Temporal range: Middle Triassic
Type specimen, with adhering jellyfish
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
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]


  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.
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