Monotremes are the only mammals that lay eggs

Monotremes constitute an order of exceptional mammals because they are the only ones in the world to lay eggs. This peculiarity is shared by the short-beaked echidna and its cousin the platypus, classified in the Ornithorhynchidae family. The echidna has moreover undergone four revisions of its name since its initial description in 1792 by George Kearsley Shaw.