coleoids, crustaceans) in the Oxford Clay at Christian Malford, Wiltshire (UK). Systematic collecting reveals that these are confined to particular horizons that differ subtly from the ‘background’ sediment. In particular, they coincide with significant peaks in P, Mo and TOC, and the horizons preserve more substantial evidence (e.g. foraminifera-floods, burrowing) for the benthic environment having switched repeatedly between anoxic and oxic states. The sum of data supports a model in which the necessary P was sourced from disseminated organics and was concentrated by scavenging Fe-oxyhydroxides in surficial layers during oxic interludes. Subsequent release of P for phosphatisation was triggered by the development of decay halos around carcasses that entered at this time. Because all of the horizons yielding phosphatised soft tissues lie at the top of minor fining-upward cycles (parasequences) and are clustered within a highstand interval, there exists, for the first time, the very real possibility of prospecting for such preservation based on an understanding of global- and basin-scale dynamics.
The Anthropocene biosphere
Mark Williams1, Jan Zalasiewicz1, Peter K. Haff2, Christian Schwägerl3, Anthony D. Barnosky4 and Erle C. Ellis5
1University of Leicester, UK
2Duke University, North Carolina, USA
3Aßmannshauser Strasse 17, Berlin, Germany
4University of California, Berkeley, USA
5University of Maryland, USA
The geological record preserves evidence for fundamental changes in Earth’s biosphere. A ‘metazoist’ might posit the most significant change during the late Precambrian and early Cambrian, culminating in the Cambrian adaptive radiation of animals. A ‘microbialist’ view, on the other hand, might point to the evolution of oxygenic photosynthesis or of the Eukarya as most significant. We suggest that the modern biosphere shows early signs of entering a new stage of evolution characterized by: 1) global homogenization of flora and fauna; 2) a single species (Homo sapiens) commandeering 25–40% of net primary production and also mining fossil net primary production (fossil fuels) to break through the photosynthetic energy barrier; 3) human-directed evolution of other species; and (4) increasing interaction of the biosphere with the technosphere (the global emergent system that includes humans, technological artefacts, and associated social and technological networks). These unique features of today’s biosphere represent a major new phase in our planet’s history with effects that may persist, and amplify, over geological timescales.
The curious case of Rollinschaeta myoplena: reconstruction of extensively phosphatized myoanatomy in extinct taxa
*Paul Wilson1, Luke Parry1, Dan Sykes2, Gregory Edgecombe2 and Jakob Vinther1
1University of Bristol, UK
2Natural History Museum, London, UK
Phosphatization, the permineralization and replacement of organic materials and structures, is a taphonomic process that frequently results in the preservation of labile tissues and other diagnostic features that normally fail to survive the process of diagenesis. As a result, phosphatized remains often elucidate key windows into the depths of the fossil record which have helped to characterize the history of life, although the volume of material preserved is generally limited. Rollinschaeta myoplena, a phosphatized polychaete from the Cretaceous Lagerstätten of Lebanon, is unique among its co-occurring taxa in that it preserves the vast majority of its muscle tissue in three dimensions while lacking almost all of its recalcitrant components, allowing the novel diagnosis of this animal based upon soft-tissues only. Extensive camera lucida mapping and comparison to extant annelids using micro-CT scanning reveals an affinity with the Amphinomidae (‘fireworms’) based upon the presence of two dorsal longitudinal muscle band pairs, a single ventral pair of longitudinal muscle bands, dorsal and ventral circular muscle tissue and a number of readily identifiable body features. This discovery has yielded important insights into the process of phosphatization and its mode of preservation is unprecedented.