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 the metatherian "Sinodelphys", both dated to 125 million years ago. [[Epipubic]] bones, a feature that strongly influenced the reproduction of most mammal clades, are first found in [[Tritylodontidae]], suggesting that it is a synapomorphy between them and [[mammaliformes]]. They are omnipresent in non-placental mammaliformes, though "[[Megazostrodon]]" and "[[Erythrotherium]]" appear to have lacked them. It has been suggested that the original function of [[lactation]] ([[milk]] production) was to keep eggs moist. Much of the argument is based on monotremes, the egg-laying mammals. Therian mammals took over the medium- to large-sized ecological niches in the [[Cenozoic]], after the [[Cretaceous–Paleogene extinction event]] approximately