Platypus facts for kids
Quick facts for kids Platypus |
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| Platypus swimming in waters near Scottsdale, Tasmania | |
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| Platypus range (red – native, yellow – introduced) |
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The platypus (Ornithorhynchus anatinus), sometimes referred to as the duck-billed platypus, is a semiaquatic, egg-laying mammal endemic to eastern Australia, including Tasmania. The platypus is the sole living representative or monotypic taxon of its family Ornithorhynchidae and genus Ornithorhynchus, though a number of related species appear in the fossil record.
Together with the four species of echidna, it is one of the five extant species of monotremes, mammals that lay eggs instead of giving birth to live young. Like other monotremes, the platypus senses prey in cloudy water through electrolocation. It is one of the few species of venomous mammals, as the male platypus has a spur on the hind foot that delivers an extremely painful venom.
The unusual appearance of this egg-laying, duck-billed, beaver-tailed, otter-footed mammal at first baffled European naturalists. In 1799, the first scientists to examine a preserved platypus body judged it a fake made of several animals sewn together.
The unique features of the platypus make it important in the study of evolutionary biology, and a recognisable and iconic symbol of Australia. It is culturally significant to several Aboriginal peoples, who also used to hunt it for food. It has appeared as a national mascot, features on the reverse of the Australian twenty-cent coin, and is an emblem of the state of New South Wales.
The platypus was hunted for its fur, but it has been a legally protected species in all states where it occurs since 1912. Its population is not under severe threat, although captive-breeding programs have had slight success, and it is vulnerable to pollution. It is classified as a near-threatened species by the IUCN, but a November 2020 report has recommended that it be upgraded to threatened species under the federal EPBC Act, due to habitat destruction and declining numbers in all states.
Contents
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. British scientists' initial hunch was that the attributes were a hoax. 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, and Robert Knox believed it might have 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.
The common name "platypus" literally means 'flat-foot', deriving from the Greek word platúpous (πλατύπους), from platús (πλατύς 'broad, wide, flat') and poús (πούς 'foot'). Shaw initially assigned the species the Linnaean name Platypus anatinus when he described it, but the genus term was quickly discovered to already be in use as the name of 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.
There is no universally-agreed plural form of "platypus" in the English language. Scientists generally use "platypuses" or simply "platypus". Alternatively, the term "platypi" is also used for the plural, although this is a form of pseudo-Latin; 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". Occasionally it is specifically called the "duck-billed platypus".
The scientific name Ornithorhynchus anatinus literally means 'duck-like bird-snout', deriving its genus name from the Greek root ornith- (όρνιθ ornith or ὄρνις órnīs 'bird') and the word rhúnkhos (ῥύγχος 'snout', 'beak'). Its species name is derived from Latin anatinus ('duck-like') from anas 'duck'. The platypus is the sole living representative or monotypic taxon of its family (Ornithorhynchidae).
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A book for children published in Germany in 1798
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Illustration from the first scientific description in 1799
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Colour print from 1863
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Description
In David Collins's account of the new colony 1788–1801, he describes "an amphibious animal, of the mole species", with a drawing.
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. The fur is waterproof, textured like that of a mole. The platypus' tail stores fat reserves, an adaptation also found in the Tasmanian devil. Webbing is more significant on the front feet, which in land walking are folded up in knuckle-walking to protect the webbing. The elongated snout and lower jaw are covered in soft skin, forming the bill. The nostrils are located on the snout's dorsal surface, while the eyes and ears are just behind the snout in a groove which closes underwater. Platypuses can give a low growl when disturbed, and a range of vocalisations have been reported in captivity.
Size varies considerably in different regions, with average weight from 0.7 to 2.4 kg (1 lb 9 oz to 5 lb 5 oz); males have average length 50 cm (20 in), while females are the smaller at 43 cm (17 in). This variation does not seem to follow any particular climatic rule and may be due to other factors such as predation and human encroachment.
The platypus has an average body temperature of about 32 °C (90 °F), lower than the 37 °C (99 °F) typical of placental mammals. Research suggests this has been a gradual adaptation to harsh environmental conditions among the few marginal surviving monotreme species, rather than a general characteristic of past monotremes.
In addition to laying eggs, the anatomy, ontogeny, and genetics of monotremes shows traces of similarity to reptiles and birds. The platypus has a reptilian gait with legs on the sides of the body, rather than underneath. The platypus's genes are a possible evolutionary link between the mammalian XY and bird/reptile ZW sex-determination systems, as one of the platypus's five X chromosomes contains the DMRT1 gene, which birds possess on their Z chromosome.
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 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 not found in other mammals. As in many other aquatic and semiaquatic vertebrates, the bones show osteosclerosis, increasing their density to provide ballast.
The platypus jaw is constructed differently from that of other mammals, and the jaw-opening muscle is different. Modern platypus young have three teeth in each of the maxillae (one premolar and two molars) and dentaries (three molars), which they lose before or just after leaving the breeding burrow; adults instead develop heavily keratinised food-grinding pads called ceratodontes. The first upper and third lower cheek teeth of platypus nestlings are small, each having one principal cusp, while the other teeth have two main cusps.
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Diving
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Surfacing
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Venom
While both male and female platypuses are born with back ankle spurs, only the males' deliver venom. It is powerful enough to kill smaller animals such as dogs, and though it is not lethal to humans, it can inflict weeks of agony. Edema rapidly develops around the wound and gradually spreads through the affected limb, and it may develop into an excruciating hyperalgesia (heightened sensitivity to pain) persisting for days or even months.
The venom is composed largely of defensin-like proteins (DLPs) produced by the immune system, three of which are unique to the platypus. In other animals, defensins kill pathogenic bacteria and viruses, but in platypuses they are also collected into a venom against predators. 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. Venom production rises among males during the breeding season, and it may be used to assert dominance.
Similar spurs are found on many archaic mammal groups, indicating that this was an ancient general characteristic among mammals.
Electrolocation
Monotremes are the only mammals (apart from the Guiana dolphin) known to have a sense of electroreception, and the platypus's electroreception is the most sensitive of any monotreme. Feeding by neither sight nor smell, the platypus closes its eyes, ears, and nose when it dives. Digging in the bottom of streams with its bill, its electroreceptors detect tiny electric currents generated by the muscular contractions of its prey, enabling it to distinguish between animate and inanimate objects. Experiments have shown the platypus will even react to an "artificial shrimp" if a small electric current is passed through it.
The electroreceptors are located in rostrocaudal rows in the skin of the bill, while mechanoreceptors for touch are uniformly distributed across the bill. The electrosensory area of the cerebral cortex is in the tactile somatosensory area, and some cortical cells receive input from both electroreceptors and mechanoreceptors, suggesting the platypus feels electric fields like touches. These receptors in the bill dominate the somatotopic map of the platypus brain, in the same way human hands dominate the Penfield homunculus map.
The platypus can feel the direction of an electric source, perhaps by comparing differences in signal strength across the sheet of electroreceptors, enhanced by the characteristic side-to-side motion of the animal's head while hunting. It may also be able to determine the distance of moving prey from the time lag between their electrical and mechanical pressure pulses.
Monotreme electrolocation for hunting in murky waters may be tied to their tooth loss. The extinct Obdurodon was electroreceptive, but unlike the modern platypus it foraged pelagically (near the ocean surface).
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, unlike most mammals.
Although the platypus's eyes are small and not used under water, several features indicate that vision was important for its ancestors. The corneal surface and the adjacent surface of the lens is flat, while the posterior surface of the lens is steeply curved, similar to the eyes of other aquatic mammals such as otters and sea-lions. A temporal (ear side) concentration of retinal ganglion cells, important for binocular vision, indicates a vestigial role in predation, though the actual visual acuity is insufficient for such activities. Limited acuity is matched by low cortical magnification, a small lateral geniculate nucleus, and a large optic tectum, suggesting that 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. This contrasts with the small number of electroreceptors in the short-beaked echidna, which dwells in dry environments, while the long-beaked echidna, which lives in moist environments, is intermediate between the other two monotremes.
Biofluorescence
In 2020, research revealed that platypus fur gives a bluish-green biofluorescent glow in black light.
Distribution, ecology, and behaviour
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.
Inland, its distribution is not well known. It was considered extinct on the South Australian mainland, with the last sighting recorded at Renmark in 1975. In the 1980s, John Wamsley created a platypus breeding program in Warrawong Sanctuary (see below), which subsequently closed. In 2017 there were some unconfirmed sightings downstream from the sanctuary, and in October 2020 a nesting platypus was filmed inside the recently reopened sanctuary.
There is a population on Kangaroo Island introduced in the 1920s, said to stand at 150 individuals in the Rocky River region of Flinders Chase National Park. In the 2019–20 Australian bushfire season, large portions of the island burnt, decimating wildlife. However, SA Department for Environment and Water recovery teams worked to reinstate their habitat, with a number of sightings reported by April 2020.
The platypus is no longer found in the main Murray–Darling Basin, possibly due to declining water quality from land clearing and irrigation. Along the coastal river systems, its distribution is unpredictable: absent in some relatively healthy rivers, but present in some quite degraded ones, for example the lower Maribyrnong.
In captivity, platypuses have survived to 17 years of age, and wild specimens have been recaptured when 11 years old. Mortality rates for adults in the wild appear to be low. Natural predators include snakes, water rats, goannas, hawks, owls, and eagles. Low platypus numbers in northern Australia are possibly due to predation by crocodiles. The introduction of red foxes in 1845 for sport hunting may have had some impact on its numbers on the mainland. The platypus is generally nocturnal and crepuscular, but can be active on overcast days. Its habitat bridges rivers and the riparian zone, where it finds both prey and river banks to dig resting and nesting burrows. 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.
The platypus is an excellent swimmer and spends much of its time in the water foraging for food. It has a swimming style unique among mammals, propelling itself by alternate strokes of the front feet, while the webbed hind feet are held against the body and only used for steering, along with the tail. It can maintain its relatively low body temperature of about 32 °C (90 °F) while foraging for hours in water below 5 °C (41 °F). Dives normally last around 30 seconds, with an estimated aerobic limit of 40 seconds, with 10 to 20 seconds at the surface between dives.
The platypus rests in a short, straight burrow in the riverbank about 30 cm (12 in) above water level, its oval entrance-hole often hidden under a tangle of roots. It may sleep up to 14 hours per day, after half a day of diving.
Diet
The platypus is a carnivore, feeding on annelid worms, insect larvae, freshwater shrimp, and yabby (crayfish) that it digs out of the riverbed with its snout or catches while swimming. It carries prey to the surface in cheek-pouches before eating it. It eats about 20% of its own weight each day, which requires it to spend an average of 12 hours daily looking for food.
Reproduction
The species has a single breeding season between June and October, with some local variation. Investigations have found both resident and transient platypuses, and suggest a polygynous mating system. Females are believed to become sexually mature in their second year, with breeding observed in animals over nine years old. The male takes no part in nesting, living in his year-long resting burrow. After mating, the female constructs a deep, elaborate nesting burrow up to 20 m (65 ft) long. It tucks fallen leaves and reeds underneath its curled tail, dragging them to the burrow to soften the tunnel floor with folded wet leaves, and to line the nest at the end with bedding.
The female has two ovaries, but only the left one is functional. It lays one to three (usually two) small, leathery eggs (similar to those of reptiles), about 11 mm (7⁄16 in) in diameter and slightly rounder than bird eggs. The eggs develop in utero for about 28 days, with only about 10 days of external incubation (in contrast to a chicken egg, which spends about one day in tract and 21 days externally). The female curls around the incubating eggs, which develop in three phases. In the first, the embryo has no functional organs and relies on the yolk sac for sustenance, until the sac is absorbed. During the second phase, the digits develop, and in the last phase, the egg tooth appears. At first, European naturalists could hardly believe that the female platypus lays eggs, but this was finally confirmed by William Hay Caldwell in 1884.
Most mammal zygotes go through holoblastic cleavage, splitting into multiple divisible daughter cells. However, monotremes like the platypus, along with reptiles and birds, undergo meroblastic cleavage, in which the ovum does not split completely. The cells at the edge of the yolk remain continuous with the egg's cytoplasm, allowing the yolk and embryo, to exchange waste and nutrients with the egg through the cytoplasm.
Young platypus are called "puggles". Newly hatched platypuses are vulnerable, blind, and hairless, and are fed by the mother's milk, that provides all the requirements for growth and development. The platypus' mammary glands lack teats, with milk released through pores in the skin. The milk pools in grooves on the mother's abdomen, allowing the young to lap it up. After they hatch, the offspring are milk-fed for three to four months.
During incubation and weaning, the mother initially leaves the burrow only for short periods to forage. She leaves behind her 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 squeezes water from her fur and allows the burrow to remain dry. 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. A platypus is born with teeth, but these drop out at a very early age, leaving the horny plates it uses to grind food.
Evolution
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| Evolutionary relationships between the platypus and other mammals |
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. 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. 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. Molecular clock and fossil dating suggest platypuses split from echidnas around 19–48 million years ago.
The oldest discovered fossil of the modern platypus dates back to about 100,000 years ago, during the Quaternary period. The extinct monotremes Teinolophos and Steropodon were once thought to be closely related to the modern platypus, but are now considered more basal taxa. The fossilised Steropodon was discovered in New South Wales and is composed of an opalised lower jawbone with three molar teeth (whereas the adult contemporary platypus is toothless). The molar teeth were initially thought to be 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. 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.
Monotrematum sudamericanum, another fossil relative of the platypus, has been found in Argentina, indicating monotremes were present in the supercontinent of Gondwana when the continents of South America and Australia were joined via Antarctica (until about 167 million years ago). A fossilised tooth of a giant platypus species, 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.
Because of the early divergence from the therian mammals and the low numbers of extant monotreme species, the platypus is a frequent subject of research in evolutionary biology. In 2004, researchers at the Australian National University discovered the platypus has ten sex chromosomes, compared with two (XY) in most other mammals. These ten chromosomes form five unique pairs of XY in males and XX in females, i.e. males are X1Y1X2Y2X3Y3X4Y4X5Y5. One of the X chromosomes of the platypus has great homology to the bird Z chromosome. The platypus genome also has both reptilian and mammalian genes associated with egg fertilisation. Though the platypus lacks the mammalian sex-determining gene SRY, a study found that the mechanism of sex determination is the AMH gene on the oldest Y chromosome. 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. An updated genome, the most complete on record, was published in 2021, together with the genome of the short-beaked echidna.
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 European settlement of Australia. However, local changes and fragmentation of distribution due to human modification of its habitat are documented. Its historical abundance is unknown and its current abundance difficult to gauge, but it is assumed to have declined in numbers, although as of 1998 was 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. Although the species gained legal protections beginning in Victoria in 1890 and throughout Australia by 1912, until about 1950 it was still at risk of drowning in the nets of inland fisheries.
The International Union for Conservation of Nature recategorised its status as "near threatened" in 2016. The species is protected by law, but the only state in which it is listed as endangered is South Australia, under the National Parks and Wildlife Act 1972. In November 2020 a recommendation was made to list the platypus as a vulnerable species across all states with a vulnerable listing being made official in Victoria under the state's Flora and Fauna Guarantee Act 1988 on 10 January 2021.
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 dams, irrigation, pollution, netting, and trapping. Reduction of watercourse flows and water levels through excessive droughts and extraction of water for industrial, agricultural, and domestic supplies are also considered a threat. The IUCN lists the platypus on its Red List as "Near Threatened" as assessed in 2016, when it was estimated that numbers had reduced by about 30 percent on average since European settlement. The animal is listed as endangered in South Australia, but it is not covered at all under the federal EPBC Act.
Researchers have worried for years that declines have been greater than assumed. In January 2020, researchers from the University of New South Wales presented evidence that the platypus is at risk of extinction, due to a combination of extraction of water resources, land clearing, climate change and severe drought. 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. 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.
A November 2020 report by scientists from the University of New South Wales, funded by a research grant from the Australian Conservation Foundation in collaboration with the World Wildlife Fund Australia and the Humane Society International Australia revealed that that platypus habitat in Australia had shrunk by 22 per cent in the previous 30 years, and recommended that the platypus should be listed as a threatened species under the EPBC Act. Declines in population had been greatest in NSW, in particular in the Murray–Darling basin.
Disease
Platypuses generally suffer from few diseases in the wild; however, as of 2008 there was concern in Tasmania about the potential impacts of a disease caused by the fungus 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.
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. 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. Healesville repeated its success in 1998 and again in 2000 with a similar stream tank. Since 2008, platypus has bred regularly at Healesville, including second-generation (captive born themselves breeding in captivity). Taronga Zoo in Sydney bred twins in 2003, and breeding was again successful there in 2006.
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. 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, Penelope and Cecil, lived longer than eighteen months.
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 until 1912, when it was prohibited by law.
See also
In Spanish: Ornitorrinco para niños
- Henry Burrell
- Ellis Joseph
- Fauna of Australia
