The Platypus looks rather like a beaver: the body and broad, flat tail are covered with brown fur, but it has webbed feet and a large, rubbery snout that that led to it being known as the "Duckbilled Platypus" for a time. Size varies considerably between less than a kilogram and over two kilograms; length from 30 to 40 cm, and the tail from 10 to 15 cm. Males are usually about one-third larger than females, and there is substantial variation in average size from one area to another which, oddly, does not seem to follow any particular climatic rule.
The male Platypus has venomous ankle spurs. The poison is not lethal to humans but produces excruciating pain and swelling that may last for several months. The venom can be lethal to dogs and smaller domestic animals.
The Platypus is a semi-aquatic animal, inhabiting small streams and rivers over an extensive range from the cold highlands of Tasmania and the Australian Alps to the tropical rainforests of coastal Queensland as far north as the base of the Cape York Peninsula. Inland, its distribution is not well known: it is extinct in South Australia (bar an introduced population on Kangaroo Island) and is no longer found in the main part of the Murray-Darling Basin, probably because of the declining water quality brought about by extensive land clearing and irrigation schemes. Along the coastal river systems, its distribution is unpredictable: it appears to absent from some relatively healthy rivers, and yet maintains a presence in others that are quite degraded (the lower Maribyrnong, for example).
It is an excellent swimmer and spends much of its time in the water. It keeps its eyes tightly shut when swimming, relying completely on its other senses. All four feet of the Platypus are webbed. When it swims, it propels itself by paddling with the front two feet. The tail and hind feet assist in steering but not propulsion.
The Platypus is a carnivore. It feeds on worms and insect larvae, freshwater shrimps, and yabbies (freshwater crayfish) that it digs out of the river bed with its snout or catches while swimming. Its bill is very sensitive, allowing it to hunt its food without using its eyesight. The Platypus is the only mammal that has a sense of electroception: it locates its prey in part by detecting their body electricity.
When not in the water, the Platypus retires to a short, straight burrow of oval cross-section, nearly always in the riverbank not far above water level, and often hidden under a protective tangle of roots. For breeding, the female digs much larger and more elaborate burrows, up to 20 metres long and blocked with plugs at intervals. She fills the nest at the end of the tunnel with reeds for bedding material.
As a monotreme, the Platypus does not give birth to live young but instead lays eggs in its nest. When the eggs hatch, the small babies emerge and cling to the mother. Like other mammals, the mother produces milk for the new babies. The Platypus does not have apparent external nipples, but excretes the milk through small openings in the skin. The young Platypus sucks the milk up from the mother's belly while she is lying on her back.
When the Platypus was first discovered by Europeans in the late 1700s, a pelt was sent back to Britain for examination by the scientific community. The British scientists were at first convinced that the seemingly-odd collection of physical attributes must be a hoax, produced by some Asian taxidermist.
Much of the world was introduced to the Platypus in 1939 when National Geographic magazine published an article on the Platypus and the efforts to study and raise it in captivity (a very difficult task, and only a few young have been successfully raised since). The main reference on the Platypus today is The Platypus - a Unique Mammal written by Tom Grant.
Whilst not a common sight, due to its aquatic, burrowing habits and dislike of populated areas, the Platypus does not appear to be in immediate danger of extinction: it is classified as vulnerable. Like most aquatic animals, it is quite sensitive to water pollution.
The scientific name ornithorhynchus literally means "bird nose" in Greek, and anatinus refers to "duck". The common name "platypus" (flat foot) was originally given to it as a Linnaean genus name, but was discovered to already belong to an obscure invertebrate, a type of beetle.