Alvarezsaurus (IPA: ; "Alvarez's lizard") was a small alvarezsaurid dinosaur from the Late Cretaceous period of Argentina, approximately 89 - 85 million years ago. Estimates suggest that it measured about 2 metres in length and weighed approximately 20 kg. It was found in the Bajo de la Carpa Formation and was named by paleontologist José Bonaparte in 1991 after the historian Don Gregorio Alvarez.