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. The generic name, derived from Greek διπλόος, diploos, "double", probably refers to the "biconcave vertebrae" Marsh mentions as a distinctive trait compared to modern forms. The type species is Diplosaurus felix.