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.