Dimetrodon (n.)

extinct reptile-like animal of the Permian period, best-known for the large spine-sail on its back but named for its large teeth of different sizes, by 1878, literally "two measures of teeth," from Latinized form of Greek di- "two" (see di- (1)) + metron "measure" (from PIE root *me- (2) "to measure") + odonys "tooth" (from PIE root *dent- "tooth").