Mussaurus (meaning "mouse lizard") is a genus of herbivorous prosauropod dinosaur that lived in southern Argentina during the Late Triassic, about 215 million years ago. It gets 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,[1] the name is something of a misnomer; adults possibly reached 3 m (10 ft) in length, and weighed 70 kilograms (150 lb).[2] Mussaurus possesses anatomical features suggesting a close, possibly transitional evolutionary relationship with true sauropods.


Infant and juvenile fossils of Mussaurus were first discovered by an expedition led by Jose Bonaparte during the 1970s to the El Tranquilo Formation.[3] There the team found fossilized eggs and hatchlings, which added insight into the reproductive strategies of Mussaurus and other prosauropod dinosaurs.[3] The first adult specimens of Mussaurus were described in 2013. Some of these specimens had first been described in 1980 and were originally attributed to the genus Plateosaurus.


Previous to the discovery of adult specimens of Mussaurus, the phylogenetic position of this taxon was difficult to establish. Infant and juvenile fossils are known to show more basal traits than adult specimens of the same taxon. Furthermore, the recently discovered one subadult and three adult specimens assigned to Mussaurus are more complete than other material assigned to it. Therefore, a cladistic analysis of basal sauropodomorphs performed by Otero and Pol (2013) to test the phylogenetic relationships of Mussaurus, included information only from adult specimens. The following cladogram is simplified after their analysis (relationships outside Plateosauria aren't shown).



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