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.
Find out more on the reptiles pages.