Clevosaurs are an extinct group of rhynchocephalian reptiles from the Triassic and Jurassic periods.

In the late 1990s, Victor-Hugo Reynoso established that three particular genera of Sphenodontia (Clevosaurus, Brachyrhinodon, and Polysphenodon) were closely related to each other.

In 2006, Bonaparte and Sues finally gave "clevosaurs" a formal name and taxonomic rank as the family Clevosauridae.

[3] Clevosaurs were among the first major groups of sphenodontians to evolve, and had a worldwide distribution in the Late Triassic and early Jurassic.

Like other rhynchocephalians, they possessed two pairs of large holes called temporal fenestrae in the back part of the skull.

[4] Below is a cladogram of the relationships within Clevosauridae based on the phylogenetic analysis of Hsiou et al. (2015):[2] Polysphenodon mulleri Brachyrhinodon taylori Clevosaurus "Clevosaurus" latidens was recovered outside of Clevosauridae, as the sister taxon of Opisthodontia.