Monotremes are mammals that lay eggs instead of giving birth to live young like marsupials and placental mammals. There are only a few surviving representatives of the order on the planet, and all of them are concentrated in Australia and New Guinea. Such Australian animals as the platypus and 4 species of echidnas are the existing examples of monotreme species. Many people know about them, as they are considered one of the symbols of the Australian animal kingdom. Such their feature as laying eggs is less known and remains quite an interesting piece of trivia.

More Info: en.wikipedia.org