Unenlagia (meaning "half-bird") was a genus of theropod dinosaur of the family Dromaeosauridae. Unenlagia, which lived in South America during the Late Cretaceous, was a member of the strange and extremely bird-like Gondwanan sub-family of dromaeosaurs called unenlagiines, and was closely related to dinosaurs such as Buitreraptor and Neuquenraptor (which might be the same species as Unenlagia). Makovicky (2005) suggested that the 'flying raptor' Rahonavis is also a member of this group, which could mean that Unenlagia is secondarily flightless, having evolved from flying, Rahonavis-like ancestors.

Unenlagia was very birdlike itself. Novas and Puerta (1997) found its pelvic region to be very similar to that of the early bird Archaeopteryx. The shoulder girdle of Unenlagia also shows adaptations for flapping and, since at 2 meters (6 feet) long Unenlagia was probably too big to fly, this provides further evidence that it evolved from flying ancestors.