Unenlagia, meaning “half-bird,” is a genus of theropod dinosaur from the Late Cretaceous Period, and lived in what is now South America. It was a member of the extremely bird-like Gondwanan sub-family dromaeosaurs called unenlagiines, and was closely related to dinosaurs such as Buitreraptor and Neuquenraptor (which may be the same species as Unenlagia).

It has been suggested by Peter J. Makovicky et al. that the flying raptor Rahonavis is also a member of this group, which would mean that either Unenlagia is secondarily flightless, having evolved from flying, Rahonavis-like ancestors, or that bird-like flight evolved at least twice. Rahonavis was also found to be a sister taxon of Unenlagia.

Unenlagia was very bird-like itself. Its pelvic region is very similar to that of the early bird Archaeopteryx. Its shoulder girdle also shows adaptations for flapping. At 6.6 feet long, Unenlagia was most likely to big to fly, meaning it either evolved from flying ancestors, or Rahonavis evolved flight from adequately adapted dromaeosaurs independently of the Archaeopteryx lineage, at a time when other bird lineages were already undergoing vigorous adaptive radiation.

Two species have been assigned to Unenlagia: U. comahuensis, the type species, described in 1997 by Novas and Puerta; and U. paynemili, described by Calvo et al. in 2004.

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