Terrestrisuchus postcranial anatomy and osteohistology + Riograndia maxillary canal + juvenile pleurosaurid from Jurassic of Germany

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

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Stephan N. F. Spiekman, Richard J. Butler & Susannah C. R. Maidment (2024)
The postcranial anatomy and osteohistology of Terrestrisuchus gracilis (Archosauria, Crocodylomorpha) from the Late Triassic of Wales
Papers in Palaeontology 10(4): e1577
doi: https://doi.org/10.1002/spp2.1577
https://onlinelibrary.wiley.com/doi/10.1002/spp2.1577

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https://onlinelibrary.wiley.com/doi/epdf/10.1002/spp2.1577



The earliest crocodylomorphs, known as non-crocodyliform crocodylomorphs, first appeared during the Late Triassic. In contrast to extant crocodylians, which are all semi-aquatic, early crocodylomorphs represent terrestrial taxa with a fully erect posture and in most cases a small body size. Their gracile skeletons suggest an active mode of life, possibly similar to contemporaneous, bipedal theropod dinosaurs. Despite this remarkable body plan, the postcranial morphology of early crocodylomorphs has rarely been documented in detail, restricting our ability to infer aspects of their functional morphology and evolution. Here, we provide a detailed description of the postcranium of Terrestrisuchus gracilis, a small-bodied crocodylomorph from the Late Triassic of Pant-y-Ffynnon Quarry (southern Wales, UK), including a description of long bone tissues based on histological thin sections. Almost all elements of the postcranial skeleton have been preserved. The skeleton of Terrestrisuchus gracilis is highly gracile, even for a non-crocodyliform crocodylomorph. Osteological correlates of the appendicular skeleton suggest that Terrestrisuchus gracilis had a digitigrade, quadrupedal posture. A quantitative analysis of limb robustness corroborates that Terrestrisuchus gracilis was a quadruped. Histological analysis suggests that all sampled specimens were skeletally immature and had fast growth at the time of death, as indicated by the lack of an external fundamental system and the predominance of fibrolamellar bone. The bone tissue is similar to that recently described for Saltoposuchus connectens and certain non-crocodylomorph pseudosuchians, but differs from Hesperosuchus agilis and crocodyliforms, in which parallel-fibred bone is more prevalent.

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Pedro Henrique Morais Fonseca, Agustín Guillermo Martinelli, Pamela G. Gill, Emily J. Rayfield, Cesar Leandro Schultz, Leonardo Kerber, Ana Maria Ribeiro & Marina Bento Soares (2024)
Anatomy of the maxillary canal of Riograndia guaibensis (Cynodontia, Probainognathia)—A prozostrodont from the Late Triassic of southern Brazil
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.25540
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25540

Free pdf:
https://anatomypubs.onlinelibrary.wiley.com/doi/epdf/10.1002/ar.25540


Investigating the evolutionary trajectory of synapsid sensory and cephalic systems is pivotal for understanding the emergence and diversification of mammals. Recent studies using CT-scanning to analyze the rostral foramina and maxillary canals morphology in fossilized specimens of probainognathian cynodonts have contributed to clarifying the homology and paleobiological interpretations of these structures. In the present work, μCT-scannings of three specimens of Riograndia guaibensis, an early Norian cynodont from southern Brazil, were analyzed and revealed an incomplete separation between the lacrimal and maxillary canals, with points of contact via non-ossified areas. While the maxillary canal exhibits a consistent morphological pattern with other Prozostrodontia, featuring three main branches along the lateral region of the snout, the rostral alveolar canal in Riograndia displays variability in the number of extra branches terminating in foramina on the lateral surface of the maxilla, showing differences among individuals and within the same skull. Additionally, pneumatization is observed in the anterior region of the skull, resembling similar structures found in reptiles and mammals. Through this pneumatization, certain branches originating from the maxillary canal extend to the canine alveolus. Further investigation is warranted to elucidate the functionality of this structure and its occurrence in other cynodont groups.

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Victor Beccari, Andrea Villa, Marc E. H. Jones, Gabriel S. Ferreira, Frank Glaw & Oliver W. M. Rauhut (2024)
A juvenile pleurosaurid (Lepidosauria: Rhynchocephalia) from the Tithonian of the Mörnsheim Formation, Germany
The Anatomical Record (advance online publication)
doi: https://doi.org/10.1002/ar.25545
https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25545


Late Jurassic rhynchocephalians from the Solnhofen Archipelago have been known for almost two centuries. The number of specimens and taxa is constantly increasing, but little is known about the ontogeny of these animals. The well-documented marine taxon Pleurosaurus is one of such cases. With over 15 described (and many more undescribed) specimens, there were no unambiguous juveniles so far. Some authors have argued that Acrosaurus, another common component of the Solnhofen Archipelago herpetofauna, might represent an early ontogenetic stage of Pleurosaurus, but the lack of proper descriptions for this taxon makes this assignment tentative, at best. Here, we describe the first unambiguous post-hatchling juvenile of Pleurosaurus and tentatively attribute it to Pleurosaurus cf. P. ginsburgi. The new specimen comes from the Lower Tithonian of the Mörnsheim Formation, Germany. This specimen is small, disarticulated, and incomplete, but preserves several of its craniomandibular bones and presacral vertebrae. It shares with Pleurosaurus a set of diagnostic features, such as an elongated and triangular skull, a low anterior flange in its dentition, and an elongated axial skeleton. It can be identified as a juvenile due to the presence of an unworn dentition, well-spaced posteriormost dentary teeth, a large gap between the last teeth and the coronoid process of the dentary, and poorly ossified vertebrae with unfused neural arches. Acrosaurus shares many anatomical features with both this specimen and Pleurosaurus, which could indicate that the two genera are indeed synonyms. The early ontogenetic stage inferred for the new Pleurosaurus specimen argues for an even earlier ontogenetic placement for specimens referred to Acrosaurus, the latter possibly pertaining to hatchlings.

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