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 referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. "[[Ambondro mahabo|Ambondro]]" is more closely related to monotremes than to therian mammals while "[[Amphilestes]]" and "[[Amphitherium]]" are more closely related to the therians; as fossils of all three genera are dated about in the [[Middle Jurassic]], this is a reasonable estimate for the appearance of the crown group. T. S. Kemp has provided a more traditional definition: "[[synapsid]]s that possess a