Platypus

The Platypus (Ornithorhynchus anatinus) is a small, semi-aquatic mammal endemic to the eastern part of Australia, and one of the four extant monotremes, the only mammals that lay eggs instead of giving birth to live young (the other three are echidnas). It is the sole representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of fossilised relatives have been found, some of them also in the Ornithorhynchus genus.

The scientific name Ornithorhynchus literally means 'bird nose' in Greek, and anatinus means 'duck'. The common name means 'flat foot' and was originally given to it as a Linnaean genus name, but it was discovered to already belong to the wood-boring ambrosia beetle.

Anatomy

Size varies considerably between less than a kilogramme and over two kilogrammes; with body length ranging from 30 to 40 centimetres, and tail length from 10 to 15 centimetres. Males are around one-third larger than females. There is substantial variation in average size from one region to another, though oddly this pattern does not seem to follow any particular climatic rule.

The male Platypus has venomous ankle spurs, used in vicious territorial battles and fights over mates. 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.

Modern Platypus young have tribosphenic 'three-cusped' molars, which are one of the hallmarks of mammals; adults are toothless. The Platypus jaw is constructed somewhat differently from that of other mammals, and the jaw opening muscle is different. As in all true mammals, the tiny bones that conduct sound to the inner ear are fully incorporated into the skull, rather than lying in the jaw as in cynodonts and other pre-mammalian synapsids. However, the external opening of the ear still lies at the base of the jaw. The Platypus has extra bones in the shoulder girdle, including an interclavicle, which is not found in other mammals. It also has a reptile-like gait, with legs that are on the sides of rather than underneath the body.

The physiology of the Platypus is unique. The metabolic rate is remarkably low compared to other mammals, with a body temperature averaging 32 degrees Celsius (90 degrees Fahrenheit) rather than the 38 degrees Celsius (100.4 degrees Fahrenheit) typical of placental mammals. The extent to which this is a characteristic of monotremes, as opposed to an adaptation on the part of the small number of surviving species to harsh environmental conditions, is uncertain.

Ecology and behaviour

The Platypus 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 sight. It is one of the few mammals known to have a sense of electroception: it locates its prey in part by detecting their body electricity. Its electroception is the most sensitive of any mammal.

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. The eggs are retained in the body for some time before they are laid, nourished actively by the parent. When the eggs hatch after an incubation period of roughly ten days, the small hairless babies cling to the mother. Like other mammals, the mother produces milk for the young. The Platypus does not have nipples, but excretes the milk through pores in her skin. The young suck milk up from the mother's belly while she lies on her back.

Scientific history

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. This is a very difficult task, and only a few young have been successfully raised since &emdash; notably at Healesville Sanctuary in Victoria.

Seeing a Platypus in the wild is more a matter of luck and of patience than of difficulty. They tend to dislike populated areas, spend almost all their time underground or under water, and are primarily nocturnal. However, they are not especially uncommon, and in suitable areas most keen anglers or birdwatchers see a Platypus feeding quietly along a riverbank every year or two.

The Platypus does not appear to be in immediate danger of extinction. It is variously classified as secure but faces future threat or common but vulnerable, mainly because the species is sensitive to water pollution.

The Platypus in mammalian evolution

This article is about the monotreme mammal. For the genus Platypus see ambrosia beetle. Also, Platypus is the name for a side project featuring John Myung, from Dream Theater, Derek Sherinian, former Dream Theater member, Ty Tabor, from King's X, and Rod Morgenstein.