Aucasaurus was a genus of medium-sized theropod dinosaur from Argentina that lived during the Santonian - Campanian stage of the Anacleto Formation. It was smaller than the related Carnotaurus, although more derived in some ways, such as its extremely reduced arms and almost total lack of fingers.The type skeleton is complete to the thirteenth caudal vertebra, and so is relatively well understood, and is the most complete abelisaurid yet described. However, the skull is damaged, causing some paleontologists to speculate that it was involved in a fight prior to death.