New Scleromochlus/pterosauromorph paper excludes tested pterosaur ancestors

Foffa et al 2022 reports,
“Pterosaurs, the first vertebrates to evolve powered flight, were key components of Mesozoic terrestrial ecosystems from their sudden appearance in the Late Triassic until their demise at the end of the Cretaceous. However, the origin and early evolution of pterosaurs are poorly understood owing to a substantial stratigraphic and morphological gap between these reptiles and their closest relatives, Lagerpetidae.

Lagerpetids are proterochampsid archosauriformes not related to pterosaurs in the large reptile tree (LRT, 2162 taxa).

“Scleromochlus taylori [Fig 1], a tiny reptile from the early Late Triassic of Scotland discovered over a century ago, was hypothesized to be a key taxon closely related to pterosaurs, but its poor preservation has limited previous studies and resulted in controversy over its phylogenetic position, with some even doubting its identification as an archosaur.

This is why vertebrate paleontologists need to build their own LRT. If you exclude pertinent taxa you will never find for yourself the origin of pterosaurs.

“Here we use microcomputed tomographic scans to provide the first accurate whole-skeletal reconstruction and a revised diagnosis of Scleromochlus, revealing new anatomical details that conclusively identify it as a close pterosaur relative within Pterosauromorpha (the lagerpetid + pterosaur clade).

Adding taxa invalidates the Foffa et al hypothesis of interrelationships.

“Scleromochlus is anatomically more similar to lagerpetids than to pterosaurs and retains numerous features that were probably present in very early diverging members of Avemetatarsalia (bird-line archosaurs). These results support the hypothesis that the first flying reptiles evolved from tiny, probably facultatively bipedal, cursorial ancestors“.

Scleromochlus IS closer to lagerpetids than pterosaurs in the LRT. And the first flying reptiles (e.g. Bergamodactylus) did evolve from tiny, bipedal cursorial ancestors.

Figure 1. Scleromochlus.

My reply to the Paleocast video (below) interview with lead author Foffa:
“A look through the citation list reveals a citation omission: Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336. Scleromochlus has tiny hands and no pedal digit 5. Pterosaurs have large hands and a tanystropheid-like pedal digit 5 shared with Cosesaurus, Sharovipteryx, Longisquama and Langobardisaurus, the four taxa (see above) nesting closer to pterosaurs than any archosaur. Cosesaurus has a sternal complex (clavicles + interclavicle + sternum), pteroid and prepubis plus extradermal membranes trailing all four limbs, as in pterosaurs. Scleromochlus lacks these traits. Scleromochlus nests with basal bipedal crocodylomorphs when permitted to do so. Taxon exclusion is the number one problem facing paleontology. Details at ReptileEvolution dot com.”

Figure 2. Scleromochlus from Foffa et al 2022 sporting a longer, previously buried tail. Note the deep chevrons. Pterosaurs and their ancestors lack these.

Davide Foffa was kind enough to send a PDF while writing today’s blogpost.
Here’s my reply, ‘Thank you for the prompt and courteous reply to my PDF request. I also heard your Paleocast podcast.

You expressed an interest in finding pterosaur precursors. I was in your shoes in the late 1990s, just getting started writing papers (without a degree). In the following years several were published including:

Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

That’s a citation missing from your reference list. In addition, a manuscript attempting to correct my freshman mistakes can be found here:

Since 2011 I have been building an online cladogram of 2160 vertebrates including Scleromochlus, pterosaurs and their precursors back to Ediacaran worms. I note that the four genera tested in the Rivista paper were omitted from your team’s taxon list. Taxon omission appears to be the number one problem in paleontology. For instance, Vancleavea nests with thalattosaurs when those taxa are included.

Pterosaur origin omissions are systematic, as chronicled here:

If you’re really interested in pterosaur ancestry, please go see Cosesaurus in Barcelona. I found it wrapped in toilet paper when it should have had a place of honor. Here’s a link to that taxon online:

I have also studied Sharovipteryx and Longisquama. You’ll find links to those two on the Cosesaurus web page and more data in the ResearchGate manuscript.

Here’s that large and growing larger cladogram that nests Lagerpeton with Tropidosuchus within the Proterochampsidae and Scleromochlus within the basal bipedal Crocodylomorpha.

I try to avoid incomplete taxa. Those are set aside in dark red on the cladogram and then omitted from the .nex file. I also show my data on the page of that website. So if there is a mistake, let me know.

The lack of a tanystropheid-like fifth toe was the first clue I had that Scleromochlus was not related to basal pterosaurs. The second clue was the tiny hand and digit four was not the longest. You’ll note that Cosesaurus, Sharovipteryx and Longisquama all have that odd fifth toe. They also increasingly emphasize manual digit 4 as taxa nest closer to pterosaurs. Cosesaurus has a prepubis and pteroid, a sternal complex (clavicles + interclavicles + sternum), an attenuated tail, uropatagia, an elongate ilium with 4-5 sacrals,  simple hinge ankle joint, an antorbital fenestra, etc. etc. None of these are found in archosaurs, but the last two by convergence.

Here’s a link to the origin of pterosaur wings from ancestral lepidosaurs:

It’s been a fascinating twenty-two years watching as colleagues I’ve interacted with at symposia have studiously avoided testing taxa presented so long ago in a peer-reviewed paper that resolved the origin of pterosaurs question.

Congratulations on getting your work published in Nature. It’s unfortunate that taxon omission ruined an otherwise laudable paper.

Let’s keep in touch. And let me know whenever I can help.

Foffa D et al (10 co-authors) 2022. Scleromochlus and the early evolution of Pterosauromorpha. Nature
Peters D 2000. A redescription of four prolacertiform genera and implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293-336.

Paleocast video interview of lead author Davide Foffa.

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