Ben Creisler
Some new non-dino papers:
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Data archiving statement:
The original CTâscan images for both specimens available on request from the Natural History Museum, London, UK. Additional data for this study are available in the Dryad Digital Repository:
https://doi.org/10.5061/dryad.qjq2bvqcgRhynchocephalians were a successful, globally distributed group of diapsid reptiles that thrived in the Mesozoic. Multiple species of Clevosaurus existed worldwide in the Late Triassic and Early Jurassic, characterized by shearing bladelike teeth perhaps functionally analogous to the carnassial teeth of mammals. Morphometric analysis shows that the dentary morphospace of clevosaurs differs significantly from that of other rhynchocephalians. Five Clevosaurus species occupied islands in the Bristol Channel archipelago of the UK, but generally not those occupied by mammaliaforms, suggesting dietary character displacement. Identifying the diet of such ancient, small tetrapods has been difficult. To identify the nature of their feeding mechanics and ecology, we apply finite element analysis to two near complete threeâdimensional skulls of the species Clevosaurus hudsoni and Clevosaurus cambrica to estimate bite force, resistance to bending and torsion and the distribution of stresses in the jaws during biting. Both species had bite forces and tooth pressures sufficient to break apart chitin indicating that, like early Mesozoic mammaliaforms, clevosaurs could feed on toughâshelled beetles and possibly small vertebrates. In addition, the mechanical advantage of the jaws falls within the range of early mammaliaforms, so though we cannot demonstrate niche partitioning between members of the two clades, it raises the prospect that they may have been functionally similar.
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A new bonebed recovered from the Late Triassic of India contains various macro- and microfossils, unionid bivalves and coprolites. The macrofossils include more than 700 identifiable skeletal specimens of 27 metoposaurid, four phytosaur and two rhynchosaur individuals whereas the microfossils comprise about 500 isolated teeth of varied chondrichthyans, dipnoans, actinopterygians, archosauriforms, and several non-mammalian cynodonts. The bonebed is a monodominant, multitaxic, parautochthonous, time-averaged, attritional assemblage. The Tiki floodplain was populated by highly diverse animal communities occupying terrestrial, semi-aquatic and aquatic realms, where scavenging and/or predation were common. Two distinct biostratinomic modes deduced are -- (i), natural death, decomposition, and differential pre-burial modifications of the large terrestrial and semi-aquatic animals, and (ii) breaching of banks during flooding events, mass death, and high energy deposition of sediment load including various aquatic fishes and unionids. Similar REE patterns of a representative sample set of bone specimens and their encasing matrices suggest same diagenetic condition and a single burial event. The MREE enrichment, cerium and uranium content indicate reducing burial microenvironment for the studied fossil specimens. The Late Triassic scenario comprised highly dynamic animal communities that had different mortality dynamics and fossilisation pathways depending on the habitats and palaeobehaviour of the animals.
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The decline in species richness from the equator to the poles is referred to as the latitudinal diversity gradient (LDG). Higher equatorial diversity has been recognized for over 200 years, but the consistency of this pattern in deep time remains uncertain. Examination of spatial biodiversity patterns in the past across different global climate regimes and continental configurations can reveal how LDGs have varied over Earth history and potentially differentiate between suggested causal mechanisms. The Late Permian-Middle Triassic represents an ideal time interval for study, because it is characterized by large-scale volcanic episodes, extreme greenhouse temperatures and the most severe mass extinction event in Earth history. We examined terrestrial and marine tetrapod spatial biodiversity patterns using a database of global tetrapod occurrences. Terrestrial tetrapods exhibit a bimodal richness distribution throughout the Late Permian-Middle Triassic, with peaks in the northern low latitudes and southern mid-latitudes around 20â40Â N and 60Â S, respectively. Marine reptile fossils are known almost exclusively from the Northern Hemisphere in the Early and Middle Triassic, with highest diversity around 20Â N. Reconstructed terrestrial LDGs contrast strongly with the generally unimodal gradients of today, potentially reflecting high global temperatures and prevailing Pangaean super-monsoonal climate system during the Permo-Triassic.
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