This is one of the rarest and most obscure specimens in our collections. Opisthias was a lizard-like reptile known as a sphenodont. Only one genus of sphenodont survives to the present day, and that is the Tuatara of New Zealand. Like all reptiles, note how the jaw is populated with a row of identical teeth. This is one thing that separates mammals from reptiles, as mammals have different types of teeth that perform different functions.
