Xavier Jenkins

Rauisuchus, the one who started it all, a friend-sized fella

(do not trust any other repurposed past skeletal reconstruction of this animal)

Skull of Scyllacerta, reconstructed based on scans of four nearly complete skulls.

Introducing a new Permian reptile: Scyllacerta creanae

With a tympanic fossa on the quadrate and no lower temporal bar, Scyllacerta challenges long-standing ideas about when-and-how hearing evolved in reptiles 🦎👂

🔗 doi.org/10.1111/pala...

Graphic illustrating the reconstruction process for Scyllacerta creanae (SAM-PK-K7710). The holotype aggregation specimen (left) comprises four skulls and at least six nearly complete skeletons preserved in lifelike positions. Using synchrotron micro-CT scans of the skulls, the bones could be segmented, digitally isolating them from the matrix and allowing their full morphology to be studied in detail (top center). Combining information from all four skulls, a reconstructed version could be assembled, depicting the likely life appearance (center, with each bone in a distinct color). This reconstruction can be used to make line drawings for science communication and skeletal reconstructions (bottom center). These reconstructions were the basis for a detailed life restoration of the head of Scyllacerta (bottom right, by @LiterallyMiguel). Despite its incredibly small size (top right, compared to a human hand), the known individuals were likely nearing full maturity.

Very excited to share Scyllacerta creanae, a new Permian stem-reptile from South Africa known from an aggregation of several individuals. This specimen provides unprecedented detail regarding the anatomy of the early reptile skull. 🦎

(1/🧵)

The first page of the paper described in the post.

First paper of 2026 is out for #FossilFriday, and the first of probably several ornithischian papers over the next interval. Here my coauthors and I describe some tantalizing bits that suggest that ornithischian diversity in the Morrison Formation is higher than previously recognized.

A small bit of grey rock containing the entwined and overlapping skeletons of several small lizard-like reptiles. On white foam with a scale bar.

This #FossilFriday we are pleased to have published the new younginid taxon Scyllacerta from the late Permian of South Africa 🇿🇦
This beautiful aggregation has the holotype and has been in the literature for 30 years as “juvenile Youngina”.
Photo taken before scanning at the @esrf.fr

Line drawing of Scyllacerta in numerous anatomical views, done by paleontologist Cy Marchant

Permian reptiles keep challenging what we know about reptile origins 🦎👂 More to come!

BTW- the CT segmentation, reconstructions, and line drawings were done by ISU undergraduate Cy Marchant @slvrhwk.bsky.social…. He’d be a great fit for any paleo lab! 👀

At the same time, we see a suite of changes:
• loss of the lower temporal bar
• origin of a cephalic condyle
• increased cranial mobility

This raises the possibility that tympanic hearing and early cranial kinesis evolved together… much earlier than previously thought.

The holotype of Youngina, a little worse for wear but bearing a conspicuous emargination on the back of its overly-prepped quadrate…

We suspect this anatomy was missed due to historical preparation techniques, especially in classic specimens like the Youngina holotype. 🔎

Newly discovered (and better-prepared) Youngina specimens all show the same feature….something that was even hinted at by Gow in the 70s….

Phylogeny of early reptiles showing the placement of Scyllacerta as an early Younginid and mapping the appearance of the tympanic fossa, loss of lower temporal bar, and appearance of the cephalic Condyle on the quadrate in these taxa.

That question led Valentin Buffa @valentinbuffa.bsky.social and I to re-examine all non-saurian neodiapsid taxa.

And we found tympanic fossae in more places than expected…. Even Youngina!

A close of a monitor lizard (Komodo dragon) with a visible external ear towards the right

That’s a big deal because tympanic ears were thought to be restricted to living reptiles, and absent in Permian stem-reptiles.

So was Scyllacerta a weird outlier… or had something been overlooked in other fossil reptiles?

Zoom in showing the middle ear, tympanum, and occiput of Scyllacerta

But the most exciting result?

Scyllacerta preserves a tympanic fossa on the quadrate.

This strongly suggests the presence of a tympanic (impedance-matching) ear. 👂

The scans made it immediately obvious that Scyllacerta is a distinct taxon.

It has a remarkably tooth-rich palate, including teeth extending onto the braincase (!) 🦷 🧠

During my PhD, I noticed several aspects of its anatomy that didn’t match Youngina at all.

So, with colleagues from Iziko Museums and University of the Witwatersrand, we CT-scanned the specimen at the European Synchrotron Radiation Facility. 🇫🇷

Biostratigraphic map of the Karoo basin in South Africa, showing where in the section Scyllacerta and other younginids are from.

Even more recently, the holotype of Scyllacerta was referred to newly named Akkedops bremneri on the basis of them being from the same locality…..

But they are separated by hundreds of miles and millions of years in stratigraphy…. As are the other specimens to referred to Akkedops 👀 🤷‍♂️

The holotype aggregation in multiple views, with numerous individuals visible

Scyllacerta was first discovered in the early 1990s and originally identified as a juvenile aggregation of Youngina capensis.

But it was older (~257 Ma vs ~253 Ma) and from a different assemblage zone in South Africa (sus).

Skull of Scyllacerta, reconstructed based on scans of four nearly complete skulls.

Introducing a new Permian reptile: Scyllacerta creanae

With a tympanic fossa on the quadrate and no lower temporal bar, Scyllacerta challenges long-standing ideas about when-and-how hearing evolved in reptiles 🦎👂

🔗 doi.org/10.1111/pala...

Top left: photograph of a grey slab containing multiple fossils, with vertebral columns clearly running vertically (SAM-Pk-K7710). This is a group of six Scyllacerta creanae individuals, including the holotype, a late Permian neodiapsid reptile from South Africa (scale bar at top right is 2 cm). Bottom right: a computer reconstruction of the skull based on three of the individuals in the fossil block. Scale bar at top right is 5 mm.

The origin of the tympanic fossa in reptiles revealed by a late Permian neodiapsid: new species Scyllacerta creanae onlinelibrary.wiley.com/doi/10.1111/... #FossilFriday @semifossorial.bsky.social @morphobank.bsky.social

Come work with the vertebrate paleontology team at the American Museum of Natural History in NYC this summer!

REU Students will have the opportunity to study and reconstruct the skulls of Permian and Triassic reptiles 😃

Reach out to me if you have any questions (: Apply by the 31st!!

peerj.com/articles/204...
My first mammal project, which I started as an REU intern at the AMNH is finally published! Huge thanks to my mentors and coauthors on this project for all their help, and to the reviewers for their comments and suggestions!

more wiki comms and stuff

There may be a way to skirt this requirement by sneaking in a zip file, but this isn’t optimal obviously

There’s a way to batch upload, but I think you need permission…. It’s a huge pain without it.

I feel personally punished for working on complete skulls 💀

Check the paper out above👆 to learn more!!

Keep an eye out for future work by @valentinbuffa.bsky.social, myself, and others on early reptiles…. 🦎🐍🐢

Some exciting stuff inbound! (:

A cladogram of early reptile relationships showing the origin of important anatomical features in the foot of these reptiles

Our postcranial observations, specifically on the foot, suggests that many features of the modern reptile hindlimb are actually present in their closest fossil relatives!

You heard it folks: milleretids are *also* postcranially very neodiapsid-like 😃

The relationship of Galesphyrus relative to other derived stem reptiles, including parapleurotans, suggests than neodiapsids must have originated sometime in the middle Permian, and certainly by the latest Capitanian. 🔨

Incorporating these observations into an expanded phylogenetic dataset, Buffa et al. place Galesphyrus as the sister to Millerettidae + Neodiapsida, a group I recently named Parapleurota (‘Clade P’ below)

When Valentin studied Galesphyrus specimens, he noted similarities in the postcranial skeleton of millerettids and neodiapsids. Interestingly, many of these features were absent in Galesphyrus. 👀

But then I met @valentinbuffa.bsky.social and found out he INDEPENDENTLY
came to same conclusion using POSTCRANIAL EVIDENCE! 🤯

This is exciting, because not only did I feel like it supported some of my hypotheses, but it sampled an anatomical region (the hindlimb) that I largely did not study 📚

During my graduate research, I argued that millerettids were indeed close relatives of crown reptiles and neodiapsids, primarily based on neurocranial evidence. I also showed that ‘Parareptilia’ is a polyphlyetic assemblage of unrelated stem reptiles

peercommunityjournal.org/articles/10....

Millerettids, as you may know by now, are a group of fossil stem reptiles from the Permian of South Africa. For much of their history, they were implicated in crown reptile origins. However, with the advent of cladistics they were placed among the #Parareptilia