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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
The body and the broad, flat tail of the Platypus are covered with brown fur. It has webbed feet and a large, rubbery snout
that are more reminiscent of a duck than any other known mammal. (This has led to it being
known as the 'Duckbilled Platypus'. Early British settlers called it the 'Water Mole'.)
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 nocturnal and semi-aquatic, 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 be absent from
some relatively healthy rivers, and yet maintains a presence in others that are quite degraded (the lower Maribyrnong, for example).
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
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. This is a very difficult task, and only a few young have been
successfully raised since. (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
The Platypus and other monotremes were very poorly understood for many years, and to this day some of the 19th century myths
that grew up around them endure, particularly in the northern hemisphere. It is still sometimes thought, for example, that the
monotremes are 'inferior' or quasi-reptilian, and that they are the distant ancestor of the 'superior' placental mammals. It is now known that modern monotremes are the survivors of an
early branching of the mammal tree; a later branching is thought to have led to the marsupial and placental groups. The oldest fossils of monotremes
(Teinolophos and Steropodon) are closely related to the modern Platypus. In summary, the Platypus is one of the closest relatives
of ancestral mammals, but not itself a link in the chain of mammalian evolution. It is a branch quite separate from any other
known one.
- 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.
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