| Named By: | W. E. Swinton in 1939 |
| Time Period: | Late Triassic-Early Jurassic |
| Location: | Belgium. Brazil. Canada. China. England. Luxembourg. South Africa. USA. Wales |
| Size: | Small, but eact meaurements depend upon the species |
| Diet: | Insesctivore |
| Fossil(s): | Numerus individuals |
| Classification: | | Chordata | Reptilia | Diapsida | Lepidosauria | Sphenodontia | Sphenodontidae | Clevosaurus | |
| Also known as: | | Dianosaurus | Glevosaurus | |
Clevosaurus (CLEE-vo-SORE-us) (Gloucester lizard) is an extinct genus of sphenodontian reptile from the Triassic and the Jurassic periods of Nova Scotia, Great Britain, (C. bairdi) and Yunnan (C. mcgilli). Clevosaurus was extremely similar to the modern tuatara in almost every way; the two genera differ in only certain features of the teeth and skull anatomies, as well as size. Clevosaurus was smaller than the modern tuatara. Clevosaurus possibly ate plants as well as insects, as suggested by the form of the teeth. Fossils of Clevosaurus, as well as other sphenodontians, early mammals and dinosaurs have been found in ancient cave systems of Great Britain. Clevosaurus is now believed to have had Pangaean distribution.