The type species is A. calvoi. It was bipedal, had a long tail, and its leg structure suggests that it was a fast runner. It may have been insectivorous and was basal to better-known members of its family, such as Mononykus and Shuvuuia. It has been alternately classified with both non-avian theropod dinosaurs and early birds.
In popular culture
Alvarezsaurus was featured in the Discovery Channel television series Dinosaur Planet, where it was presented as a predator of young Saltasaurus. However, these genera did not coexist, Alvarezsaurus being approximately 5 million years older than Saltasaurus.