The torso of Cosesaurus, a pre-pterosaur tiny tanystropheid, ignored for 26 years

Thursday, September 10, 2026 9:43

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Middle Triassic Cosesaurus
is central to understanding the origin of pterosaurs, but you won’t learn about this in Pterosaurs 101. It has been ignored for the last 26 years. Here’s an image of the torso (Fig 1).

Figure 1. Torso and forelimbs of Middle Triassic Cosesaurus, a tiny tanystropheid and a pterosaur ancestor in the LRT.

Note the interclavicle,
clavicles and sternum before they merged to become the sternal complex, first reported by Wild 1993 for the Late Triassic pterosaur, MCSNB 8950.

Figure 2. A series of fenestrasaur and pterosaur sternal complexes scaled to a common humerus length in phylogenetic order. Colors divide the interclavicle, clavicles and sternum fused in pterosaurs. See figure 3. Click to enlarge.

Note the elongate curved coracoids.
Ventrally they articulate to the interclavicle where they are locked down enabling flapping. Dorsally coracoids raise the strap-like scapulae, again as in flapping birds and pterosaurs. This expands the muscle space between sternal complex and deltopectoral crest for flapping.

Note the aktinofibrils trailing from the forelimb. Those interweave into wing membranes that stretch from elbow to wingtip with a short fuselage fillet.

Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Unfortunately for paleontology,
Cosesaurus has been ignored and suppressed by academics even though it also has an antorbital fenestra, pteroid, prepubis and a pterosaur-like = tiny tanystropheid foot with a metapodial digit 5, all traits lacking in Scleromochlus and lagerpetids mistakenly proposed by authors as pterosaur ancestors.

Paleontologists also ignored the birds are dinosaurs hypothesis of Huxley and later Ostrom for over a century. So, this is part of the pattern. This general reticence to show a little curiosity in the pterosaur clade also has a long history.

Figure 4. Cosesaurus flapping There should be some bounce in the tail and neck, but that would involve more effort and physics.

Cosesaurus has been described by academics
as ‘poorly preserved’, but the matrix also preserves a Middle Triassic jellyfish, and a few air bubbles in addition to uropatagia and dorsal frills. Now that you’ve seen the fossil, you can decide what adjectives apply here and what motivates academics to suppress this ‘Archaeopteryx of pterosaurs’.

Links, citations, additional images here.

The above slightly expands
a Facebook post to ‘Pterosaurs Aviators of the Mesozoic‘.

References
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Ellenberger P 1978. L’Origine des Oiseaux. Historique et méthodes nouvelles. Les problémes des Archaeornithes. La venue au jour de Cosesaurus aviceps (Muschelkalk supérieur) in Aspects Modernes des Recherches sur l’Evolution. In Bons, J. (ed.) Compt Ren. Coll. Montpellier 12-16 Sept. 1977. Vol. 1. Montpellier, Mém. Trav. Ecole Prat. Hautes Etudes, De l’Institut de Montpellier 4: 89-117.
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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Peters D 2009. A reinterpretation of pteroid articulation in pterosaurs. Journal of Vertebrate Paleontology 29: 1327-1330.
Sanz JL and López-Martinez N 1984. The prolacertid lepidosaurian Cosesaurus aviceps Ellenberger & Villalta, a claimed ‘protoavian’ from the Middle Triassic of Spain. Géobios 17: 747-753.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95-120.