Diplosaurus is an extinct genus of goniopholidid mesoeucrocodylian. Fossils have been found from the western United States and range from Late Jurassic to Early Cretaceous in age. The genus was first named and described in a paper written in 1877 by Othniel Charles Marsh. In it, Marsh recombined Hyposaurus vebbii, named by Edward Drinker Cope, with a new species, Diplosaurus vebbi. Along with D. vebbi, another new species was constructed in 1877 by Marsh after he reassigned "Goniopholis" felix to Diplosaurus and named D. felix. D. nanus was named by Marsh in 1895 but is now considered to be a nomen dubium. In 1999, Diplosaurus felise was named on the basis of a specimen found in Lakes' Quarry 1 at Como Bluff, Wyoming, part of the Morrison Formation.