Platypus

For other uses, see Platypus (disambiguation).

Platypus
File:Ornithorhynchidae-00.jpg
Conservation status
Least Concern
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Monotremata
Family:	Ornithorhynchidae
Genus:	Ornithorhynchus Blumenbach, 1800
Species:	O. anatinus
Binomial name
Ornithorhynchus anatinus (Shaw, 1799)
Platypus range

The platypus (Ornithorhynchus anatinus) is a 39–60 cm long, semi-aquatic mammal endemic to eastern Australia and Tasmania, and one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young (the other four are echidnas). It is the sole extant 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.

This egg-laying, duck-billed mammal whose males have a venomous spur on the hind foot, baffled naturalists when it was first discovered. The uniqueness of the platypus makes it a recognizable symbol of Australia (along with the kangaroo and koala); it is featured on the reverse of the Australian 20-cent coin.

Taxonomy and etymology

When the platypus was first discovered by Europeans in the late 1700s, a pelt was sent back to the United Kingdom. The British scientists were at first convinced that the odd collection of physical attributes must be a hoax. George Shaw, who produced the first description of the animal in the Naturalist's Miscellany in 1799 stated that it was impossible not to entertain doubts as to its genuine nature, and Robert Knox believed it may been produced by some Asian taxidermist. It was thought that somebody had sewn a duck's beak onto the body of a beaver-like animal. Shaw even took a pair of scissors to the dried skin to check for stitches.

An early colour print of platypus from 1863

The common name, platypus, is Latin derived from the Greek words πλατύς ("platys", flat) and πους ("pous", foot), meaning "flat foot" and was originally given to it as a Linnaean genus name by Shaw when he initially described it, but it was discovered to already belong to the wood-boring ambrosia beetle (genus Platypus). It was independently described as Ornithorhynchus paradoxus by Johann Blumenbach in 1800 (from a specimen given to him by Sir Joseph Banks) and following the rules of priority of nomenclature it was later officially recognised as Ornithorhynchus anatinus. The scientific name Ornithorhynchus is derived from ορνιθόρυγχος ("ornithorhynkhos"), which literally means "bird snout" in Greek, and anatinus which means "duck-like".

There is no universally agreed upon plural of "platypus" in the English language. Scientists generally use "platypuses", "platypoda", or simply "platypus". Colloquially, "platypi" is also used for the plural, although this is pseudo-Latin. Early British settlers called it by many names, such as watermole, duckbill, and duckmole. The name platypus is often prefixed with the adjective "duck-billed" to form duck-billed platypus, despite there being only one species of platypus. To Aborigines the platypus is known as Mallangong, Tambreet or Boonaburra.

Physical description

The platypus's body temperature averages 31–32 °C (88–90 °F) rather than the 38 °C (100 °F) 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.

The body and the broad, flat tail of the platypus are covered with brown fur that traps a layer of insulating air to keep the animal warm. Like the Tasmanian Devil, the platypus uses the tail for fat storage. It has webbed feet and a large, rubbery snout that are more reminiscent of a duck's features than those of any known mammal. The snout does not open like a bird's beak, with both the upper and lower parts of the beak separating to reveal its mouth. The platypus snout is a sensory organ with an opening on the underside.

Weight varies considerably between 700 g (1.54 lb) to 2.4 kg (5.3 lb) with males being larger than females: males average 50 cm total length while females average 43 cm. There is substantial variation in average size from one region to another, although this pattern does not seem to follow any particular climatic rule.

File:Oz20cent.jpg

The Australian 20 cent coin features a platypus

Modern platypus young have tribosphenic (three-cusped) molars, which are one of the hallmarks of mammals. They lose these before or just after leaving the breeding burrow; adults have heavily keratinised pads in their place. 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 in the middle 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 the body, rather than underneath. The platypus manoeuvres with its flat tail and hind feet, which allows it to dive quickly and stabilise itself.

Venom

The male platypus has venomous ankle spurs which produce a cocktail of venom, composed largely of defensin-like proteins or DLPs, which are unique to the platypus. The venom is not lethal to humans but will produce excruciating pain — so intense that the victim may be incapacitated. Oedema rapidly develops around the wound and gradually spreads throughout the affected limb. Information obtained from case histories and anecdotal evidence indicates that the pain develops into a long-lasting hyperalgesia that persists for days or even months. The venom can be lethal to small animals. Venom is produced in the crural glands of the male, which are kidney-shaped alveolar glands connected by a thin-walled duct to the spur, and is inflicted through a calcaneus spur on each hind limb. Females, like echidnas, have rudimentary spur buds which do not develop and do not have functional crural glands.

Calcaneous spur

The venom appears to have a different function from venoms produced by non-mammalian species, its effects are non-life threatening but nevertheless may seriously impair the victim. Since only males produce venom and the production rises during the breeding season it is theorized that it is used as an offensive weapon to assert dominance during this period.

Electrolocation

Monotremes are the only mammals known to have a sense of electroception: they locate their prey in part by detecting electric fields generated by their bodies. The platypus' electroception is the most sensitive of any monotreme.

In the platypus, electroreceptors are located in rostro-caudal rows in the skin of the bill, while mechanoreceptors are uniformly distributed across the bill. The electrosensory area of the cerebral cortex is contained within the tactile somatosensory area, and some cortical cells receive input from both electroreceptors and mechanoreceptors, suggesting a close association between the tactile and electric senses. The platypus can determine the direction of an electric source, perhaps by comparing differences in signal strength across the sheet of electroreceptors. This would explain the animal's characteristic side-to-side motion of its head while hunting. The cortical convergence of electrosensory and tactile inputs suggests a mechanism for determining the distance of prey items which, when they move, emit both electrical signals and mechanical pressure pulses, which would also allow for computation of distance from the difference in time of arrival of the two signals.

The platypus feeds by digging in the bottom of streams with the bill. The electroreceptors could also be used to distinguish animate and inanimate objects in this situation (in which the mechanoreceptors would be continuously stimulated).

Ecology and behaviour

The platypus is very hard to spot even on the surface of a river — and they tend to dive back in promptly.

The platypus is 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 generally regarded as nocturnal, but is commonly active at dawn and dusk, and many individuals are also active during the day, particularly on cloudy days.

The species is endothermic, maintaining its low body temperature, even while foraging for hours in water below 5 °C (41 °F). Its major habitat requirements include both riverine and riparian features which maintain a supply of benthic prey species and consolidated banks into which resting and nesting burrows can be excavated.

The platypus is an excellent swimmer and spends much of its time in the water foraging for food. When swimming they are distinguished from other Australian mammals by the absence of visible ears. 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.

It may be observed that, when the platypus dives, it sends up a bubble of air after approximately some time, then some time later it sends up another bubble of air, and some additional time after that, it surfaces, lies spread-eagled on the top of the water, and chews its food. Then it dives again. A normal dive lasts between 30 seconds and a minute, but can last longer in favourable conditions. 10 to 20 seconds are commonly spent on the surface chewing.

The platypus is a carnivore. It feeds on annelid worms and insect larvae, freshwater shrimps, and yabbies (freshwater crayfish) that it digs out of the riverbed with its snout or catches while swimming. Its bill is very sensitive, allowing it to hunt its food without using sight. The platypus needs to eat about 20% of its own weight every day. This requires the platypus to spend about 10 hours each day looking for food. 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.

Reproduction

When the platypus was first discovered scientists were divided over whether the female laid eggs. This was not confirmed until 1884 W.H. Caldwell was sent to Australia where, with the help of 150 Aborigines he managed to discover a few eggs.

The species exhibits a single breeding season, with mating occurring in late winter or spring and young first emerging into the water after three to four months of nurture by the lactating females in the nesting burrows. Historical observation, mark and recapture studies and preliminary investigations of population genetics indicate the possibility of resident and transient members of populations and suggest a polygynous mating system.

Outside the mating season, the platypus lives in a simple ground burrow whose entrance is about 30 cm (1 ft) above the water level. After mating, the female constructs a deeper, more elaborate burrow up to 20 m (66 ft) long and blocked with plugs at intervals as a safeguard against rising waters. The male takes no part in caring for its young, and retreats to its yearlong burrow. The female softens the ground in the burrow with dead, folded, wet leaves and she fills the nest at the end of the tunnel with fallen leaves and reeds for bedding material. This material is dragged to the nest by tucking it underneath her curled tail.

The platypus lays small, leathery eggs similar to those of reptiles, which are slightly rounder than bird eggs. Females usually lay two eggs at a time, but sometimes they lay one egg or three, which are about 11 mm (7/16 in) in diameter. After laying her eggs, the female curls around them. The incubation period is separated into three parts. In the first, the embryo has no functional organs and relies on the yolk sac for respiration. During the second, the fingers and toes appear, and in the last, the egg tooth appears. When the eggs hatch after an incubation period of roughly ten days, the small hairless young cling to the mother.

The newly hatched young are vulnerable, blind, and nude, and are fed by the mother's milk. The milk is released through pores in her abdomen. There are grooves on her abdomen that form pools of milk, allowing the young to lap up the milk. After the eggs hatch, the mother leaves the burrow only for short periods of time to feed and wet her fur. When the mother leaves her young, she plugs the entrance with soil to protect her offspring. The offspring are suckled for three to four months after they have hatched. They leave the burrow when they are seventeen weeks old.

The platypus in mammalian evolution

Platypus skeleton

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, 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. The Steropodon fossil is composed of an opalised lower jawbone with three molar teeth, and was discovered in New South Wales, Australia (whereas the contemporary platypus is toothless.) The fossil is thought to be about 110 million years old, which means that the platypus-like animal was alive during the Cretaceous period, around the time of the dinosaurs. It is the oldest mammal fossil found in Australia so far.

Another fossil relative of the platypus has been found in Argentina, indicating that monotremes may have reached South America from Australia while the two continents were joined via Antarctica.

The oldest fossil found of the present-day platypus dates back to about 100,000 years ago, the Quaternary period. It is a branch quite separate from any other known.

Fossil evidence also shows that monotremes existed during the Mesozoic Era (which includes the Cretaceous period, as well as the Triassic and Jurassic eras).

There are two theories to explain how the platypus has evolved into what it is today. The first (theory B) shows that relatives of monotremes formed their own evolutionary branch that was completely different from development of both marsupials and placentals. This change is thought to have occurred 135 million years ago, the beginning of the Cretaceous period. The marsupials and the placentals divided at some point 135–65 million years ago.

The second (theory A) was proposed by Gregory (1947) and was not popular until the 1970s. He said that between 135–65 million years ago, the placentals and marsupials separated to their own way then later the monotremes and the marsupials went their own way.

Evidence for this theory is that the reproductive systems of monotremes and marsupials are extremely similar. The embryos of both have some stage of encased shells in the gestation period. The only difference is that monotremes have the encased shells throughout the entire gestation period, whereas marsupials only have the encased shells for about two thirds of the gestation period.

In 2004, researchers at the Australian National University discovered the platypus has ten sex chromosomes, compared to two (XY) found in most other mammals (for instance, a male platypus is always XYXYXYXYXY). Furthermore, one of the platypus’s Y chromosomes shares genes with the ZZ/ZW sex chromosomes found in birds. This news has further pronounced the individuality of the platypus amongst the animal kingdom, and a target for further research into evolutionary links between mammals, birds and reptiles.

Conservation status

The platypus occupies much the same general distribution as it did prior to European settlement of Australia, except for its loss from the state of South Australia. However, local changes and fragmentation of distribution due to human modification of its habitat are documented. The species currently inhabits eastern Australia from around Cooktown in the north to Tasmania in the south. Although not found in the west-flowing rivers of northern Queensland, it inhabits the upper reaches of rivers flowing to the west and north of the dividing ranges in the south of the state and in New South Wales and Victoria. Its current and historical abundance, however, is less well known and it has probably declined in numbers, although still being considered as common over most of its current range. The species was extensively hunted for its fur until the early years of the 20th century and until about 1950 it was at risk of drowning in the nets of inland fisheries. The platypus does not appear to be in immediate danger of extinction due to conservation measures, but it could be impacted by habitat disruption caused by dams, irrigation, pollution, netting and trapping. It is variously classified as "secure but faces future threat" or "common but vulnerable", mainly because the species is sensitive to water pollution. It is a protected species within Australia. The IUCN lists the platypus on its Red List as Least Concern.

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 difficult task, and only a few young have been successfully raised since — notably at Healesville Sanctuary in Victoria.

The leading figure in these efforts was David Fleay who established a platypussary — a simulated stream in a tank — at the Healesville Sanctuary and had a successful breeding in 1943. Healesville repeated its successes in 1998 and in 2000 with a similar stream tank. Taronga Zoo in Sydney had success in 2003 with twins being bred, and again in 2006. In 1972, David Fleay also found a dead baby about 50 days old, presumably bred in captivity, at his wildlife park at Burleigh Heads on the Gold Coast, Queensland.

In popular culture

A depiction of a platypus from a book for children published in Germany in 1798

• The platypus has been used several times as a mascot
  • "Syd" the platypus was one of the three mascots chosen for the Sydney 2000 Olympics. The other mascots were an echidna and a Kookaburra.
  • Hexley the platypus is the mascot for Apple Computer's BSD-based Darwin operating system, Mac OS X.

• A platypus named Ovide was the star of the cartoon Ovide and the Gang.

• The platypus is also sometimes jokingly referred to as "proof that God has a sense of humor", because of its perceived odd appearance.

• In 1995, United Paramount Network broadcast a short-lived television series entitled Platypus Man, starring comedian Richard Jeni. The title came from a joke, repeated at the beginning of each episode, comparing the platypus' solitary behavior with the lead character's personal life. Aside from this, and the use of a cartoon platypus as the series mascot, the show had nothing to do with actual platypuses.

• A platypus named Phyl appears on several of the books written by Timothy Budd. The platypus is used to illustrate two important principles of object-oriented programming: inheritance and overriding.

• Two platypuses (brothers named Timothy and Daniel) appear in a children's cartoon Taz-Mania. The brothers are rather unsuccessful inventors and other than having the generic appearance of platypodes they have nothing else in common with the animal.

• A young platypus named Flap is a regular character in each of the Blinky Bill cartoon series; indeed, the opening theme of the first series mentions him by name.

• In the childrens' television show "Mr. Rogers' Neighborhood", a platypus family lived in the Neighborhood of Make-Believe.

• In the animated show Camp Lazlo, the character of Edward is a platypus.

• The satirist Barry Humphries exhibited the box of a mock pesticide product called "Platytox" during his early surrealist period.

• Expirimental rock band Mr. Bungle has a track named after the creature on their second major album Disco Volante. The song includes several humorous lyrics including "The platypus has the brain of a dolphin and can be seen driving a forklift in his habitat of kelp"

See also

• Australian fauna
• List of venomous mammals

References

Documentary and external links

• Eye of the Storm. Documentary by the Australian Broadcasting Corporation.
• Nature abstract on sex chromosome discovery
• Australian Platypus Conservancy Fact File
• PBS.org
• Tasmanian Department of Primary Industries, Water, and Environment
• Platypus at WikiFauna
• Platypus-Evolution and Conservation

Books

• Augee, Michael L. Platypus. World Book Encyclopedia. 2001 ed.
• Burrell, H. The Platypus. Adelaide: Rigby, 1974.
• Grant, Tom. The platypus: a unique mammal. Sydney: University of New South Wales Press, 1995. ISBN 0-86840-143-9.
• Griffiths, Mervyn. The Biology of the Monotremes. Academic Press, 1978.
• Groves, C. P. (2005). Wilson, D. E.; Reeder, D. M. (eds.). Mammal Species of the World: A Taxonomic and Geographic Reference (3rd ed.). Baltimore: Johns Hopkins University Press. p. 2. ISBN 0-801-88221-4. OCLC 62265494.
• Michael Hutch, Melissa C. McDade, eds. Grzimek's Animal Life Encyclopedia; Volume 12. Detroit: Gale, 2004.
• Moyal, Ann. Platypus: The Extraordinary Story of How a Curious Creature Baffled the World. Smithsonian Books, 2001. ISBN 1-56098-977-7.
• Strahan, R. The Mammals of Australia. New South Wales: Reed Books, 1995.