Platypus

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Platypus [1]
Temporal range: 9–0  Ma
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Miocene to Recent
Wild Platypus 4.jpg
Scientific classification Red Pencil Icon.png
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)

The platypus (Ornithorhynchus anatinus), sometimes referred to as the duck-billed platypus, is a semiaquatic egg-laying mammal [3] endemic to eastern Australia, including Tasmania. The platypus is the sole living representative of its family (Ornithorhynchidae) and genus (Ornithorhynchus), though a number of related species appear in the fossil record.

Mammal class of tetrapods

Mammals are vertebrate animals constituting the class Mammalia, and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex, fur or hair, and three middle ear bones. These characteristics distinguish them from reptiles and birds, from which they diverged in the late Triassic, 201–227 million years ago. There are around 5,450 species of mammals. The largest orders are the rodents, bats and Soricomorpha. The next three are the Primates, the Cetartiodactyla, and the Carnivora.

Eastern states of Australia

The eastern states of Australia are the states adjoining the east coast of Australia. These are the mainland states of Victoria, Queensland, and New South Wales; the Australian Capital Territory and Jervis Bay Territory, while not states, are also included. The term usually includes the island state of Tasmania. On some occasions, the state of South Australia is included in this grouping.

Tasmania island state of Australia

Tasmania is an island state of Australia. It is located 240 km (150 mi) to the south of the Australian mainland, separated by Bass Strait. The state encompasses the main island of Tasmania, the 26th-largest island in the world, and the surrounding 334 islands. The state has a population of around 526,700 as of March 2018. Just over forty percent of the population resides in the Greater Hobart precinct, which forms the metropolitan area of the state capital and largest city, Hobart.

Contents

Together with the four species of echidna, it is one of the five extant species of monotremes, the only mammals that lay eggs instead of giving birth to live young. Like other monotremes it senses prey 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 a venom capable of causing severe pain to humans.

Echidna family of mammals

Echidnas, sometimes known as spiny anteaters, belong to the family Tachyglossidae in the monotreme order of egg-laying mammals. The four extant species of Echidnas and the platypus are the only living mammals that lay eggs and the only surviving members of the order Monotremata. The diet of some species consists of ants and termites, but they are not closely related to the true anteaters of the Americas, which are xenarthrans, along with sloths and armadillos. Echidnas live in Australia and New Guinea.

Monotreme order of mammals that lay eggs

Monotremes are one of the three main groups of living mammals, along with placentals (Eutheria) and marsupials (Metatheria). The monotremes are typified by structural differences in their brains, jaws, digestive tract, reproductive tract, and other body parts compared to the more common mammalian types. In addition they lay eggs rather than bear live young, but like all mammals, the female monotremes nurse their young with milk.

Electroreception

Electroreception or electroception is the biological ability to perceive natural electrical stimuli. It has been observed almost exclusively in aquatic or amphibious animals, because water is a much better conductor than air. The known exceptions are the monotremes (echidnas and platypuses), cockroaches and bees. Electroreception is used in electrolocation and for electrocommunication.

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) [4] judged it a fake, made of several animals sewn together. [5]

Duck common name for many species in the bird family Anatidae

Duck is the common name for a large number of species in the waterfowl family Anatidae which also includes swans and geese. Ducks are divided among several subfamilies in the family Anatidae; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered ducks. Ducks are mostly aquatic birds, mostly smaller than the swans and geese, and may be found in both fresh water and sea water.

Beaver genus of mammals

The beaver is a large, primarily nocturnal, semiaquatic rodent. Castor includes two extant species, the North American beaver and Eurasian beaver (Eurasia). Beavers are known for building dams, canals, and lodges (homes). They are the second-largest rodent in the world. Their colonies create one or more dams to provide still, deep water to protect against predators, and to float food and building material. The North American beaver population was once more than 60 million, but as of 1988 was 6–12 million. This population decline is the result of extensive hunting for fur, for glands used as medicine and perfume, and because the beavers' harvesting of trees and flooding of waterways may interfere with other land uses.

Otter subfamily of mammals

Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic or marine, with diets based on fish and invertebrates. Lutrinae is a branch of the weasel family Mustelidae, which also includes badgers, honey badgers, martens, minks, polecats, and wolverines.

The unique features of the platypus make it an important subject in the study of evolutionary biology, and a recognizable and iconic symbol of Australia. 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. [6]

Evolutionary biology Study of the processes that produced the diversity of life

Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth, starting from a single common ancestor. These processes include natural selection, common descent, and speciation.

Australia Country in Oceania

Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. It is the largest country in Oceania and the world's sixth-largest country by total area. The neighbouring countries are Papua New Guinea, Indonesia, and East Timor to the north; the Solomon Islands and Vanuatu to the north-east; and New Zealand to the south-east. The population of 25 million is highly urbanised and heavily concentrated on the eastern seaboard. Australia's capital is Canberra, and its largest city is Sydney. The country's other major metropolitan areas are Melbourne, Brisbane, Perth, and Adelaide.

Obverse and reverse Front and back side of coins, medals, orders of merit, and paper bills

Obverse and its opposite, reverse, refer to the two flat faces of coins and some other two-sided objects, including paper money, flags, seals, medals, drawings, old master prints and other works of art, and printed fabrics. In this usage, obverse means the front face of the object and reverse means the back face. The obverse of a coin is commonly called heads, because it often depicts the head of a prominent person, and the reverse tails.

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.

Captive breeding is the process of maintaining plants or animals in controlled environments, such as wildlife reserves, zoos, botanic gardens, and other conservation facilities. It is sometimes employed to help species that are being threatened by human activities such as habitat loss, fragmentation, over hunting or fishing, pollution, predation, disease, and parasitism. In some cases a captive breeding program can save a species from extinction, but for success, breeders must consider many factors—including genetic, ecological, behavioral, and ethical issues. Most successful attempts involve the cooperation and coordination of many institutions.

Taxonomy and etymology

Platypus (Ornithorhynchus anatinus). First Description 1799 Platypus (Ornithorhynchus anatinus). First Description 1799.jpg
Platypus (Ornithorhynchus anatinus). First Description 1799

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. [7] British scientists' initial hunch was that the attributes were a hoax. [8] 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, [9] and Robert Knox believed it might have been produced by some Asian taxidermist. [8] 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. [10]

Kingdom of Great Britain Constitutional monarchy in Western Europe between 1707 and 1801

The Kingdom of Great Britain, officially called simply Great Britain, was a sovereign state in western Europe from 1 May 1707 to 31 December 1800. The state came into being following the Treaty of Union in 1706, ratified by the Acts of Union 1707, which united the kingdoms of England and Scotland to form a single kingdom encompassing the whole island of Great Britain and its outlying islands, with the exception of the Isle of Man and the Channel Islands. The unitary state was governed by a single parliament and government that was based in Westminster. The former kingdoms had been in personal union since James VI of Scotland became King of England and King of Ireland in 1603 following the death of Elizabeth I, bringing about the "Union of the Crowns". After the accession of George I to the throne of Great Britain in 1714, the kingdom was in a personal union with the Electorate of Hanover.

New South Wales State of Australia

New South Wales is a state on the east coast of Australia. It borders Queensland to the north, Victoria to the south, and South Australia to the west. Its coast borders the Tasman Sea to the east. The Australian Capital Territory is an enclave within the state. New South Wales' state capital is Sydney, which is also Australia's most populous city. In September 2018, the population of New South Wales was over 8 million, making it Australia's most populous state. Just under two-thirds of the state's population, 5.1 million, live in the Greater Sydney area. Inhabitants of New South Wales are referred to as New South Welshmen.

George Shaw English botanist and zoologist

George Kearsley Shaw was an English botanist and zoologist.

The common name "platypus" is the latinisation of the Greek word πλατύπους (platupous), "flat-footed", [11] from πλατύς (platus), "broad, wide, flat" [12] and πούς (pous), "foot". [13] [14] Shaw assigned the species the Linnaean name Platypus anatinus when he initially 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 . [15] It was independently described as Ornithorhynchus paradoxus by Johann Blumenbach in 1800 (from a specimen given to him by Sir Joseph Banks) [16] and following the rules of priority of nomenclature, it was later officially recognised as Ornithorhynchus anatinus. [15] The scientific name Ornithorhynchus anatinus is derived from ορνιθόρυγχος (ornithorhynkhos), which literally means "bird snout" in Greek; and anatinus, which means "duck-like" in Latin.

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 technically incorrect and a form of pseudo-Latin; [10] the correct Greek plural would be "platypodes". Early British settlers called it by many names, such as "watermole", "duckbill", and "duckmole". [10] The name platypus is occasionally prefixed with the adjective "duck-billed" to form duck-billed platypus.

Description

Platypus in Broken River, Queensland Schnabeltier 1.jpg
Platypus in Broken River, Queensland

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. [17]

The body and the broad, flat tail of the platypus are covered with dense, brown fur that traps a layer of insulating air to keep the animal warm. [10] [15] The fur is waterproof, and the texture is akin to that of a mole. [18] The platypus uses its tail for storage of fat reserves (an adaptation also found in animals such as the Tasmanian devil [19] ). 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. [15] Platypuses have been heard to emit a low growl when disturbed and a range of other vocalisations have been reported in captive specimens. [10]

A colour print of platypuses from 1863 Platypus-sketch.jpg
A colour print of platypuses from 1863

Weight varies considerably from 0.7 to 2.4 kg (1.5 to 5.3 lb), with males being larger than females; males average 50 cm (20 in) in total length, while females average 43 cm (17 in), [15] with substantial variation in average size from one region to another, and 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. [20]

The platypus has an average body temperature of about 32 °C (90 °F) rather than the 37 °C (99 °F) typical of placental mammals. [21] 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. [22] [23]

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; [15] adults have heavily keratinised pads in their place. [15] 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. [24] The platypus jaw is constructed differently from that of other mammals, and the jaw-opening muscle is different. [15] 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 premammalian synapsids. However, the external opening of the ear still lies at the base of the jaw. [15] The platypus has extra bones in the shoulder girdle, including an interclavicle, which is not found in other mammals. [15] As in many other aquatic and semiaquatic vertebrates, the bones show osteosclerosis, increasing their density to provide ballast. [25] It has a reptilian gait, with the legs on the sides of the body, rather than underneath. [15] When on land, it engages in knuckle-walking on its front feet, to protect the webbing between the toes. [26]

Venom

The calcaneus spur found on the male's hind limb is used to deliver venom. Platypus spur.JPG
The calcaneus spur found on the male's hind limb is used to deliver venom.

While both male and female platypuses are born with ankle spurs, only the male's spurs deliver venom, [27] [28] [29] composed largely of defensin-like proteins (DLPs), three of which are unique to the platypus. [30] 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 defense. 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. [30] [31] 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. [32] [33] 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. [15]

The venom appears to have a different function from those produced by nonmammalian 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. [30]

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. [34]

Electrolocation

Platypus shown to children. Platypus in Geelong.jpg
Platypus shown to children.

Monotremes (for the other species, see Echidna) are the only mammals (apart from at least one species of dolphin) [35] known to have a sense of 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. [36] [37]

The electroreceptors are located in rostrocaudal rows in the skin of the bill, while mechanoreceptors (which detect touch) 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. Both electroreceptors and mechanoreceptors in the bill dominate the somatotopic map of the platypus brain, in the same way human hands dominate the Penfield homunculus map. [38] [39]

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, seen also in the Hammerhead shark while foraging. 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. [37]

Feeding by neither sight nor smell, [40] the platypus closes its eyes, ears, and nose each time it dives. [41] 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. [37] Experiments have shown the platypus will even react to an "artificial shrimp" if a small electric current is passed through it. [42]

Monotreme electrolocation probably evolved in order to allow the animals to forage in murky waters, and may be tied to their tooth loss. [43] The extinct Obdurodon was electroreceptive, but unlike the modern platypus it foraged pelagically (near the ocean surface). [43]

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. [44]

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 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 role in predation, while the accompanying visual acuity is insufficient for such activities. Furthermore, this limited acuity is matched by a 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; 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. [38]

Ecology and behaviour

Dentition, as illustrated in Knight's Sketches in Natural History Animaldentition ornithoryncusanatinus.png
Dentition, as illustrated in Knight's Sketches in Natural History
The platypus is very difficult to spot even on the surface of a river. Platipus-on-the-surface.jpg
The platypus is very difficult to spot even on the surface of a river.
Platypus swimming Platypus.jpg
Platypus swimming
Swimming underwater at 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. [45] Inland, its distribution is not well known; it is extinct in South Australia (apart from an introduced population on Kangaroo Island) [46] and 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. [47] 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. [48]

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. [15] Natural predators include snakes, water rats, goannas, hawks, owls, and eagles. Low platypus numbers in northern Australia are possibly due to predation by crocodiles. [49] The introduction of red foxes in 1845 for hunting may have had some impact on its numbers on the mainland. [20] The platypus is generally regarded as nocturnal and crepuscular, but individuals are also active during the day, particularly when the sky is overcast. [50] [51] 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. [51] 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. [52]

The platypus is an excellent swimmer and spends much of its time in the water foraging for food. When swimming, it can be distinguished from other Australian mammals by the absence of visible ears. [53] 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. [54] 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). [15]

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. [55] [56]

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. [53]

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. [57]

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. [53] 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. [55]

Reproduction

Platypus' nest with eggs replica Ornithorhynchus anatinus - nest with eggs - MUSE.JPG
Platypus' nest with eggs replica

When the platypus was first encountered by European naturalists, they were divided over whether the female laid eggs. This was not confirmed until 1884, when William Hay Caldwell was sent to Australia, where, after extensive searching assisted by a team of 150 Aborigines, he managed to discover a few eggs. [15] [30] Mindful of the high cost per word, Caldwell tersely wired London, "Monotremes oviparous, ovum meroblastic." That is, monotremes lay eggs, and the eggs are similar to those of reptiles in that only part of the egg divides as it develops.

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. [49] 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. [58] 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. [58]

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 (66 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). [59] The male takes no part in caring for its 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. [10]

The female platypus has a pair of ovaries, but only the left one is functional. [50] The platypus's genes are a possible evolutionary link between the mammalian XY and bird/reptile ZW sex-determination systems because one of the platypus's five X chromosomes contains the DMRT1 gene, which birds possess on their Z chromosome. [60] It lays one to three (usually two) small, leathery eggs (similar to those of reptiles), about 11 mm (0.43 in) in diameter and slightly rounder than bird eggs. [61] 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). [50] After laying her eggs, the female curls around them. The incubation period is divided into three phases. [62] 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. [63] During the second phase, the digits develop, and in the last phase, the egg tooth appears. [62]

Most mammal zygotes go through holoblastic cleavage, meaning that following fertilization the ovum is split due to cell divisions into multiple, divisible daughter cells. This is in comparison to the more ancestral process of meroblastic division in non-mammals (including platypuses), which causes the ovum to split but not 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. [64]

The newly hatched young 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. [10] [49] 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. [65] 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. [49] A platypus is born with teeth, but these drop out at a very early age, leaving the horny plates it uses to grind food. [66]

Evolution

Reconstruction of ancient platypus relative Steropodon Steropodon BW.jpg
Reconstruction of ancient platypus relative Steropodon

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. [67] 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. [67] [68] 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. [67] [69] Molecular clock and fossil dating suggest platypuses split from echidnas around 19–48 million years ago. [70]

Platypus

Echidnas

 live birth 

Marsupials

 true placenta 

Eutherians

Evolutionary relationships between the platypus and other mammals. [71]

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, [68] but are now considered more basal taxa. [72] 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. [73] 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. [72]

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 (up to about 167 million years ago). [73] [74] A fossilized tooth of a giant platypus species, Obdurodon tharalkooschild , was dated 5–15 million years ago. Judging by the tooth, the animal measured 1.3 meters long, making it the largest platypus on record. [75]

Platypus skeleton Platypus skeleton Pengo.jpg
Platypus skeleton

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. [76] One of the X chromosomes of the platypus have been found to have great homology to the bird Z chromosome. [77] The platypus genome also has both reptilian and mammalian genes associated with egg fertilisation. [40] [78] 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. [79] [80] 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. [40]

Conservation

A depiction of a platypus from a book for children published in Germany in 1798 Platypus-plate.jpg
A depiction of a platypus from a book for children published in Germany in 1798

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 current and historical abundance, however, are less well-known and it has probably declined in numbers, although still being considered as common over most of its current range. [51] The species was extensively hunted for its fur until the early years of the 20th century and, although protected throughout Australia since 1905, [65] until about 1950 it was still at risk of drowning in the nets of inland fisheries. [47] The platypus does not appear to be in immediate danger of extinction, because conservation measures have been successful, but it could be 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". [2]

Platypuses generally suffer from few diseases in the wild; however, public concern in Tasmania is widespread about the potential impacts of a disease caused by the fungus Mucor amphibiorum . The disease (termed mucormycosis) affects only Tasmanian platypuses, and has 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 are collaborating 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 current spread of the disease. [81]

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. [82] 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. [83] Healesville repeated its success in 1998 and again in 2000 with a similar stream tank. [84] Since 2008, platypus has bred regularly at Healesville, [85] including second-generation (captive born themselves breeding in captivity). [86] Taronga Zoo in Sydney bred twins in 2003, and breeding was again successful there in 2006. [84]

Platypus in wildlife sanctuaries

The platypus is kept, for conservation purposes, in special aquariums at the following Australian wildlife sanctuaries:

Queensland

Platypus House at Lone Pine Koala Sanctuary in Brisbane, Queensland Platypus house at Lone Pine Koala Sanctuary.jpg
Platypus House at Lone Pine Koala Sanctuary in Brisbane, Queensland

New South Wales

Victoria

  • Healesville Sanctuary, near Melbourne, Victoria, where the platypus was first bred in captivity by naturalist David Fleay in 1943. [82] The first platypus "born" in captivity was named "Corrie" and was quite popular with the public. In 1955, three months before a new "platypussary" (after "aviary") was opened, she unfortunately escaped from her pen into the nearby Badger Creek and apparently was never recovered.

International

As of 2017, there is no platypus in captivity outside of Australia. [86] 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. [90]

Cultural references

Big Platypus at the Australian Axeman's Hall of Fame Latrobe BigPlatypus.jpg
Big Platypus at the Australian Axeman's Hall of Fame

The platypus has been a subject in the Dreamtime stories of indigenous Australians, who believed the animal was a hybrid of a duck and a water rat. [91] :57–60 According to one story, 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. [91] :83–85

A platypus fur cape. Made in 1890. Donated to the National Gallery of Victoria by Mrs F Smith in 1985 Platypus cape unknown tasmania.jpg
A platypus fur cape. Made in 1890. Donated to the National Gallery of Victoria by Mrs F Smith in 1985

Platypuses has been used several times as a mascot: "Syd" the platypus was one of the three mascots chosen for the Sydney 2000 Olympics along with an echidna and a kookaburra, [92] "Expo Oz" the platypus was the mascot for World Expo 88, which was held in Brisbane in 1988, [93] and Hexley the platypus is the mascot for the Darwin operating system, the BSD-based core of macOS and other operating systems from Apple Inc. [94]

The platypus has been featured in songs, such as Green Day's "Platypus (I Hate You)" and Mr. Bungle's "Platypus". It is the subject of a children's poem by Banjo Paterson.

Australianstamp 1551.jpg
9d postage stamp from 1937

The platypus has frequently appeared in Australian postage stamps and coins. The earliest appearance is the 9d Australian stamp from 1937. The platypus re-appeared in the 1960–64 Australian Native Animal Series. Souvenir sheet of "from" Laos and Equatorial Guinea has also featured the animal. The platypus has appeared on a 1987 36 cent stamp and an Australian 1996 95 cent stamp. The 2006 Australian Bush Babies stamp series features a $4.65AUD stamp of a young platypus. A 5 cent stamp also produced in 2006 features the platypus also. 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.

In the animated series Phineas and Ferb , the title characters own a pet platypus, named Perry, who unknown to them, is a secret agent. The choice of a platypus was inspired by media underuse, as well as to exploit the animal's striking appearance. [95] As a character, Perry has been well received by both fans and critics. [96] [97]

See also

Notes

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Teinolophos trusleri is a prehistoric species of monotreme, or egg-laying mammal. It is known from four specimens, each consisting of a partial lower jawbone collected from Flat Rocks, Victoria, Australia. It lived during the Aptian age of the Lower Cretaceous.

Long-beaked echidna genus of mammals

The long-beaked echidnas make up one of the two extant genera of echidnas, spiny monotremes that live in New Guinea. There are three living species and two extinct species in this genus. The extinct species were present in Australia. Echidnas are one of the two types of mammals that lay eggs, the other being the platypus. The echidnas retain reptilian features such as egg-laying but display mammalian features such as fur and lactation.

<i>Obdurodon dicksoni</i> species of mammal

Obdurodon dicksoni is a extinct species of monotreme discovered in Australia, a semi-aquatic ornithorhynchid that resembled the platypus, Ornithorhynchus anatinus, that still inhabits the continent. The animal is known from Riversleigh fossils and is thought to have existed in the early to mid Miocene era, inhabiting pools and streams of freshwater in a once forested environment. Unlike the modern species, the animal possessed molars and a spoon-shaped bill that suggest they fed near the surface or edge of the water.

David Fleay Australian scientist

David Howells Fleay AM MBE was an Australian naturalist who pioneered the captive breeding of endangered species, and was the first person to breed the platypus in captivity.

Short-beaked echidna Spiny furred egg-laying mammal from Australia

The short-beaked echidna is one of four living species of echidna and the only member of the genus Tachyglossus. It is covered in fur and spines and has a distinctive snout and a specialized tongue, which it uses to catch its insect prey at a great speed. Like the other extant monotremes, the short-beaked echidna lays eggs; the monotremes are the only group of mammals to do so.

Venomous mammal animal of the class Mammalia that produces venom, which it use to kill or disable prey, or to defend from predators or conspecifics

Venomous mammals are animals of the class Mammalia that produce venom, which they use to kill or disable prey, to defend themselves from predators or conspecifics or in agonistic encounters. In modern nature, venomous mammals are rare. Mammalian venoms form a heterogeneous group having different compositions and modes of action and are present in three orders of mammals, Eulipotyphla, Monotremata, and Chiroptera. A fourth order, Primates, is proposed to have venomous representatives. To explain the rarity of venom delivery in Mammalia, Mark Dufton of the University of Strathclyde has suggested that modern mammalian predators do not need venom because they are able to kill quickly with their teeth or claws, whereas venom, no matter how sophisticated, requires time to disable prey.

Eastern long-beaked echidna species of mammal

The eastern long-beaked echidna, also known as Barton's long-beaked echidna, is one of three species from the genus Zaglossus to occur in New Guinea. It is found mainly in Papua New Guinea at elevations between 2,000 and 3,000 metres.

Platypus venom venom produced by the platypus

The platypus is one of the few living mammals to produce venom. Males have a pair of spurs on their hind limbs that secrete venom that is active only in breeding season, supporting the hypothesis that the use of venom is for competition for mates, not for protection. While the spur remains available for defense, outside of breeding season the platypus's venom gland lacks secretion. While the venom's effects are described as excruciatingly painful, it is not lethal to humans. Many archaic mammal groups possess similar tarsal spurs, so it is thought that, rather than having developed this characteristic uniquely, the platypus simply inherited its venom from its distant ancestors. Rather than being a unique outlier, the platypus is the last demonstration of what was once a common mammalian characteristic, and it can be used as a model for non-therian mammals and their venom delivery and properties.

<i>Zaglossus hacketti</i> species of mammal

Zaglossus hacketti is an extinct species of long-beaked echidna from Western Australia that is dated to the Pleistocene. It is known only from a few bones. It was about 1 m long and probably weighed about 30 kg (66 lb). This makes it the largest monotreme known to have ever lived. Due to the lack of cranial material, placement of Z. hacketti into the modern long-beaked echidna genus Zaglossus is uncertain.

Zaglossus robustus is an extinct species of long-beaked echidna known from the middle Miocene of Gulgong, New South Wales, Australia. It may belong in the genus Megalibgwilia. The supposed fossil platypus Ornithorhynchus maximus was based on a humerus of this species.

Mammalian reproduction

Most mammals are viviparous, giving birth to live young. However, the five species of monotreme, the platypuses and the echidnas, lay eggs. The monotremes have a sex determination system different from that of most other mammals. In particular, the sex chromosomes of a platypus are more like those of a chicken than those of a therian mammal.

Yinotheria affinities of metatheria

Yinotheria is a proposed basal subclass clade of crown mammals that contains a few fossils of the Mesozoic and the extant monotremes. Today, there are only five surviving species, which live in Australia and New Guinea, but fossils have been found in England, China, Madagascar and Argentina. The surviving species consist of the platypus and four species of echidna.

The monotremes represent the most primitive order of extant mammals. The platypus is indigenous to eastern Australia; the short-beaked echidna is indigenous to Australia and Papua New Guinea; whereas the long-beaked echidna is restricted to Papua New Guinea and Irian Jaya. Since monotremes exhibit characteristics common with both reptiles and mammals that are of great interest for the study of mammalian evolution.

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