Any of three living species of egg-laying platypus and two species of echidna .
Monotremes are found only in Australia, Tasmania, and New Guinea. Except for their egg laying, they have mammalian characteristics, such as mammary glands, hair, and a complete diaphragm. They lack teats; the young suck milk through pores on the mother's skin. The earliest fossil monotremes, found in Australia, are only about 2 million years old and differ little from present species. Monotremes probably originated from a line of mammal-like reptiles different from the line that gave rise to placental mammals and {{link=marsupial">marsupials .