Monotremes are the only living mammals that lay eggs, rather than give birth to live offspring. Despite their egg-laying reproductive strategy, like other mammals, monotremes are warm blooded, produce milk and have hair on their bodies. The most famous species of monotreme is the platypus, a duck billed, beaver tailed, and otter footed native of eastern Australia. The platypus perplexed zoologists upon their discovery, and even to this day, the evolution of the platypus is not well understood. The other 4 surviving monotreme species, the echidnas, bear almost no similarity to the platypus, and more strongly resemble other mammals. It remains a mystery why monotremes retained the ability to lay eggs, while other mammals are placental or marsupial.