If basal fenestrasaurs did not exist, where else would pterosaurs nest?

The utility of having a very large gamut reptile family tree with full resolution is the complete freedom to make deletions to test “what if” scenarios. Today we’ll take away the closest known ancestors of pterosaurs in a stepwise fashion to see when and if pterosaurs break from their natural nesting and go join an unrelated clade by default. It will be as if these disappearing genera were never discovered or were never born (shades of Frank Capra’s “It’s A Wonderful Life”)!

Figure 1. Click to enlarge. Kyrgyzsaurus to scale alongside other basal fenestrasaurs, Cosesaurus, Sharovipteryx and Longisquama. Kyrgyzsaurus likely was a biped with long legs. We know from the shape of its coracoids that it was a flapper.

Figure 1. Click to enlarge. Kyrgyzsaurus to scale alongside other basal fenestrasaurs, Cosesaurus, Sharovipteryx and Longisquama. Kyrgyzsaurus likely was a biped with long legs. We know from the shape of its coracoids that it was a flapper.

Deletion of the Fenestrasaurs – 
If Cosesaurus, Kyrgyzsaurus, Sharovipteryx and Longisquama (Fig.1) were unknown the basal pterosaur MPUM6009 would nest between Macrocnemus and Jesairosaurus (Fig. 2) at the base of the drepanosauromorpha) leaving the large reptile tree topology unchanged.

Another Deletion –
If Macrocnemus, Jesairosaurus (Fig. 2) and the drepanosauromorpha were unknown, the pterosaur would nest with Huehuecuetzpalli (Fig. 2).

One Addition, Then Another
If only Jesairosaurus is added back in, the pterosaur would nest with it. If only Macrocnemus is added back in, the pterosaur would nest with it.

And a Final Deletion –
If Huehuecuetzpalli were unknown, the pterosaur MPUM6009 would finally “jump ship” and nest by default between Proterosuchus and Doswellia. As it turns out, the outgroup taxon to Huehuecuetzpalli, the basal lepidosaurs Tijubina and Lacertulus (Fig. 2) are not as attractive to MPUM  6009 as those archosauriforms.

So this is the breaking point. 
At this point pterosaurs move to archosauriforms, where everyone else thinks they should go, but just in the absence of good data from the above named taxa. Strangely pterosaurs don’t bounce to Scleromochlus, which is sitting there waiting…

Why Proterosuchus?
Like pterosaurs, Proterosuchus had an antorbiteal fenestra without the fossa that appeared in all more derived archosauriforms. Proterosuchus also had an asymmetric pes with a longer digit 4 than digit 3, as in basal pterosaurs. Scleromochlus doesn’t offer those traits, which is why in Bennett (1996) pterosaurs nested close to Proterosuchus after the deletion of hind limb traits. Hone and Benton (2009) nested Cosesaurus next to Proterosuchus (Fig. 3) perhaps for the same reason. Not sure about that mixed up study.

Fig. 6. Hone and Benton recovered Cosesaurus as a sister to Proterosuchus, which, on the face of it, appears unlikely.

Fig. 3. Hone and Benton recovered Cosesaurus as a sister to Proterosuchus, which, on the face of it, appears unlikely.

Recent Pterosaur Studies in the Archosauria
So now we turn to recent studies (Nesbitt 2011) in which pterosaurs nested by default between phytosaurs and Lagerpeton and Marasuchus. And Brusatte et al. (2010), in which pterosaurs nested with Scleromochlus and that clade was derived from Proterochampa and Euparkeria. None of these recent studies included Huehuecuetzpalli, Jesairosaurus, Macrocnemus and the fenestrasaurs. So it was not possible for pterosaurs to nest with their more natural, more parsimonious sisters.

Pterosaurs did not nest with Proterosuchus in Nesbitt (2011) and Bursatte et al. (2010) because the list of tested characters differed. More emphasis was placed in these two studies on archosaurian traits than generalized reptile traits, as in the large reptile tree.

Archosauriformes only
Reducing the inclusion set to just a pterosaur and all archosauriforms recovers the pterosaurs as the outgroup. Adding Mesosuchus and Prolacerta nests the pterosaur with Prolacerta… but not very well matched.

You might remember
that Witton (2013) dismissed the idea that pterosaurs could be squamates and the present tests agree with this supposition. When give the opportunity, pterosaurs do nest closer to Proterosuchus than to squamates whenever the above taxa are deleted. Unfortunately Witton (2013) omitted the fact that the Tritosauria (now containing several former prolacertiformes) nest outside the Squamata. By putting on those blinders, or not giving you all the facts, he lost his chance to confirm the nesting of pterosaurs with fenestrasaurs. Huehuecuetzpalli is the key taxon uniting the plain old basal tritosaur lizards with the wildly outrageous taxa that followed.

You may be thinking I forgot some taxa
Yes, the clade including AmotosaurusLangobardisaurus (Fig. 2), Tanytrachelos and two Tanystropheus do indeed nest between drepanosauromorphs and fenestrasaurs. At present they appear only in the large pterosaur tree, not the large reptile tree. No wonder Tanystropheus was first considered a pterosaur! Absent those other sisters (listed above), that bizarre giant would have been the closest known taxon to pterosaurs, and probably was for several decades in the 19th century.

Click to enlarge. Squamates, tritosaurs and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

Click to enlarge. Squamates, tritosaurs and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

As an aside
Earlier we looked at the deletion of all Lepidosauromorpha (one entire branch of the diphyletic Reptilia) – except the turtle Proganochelys and the pterosaur MPUM6009. Together they nested at the base of the Sauropterygia, largely due to the influence of the turtle.

Professional paleontolgists have a choice
They can either add the above taxa to pterosaur studies or pretend they never were born. So far, unfortunately, the latter paradigm rules.

References
Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoo J Linn Soc118:261–309.
Brusatte SL , Benton MJ , Desojo JB and Langer MC 2010.The higher-level phylogeny of Archosauria (Tetrapoda: Diapsida), Journal of Systematic Palaeontology, 8:1, 3-47.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

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