| Named By: | J. F. Bonaparte & M. Vince in 1979 |
| Time Period: | Late Triassic, 215-203 Ma |
| Location: | Argentina, Santa Cruz Province - El Tranquilo Formation |
| Size: | First juveniles ranged between 20 and 37 centimetres long. Adult specimens now known and the estimated adult size is 3 meters |
| Diet: | Herbivore |
| Fossil(s): | Initially only known from juveniles, adult specimens are now also know. |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropodomorpha | Prosauropoda | |
Mussaurus (meaning "mouse lizard") is a genus of herbivorous sauropodomorph dinosaur that lived in southern Argentina during the Late Triassic, about 215 million years ago. It receives its name from the small size of the skeletons of juvenile and infant individuals, which were once the only known specimens of the genus. However, since Mussaurus is now known from adult specimens, the name is something of a misnomer; adults possibly reached 3 m (10 ft) in length, and weighed 70 kilograms (150 lb). Mussaurus possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.