Platypus

Name and taxonomy

The scientific name is Ornithorhynchus anatinus, which means a duck-like bird snout in Greek and Latin. George Shaw described the animal in 1799 and first called it Platypus anatinus, meaning flat foot. That genus name already belonged to a beetle, so the name Blumenbach gave a year later, Ornithorhynchus, took its place. The platypus is the sole living species of its genus and of its family, Ornithorhynchidae, in the order Monotremata.

Aboriginal languages hold dozens of names for it, among them boondaburra, mallingong, tambreet, dulai warrung and biladurang. Early settlers called it the watermole, the duckbill or the duckmole. Dictionaries accept platypuses or platypus as the plural, and platypi is a false Latin form. A young platypus has no official name, though puggle and platypup are both in use.

Evolution and relatives

Monotremes branched off early in the history of mammals, before the split between marsupials and placental mammals. Molecular clocks and fossils place the split between the platypus and the echidnas at about 19 to 48 million years ago. Cretaceous monotremes such as Steropodon and Teinolophos from New South Wales lie near the base of the group. Fossils named in 2024, Opalios and Dharragarra, may be the oldest members of the platypus family. Relatives found in Argentina show that monotremes once crossed from Australia to South America by way of Antarctica.

The closest fossil relative is Obdurodon, which lived in Australia from the late Oligocene to the Miocene and still had molar teeth. One giant species, Obdurodon tharalkooschild, is known from a single tooth and probably reached 1.3 metres in length. The modern platypus lost its teeth only about 2.5 million years ago. At that time the rakali, a large water rat, reached Australia from New Guinea. The rat took the hard-shelled prey, and the platypus is thought to have shifted to soft prey that horny pads can crush. The oldest fossil of the living species is about 100,000 years old.

Appearance

The body is low and streamlined, with short legs held out to the sides. Males average about 50 centimetres and 1.7 kilograms, and females about 43 cm and 0.9 kg. Animals grow larger towards the cold south of the range, in line with Bergmann's rule. Dense brown fur traps a layer of air that keeps the animal warm in cold water, and only otters have a thicker coat. The belly is paler, from pale brown to silver grey. Under ultraviolet light the fur glows blue-green, and this may hide the animal from predators that see ultraviolet.

The bill is soft skin over a long snout and lower jaw, with the nostrils on top near the tip. The eyes and ears sit in a groove behind the bill, and the groove closes when the animal dives. The front feet carry full webbing, which folds back when the animal walks on its knuckles on land. The tail is flat and furry, stores fat and works as a rudder. Adults have no teeth, only horny grinding pads, and no working stomach. Body temperature averages about 32 degrees Celsius, below the 37 degrees typical of placental mammals.

Habitat and range

The platypus lives only in the fresh waters of eastern Australia, from Queensland south to Tasmania and King Island. It uses rivers, streams, lakes and lagoon-like pools, from tropical rainforest to cold alpine country. It favours banks with tree roots, overhanging plants, reeds and logs, and water usually less than 5 metres deep. Some populations live above 1,000 metres.

On the South Australian mainland the species was thought extinct after a last sighting at Renmark in 1975. A nesting platypus was filmed there in 2020 at the reopened Warrawong Sanctuary. A population introduced to Kangaroo Island in the 1920s was said to number about 150 before the fires of the 2019 to 2020 season. The animal has almost vanished from the Murray-Darling Basin, probably because of poor water management. GBIF holds records from 6 countries, but every record outside Australia is probably a zoo or a museum specimen.

Diet and hunting

The platypus eats aquatic invertebrates: insect larvae, worms, shrimp, crayfish, mussels, tadpoles, fish eggs and small fish. It forages along the bottom with its eyes, ears and nostrils closed and digs into the mud with its bill. Rows of electric sensors in the bill pick up the tiny currents made when a shrimp moves its muscles. In experiments a platypus attacked an artificial shrimp carrying a small electric current. The Australian Museum reports that a platypus feeds for 10 to 12 hours a day.

Food goes into cheek pouches and is chewed at the surface between horny pads, with grit from the bottom to help. A dive lasts 30 to 140 seconds, and the animal can feed in water colder than 5 degrees Celsius. ADW notes that it takes trout, though nobody in Australia treats the loss as a problem. Like other small mammals that swim in cold water, it must eat a large share of its body weight each day.

Behaviour and social life

The platypus lives alone, and males avoid one another most of all. Where the ranges of two males overlap, they feed at different times so that they do not meet. It is mainly nocturnal, but it hunts at dusk in summer and by day in winter. It may spend half the day in the water and then rest in a burrow dug into the bank. A simple resting burrow is short, but a nesting burrow can run 30 metres into the bank.

Its swimming stroke is unique among mammals: the front feet paddle in turn while the hind feet and tail steer. A home range can stretch 0.37 to 7 kilometres of waterway, and a male's range overlaps those of three or four females. Animals that forage in streams use more ground than those in ponds. In captivity a platypus has lived up to 30 years, and one wild animal was caught again at 24 years old.

Communication and senses

Apart from one dolphin, monotremes are the only mammals with a sense of electricity. About 40,000 electric sensors lie in rows along the bill, and touch sensors cover the whole surface. In the brain the two senses share the same area, so the platypus may feel an electric field as a touch. It sweeps its head from side to side while hunting, which probably helps it judge the direction of a signal. The delay between the electric pulse and the pressure wave may tell it how far away the prey is.

The eyes are small and shut under water, and their acuity is poor, but they keep old traits shared with lungfish and amphibians. The ears work in air rather than under water, and the sense of smell is simpler than an echidna's. The animal is quiet: it growls when disturbed and squeaks when hurt. ADW notes that it makes some sounds, but nobody has shown what they mean.

Reproduction and life cycle

Breeding is seasonal, and it happens later in the south than in the north. In New South Wales and Victoria mating runs from about August to October. Males start most encounters, but the female decides: she swims off through logs if she is unwilling. If she is willing, the male grips her tail in his bill, curls his body around hers and bites the fur of her shoulder. The mating system is thought to be polygynous.

The eggs develop inside the female for about 28 days, and she then lays them in a grass-lined burrow. She usually lays 2 leathery eggs, each about 17 millimetres long, and curls around them for about 10 days. She blocks the tunnel with plugs of soil, which squeeze water from her fur each time she returns. The hatchlings are blind and hairless, and they lap thick milk from pores in her belly, because she has no teats. Egg laying was confirmed only in 1884, by William Hay Caldwell.

The young suckle for about 4 months and leave the burrow with a full coat at about 67% of adult weight. Young males travel further from home than young females, and both are full grown at about 2 years. Females breed from 2 years and go on past 9, though ADW says most start at 4. ADW gives a wild lifespan of up to 12 years, and AnAge records a captive that lived 22.6 years.

Predators and threats

Goannas, Murray cod, carpet pythons, eagles and saltwater crocodiles all take platypuses, and large eels may too. The red fox, feral cats and dogs are newer threats that arrived with Europeans. A male's venom spur is a weapon against other males in the breeding season, and males carry more spur wounds than females. The venom is a mix of defensin-like proteins made in glands in the thighs.

Platypuses carry ticks, fleas and mites, and one tick species, Ixodes ornithorhynchi, lives mainly on them. In Tasmania the fungus Mucor amphibiorum causes ulcers along the body, but the species seems to tolerate most parasites well. Opera house traps set for yabbies drown platypuses, and several states now ban them. Dams, pollution, urban runoff and water extraction damage the streams it needs.

Population and conservation

The IUCN rated the platypus Near Threatened in 2016, on an estimate that numbers had fallen by about 30% since European settlement. Some biologists think the true fall may be closer to 50%. No one seems to know how many platypuses remain, because the animal is shy and nocturnal. Victoria protected it in 1890, and every state followed by 1912.

A 2020 study from the University of New South Wales predicted a fall in abundance of 47 to 66% over fifty years under current threats. It warned of local extinction across about 40% of the range. A report that November found that platypus habitat had shrunk by 22% in thirty years, mostly in the Murray-Darling basin. South Australia lists the species as endangered, and Victoria listed it as vulnerable in 2021. The federal EPBC Act does not yet cover it, though scientists have asked for a threatened listing.

Relationship with humans

Aboriginal Australians hunted the platypus for food and prized its fatty tail. From the late 19th century Europeans shot it for fur, which went into hats, slippers and rugs, until the law stopped the trade in 1912. Naturalists also killed animals and took eggs, partly for science and partly to beat rivals from other countries. During the Second World War Australia sent live platypuses abroad as diplomatic gifts, and one meant for Winston Churchill died at sea.

Captive breeding is hard: David Fleay first managed it at Healesville Sanctuary in 1943, and success there came again in 1998 and 2000. Taronga Zoo bred twins in 2003 and has since released young into the wild. As of 2019 the only platypuses outside Australia lived at the San Diego Zoo Safari Park. The animal is a symbol of Australia and appears on stamps and coins, and it was a mascot of the Sydney Olympics in 2000.

A male can hurt a person who handles it: the spur causes swelling and a pain that can last for months. No death of a person from platypus venom appears in the sources. The animal is otherwise shy and harmless and avoids people.

In culture and myth

The platypus appears in the Dreamtime stories of several Aboriginal peoples. Some of them saw it as a cross between a duck and a water rat. In a story from the upper Darling River, a large water rat named Biggoon kidnaps a duck who strays from her flock. She escapes, returns and lays two eggs, which hatch into the first platypuses, and the family goes to live in the mountains. In another upper Darling story, the land animals, the water animals and the birds all ask the platypus to join them. It refuses every group, saying that it is special on its own, and stays friends with all of them.

The platypus is a totem for some Aboriginal peoples, and it holds special meaning for the Wadi Wadi of the Murray River. Those peoples protect the animal as part of their care for country. For Europeans it became a symbol of the strangeness of Australia, from the doubted skin of 1799 to the egg debate of 1884. Modern blogs read it as a symbol of individuality, which is probably a gloss on the Dreamtime story rather than a tradition.