Like reptiles, Monotremes have posterior end of the intestine, ducts of the excretory system and genital ducts all emptying into a common chamber called a cloaca. The platypus is confined to eastern Australia and Tasmania. It inhabits permanent streams and some lakes with banks that are easily burrowed. Once almost extinct, the platypus is now repopulating areas since new anti-hunting laws are in effect. Echidna, or spiny anteaters, are distributed across Australia, New Guinea and Tasmania.
Habitats vary from semi-arid to alpine.
The fossil record of the monotremes has changed little in the last 10 million years. The logical assumption is that monotremes are an old, specialized offshoot of an early mammal stock that has survived only by being isolated in the Australian area. Platypus have short limbs and a body length between 39-60 cm. Adults weigh between 2.5 and 8 kg. Water proof fur helps insulate against cold temperatures.