Othnielia (meaning “of Othniel”) is a genus in the clade of Neornithischia from the Late Jurassic in what is now the Morrison Formation in western United States. It was named by Othniel Charles Marsh in 1877 as Nanosaurus rex. In 1977, however, Peter Galton renamed it Othnielia rex, to honor Marsh. It is only about 5 to 7 feet (1.5 to 2 meters) in length. In 2001, Kathleen Brill and Kenneth Carpenter said they have discovered a juvenile specimen of Othnielia, however it cannot be fully determined if it belongs to Othnielia.