When pterosaurs essentially went back to their roots = big reversals

At the transition between the Jurassic and Cretaceous
tiny pterosaurs (Fig 1), the size of their Middle Triassic ancestor, Cosesaurus (Fig 1) were the ones that somehow survived that chronological transition, thereafter growing in size into the wide variety of middle-to-large-to-giant pterosaurs we are most familiar with.

Figure 1. Some of the smallest pterosaurs, the products of phylogenetic miniaturization, here compared to their Middle Triassic ancestor, Cosesaurus. ” data-image-caption=”

Figure 1. Some of the smallest pterosaurs, the products of phylogenetic miniaturization, here compared to their Middle Triassic ancestor, Cosesaurus.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/08/no9no31-588.jpg?w=135″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/08/no9no31-588.jpg?w=462″ tabindex=”0″ role=”button” class=”size-full wp-image-88037″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/08/no9no31-588.jpg” alt=”Figure 1. Some of the smallest pterosaurs, the products of phylogenetic miniaturization, here compared to their Middle Triassic ancestor, Cosesaurus. ” width=”584″ height=”1295″ />

Figure 1. Some of the smallest pterosaurs, the products of phylogenetic miniaturization, here compared to their Middle Triassic ancestor, Cosesaurus.  Even their skulls were quite similar to that of Cosesaurus. All these lepidosaur taxa flapped their forleimbs, but could drop down to all fours at will, unlike birds.

You’ll note the long metacarpals,
and reduced tail in the tiny Late Jurassic pterosaurs. The naris is still separate from the antorbital fenestra. Pedal digit 5 can be reduced, but not as much as in derived pterodactylids and germanodactylids, also from the Late Jurassic.

That means you didn’t have to be tiny to survive, but you had to have tiny rather recent ancestors, and whatever benefit that phylogenetic miniaturization provided.

In the in the large pterosaur tree
(LPT, 263 taxa). sharp-snouted germanodactylids were ancestral to sharp-snouted pterandontids, tapejarids, shenzhoupterids, and tapejarids. Toothy scaphognathids were ancestral to ornithocheirids. cycnorhamphids, pterodactylids and sharp-snouted germanodactylids. Toothy dorygnathids were ancestral to primitively toothy azhdarchids and super-toothy ctenochasmatids (Peters 2007).

Prior pterosaur cladograms,
beginning with Kellner 2003 and Unwin 2003, omitted tiny pterosaurs and so missed the key factor in the evolution of pterosaur clades: phylogenetic miniaturization. They also omitted Cosesaurus and kin for outgroups.

Today’s blogpost was inspired by
the resemblance finally noted between Cosesaurus and tiny phylogenetically miniaturized, neotonous tiny pterosaurs. That is why reconstructions can be more helpful than roadkill fossils.

Tiny Late Jurassic pterosaurs
(Fig 1) appear to have pulled some of their traits from long-ignored genes in a process called reversa. As in odontocete teeth, the whole organism doesn’t reverse. Only those parts that do reverse, including overall size.

This is not neotony,
except perhaps with regard to retention of embryonic features, because hatchling and juvenile pterosaurs had adult proportions.

References
Kellner AWA 2003. Pterosaur phylogeny and comments on the evolutionary history of the group. Pp, 105-137 in: Buffetaut E and Mazin JM (Eds) – Evolution and palaeobiology of pterosaurs: Geo. Soc. Sp. Pub. 217.
Peters D 2000b. 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. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Unwin DM 2003. On the phylogeny and evolutionary history of pterosaurs. Pp. 139-190 in: Buffetaut E and Mazin JM (Eds) – Evolution and Palaeobiology of Pterosaurs. Geo. Soc. Sp. Pub. 217.