Illustration of a duck-billed platypus (Ornithorhynchus anatinus), 18th century. Colored etching by J. F. Cazenave after Vauthier. The platypus (Ornithorhynchus anatinus) is a semiaquatic mammal endemic to eastern Australia, including Tasmania. Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth. The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal baffled European naturalists when they first encountered it, with some considering it an elaborate hoax.