Leidyosuchus and Stangerochampsa endocranial anatomy + squamate osteoderm evolution + procolophonid jaw from Lower Triassic of Brazil

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

New reptile papers:

Free pdf:

G. Donzé, G. Perrichon, P. Vincent, F. Therrien & J. E. Martin (2026)
Comparative endocranial anatomy in the crocodylians Leidyosuchus canadensis and Stangerochampsa mccabei from the upper Cretaceous of Alberta, Canada
Journal of Anatomy (advance online publication)
doi: https://doi.org/10.1111/joa.70096
https://onlinelibrary.wiley.com/doi/10.1111/joa.70096

Free pdf:
https://onlinelibrary.wiley.com/doi/epdf/10.1111/joa.70096

Crocodylians evolved a high variety of rostral morphologies during their evolutionary history, highlighting the strong links between morphological plasticity and environmental and ecological parameters. Two Late Cretaceous alligatoroids, the mesorostrine Leidyosuchus canadensis Lambe, 1907, and the brevirostrine Stangerochampsa mccabei Wu et al., 1996, from Alberta, Canada, preserve a large groove-shaped recess on the posterior part of the maxilla that has not been documented in other alligatoroids. Despite the potential phylogenetic and paleoecological significance of this neurovascular feature, internal and endocranial structures remain under-explored among stem alligatoroids. The endocranial morphology, including the paratympanic sinus system of Leidyosuchus canadensis and Stangerochampsa mccabei, was compared to those of extant crocodylians and of the extinct alligatoroid Diplocynodon ratelii based on computed tomography data. The Cretaceous alligatoroids share endocranial features, such as a posteroventral neurovascular projection of the labiolateral canal that connects to the groove-like recess at the posterior edge of the maxilla and a paratympanic sinus system most similar to those of small-bodied and young extant crocodylians, suggesting that these pedomorphic features may reflect the ancestral crocodylian condition. Future phylogenetic studies should consider internal and endocranial characters alike to improve our understanding on the relationships among crocodylians.

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Free pdf:

Roy Ebel, Jane Melville & J Scott Keogh (2026)
Lizards in chain mail: reconstructing the enigmatic past of dermal armour in squamate reptiles
Biological Journal of the Linnean Society 147(1): blaf129
doi: https://doi.org/10.1093/biolinnean/blaf129
https://academic.oup.com/biolinnean/article/147/1/blaf129/8422532


Osteoderms, bone plates in the skin, occur widely but inconsistently throughout the tetrapod tree of life. Their evolutionary history remains poorly understood. Squamate reptiles (lizards and snakes) represent an ideal study system. It is often assumed that different squamate lineages acquired their osteoderms independently. However, this had yet to be tested. Covering 320 Myr of reptile evolution, we present here an ancestral character state reconstruction for the phenotypic osteoderm expression in 643 taxa of all major squamate crown-groups, including 70 extinct and outgroup representatives. Osteoderms were largely acquired in a series of events during the Late Jurassic and Early Cretaceous. Subsequent rate deceleration and absence of reversions ultimately led towards a state of evolutionary stability. As an exception, we reconstructed the loss of osteoderms in the varanid stem-lineage, and secondary re-acquisitions in Australopapuan varanids during an acquisition series in the Miocene. We discuss how lifestyle, locomotion, and biogeographical history may have driven these events. Foremost, we demonstrate that squamate osteoderm expression is the product of multiple independent acquisitions. This solidifies the foundation for future discussions on the underlying evolutionary mechanisms. Our findings also contribute towards a better understanding of the selective pressures and evolutionary trajectories that shaped present-day reptile biodiversity.

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Caroline D’Ávila Burgardt, Karine Pohlmann, Arielli Fabrício Machado, Mateus A. Costa Santos, João L. Meira & Felipe L. Pinheiro (2026)
A peculiar procolophonid lower jaw from the Sanga do Cabral Formation (Lower Triassic, Brazil)
Historical Biology (advance online publication)
doi: https://doi.org/10.1080/08912963.2025.2608698
https://www.tandfonline.com/doi/full/10.1080/08912963.2025.2608698



In Brazil, the Lower Triassic is represented by the Sanga do Cabral Formation, known for its fragmented fossil tetrapods. However, in the last decade, some outcrops have revealed well-preserved remains, providing information about the first Triassic faunas of Western Gondwana. The Sanga do Cabral Formation fauna includes temnospondyls, procolophonids, and archosauromorphs. In this study, we describe a new procolophonid left hemimandible (UNIPAMPA 916) from the Sanga do Cabral Formation. The specimen differs from previously reported species for the site (Procolophon trigoniceps and Oryporan insolitus) in dental morphology, indicating a still hidden diversity of these parareptiles for the Brazilian Lower Triassic. The presence of a new procolophonoid morphotype for the Sanga do Cabral Formation underlines the importance of the Brazilian fossil record for understanding the recovery of ecosystems after the End-Permian Mass Extinction.

[Mickey Mortimer]

Ebel et al.'s paper last year surveying squamate osteoderms using CT scans was amazing, and this follow-up mapping their evolution is fine, but it is funny where they chose outgroups for osteoderm status-

"we considered the following extinct and outgroup taxa as osteoderm-bearing: ... Coelurosauravus"
I mean, the patagial rods are dermal (Buffa et al., 2025 online), but I don't think anyone would call them osteoderms. Just like how gastralia aren't counted by the authors.
"Conversely, no osteoderms were reported for the following extinct and outgroup taxa: ... Brachiosaurus"
Giraffatitan must not have made its way to the lizard workers yet, as Brachiosaurus itself is way too fragmentary to score.
"Chromogisaurus"

I'm really curious how THIS genus got chosen of all things. It's obscure and extremely fragmentary, so we really don't know its osteoderm status. If your only other sauropodomorphs are Brachiosaurus and Saltasaurus, Plateosaurus is right there.

"Taytalura, which is only known from a single skull"

So they say this themselves but still score it? So confusing.

This entire section is basically useless, since all you need are the few non-squamate lepidosaurs they used to polarize the basal condition as lacking osteoderms. What good does putting 17 archosaurs like Gallus and Triceratops in there do when the evidence is basically conclusive the clade was primitively armored? And for taxa like Coelurosauravus, Cryptolacerta, Hupehsuchus, Placodus, Plesiosaurus, and Stenopterygius, we don't even know where they go compared to lepidosaurs and archosaurs, and e.g. the four euryapsids aren't going to map out the correct osteoderm distribution in that clade anyway (assuming it's real).

Mickey Mortimer