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Temporal range: Middle Triassic
Type specimen, with adhering jellyfish
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Clade: Archosauromorpha
Order: Protorosauria
Genus: Cosesaurus
Ellenberger & de Villalta 1974
Species: † C. aviceps
Binomial name
Cosesaurus aviceps
Ellenberger & de Villalta 1974

Cosesaurus is a genus of protorosaur archosauromorph reptile. It is known from a single, hand-sized fossil from the middle Triassic period of Spain.

In 1977, Ellenberger proposed that Cosesaurus was an ancestor of modern birds.[1] That publication followed the description of the bird-like theropod, Deinonychus, but it appeared long before the theropod ancestry of birds had been widely accepted. In his large and highly detailed treatise, Ellenberger interpreted the following traits in the fossil: a strap-like scapula, a furcula (wishbone), a keeled sternum, beak-like jaws, a retroverted pubis and tail feathers. Some of these interpretations have not been supported by subsequent research. Padian and Chiappe (1998) regarded Cosesaurus as a member of the archosauromorph clade Prolacertiformes.[2]

The independent researcher David Peters found that Cosesaurus nested with Sharovipteryx, Longisquama and pterosaurs in a clade, the "Fenestrasauria",[3][4]though at least his inclusion of pterosaurs in this group has not been supported by any other researchers, who criticized his methods as flawed and pseudoscientific.[5][6]


  1. ^ Ellenberger, P.-P. (1977). "Quelques precisions sur l'anatomie et la place systematique tres speciale de Cosesaurus aviceps (Ladinien superieur de Montral, Catalogne)". Caud. Geologica Iberica 4: 169–188. 
  2. ^ Padian, K.; Chiappe, L.M. (1998). "The origin and early evolution of birds". Biol. Rev. 73: 1–42. doi:10.1017/S0006323197005100. 
  3. ^ Peters, D. (2000b). "A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis". Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336. 
  4. ^ Hone, D.W.; Benton, M.J. (2007). "An evaluation of the phylogenetic relationships of the pterosaurs among archosauromorph reptiles". Journal of Systematic Palaeontology 5 (4): 465–469. doi:10.1017/S1477201907002064. 
  5. ^ Nesbitt, S.J. (2011). "The early evolution of archosaurs: relationships and the origin of major clades". Bulletin of the American Museum of Natural History 352: 1–292. doi:10.1206/352.1. 
  6. ^ Naish, Darren. "Why the world has to ignore". Scientific American.