Cosesaurus pycnofibers, frills, membranes and hair

It is well known that pterosaurs were hairy
After all, Sordes is the “hairy devil.” The origin of pterosaur pycnofibers (ptero-hair) is the topic of this post. We covered the extradermal fibers on Sharovipteryx and Longisquama earlier here and here. Today we feature yet another hairy lizard and a sister to the ancestor of all three higher fenestrasaurs.

As reported earlier here and here, no one has done more work on the basal fenestrasaur, Cosesaurus aviceps than Dr. Paul Ellenberger (1993). Unfortunately Dr. Ellenberger’s bias towards birds blinded him to the pterosaur-like interpretations that would have revealed the prepubis, pteroid, quadrant-shaped coracoid and other pterosaur-like traits that he traced, but did not correctly interpret. On the other hand, Dr. Ellenberger did a good job of tracing the various extradermal membranes found around the sole specimen of Cosesaurus (Fig. 1). I use his illustration (Ellenberger 1993) to show that I am not the only one seeing these traces.

Cosesaurus fibers, frills and membranes. Here the same extradermal membranes found in Sharovipteryx, Longisquama and pterosaurs are found here.

Figure 1. Cosesaurus fibers, frills and membranes. Here the same extradermal membranes found in Sharovipteryx, Longisquama and pterosaurs are found here. I’m using Ellenberger’s interpretation because mine are sometimes considered suspect.

Skull and Dorsal Fibers/Frills
A single row of fibers grading into frills tops the cranium and extends to at least the sacral area. These are homologous to the same structures in Huehuecuetzpalli, Macrocnemus, Iguana and Sphenodon. These structures reach an acme with Longisquama.

Tail Fibers
Ellenberger considered these the quills of primitive feathers. These fibers ultimately coalesce to become a tail vane in derived pterosaurs.

Arm Fibers
Posterior to the ulna are fibers that ultimately become a wing membrane in Longisquama and pterosaurs.

Leg Fibers
Anterior to the knee are fibers that are homologous to pycnofibers of pterosaurs. These are likely decorative and insular.

Posterior to the legs are decorative frill/membranes that ultimately become the gliding membranes in Sharovipteryx, Longisquama and, to a lesser extent, in pterosaurs.

Not sure if we’ll find fibers prior to Cosesaurus. Its seems that Langobardisaurus has been too thoroughly prepared to ever know this and it has scales. Jesairosaurus does not preserve hairs and it was a lethargic type rather than a hyper-active taxon like Cosesaurus (remember the flap over flapping?).

In letters to a previous post, J. Headden questioned the identity of fiber-like shapes found in the neck skin of Sharovipteryx. With Cosesaurus having fibers and Longisquama having fibers and pterosaurs having fibers, phylogenetic bracketing (in spite of or in support of the fossil evidence) indicates that Sharovipteryx also had fibers.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

Ellenberger P 1993. 
Cosesaurus aviceps. Vertébré aviforme du Trias Moyen de Catalogne. Étude descriptive et comparative. Mémoire Avec le concours de l’École Pratique des Hautes Etudes. Laboratorie de Paléontologie des Vertébrés. Univ. Sci. Tech. Languedoc, Montpellier (France). Pp. 1-664.

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