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Reposted by Aaron Kufner

Xavier A. Jenkins @semifossorial.bsky.social · 30/09/2026

Out today: We show that Westlothiana lizziae or "Lizzie," described 35 years ago as the world's oldest reptile - is not a stem amniote at all, but a stem tetrapod. www.nature.com/articles/s41...

The part and counterpart of the holotype specimen of Westlothiana.

Paleoartistic reconstruct of Westlothiana by Jacob Schick based on our new data

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Aaron Kufner @akufner.bsky.social · 25/09/2026

Yes! And I've seen some collection tags with Eupelor and Metoposaurus 🙃

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Aaron Kufner @akufner.bsky.social · 24/09/2026

It's a great week for temnospondyl research!

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Aaron Kufner @akufner.bsky.social · 24/09/2026

I made all of these illustrations in Illustrator. My old office mate can attest 😂

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Aaron Kufner @akufner.bsky.social · 23/09/2026

TL;DR: We may have been underestimating the species diversity of North American metoposaurids. Figuring out their species is still pretty hard. Maybe it's better to put each species in its own genus so we aren't always flip-flopping generic names. Support your local museums and historical societies.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Loss of public awareness can put these scientifically and culturally important collections in precarious positions and may even result in the loss of reproducibility of scientific works in extreme cases.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

While the public-facing side of a museum is only a small fraction of its purpose, it is vital to broader public awareness of many museums and their missions. Indeed, one of the museums that I visited in Texas for this work has now been closed to the public for more than a year.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Lastly, all of this work was conducted through museum collections, and I'd be remiss not to say something at this time of uncertainty in several museums' futures.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

These results are more in line with some older schools of thought by authors like Colbert and Imbrie (1956) who suggested Anaschisma browni from WY is distinct from other metoposaurids in North America based on their "biometric" analyses (what we'd now call linear or traditional morphometrics).

A figure comparing the dimensions of three metoposaurid species by Colbert and Imbrie (1956). They suggested based on the position of the orbit and relative length of the postparietals that Anaschisma (their Eupelor) browni is distinct from other metoposaurids.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

As a result of this uncertainty in interspecies relationships, I ended up naming new genera to accommodate the species once referred to Anaschisma browni because I could not firmly establish them in an existing genus without synonymizing other genera that are generally considered distinct.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Once again, there is mostly no resolution for interspecies relationships of metoposaurids. Huzzah! Previous results have been replicated. Science works. BUT there are reasonably well resolved clades of specimens of the species B. bakeri, A. gregorii, and P. howardensis.

A comparison of phylogenetic analyses done using Bayesian and parsimony and excluding specimens of Metoposaurus krasiejowensis that were not directly observed. Clades of specimens representing species are highlighted with different colors.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Alright, I'm going to try and keep the rest of this short. If this interests you, I'd recommend reading the article, but then again, I'm a little biased. So what about the results of the phylogenetic analysis? Well, it's consistent with previous analyses of metoposaurids which is good(?)

A comparison of phylogenetic trees resulting from Bayesian and parsimony analyses. The metoposaurid specimens from North America are highlighted by colors based on their species referrals.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Unfortunately, I could not establish this referral for other specimens from the same site. So if you have large Norian-aged metoposaurids, take a closer look at them! And hit me up if anything stands out!

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Aaron Kufner @akufner.bsky.social · 23/09/2026

So where are the adults? Well, they may have been sitting in front of us all along. I tentatively referred UCMP 27051 to Apachesaurus gregorii based on the abrupt curvature of the temporal LLS toward the squamosal (though not clearly passing onto it) and a narrow cultiform process.

UCMP 27051, a putative adult specimen of Apachesaurus gregorii. Returning to a toilet lid-shaped and sized skull of a classic metoposaurid amphibian.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Underdevelopment of the LLS in Apachesaurus has been used to infer that this species may have been "more terrestrial", but read the paper to see why I think this is not the case.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

But importantly, the discontinuous cranial LLS present in the type locality specimens (and another small referred specimen 📸 here) of Apachesaurus gregorii may be an indicator of juvenile ontogenetic status.

A very small cranial specimen referred to the metoposaurid amphibian Apachesaurus gregorii. Once again, toilet lid-shaped but much too small for a human sized toilet. Scale bar equals 5 cm.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Is a modification to this developmental sequence responsible for the presence of sulci rather than roofed canals among stereospondyls? And what other kinds of modifications to this developmental sequence may have been possible? I would argue definitively...Probably? More work needs to be done!

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Lateral line canals in ray-finned fish tend to following a specific sequence that concludes after or near the end of a larval stage resulting in the integration of the canal neuromasts into canals. But these begin formation as a series of disconnected segments. 📸 Pastana et al. (2019)

Sequence of the formation of cranial lateral line canals in modern ray-finned fish. Note pit formation initiated by the presence of a canal neuromast that forms a segment that eventually connects to nearby segments. The formation of a roofing autogenous ossification does not seem to have occurred in stereospondyls.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

The extent of the temporal sulcus onto the squamosal seems to be autapomorphic (at least among metoposaurids, and also present in the holotype), but the discontinuity of this lateral line sulcus (LLS) is worth exploring. It may be related to development of the lateral line system.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

I was fully on board with the idea that Apachesaurus may actually represent a juvenile of what was at the time called Anaschisma, and to my surprise, I found solid evidence for its validity including a unique configuration of the cranial lateral line sulci, see UCMP 63846 from the type locality.

UCMP 63846, the back of the left half of a skull roof of the metoposaurid Apachesaurus gregorii. It shows two noteworthy features: a temporal sulcus (ts) that extends onto the squamosal, and the temporal sulcus is also discontinuous.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

There has been some back and forth about the ontogenetic status of referred specimens of Apachesaurus because all specimens of this taxon are small-bodied. Histology of small Apachesaurus-like intercentra suggests very convincingly that these are juvenile forms. peerj.com/articles/3183/

peerj.com

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Aaron Kufner @akufner.bsky.social · 23/09/2026

With my guilt now acknowledged, let's get on to what I consider the most interesting part of this work: Apachesaurus gregorii.

The holotype skull of the metoposaurid Apachesaurus gregorii. While similarly toilet-lid shaped to the other metoposaurids in this thread, this one is much smaller than the size of a toilet lid.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

At this point, I have to apologize to all museum curators, collection managers, and exhibit designers who recently changed their Buettneria signs and labels to Anaschisma. Give it another 5-10 years to see how this plays out before making another change 😅

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Aaron Kufner @akufner.bsky.social · 23/09/2026

The second I am calling Tecovaserpeton perfectum, and it is known (not surprisingly) primarily from the Tecovas Fm in TX. Its holotype was originally named Buettneria perfecta by Case in 1922, and it is a shockingly "perfect" specimen aside from being squished and missing the tabular horns.

The holotype skull of Tecovaserpeton perfectum, another toilet-lid headed amphibian from the Upper Triassic of Texas. This specimens is exceptionally well preserved with details of nearly all of the teeth and the dorsal surface of the skull clearly visible.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

This is probably a good time to allude to but not rehash the taxonomic kerfuffle of Buettneria from the mid-2000s. The occupation of the name Buettneria certainly did not simplify the taxonomic history of these metoposaurids. We see you Buettneria maculiceps (although I've literally never seen it).

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Aaron Kufner @akufner.bsky.social · 23/09/2026

The first is one I am calling Paranaschisma howardensis. Buettneria howardensis was originally described in 1945 by Sawin based on the material from Otis Chalk Quarry 3 in TX. It has bounced around in being considered valid or invalid, but I was able to find a handful of apomorphies for this taxon.

The lectotype specimen of Paranaschisma howardensis a large skull of a Triassic amphibian shaped very roughly like a toilet lid.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

What about the rest of the specimens previously referred to Anaschisma? Well, there seem to be at least two, maybe three, species in this boat. Which all already have pre-existing type material.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

The results were a little surprising to me since I was able to find evidence that Anaschisma browni may have been a bit of a wastebasket and ended up restricting that species to just specimens from the Popo Agie Fm of WY. (And a rare lateral view of a metoposaurid for your viewing pleasure)

The holotype specimen of Anaschisma browni in right lateral view. To no one's surprise, it is very flat.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

I added 29 new characters and modified some pre-existing ones to the matrix of Gee and Kufner (2022; some of these additions were splitting of compound characters), and I scored over 50 specimens from firsthand observation and seven from the work of Sulej (2007).

static.klipy.com

Cute Cat Typing on Laptop

Alt: Cute Cat Typing on Laptop

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Aaron Kufner @akufner.bsky.social · 23/09/2026

Recent redescriptions of several metoposaurid taxa including Anaschisma browni (left) and Buettnererpeton bakeri (right) and character matrices attempting to discern metoposaurids relationships made this work reasonably straightforward.

Holotype of Anaschisma browni, redescribed by Gee, Parker, and Marsh (2020).

Holotype of Buettnererpeton bakeri redescribed by Gee and Kufner (2022).

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Aaron Kufner @akufner.bsky.social · 23/09/2026

So what did I do? I went around to museum collections that hold type specimens and numerous referred specimens of metoposaurids from North America and documented as much of the cranial morphology as I could. (See current profile pic for an example 🙂)

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Aaron Kufner @akufner.bsky.social · 23/09/2026

One interesting example is Metoposaurus krasiejowensis described by Sulej (2007) which exhibits variation in the contribution of the lacrimal to the orbital margin. This character has been used extensively for taxonomic differentiation, so seeing variation within a population is...disconcerting.

Specimen of Metoposaurus krasiejowensis figured by Sulej (2007) that lacks an orbital contribution from the lacrimal.

Holotype specimen of Metoposaurus krasiejowensis from Sulej (2007) with a lacrimal contribution to the orbital margin (the majority condition among specimens of this species).

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Aaron Kufner @akufner.bsky.social · 23/09/2026

In this study and as the title suggests, I set out to reevaluate the taxonomy of North American metoposaurids in light of studies from the last two decades documenting intraspecific variation in populations of metoposaurids known from bone beds.

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Aaron Kufner @akufner.bsky.social · 23/09/2026

This one has been a long time coming! I'm happy to share that another chapter of my PhD has been published! In this one, I'm shaking up the taxonomy of North American metoposaurids. This work was largely done in museum collections, and more on that below. peerj.com/articles/217...

A figure with maps showing the distribution of metoposaurid occurrences in Upper Triassic outcrops of western and eastern North America (centered on the USA). The approximate chronostratigraphic ranges of the now five recognized species are plotted, and line drawings of all of the potentially or definitively diagnostic holotypes of North American metoposaurids are included.

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Reposted by Aaron Kufner

Xavier A. Jenkins @semifossorial.bsky.social · 28/05/2026

Our paper on turtle origins is finally out in Current Biology, with two major implications for our understanding of reptile evolution 🐢 #Paleontology #Turtles #Evolution www.cell.com/current-biol...

A pair of Eunotosaurus by Gabriel Ugueto: a sense of scale is provided by Glossopterus leaves in the fore-and-background and by a prosbolid hemipteran insect

Phylogeny of major reptile groups, showing turtles (Pantestudines) as early archosauromorphs and the putative stem-turtle Eunotosaurus as a millerettid stem reptile

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Aaron Kufner @akufner.bsky.social · 23/02/2026

In my limited interactions with Hans, he was personable, kind, and encouraging. A true powerhouse in the Triassic and vertebrate paleontology as a whole. And his humor and love for cats was infectious. He will be sorely missed.

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Reposted by Aaron Kufner

Bryan Gee @koskinonodon.bsky.social · 02/01/2026

The yearly round-up of #temnospondyl research from the past year for the first #FossilFriday post of the year: once again, a lot of stuff on European taxa but also a great mix of researchers involved in all sorts of interesting work! 🧵👇 (1/25ish?) #temnospondyls #fossils #histology #anatomy

Photographs and interpretive line drawings of various skulls of Plagiosternum granulosum from the Late Triassic of Germany. The skull is much wider than long, as is typical for plagiosaurids, and broadly parabolic. The orbits are greatly enlarged, taking up more than half the length of the skull, with a very narrow interorbital region; similarly large interpterygoid vacuities occur on the palate. Figure from Schoch et al. (2025).

Photograph and illustration of a specimen of the stereospondylomorph Glanochthon lellbachae from the early Permian of Germany. The skeleton is nearly complete and articulated, though it is flattened dorsoventrally such that elements normally found ventral to others like the jaws and pectoral girdle are splayed to the side. The impression of the tail is fully preserved, giving a clear indication of the full length of the tail relative to the torso. Figure from Werneburg (2025)

Photograph and illustration of the skull of the new neotype of the early Permian dissorophid Aspidosaurus chiton, from Texas, in dorsal view. The skull is an orange-brown color, longer than wide, and largely undistorted. Figure from Gee et al. (2025).

Comparison of the four predominant tissue types found in the pectoral girdle samples of the Late Triassic metoposaurid Metoposaurus krasiejowensis from Poland, imaged under circular cross-polarized light: (a) interwoven structural fibered matrix; (b) coarse PFB; (c) fine PFB; (d) LB fibered matrix. Figure from Kalita et al. (2025).

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Reposted by Aaron Kufner

BatmanelVisigodo @batmanelvisigodo.bsky.social · 25/11/2025

#temnovember2025 day 25 :Buettnererpeton Day 25 and now its time for #Buettnererpeton, a thin skull #metoposaur from the late #Triassic of northamerica #Paleoart #sciart #amphibian #temnospondyl #metoposaurus

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Reposted by Aaron Kufner

Bryan Gee @koskinonodon.bsky.social · 11/07/2025

New paper out today in @zoojlinnsoc.bsky.social for #FossilFriday AKA here's-Bryan's-one-paleo-paper-this-year-to-remind-people-I-still-do-paleo-sometimes: a revision of the #Permian #dissorophid #temnospondyl Aspidosaurus chiton based on a new specimen: doi.org/10.1093/zool... (1/n)

Photograph and illustration of the skull of the new neotype of Aspidosaurus chiton in dorsal view. The skull is an orange-brown color, longer than wide, and largely undistorted.

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Reposted by Aaron Kufner

Robert Evans (the Only Robert Evans) @iwriteok.bsky.social · 02/04/2025

Elon Musk: pours tens of millions into a race that has never seen even a fraction of that much money. bribes multiple voters with $1 million checks to vote. offers any Wisconsin voter who proves they voted $50. wears a fucking cheesehead Wisconsin: votes against his candidate by historic margins

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Aaron Kufner @akufner.bsky.social · 02/04/2025

While this site is exceptional insofar as the metoposaurids are concerned, it has so much more to offer in improving our understanding of the paleoecology of the continental early Late Triassic in North America! 16/16

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Aaron Kufner @akufner.bsky.social · 02/04/2025

Last but certainly not least, plants and poops. None of us is a paleobotanist, so take our IDs with a grain of salt. These might represent some of the more complete plants from the Popo Agie, but we'd love to work with someone interested in Triassic plants. And coprolites too... 15/16

Possible plant fossils including fragments that appear to be stems and a potential root. The lower panel includes fragmentary coprolites that are subrectangular in outline and all white in color.

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Aaron Kufner @akufner.bsky.social · 02/04/2025

The bivalves from NK have unironically become my favorites because they are a bit of a puzzle. Only external molds on + and - relief! We propose they formed by 1) burial, 2) dissolution of biomineral and retention of outer organic layer, 3) lithification, and 4) loss of organic layer. 🤷‍♂️ 14/16

Representative unionoid bivalve fossils from the NK bonebed. All of these fossils are preserved as molds of the external surface and appear as smooth ovoid structures with some lineations in red mudstone.

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Aaron Kufner @akufner.bsky.social · 02/04/2025

"Fish bits" from within the bonebed including what we think is an almost complete fin. We suggest these are all redfieldiid based on the supracleithrum, but it's possible if not likely there were other ray-finned fish present. We need more complete fish material! 13/16

Fish remains from the NK bonebed including a probable fin with an inset showing linear structures interpreted as fin rays (lepidotrichia), a diamond-shaped scale, a tiny toothed element, and a mold and partial fossil of a bone of the gill/skull skeleton called the supracleithrum.

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Aaron Kufner @akufner.bsky.social · 02/04/2025

The shed archosauriform teeth are from the bonebed, but this partial phytosaur mandible is from somewhere in the overburden. It's the lowest definitive occurrence of a phytosaur from the Popo Agie aside from some unsubstantiated reports. 12/16

Two shed teeth from archosauriform reptiles from the NK bonebed that are conical with faint serrations, and a partial phytosaur mandible from above the NK bonebed with a colored in skull showing where the elements in context.

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Aaron Kufner @akufner.bsky.social · 02/04/2025

Now for the critters! The star of the show is Buettnererpeton bakeri, a metoposaurid species placed in its own genus by @koskinonodon.bsky.social and me a couple years back. That little block with articulated palatal plates (E,F) was found by Bryan when he came out to the site in 2018! 11/16

A skull roof of the metoposaurid Buettnererpeton bakeri that evokes memories of Pac-Man ghosts. There are also examples of denticulate palatal plates that form interlocking polygons that would have been embedded in the soft tissue of the palate in life.

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Aaron Kufner @akufner.bsky.social · 02/04/2025

Tangent: I don't find the "breeding colony die-off" hypothesis in some previous studies particularly convincing because 1) post-breeding die-off is fairly specialized among vertebrates and 2) afaik, it's unknown among any modern amphibians. 10/16

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Aaron Kufner @akufner.bsky.social · 02/04/2025

Still, the cause of death is unknown. I wish we knew what the sediment looks like lateral to the bonebed, but we keep finding bones! If there are mudcracks in the same layer like Site XIII, that would suggest drying, and if not, then it could be biological such as an algal bloom or disease. 9/16

Our interpretation of the depositional setting with getting closer to present from bottom to top. 1) regional view of a floodplain with oxbow lakes and intermeander ponds. 2) local view of a ponded environment (life is good!). 3a) biological cause of death for metoposaurids such as an algal bloom. 3b) abiological cause of death such as seasonal aridity. 4) return to normal and burial of dead individuals.

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