Maiothisavros dianeae: a tiny Early Permian ‘diapid’ enters the LRT as the earliest archosauriform

Unfortunately authors Mooney, Maho, Bevitt and Reisz 2022
did not create a reconstruction from their excellent neutron CT scans (Fig 1) nor did they undertake an analysis of their tiny new Early Permian taxon, Maiothisavros dianeae (Fig 2). So their headline discussed a dental pathology rather than the real headline: this is the basalmost and earliest archosauriform currently known… by 40 milllion years.

Here
in the large reptile tree (LRT, 2173 taxa), even with so few traits to score, Early Permian Maiothisavros nests between the Late Permian AMNH 5561 specimen of Youngina capensis (Fig 1) and the much larger Early Triassic BPI 41061 specimen of Proterosuchus (Fig 1).

Phylogenetic miniaturization once again appears
at the genesis of a novel clade. The authors wrote, “the available material is insufficiently informative to allow us to undertake a phylogenetic analysis to evaluate its position within Diapsida and in particular among Neodiapsida.”

According to Wikipedia, “Neodiapsida is a clade, or major branch, of the reptilian family tree, typically defined as including all diapsids apart from some early primitive types known as the araeoscelidians. Modern reptiles and birds belong to the neodiapsid subclade Sauria.”

Simply adding a few taxa completely invalidates this clade and its definition. This has been online for over a decade.

Next time, don’t give up. If you want to toss in the towel, send me the data and I’ll run it through the LRT prior to submission. It only took a few hours. Unfortunately, now it’s too late for Mooney, Maho, Bevitt and Reisz who have had their fossil’s special status identified by an amateur from a small town in Illinois, USA.

“We suggest that despite their fragmentary nature, the known remains show a surprisingly large number of autapomorphies, and its actual position within Neodiapsida may be only determined with new additional discoveries of more complete materials.”

No additional materials were necessary for the LRT. The Mooney et al. paper does not include the term ‘archosauriform’. So it wasn’t even on their radar. But they did see similarities in the palate of Early Permian Maiothisavros to Late Permian Youngina (Fig 2). Next time let your own LRT tell you where a new taxon nests. Don’t fiddle about Pulling a Larry Martin.

So ‘surprisingly poorly known’ by these authors, they don’t realize the diapsid configuration evolved more than once. Adding taxa reveals this. The LRT had this online for a decade. No one was curious enough in academia to check that out. That’s the problem when professors teach from outdated textbooks.

“Notwithstanding the hypothesis that varanopids are diapsids rather than synapsids, there are only four araeoscelidians and one neodiapsid present in the late Carboniferous and early Permian.

Adding taxa in the LRT resolved this issue several years ago. Large varanopids are synapsids. Small ones (generally) are protodiapsids, in the lineage of diapsids like Petrolacosaurus. Early Permian Vaughnictis is the last common ancestor. These are all late survivors of earlier radiations.

“Here we describe the fragmentary remains of a very unusual new amniote from the famous cave deposits near Richards Spur, Oklahoma, that we recognize as a diapsid reptile, readily distinguishable from all other early amniotes by the unique dentition and lower jaw anatomy.

Actually it’s not unusual at all.
It only appeared unusual because sister taxa were not tested.

“The teeth have an unusual reeding pattern on the crown (long parallel ridges with rounded surfaces), with some teeth posteriorly tilted and strongly recurved, while a ventral protuberance forms the anterior terminus of the dentary. Overall, the lower jaw is unusually slender with a flattened ventral surface formed by the dentary and splenial anteriorly and the angular in the midregion. The presence of a very slender triradiate jugal revealed through computed tomography confirms the existence of a large lower temporal fenestra, while the medial edge of the maxilla and the anatomy of the palatine confirm the presence of a large suborbital fenestra.

The authors would have benefited by creating a reconstruction (Fig 1), then scoring it with a wide gamut of candidate sister taxa. It only took a few hours here while nursing a cold.

“Computed tomography of this new taxon reveals maxillary innervation that is characteristically reptile, not synapsid.

Dr. Reisz: synapsids ARE reptiles = amniotes. You’re teaching from an outdated textbook. You should know the basics.

“Although no other definitively identifiable skull roof elements exist, the suborbital fenestra borders preserved on the palatine and maxilla supports the hypothesis that this is a diapsid reptile.

Dr. Reisz: Diapsids are diphyletic. You’re teaching from an outdated textbook. The LRT nests Maiothisavros as a basal archosauriform, derived from Late Carboniferous members of the redefined Diapsida, distinct from members of the Lepidosauria, which also have a diapsid skull configuration by convergence.

“Interestingly, the right dentary shows evidence of pathology, a rarely reported occurrence in Paleozoic amniotes, with several empty tooth sockets filled by bone. This small predator with delicate subthecodont implanted dentition provides strong evidence that diapsid reptiles were already diversifying rapidly in the early Permian, but likely were relatively rare members of terrestrial vertebrate assemblages.”

Or not rare. Fossils are rare.

Co-author Robert Reisz was the team leader in this study.
Despite his major influence and respect in the paleo community, taxon exclusion mars many of his studies. That’s why the LRT was designed to minimize taxon exclusion. It documents ancestors for every included taxa back to Ediacaran worms. Don’t expect changes to appear in textbooks to reflect LRT changes for at least a generation. The die has been cast. The academic system is feudal. Changes are glacial. New ideas are greeted with name-calling and demeaning blogposts, rather than a modicum of curiosity and simply adding taxa.

References
Mooney ED, Maho T, Bevitt JJ, Reisz RR 2022. An intriguing new diapsid reptile with
evidence of mandibulo-dental pathology from the early Permian of Oklahoma revealed by neutron tomography. PLoS ONE 17(11): e0276772.
https://doi.org/10.1371/journal.pone.0276772

http://reptileevolution.com/proterosuchus.htm