Alvarezsaurus

Alvarezsaurus calvoi Temporal range: Late Cretaceous, 86–83 Ma PreЄ Є O S D C P T J K Pg N ↓
Skeleton restoration
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Family:	†Alvarezsauridae
Genus:	†Alvarezsaurus Bonaparte, 1991
Species:	†A. calvoi
Binomial name
Alvarezsaurus calvoi Bonaparte, 1991

Alvarezsaurus (/ˌælvərɛzˈsɔːrəs/; "Alvarez's lizard") is a genus of small alvarezsaurid dinosaur from the Late Cretaceous period of Argentina, approximately 86 - 83 million years ago. Estimates suggest that it measured about 2 meters (6.5 ft) in length and weighed approximately 20 kg (45 lbs). Gregory S. Paul estimated in 2010 its weight at 3 kg and length at 1 m. 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. The type species is A. calvoi.

Alvarezsaurus was bipedal theropod. Like other lightweight theropods, it had a long tail, and its leg structure suggests that it was a fast runner. The most proximal elements of Alvarezsaurus caudal vertebrae exhibited ventrally sharp centra and the transerve processes of these vertebrae were sub-triangular and laterodistally directed, features seen in other alvarezsaurids like Shuvuuia. Spinal processes were entirely absent or poorly developed, and each caudal vertebra supported short prezygapophyses. The scapula was visibly curved and proportionally smaller than those of other alvarezsaurids, and unlike its relatives Alvarezsaurus did not have a fused astragalus and calcaneum. It was unique in that its metatarsal III was its longest, followed by an unusually long metatarsal IV. It may have been insectivorous.