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Reposted by Xavier Jenkins

Skeleton Crew Paleo @skeletoncrewpaleo.bsky.social · 20h

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Keep an eye out for an incoming paper by @valentinbuffa.bsky.social that better investigates the postcranial evolution of these reptiles and their relatives (:

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

So what's next? I am expanding this phylogenetic dataset to better tackle the explosive radiation of early neodiapsids in the late Permian and crown reptiles in the Triassic. I also hope to detail some of our observations on synapsid evolution soon!

And, it goes without saying...more descriptions!

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Specifically, by placing 'the earliest reptile' Hylonomus on the amniote stem and removing a ~50 million and ~30 million year ghost lineage for Millerettidae and Neodiapsida, we greatly improve the stratigraphic record of early reptiles and amniotes more broadly!

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

We found that this topology greatly improves the fit of the reptile evolutionary tree to the stratigraphic record by at least 27% compared to studies finding a 'Eureptilia' or 'Parareptilia'...

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Beyond anatomical and statistical support, how does our phylogenetic hypothesis match the fossil record for early reptiles? To test this, we performed a series of stratigraphic fit analyses...

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

With our new data, millerettids are most parsimoniously interpreted as close relatives of neodiapsids even when the monophyly of clades such as 'Diapsida', 'Eureptilia', and 'Parareptilia' are enforced...

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

We (and our reviewers) were also genuinely curious as to how robust our phylogenetic hypothesis for Millerettidae was compared to traditional frameworks of early reptile evolution, so we performed a series of constraint analyses...

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Millerettids and neodiapsids also share several derived features involved in the reorganization of the gastralia and caudofemoralis musculature. Parapleurotans are the only Paleozoic reptiles with a midline gastral element and fused, laterally directed caudal ribs, for example.

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Our ancestral state reconstruction supports a middle Permian origin of the reptile tympanum, Future work on non-saurian neodiapsids will shed light on this question, but I'll note that a tympanum was recently described in tangasaurids....

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

In fact, we suggest that the tympanum of modern reptiles originated in the common ancestor of Parapleurota in the middle Permian. Excitingly, recent developmental work by Bronzati et al. has shown that the modern reptile tympanum was present in their common ancestor, congruent with this hypothesis

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

We name this clade Parapleurota, which is currently supported by 21 unambiguous synapomorphies across the skeleton. These include numerous features related to a reorganization of the middle ear and cranial nerves.....

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

When these observations were incorporated into an expanded phylogenetic analysis (647 characters, the largest such study on early reptile origins), we find Millerettidae in a crownward position as sister to Neodiapsida, a group of reptiles which includes modern reptiles and their closest relatives.

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Perhaps not so surprisingly, these 'eureptiles' were generally considered stem amniotes in pre-cladistic works. More specifically, they were thought to have 'given rise' or were 'directly ancestral' to all other amniote. This includes Hylonomus, the putative 'earliest reptile'...

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

I carefully checked for these features in numerous other Carboniferous and Permian stem reptiles. Surprisingly, derived features millerettids shared with modern reptiles were absent in nearly all early 'eureptiles' such as captorhinids and protorothyridids.

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Looking at their anatomy, I quickly realized that millerettids shared more features with neodiapsid reptiles, particularly in their braincase and postcranial skeleton.

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

During my dissertation, my research focused on the Millerettidae, a group that was classically interpreted as 'eosuchians' or close relatives of modern reptiles. Despite this, millerettids have been interpreted as among the basalmost members of Parareptilia for the last few decades 🤔

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

Since the advent of cladistics, reptiles have generally been split into 'eureptiles' and 'parareptiles'. This early dichotomy in the evolution of reptiles has implied long ghost lineages for numerous reptile groups, conflicting with more traditional hypotheses of reptile origins by Romer and Watson

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Xavier Jenkins @semifossorial.bsky.social · Aug 28

It’s finally out!

Our work addressing the origins of reptiles is published in PCJ! peercommunityjournal.org/articles/10....

We use novel info gleaned from the scan data of dozens of stem reptiles to substantially revise our understanding of early reptile evolution #paleontology #herpetology

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Xavier Jenkins @semifossorial.bsky.social · Aug 22

To be formally published soon, with a detailed thread to follow there

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Xavier Jenkins @semifossorial.bsky.social · Aug 22

Huge thanks to Michel Laurin for his recommendation of my work on reptile origins in PCI Paleontology! First of many works to come (:

Also thanks to Valentin Buffa, David Majanović, and others for their reviews (:

paleo.peercommunityin.org/articles/rec...

Graphical abstract and simplified phylogeny of early reptile relationships showing the gradual evolution of the reptile middle ear

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Reposted by Xavier Jenkins

Henry Thomas 🦤🏳️‍🌈 @zhejiang0pterus.bsky.social · Aug 7

And I named one of them!!! Meet Aulacephalodon kapoliwacela - the Iron Hog - the first and so far only geikiid known from the Luangwa Basin! I worked on this taxon for my Master's thesis, and it's been lovely

NHCC LB737, holotype of Aulacephalodon kapoliwacela, in dorsal (left) and ventral (right) views. Scale bar 10 cm

NHCC LB737, holotype of Aulacephalodon kapoliwacela, in lateral (left) and posterior (back) views. Scale bar 10 cm

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Xavier Jenkins @semifossorial.bsky.social · Aug 7

This was a really exciting project thanks to my PhD advisor @gondwannabe.bsky.social and mentors Jonah Choiniere and Claire Browning, who helped with our study of Permian amniote material across Southern Africa. More to come!

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Xavier Jenkins @semifossorial.bsky.social · Aug 7

Cladistic analysis demonstrates that Amenoyengi forms a group with other late-surving and small-bodied moradisaurines. Was there a trend towards smaller body-size late in captorhinid evolution, or are there other biogeographical variables at play? #Captorhinidae #captorhinid

Simple cladogram demonstrating the relationships of Amenoyengi (on the left) with other moradisaurine captorhinids. Skull silhouettes show the size disparity present in this group

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Xavier Jenkins @semifossorial.bsky.social · Aug 7

Collected in the 1960s, this specimen was interpreted as an unnamed species of Captorhinus (an older taxon from North America) for decades. CT-scanning at Wits University has revealed the presence of multiple rows of dentition similar to moradisaurines, including those from Niger and India.

Maxilla of Amenoyengi in ventral view showing four rows of dentition, which are numbered from 1-4. A small diastema, or gap in the tooth row, is present anteriorly

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