Article Prenatal development in pterosaurs and its implications for ...

Unwin and Deeming follow the invalidated hypothesis that pterosaurs were archosaurs/archosauromorphs that laid and buried their eggs at an early stage of development, much as some birds and all crocodilians do.

No citation to Peters 2000 was mentioned. Peters 2000 added several taxa (Cosesaurus, Sharaovipteryx and Longisquama among them) to three previously published analysis. The added taxa nested closer to pterosaurs. Peters 2007 reported that pterosaurs and the added taxa nested within Lepidosauria. Huehuecuetzpalli was among the outgroup taxa.

Lepidosaurs generally carry their eggs longer within the mother than birds or crocs do, sometimes until the moment of hatching. This is not only a more parsimonious hypothesis for pterosaur reproduction based on the evidence of lizard-like eggshell thickness and leathery lizardy texture in pterosaur eggs, but hypothetically hatching in open air, without the need to resurrect itself from burial is to be preferred in tiny pterosaurs with fragile, bat-like wing membranes… much more fragile than wet hatchling bird feathers found in precocial mound building birds.

Not only do workers openly admit they lack pterosaur precursors within Archosauria, birds and crocs follow an allometric growth trajectory after hatching with a short snout and large eyes. On the other hand, it is well known that pterosaurs, like other lepidosaurs, follow an isometric growth series, as documented most clearly by Zhejiangopterus and Pterodaustro. Both have juveniles with a long rostrum and small eyes, like the adults they resemble.

Unwin and Deeming identify, without phylogenetic analysis, a list of small pterosaurs the authors label juveniles. After phylogenetic analysis (citation below), many of these turn out to be small adults (Peters 2007), transitional taxa experiencing phylogenetic miniaturization to survive whatever calamity killed off their larger pterosaur sisters.

References

Bennett SC 1996. The phylogenetic position of the Pterosauria within the Archosauromorpha. Zoo. J. Linn. Soc. 118, 261–308.

Bennett SC 2012/13. The phylogenetic position of the Pterosauria reexamined. Hist. Biol. 25, 545–563.

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

Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27

Unwin DM and Deeming DC 2019. Prenatal development in pterosaurs and its implications for their postnatal locomotory ability. Proceedings of the Royal Society B https://doi.org/10.1098/rspb.2019.0409

Online cladogram of 238 taxa including small, tiny and embryo pterosaurs:

http://reptileevolution.com/MPUM6009-3.htm

Online cladogram of 1504 vertebrate taxa nesting pterosaurs within Lepidosauria:

http://reptileevolution.com/reptile-tree.htm