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Platypus

Source: Wikipedia, the free encyclopedia.
(Redirected from
Duck-billed platypus
)

Platypus
Temporal range: 9–0 
Ma
Miocene to Recent
Wild Platypus 4.jpg

Near Threatened (IUCN 3.1)[1]
Scientific classification edit
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Monotremata
Family: Ornithorhynchidae
Genus: Ornithorhynchus
Blumenbach, 1800
Species:
O. anatinus
Binomial name
Ornithorhynchus anatinus
(Shaw, 1799)
Distribution of the Platypus (Ornithorhynchus anatinus).png
Platypus range
(red – native, yellow – introduced)
Synonyms[2]
  • Ornithorhynchus agilis (de Vis, 1886)
  • Platypus anatinus (Shaw, 1799)

The platypus (Ornithorhynchus anatinus),

related species
appear in the fossil record.

Together with the four species of

venomous mammals, as the male platypus has a spur on the hind foot that delivers a venom, capable of causing severe pain to humans. The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter
-footed mammal baffled European naturalists when they first encountered it, and the first scientists to examine a preserved platypus body (in 1799) judged it a fake, made of several animals sewn together.

The unique features of the platypus make it an important subject in the study of evolutionary biology, and a recognisable and iconic symbol of Australia. It is culturally significant to several Aboriginal peoples of Australia, who also used to hunt the animal for food. It has appeared as a mascot at national events and features on the reverse of the Australian twenty-cent coin, and the platypus is the animal emblem of the state of New South Wales. Until the early 20th century, humans hunted the platypus for its fur, but it is now protected throughout its range. Although captive-breeding programs have had only limited success, and the platypus is vulnerable to the effects of pollution, it is not under any immediate threat.

As of 2020, the platypus is a legally

EPBC Act, due to habitat destruction
and declining numbers in all states.

Taxonomy and naming

When the platypus was first encountered by Europeans in 1798, a

pelt and sketch were sent back to Great Britain by Captain John Hunter, the second Governor of New South Wales.[4] British scientists' initial hunch was that the attributes were a hoax.[5] George Shaw, who produced the first description of the animal in the Naturalist's Miscellany in 1799, stated it was impossible not to entertain doubts as to its genuine nature,[6] and Robert Knox believed it might have been produced by some Asian taxidermist.[5] 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.[7][6]

The common name "platypus" literally means 'flat-foot', deriving from the

Sir Joseph Banks)[14] and following the rules of priority of nomenclature, it was later officially recognised as Ornithorhynchus anatinus.[13]

There is no universally-agreed plural form of "platypus" in the English language. Scientists generally use "platypuses" or simply "platypus". Colloquially, the term "platypi" is also used for the plural, although this is a form of pseudo-Latin;[7] going by the word's Greek roots the plural would be "platypodes". Early British settlers called it by many names, such as "watermole", "duckbill", and "duckmole".[7] Occasionally it is specifically called the "duck-billed platypus".

The scientific name Ornithorhynchus anatinus literally means 'duck-like bird-snout',

species name is derived from Latin anatinus ('duck-like') from anas 'duck'.[12][17] The platypus is the sole living representative or monotypic taxon of its family (Ornithorhynchidae).[18]

Description

In David Collins's account of the new colony 1788–1801, he describes coming across "an amphibious animal, of the mole species". His account includes a drawing of the animal.[19]

The body and the broad, flat tail of the platypus are covered with dense, brown, biofluorescent fur that traps a layer of insulating air to keep the animal warm.[7][13][20] The fur is waterproof, and the texture is akin to that of a mole.[21] The platypus uses its tail for storage of fat reserves (an adaptation also found in animals such as the Tasmanian devil[22]). The webbing on the feet is more significant on the front feet and is folded back when walking on land. The elongated snout and lower jaw are covered in soft skin, forming the bill. The nostrils are located on the dorsal surface of the snout, while the eyes and ears are located in a groove set just back from it; this groove is closed when swimming.[13] Platypuses have been heard to emit a low growl when disturbed and a range of other vocalisations have been reported in captive specimens.[7]

Weight varies considerably from 0.7 to 2.4 kg (1 lb 9 oz to 5 lb 5 oz), with males being larger than females. Males average 50 cm (20 in) in total length, while females average 43 cm (17 in),[13] with substantial variation in average size from one region to another. This pattern does not seem to follow any particular climatic rule and may be due to other environmental factors, such as predation and human encroachment.[23]

The platypus has an average

body temperature of about 32 °C (90 °F) rather than the 37 °C (99 °F) typical of placental mammals.[24] Research suggests this has been a gradual adaptation to harsh environmental conditions on the part of the small number of surviving monotreme species rather than a historical characteristic of monotremes.[25][26]

Modern platypus young have three teeth in each of the

vertebrates, the bones show osteosclerosis, increasing their density to provide ballast.[30] It has a reptilian gait, with the legs on the sides of the body, rather than underneath.[13] When on land, it engages in knuckle-walking on its front feet, to protect the webbing between the toes.[31]

Venom

While both male and female platypuses are born with ankle spurs, only the spurs on the male's back ankles deliver venom,[32][33][34] composed largely of defensin-like proteins (DLPs), three of which are unique to the platypus.[35] The DLPs are produced by the immune system of the platypus. The function of defensins is to cause lysis in pathogenic bacteria and viruses, but in platypuses they also are formed into venom for defence. Although powerful enough to kill smaller animals such as dogs, the venom is not lethal to humans, but the pain is so excruciating that the victim may be incapacitated.[35][36] Oedema rapidly develops around the wound and gradually spreads throughout the affected limb. Information obtained from case histories and anecdotal evidence indicates the pain develops into a long-lasting hyperalgesia (a heightened sensitivity to pain) that persists for days or even months.[37][38] Venom is produced in the crural glands of the male, which are kidney-shaped alveolar glands connected by a thin-walled duct to a calcaneus spur on each hind limb. The female platypus, in common with echidnas, has rudimentary spur buds that do not develop (dropping off before the end of their first year) and lack functional crural glands.[13]

The venom appears to have a different function from those produced by non-mammalian species; its effects are not life-threatening to humans, but nevertheless powerful enough to seriously impair the victim. Since only males produce venom and production rises during the breeding season, it may be used as an offensive weapon to assert dominance during this period.[35]

Similar spurs are found on many archaic mammal groups, indicating that this is an ancient characteristic for mammals as a whole, and not exclusive to the platypus or other monotremes.[39]

Electrolocation

The platypus has secondarily acquired electroreception. Its receptors are arranged in stripes on its bill, giving it high sensitivity to the sides and below; it makes quick turns of its head as it swims to detect prey.[40]

electroreception: they locate their prey in part by detecting electric fields generated by muscular contractions. The platypus's electroreception is the most sensitive of any monotreme.[42][40]

The

somatotopic map of the platypus brain, in the same way human hands dominate the Penfield homunculus map.[43][44]

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 characteristic side-to-side motion of the animal's head while hunting. The cortical convergence of electrosensory and tactile inputs suggests a mechanism that determines the distance of prey that, when they move, emit both electrical signals and mechanical pressure pulses. The platypus uses the difference between arrival times of the two signals to sense distance.[40]

Feeding by neither sight nor smell,[45] the platypus closes its eyes, ears, and nose each time it dives.[46] Rather, when it digs in the bottom of streams with its bill, its electroreceptors detect tiny electric currents generated by muscular contractions of its prey, so enabling it to distinguish between animate and inanimate objects, which continuously stimulate its mechanoreceptors.[40] Experiments have shown the platypus will even react to an "artificial shrimp" if a small electric current is passed through it.[47]

Monotreme electrolocation probably evolved in order to allow the animals to forage in murky waters, and may be tied to their tooth loss.[48] The extinct Obdurodon was electroreceptive, but unlike the modern platypus it foraged pelagically (near the ocean surface).[48]

Eyes

In recent studies it has been suggested that the eyes of the platypus are more similar to those of Pacific hagfish or Northern Hemisphere lampreys than to those of most tetrapods. The eyes also contain double cones, which most mammals do not have.[49]

Although the platypus's eyes are small and not used under water, several features indicate that vision played an important role in its ancestors. The

visual midbrain plays a more important role than the visual cortex, as in some rodents. These features suggest that the platypus has adapted to an aquatic and nocturnal lifestyle, developing its electrosensory system at the cost of its visual system; an evolutionary process paralleled by the small number of electroreceptors in the short-beaked echidna, which dwells in dry environments, whilst the long-beaked echidna, which lives in moist environments, is intermediate between the other two monotremes.[43]

Biofluorescence

In 2020, research in biofluorescence revealed that the platypus glows a bluish-green color when exposed to black light.[50]

Distribution, ecology, and behaviour

Sydney Aquarium
, Australia

The platypus is semiaquatic, 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.[51]

Inland, its distribution is not well known. It was considered extinct on the

Warrawong Sanctuary (see below) in the 1980s, setting a platypus breeding program there, and it had subsequently closed.[53][54] In 2017 there were some unconfirmed sightings downstream, outside the sanctuary,[52] and in October 2020 a nesting platypus was filmed inside the recently reopened sanctuary.[55] There is a population on Kangaroo Island[56] introduced in the 1920s, which was said to stand at 150 individuals in the Rocky River region of Flinders Chase National Park before the 2019–20 Australian bushfire season, in which large portions of the island burnt, decimating all wildlife. However, with the SA Department for Environment and Water recovery teams working hard to reinstate their habitat, there had been a number of sightings reported by April 2020.[57]

The platypus is no longer found in the main part of the

Murray-Darling Basin, possibly due to the declining water quality brought about by extensive land clearing and irrigation schemes.[58] 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, for example, the lower Maribyrnong, that are quite degraded.[59]

In captivity, platypuses have survived to 17 years of age, and wild specimens have been recaptured when 11 years old.

crepuscular, but individuals are also active during the day, particularly when the sky is overcast.[61][62] Its habitat bridges rivers and the riparian zone for both a food supply of prey species, and banks where it can dig resting and nesting burrows.[62] It may have a range of up to 7 km (4.3 mi), with a male's home range overlapping those of three or four females.[63]

The platypus is an excellent swimmer and spends much of its time in the water foraging for food. It has a very characteristic swimming style and no external ears.[64] Uniquely among mammals, it propels itself when swimming by an alternate rowing motion of the front feet; although all four feet of the platypus are webbed, the hind feet (which are held against the body) do not assist in propulsion, but are used for steering in combination with the tail.[65] The species is endothermic, maintaining its body temperature at about 32 °C (90 °F), lower than most mammals, even while foraging for hours in water below 5 °C (41 °F).[13]

Dives normally last around 30 seconds, but can last longer, although few exceed the estimated aerobic limit of 40 seconds. Recovery at the surface between dives commonly takes from 10 to 20 seconds.[66][67]

When not in the water, the platypus retires to a short, straight resting burrow of oval cross-section, nearly always in the riverbank not far above water level, and often hidden under a protective tangle of roots.[64]

The average sleep time of a platypus is said to be as long as 14 hours per day, possibly because it eats

crustaceans, which provide a high level of calories.[68]

Diet

The platypus is a carnivore: it feeds on annelid worms, insect larvae, freshwater shrimp, and freshwater yabby (crayfish) that it digs out of the riverbed with its snout or catches while swimming. It uses cheek-pouches to carry prey to the surface, where it is eaten.[64] The platypus needs to eat about 20% of its own weight each day, which requires it to spend an average of 12 hours daily looking for food.[66]

Reproduction

When the platypus was first encountered by European naturalists, they were divided over whether the female lays eggs. This was finally confirmed by William Hay Caldwell's team in 1884.[13][35]

The species exhibits a single

breeding season; mating occurs between June and October, with some local variation taking place between different populations across its range.[60] Historical observation, mark-and-recapture studies, and preliminary investigations of population genetics indicate the possibility of both resident and transient members of populations, and suggest a polygynous mating system.[69] Females are thought likely to become sexually mature in their second year, with breeding confirmed still to take place in animals over nine years old.[69]

Outside the mating season, the platypus lives in a simple ground burrow, the entrance of which is about 30 cm (12 in) above the water level. After mating, the female constructs a deeper, more elaborate burrow up to 20 m (65 ft) long and blocked at intervals with plugs (which may act as a safeguard against rising waters or predators, or as a method of regulating humidity and temperature).[70] The male takes no part in caring for his young, and retreats to his year-long 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.[7]

The female platypus has a pair of

incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally).[61] After laying her eggs, the female curls around them. The incubation period is divided into three phases.[73] In the first phase, the embryo has no functional organs and relies on the yolk sac for sustenance. The yolk is absorbed by the developing young.[74] During the second phase, the digits develop, and in the last phase, the egg tooth appears.[73]

Most mammal zygotes go through

monotremes like the platypus and in non-mammals like reptiles and birds. In meroblastic cleavage, the ovum does not split completely. This causes the cells at the edge of the yolk to be cytoplasmically continuous with the egg's cytoplasm. This allows the yolk, which contains the embryo, to exchange waste and nutrients with the cytoplasm.[75]

There is no official term for platypus young, but the term "platypup" sees unofficial use, as does "puggle".[76][77] Newly hatched platypuses are vulnerable, blind, and hairless, and are fed by the mother's milk. Although possessing mammary glands, the platypus lacks teats. Instead, milk is released through pores in the skin. The milk pools in grooves on her abdomen, allowing the young to lap it up.[7][60] After they hatch, the offspring are suckled for three to four months. During incubation and weaning, the mother initially leaves the burrow only for short periods, to forage. When doing so, she creates a number of thin soil plugs along the length of the burrow, possibly to protect the young from predators; pushing past these on her return forces water from her fur and allows the burrow to remain dry.[78] After about five weeks, the mother begins to spend more time away from her young, and at around four months, the young emerge from the burrow.[60] A platypus is born with teeth, but these drop out at a very early age, leaving the horny plates it uses to grind food.[27]

Evolution

Platypus

Echidnas

 live birth 

Marsupials

 true placenta 

Eutherians

Evolutionary relationships between the platypus and other mammals[79]

The platypus and other monotremes were very poorly understood, and some of the 19th century myths that grew up around them – for example, that the monotremes were "inferior" or quasireptilian – still endure.[80] In 1947, William King Gregory theorised that placental mammals and marsupials may have diverged earlier, and a subsequent branching divided the monotremes and marsupials, but later research and fossil discoveries have suggested this is incorrect.[80][81] In fact, modern monotremes are the survivors of an early branching of the mammal tree, and a later branching is thought to have led to the marsupial and placental groups.[80][82] Molecular clock and fossil dating suggest platypuses split from echidnas around 19–48 million years ago.[83]

The oldest discovered fossil of the modern platypus dates back to about 100,000 years ago, during the

tribosphenic, which would have supported a variation of Gregory's theory, but later research has suggested, while they have three cusps, they evolved under a separate process.[85] The fossil is thought to be about 110 million years old, making it the oldest mammal fossil found in Australia. Unlike the modern platypus (and echidnas), Teinolophos lacked a beak.[84]

Obdurodon tharalkooschild, was dated 5–15 million years ago. Judging by the tooth, the animal measured 1.3 metres long, making it the largest platypus on record.[87]

Because of the early divergence from the

SRY, a study found that the mechanism of sex determination is the AMH gene on the oldest Y chromosome.[91][92] A draft version of the platypus genome sequence was published in Nature on 8 May 2008, revealing both reptilian and mammalian elements, as well as two genes found previously only in birds, amphibians, and fish. More than 80% of the platypus's genes are common to the other mammals whose genomes have been sequenced.[45] An updated genome, the most complete on record, was published in 2021, together with the genome of the short-beaked echidna.[93]

Conservation

Status and threats

Except for its loss from the state of South Australia, the platypus occupies the same general distribution as it did prior to

The

National Parks and Wildlife Act 1972. In 2020 it has been recommended to be listed as a vulnerable species in Victoria under the state's Flora and Fauna Guarantee Act 1988.[95]

Habitat destruction

The platypus is not considered to be in immediate danger of extinction, because conservation measures have been successful, but it could be adversely affected by habitat disruption caused by

Researchers have worried for years that declines have been greater than assumed.

land clearing, climate change and severe drought.[98][99] The study predicted that, considering current threats, the animals' abundance would decline by 47%–66% and metapopulation occupancy by 22%–32% over 50 years, causing "extinction of local populations across about 40% of the range". Under projections of climate change projections to 2070, reduced habitat due to drought would lead to 51–73% reduced abundance and 36–56% reduced metapopulation occupancy within 50 years respectively. These predictions suggested that the species would fall under the "Vulnerable" classification. The authors stressed the need for national conservation efforts, which might include conducting more surveys, tracking trends, reduction of threats and improvement of river management to ensure healthy platypus habitat.[100] Co-author Gilad Bino is concerned that the estimates of the 2016 baseline numbers could be wrong, and numbers may have been reduced by as much as half already.[96]

A November 2020 report by scientists from the

Disease

Platypuses generally suffer from few

Mucor amphibiorum. The disease (termed mucormycosis) affects only Tasmanian platypuses, and had not been observed in platypuses in mainland Australia. Affected platypuses can develop skin lesions or ulcers on various parts of their bodies, including their backs, tails, and legs. Mucormycosis can kill platypuses, death arising from secondary infection and by affecting the animals' ability to maintain body temperature and forage efficiently. The Biodiversity Conservation Branch at the Department of Primary Industries and Water collaborated with NRM north and University of Tasmania researchers to determine the impacts of the disease on Tasmanian platypuses, as well as the mechanism of transmission and spread of the disease.[104]

Wildlife sanctuaries

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. The latter 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 platypusary (a simulated stream in a tank) at the Healesville Sanctuary, where breeding was successful in 1943.[105] In 1972, he found a dead baby of about 50 days old, which had presumably been born in captivity, at his wildlife park at Burleigh Heads on the Gold Coast, Queensland.[106] Healesville repeated its success in 1998 and again in 2000 with a similar stream tank.[107] Since 2008, platypus has bred regularly at Healesville,[108] including second-generation (captive born themselves breeding in captivity).[109] Taronga Zoo in Sydney bred twins in 2003, and breeding was again successful there in 2006.[107]

Captivity

As of 2019, the only platypuses in captivity outside of Australia are in the San Diego Zoo Safari Park in the U.S. state of California.[110][111] Three attempts were made to bring the animals to the Bronx Zoo, in 1922, 1947, and 1958; of these, only two of the three animals introduced in 1947 lived longer than eighteen months.[112]

Human interactions

Usage

Aboriginal Australians used to hunt platypuses for food (their fatty tails being particularly nutritious), while, after colonisation, Europeans hunted them for fur from the late 19th century and until 1912, when it was prohibited by law. In addition, European researchers captured and killed platypus or removed their eggs, partly in order to increase scientific knowledge, but also to gain prestige and outcompete rivals from different countries.[95]

Cultural references

The platypus has been a subject in the

Dreamtime stories of Aboriginal Australians, some of whom believed the animal was a hybrid of a duck and a water rat.[113]
: 57–60 

According to one story of the upper Darling River,[95] the major animal groups, the land animals, water animals and birds, all competed for the platypus to join their respective groups, but the platypus ultimately decided to not join any of them, feeling that he did not need to be part of a group to be special,[113]: 83–85  and wished to remain friends with all of those groups.[95] Another Dreaming story emanate of the upper Darling tells of a young duck which ventured too far, ignoring the warnings of her tribe, and was kidnapped by a large water-rat called Biggoon. After managing to escape after some time, she returned and laid two eggs which hatched into strange furry creatures, so they were all banished and went to live in the mountains.[95]

matchbox
label art

The platypus is also used by some

connection to country, the platypus is protected and conserved by these Indigenous peoples.[95]

The platypus has often been used as a symbol of Australia's

Second World War, in order to strengthen ties and boost morale.[95]

Platypuses have been used several times as mascots: Syd the platypus was one of the three mascots chosen for the

BSD-based core of macOS and other operating systems from Apple Inc.[116]

Since the introduction of

decimal currency to Australia in 1966, the embossed image of a platypus, designed and sculpted by Stuart Devlin, has appeared on the reverse (tails) side of the 20-cent coin.[117] The platypus has frequently appeared in Australian postage stamps, most recently the 2015 "Native Animals" series and the 2016 "Australian Animals Monotremes" series.[118][119]

In the American animated series Phineas and Ferb (2007–2015), the title characters own a pet bluish-green platypus named Perry who, unknown to them, is a secret agent. Such choices were inspired by media underuse, as well as to exploit the animal's striking appearance;[120] additionally, show creator Dan Povenmire, who also wrote the character's theme song, said that its opening lyrics are based on the introductory sentence of the Platypus article on Wikipedia, copying the "semiaquatic egg-laying mammal" phrase word for word, and appending the phrase "of action".[121] As a character, Perry has been well received by both fans and critics.[122][123] Coincidentally, real platypuses show a similar cyan color when seen under ultraviolet lighting.[124]

See also

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References

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