Fauna of Australia species are nocturnal and many arboreal. Two of the five living species of monotreme occur in Australia: the platypus and the short-beaked echidna. The monotremes differ from other mammals in their methods of reproduction; in particular, they lay eggs instead of giving birth to live young. The platypus—a venomous, egg-laying, duck-billed amphibious mammal—is considered to be one of the strangest creatures in the animal kingdom. When it was first presented by Joseph Banks to English naturalists it was thought to be so strange that it was a cleverly created hoax. The short-beaked echidna is similarly strange, covered in hairy spikes
Mammal contain their [[fetus]] during gestation periods. A narrow pelvic outlet indicates that the young were very small at birth and therefore [[Pregnancy (mammals)|pregnancy]] was short, as in modern marsupials. This suggests that the placenta was a later development. One of the earliest known monotremes was "[[Teinolophos]]", which lived about 120 million years ago in Australia. Monotremes have some features which may be inherited from the original amniotes such as the same orifice to urinate, defecate and reproduce ([[cloaca]]) – as lizards and birds also do – and they lay [[Egg (biology)|eggs]] which are leathery and uncalcified. "Hadrocodium", whose fossils date