This streamlined and mainly aquatic monotreme has dense, short brown fur, a leathery bill and webbed feet.
The female Platypus lays two leathery eggs in a burrow, which it digs in the stream bank.
When the young hatch, they feed on milk, which the mother exudes through pores on her abdomen.
Males have a poison spur on the hind leg, which can inflict a painful wound to intruders.
The eyes are closed when swimming underwater and the Platypus relies on its sensitive bill to detect prey which includes larval mayflies, caddis flies and small molluscs. Highly developed touch and electricity-sensing cells, enable the Platypus to feed at night or in murky water.
The Platypus is still common even in streams and rivers close to cities, despite sewage, insecticides, fishing nets, and increased water temperatures.
Fossil platypus material has been recognised from the Australian continent for many years. It includes material from Lake Palankarinna, South Australia, Riversleigh in Queensland and Lightning Ridge. In addition, there is an as yet unnamed fossil monotreme from Dinosaur Cove.
In 1991 the discovery of a molar tooth from an early Palaeocene South American Platypus in sediments from Patagonia, Argentina was significant in that it provided new links between South America and Australia.
Until they separated from Antarctica in the early Tertiary, both contained mainly elements of Gondwanan biotas. After the separation, Australia failed to establish any continuous land bridge with the north, while South America had brief connections with North America, Africa and Antarctica allowing for the invasion of other mammal groups, possibly leading to its extinction.