Mussaurus

Mussaurus patagonicus was a large herbivorous prosauropod that lived in Argentina 215 million years ago during the Late Triassic period. First specimens were discovered in 1979 by José F. Bonaparte and Martin Vince. Mussaurus means 'Mouse Lizard'. All specimens which have been discovered are of infants, complete with egg scales. Adults possibly reached 3 meters in length.

More real-life information: Mussaurus at Wikipedia.

Jurassic Park Series
Mussaurus only appears briefly in the novels and comics, it's doesn't appear in the movies or games.

The Lost World (novel)
Mussaurus is the first living dinosaur Richard Levine sees on Isla Sorna. In honour to the available data this Mussaurus is an infant.

Comics
Mussaurus appears in the Jurassic Park: Redemption series. In part 3 Dr. Backer is put in the Mussaurus cage.