The “mouse lizard,” Mussaurus was discovered at the El Tranquilo Formation in Santa Cruz, Argentina, and was described and named by José F. Bonaparte and Martin Vince in 1979. Mussaurus was a prosauropod that lived in the Late Triassic period about 215 million years ago. Its name is rather misleading, but there is a reason for this: the original skeleton, which was very small, was from an infant about 6 inches long. At the largest, Mussaurus actually grew to 26 ft (7.9 m) in length, 10 ft (3 m) in height, and could weigh up to 2 tons (1.78 tonnes).
Richard Levine encountered a Mussaurus patagonicus on Isla Sorna, the first living dinosaur he encountered. However, the novel seems to present this animal as being a fully-grown adult even though it was small enough to fit in Levine’s hand. As it is now known that the actual animal grew much larger than this, we are give no choice but to assign a modified name to Isla Sorna’s populations of Mussaurus.