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[dinosaur] Lepidosaur skull convergence for digging lifestyle + Dvinosaurus histology + Russian Triassic tetrapods




Ben Creisler
bcreisler@gmail.com

Some recent non-dino papers:


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Roy Ebel, Johannes MÃller, Till Ramm, Christy Hipsley & Eli Amson (2020)
First evidence of convergent lifestyle signal in reptile skull roof microanatomy.
BMC Biology 18, Article number: 185
doi: https://doi.org/10.1186/s12915-020-00908-y
https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-020-00908-y

Background

The study of convergently acquired adaptations allows fundamental insight into lifeâs evolutionary history. Within lepidosaur reptiles--i.e. lizards, tuatara, and snakes--a fully fossorial ('burrowing') lifestyle has independently evolved in most major clades. However, despite their consistent use of the skull as a digging tool, cranial modifications common to all these lineages are yet to be found. In particular, bone microanatomy, although highly diagnostic for lifestyle, remains unexplored in the lepidosaur cranium. This constitutes a key gap in our understanding of their complexly interwoven ecology, morphology, and evolution. In order to bridge this gap, we reconstructed the acquisition of a fossorial lifestyle in 2813 lepidosaurs and assessed the skull roof compactness from microCT cross-sections in a representative subset (n =â99). We tested this and five macroscopic morphological traits for their convergent evolution.

Results

We found that fossoriality evolved independently in 54 lepidosaur lineages. Furthermore, a highly compact skull roof, small skull diameter, elongate cranium, and low length ratio of frontal and parietal were repeatedly acquired in concert with a fossorial lifestyle.

Conclusions

We report a novel case of convergence that concerns lepidosaur diversity as a whole. Our findings further indicate an early evolution of fossorial modifications in the amphisbaenian 'âworm-lizards' and support a fossorial origin for snakes. Nonetheless, our results suggest distinct evolutionary pathways between fossorial lizards and snakes through different contingencies. We thus provide novel insights into the evolutionary mechanisms and constraints underlying amniote diversity and a powerful tool for the reconstruction of extinct reptile ecology.

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Final English translation versions of articles posted earlier in original Russian form:

A. V. Uliakhin, P. P. Skutschas & P. G. Saburov (2020)
Histology of Dvinosaurus campbelli (Temnospondyli, Dvinosauria) from the Late Permian Locality Gorokhovets, Vladimir Region.
Paleontological Journal 54: 632--639
DOI: https://doi.org/10.1134/S0031030120060106
https://link.springer.com/article/10.1134/S0031030120060106


This study describes the microanatomical and histological structure of the femur and hypocentra of the neotenic temnospondyl amphibian Dvinosaurus campbelli from the Late Permian locality Gorokhovets, Vladimir Region (Upper Vyatkian Substage, subzone Chroniosuchus paradoxus of the Scutosaurus karpinskii zone). The femur of D. campbelli is characterized by a "pachyosteous" structure (dense thick periosteal cortex in the diaphysis) and a large number of growth marks (about 57); the hypocentrum has an âosteoporoticâ structure. The neotenic nature of D. campbelli is confirmed by the presence of unresorbed cartilage in the skeletal elements of large-sized forms. Microanatomical and morphological features indicate that D. campbelli was an ambush feeder (using concealment during hunting).


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I. V. Novikov, A. G. Sennikov & A. V. Ivanov (2020)
Rare and Endemic Elements in Triassic Tetrapod Assemblages of Obshchii Syrt Highland (Eastern Europe).
Paleontological Journal 54: 640--651
DOI: https://doi.org/10.1134/S0031030120050111
https://link.springer.com/article/10.1134/S0031030120050111


The historical sequence of Early Triassic tetrapod communities in the Obshchii Syrt area includes eight consecutive faunal assemblages: this degree of detail in the identification of evolutionary stages is unique on a global scale. Temnospondyl amphibians are the dominant elements in these tetrapod assemblages, with three capitosauromorph groups (capitosaurids, benthosuchids, and trematosaurids) characterized by the widest distribution. Reptile remains are much less frequent. The paper provides a brief overview of the findings of rare and endemic tetrapod groups known from the Lower Triassic of Obshchii Syrt. These include amphibians (qantasids, lonchorhynchids, selenocarine capitosaurids, rhytidosteids, plagiosaurs, some forms of benthosuchids and trematosaurids, and chroniosuchians, the relict anthracosaurs) and reptiles (eosauropterygians, theriodonts, individual procolophonid, protorosaurian, and thecodontian genera). The peculiarity of the systematic composition of the Early Triassic tetrapod communities of Obshchii Syrt and Southern Cis-Urals with respect to that of the coeval fauna of terrestrial vertebrates of the more northern regions of Eastern Europe is emphasized, as is the legitimacy of considering these two areas as a specific region characterized by the distinctive character of their zoogeographical connections.

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