Unquillosaurus (meaning "Unquillo river lizard") is a genus of large theropod dinosaur from the Late Cretaceous Los Blanquitos Formation of Salta Province, Argentina.

[1] The specimen, which consists of a left pubis measuring 51.4 centimetres (1 ft 8.2 in) long, was re-studied by Fernando Novas and Federico Agnolin in 2004, who concluded that the orientation of the pubis had been misinterpreted: it pointed backwards, as was shown by the fossil still being attached to a displaced part of the pubic peduncle of the ilium.

The generic name, "Unquillosaurus," is derived from the river Unquillo and the Greek word, "sauros," meaning "lizard."

[2] In 2004, Novas and Agnolín concluded from the opisthopubic pelvic anatomy that Unquillosaurus was part of the Maniraptora or at least Maniraptoriformes, and likely closely related to either the Avialae or the bird-like Alvarezsauridae; perhaps it was itself a bird, a basal member of the Metornithes.

[4] In 2013, Agnolín and Novas interpreted Unquillosaurus as a very large averaptoran instead, suggesting that the distal pubis shows condition of a coelurosaur and different from that of a carnosaur.