Alongside the four kinds of echidnas, the platypus is among the five remaining species of monotremes, mammals that lay eggs rather than birthing live young. Like its fellow monotremes, the platypus detects prey in murky water through a method called electrolocation. It’s also one of the rare venomous mammals, with the male sporting a spur on his hind foot that injects a venom causing intense pain.

European naturalists were initially puzzled by this strange, egg-laying, duck-billed, beaver-tailed, otter-footed mammal. In 1799, the first scientists to study a preserved platypus specimen thought it was a hoax, believing it to be made up of parts from different animals stitched together.

The platypus’s distinctive traits make it a key subject in evolutionary biology studies and an unmistakable symbol of Australia. It holds cultural significance for several Aboriginal communities, who historically hunted it for food. The platypus has also been a national mascot, appears on the reverse side of the Australian twenty-cent coin, and serves as an emblem for the state of New South Wales.

Though once hunted for its fur, the platypus has been legally protected across all states where it lives since 1912. While its population isn’t in grave danger, it faces challenges from pollution and habitat loss, and captive-breeding programs have seen limited success. Currently classified as near-threatened by the IUCN, a report from November 2020 recommended upgrading its status to threatened under the federal EPBC Act due to habitat destruction and decreasing numbers in all states.

On naming

When Europeans first stumbled upon the platypus back in 1798, Captain John Hunter, the second Governor of New South Wales, sent a pelt and a sketch of the creature over to Great Britain. The British scientists were initially sceptical, thinking it might be a prank. George Shaw, who penned the first description in the “Naturalist’s Miscellany” in 1799, admitted that it was hard not to doubt its authenticity. Meanwhile, Robert Knox suspected it might have been the handiwork of an Asian taxidermist. They even thought someone might have stitched a duck’s beak onto a beaver-like animal. Shaw went so far as to snip the dried skin with scissors to check for stitches.

The name “platypus” comes from the Greek words ‘platús’ meaning ‘broad, wide, flat,’ and ‘poús’ meaning ‘foot,’ so it literally means ‘flat-foot.’ Shaw originally named it Platypus anatinus, but it turned out that the name Platypus was already taken by a genus of wood-boring beetles. Johann Blumenbach described it separately as Ornithorhynchus paradoxus in 1800, using a specimen from Sir Joseph Banks. Eventually, the name Ornithorhynchus anatinus stuck, following the rules of scientific naming.

There’s no universally agreed-upon plural for “platypus” in English. Scientists usually go with “platypuses” or just “platypus.” Some folks use “platypi,” though that’s a bit of pseudo-Latin. If we were to stick strictly to its Greek roots, the plural would be “platypodes.” Early British settlers had a bunch of names for it, like “watermole,” “duckbill,” and “duckmole.” Sometimes, it’s specifically called the “duck-billed platypus.”

The scientific name Ornithorhynchus anatinus translates to ‘duck-like bird-snout,’ with the genus name coming from the Greek ‘ornith-‘ for ‘bird’ and ‘rhúnkhos’ for ‘snout’ or ‘beak.’ The species name ‘anatinus’ is Latin for ‘duck-like,’ derived from ‘anas,’ meaning ‘duck.’ The platypus is the only living member of its family, Ornithorhynchidae, making it a unique and fascinating creature.

Description

In David Collins’s account of the new colony from 1788 to 1801, he mentions a peculiar creature, referring to it as “an amphibious animal, of the mole species,” which he also illustrated.

The platypus is quite a fascinating animal. Its body and broad, flat tail are clad in dense, brown, biofluorescent fur, which traps a layer of insulating air to keep the critter warm. This fur is waterproof and feels a bit like that of a mole. The tail also serves as a storage for fat reserves, similar to what you see in the Tasmanian devil. The webbing on its front feet is more pronounced, and when the platypus walks on land, it folds up the webbing in a knuckle-walking manner to protect it.[26] The elongated snout and lower jaw, covered in soft skin, form the bill. The nostrils sit on the top of the snout, while the eyes and ears are just behind in a groove that closes when the animal is underwater. Interestingly, platypuses can emit a low growl when they’re disturbed, and various vocal sounds have been recorded in captivity.

The size of these critters can vary quite a bit depending on the region. They typically weigh between 0.7 and 2.4 kg (1 lb 9 oz to 5 lb 5 oz); males are usually about 50 cm (20 in) long, while females are a bit smaller at 43 cm (17 in). This variation doesn’t seem to follow any specific climate patterns and might be influenced by factors like predation and human activities.

Platypuses have an average body temperature of around 32 °C (90 °F), which is lower than the typical 37 °C (99 °F) seen in placental mammals. Researchers think this has been a gradual adaptation to tough environmental conditions among the few remaining monotreme species, rather than a trait of past monotremes.

Besides laying eggs, the anatomy, development, and genetics of monotremes show some similarities to reptiles and birds. For instance, the platypus has a reptilian gait, with legs positioned on the sides of its body rather than underneath. Its genes might represent an 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 have on their Z chromosome.

Like all true mammals, the tiny bones that conduct sound in the middle ear are fully integrated into the skull, rather than lying in the jaw as seen in pre-mammalian synapsids. However, the external ear opening still lies at the base of the jaw.[16] The platypus also has extra bones in the shoulder girdle, including an interclavicle not found in other mammals.[16] Similar to many other aquatic and semiaquatic vertebrates, their bones show osteosclerosis, which increases their density to provide ballast.

The platypus jaw is constructed differently from that of other mammals, and the muscle used to open the jaw is different too. Modern platypus young have three teeth in each of the maxillae (one premolar and two molars) and dentaries (three molars), but they lose these teeth before or just after they leave the breeding burrow; adults develop heavily keratinised food-grinding pads known as ceratodontes instead. The first upper and third lower cheek teeth of platypus nestlings are small, each with one principal cusp, while the other teeth have two main cusps.

Venom

The heel spur on a male platypus’s back leg is used to inject venom. While both male and female platypuses are born with these spurs, only the males’ are capable of delivering venom. This venom is strong enough to kill smaller creatures like dogs, and although it’s not deadly to humans, it can cause weeks of severe pain. Swelling quickly appears around the bite and spreads through the affected area, sometimes leading to intense pain that can last for days or even months.

The venom mainly consists of defensin-like proteins (DLPs) created by the immune system, three of which are unique to the platypus. In other creatures, defensins are used to kill harmful bacteria and viruses, but in platypuses, they are also gathered into venom to fend off predators. The venom is produced in the male’s crural glands, which are kidney-shaped and connected by a thin duct to a heel spur on each back leg. Female platypuses, like echidnas, have small spur buds that do not develop and fall off before they turn one year old, and they lack functional crural glands. Venom production increases in males during the breeding season and may be used to establish dominance.

Similar spurs are found in many ancient mammal groups, suggesting this was a common feature among early mammals.

Electrolocation

In a rather fascinating twist, the platypus has developed electroreception, a trait it has acquired secondarily. The receptors responsible for this ability are arranged in stripes on its bill, granting it heightened sensitivity to the sides and below. This peculiar arrangement allows the platypus to make swift head movements while swimming to detect its prey.

Monotremes, which include the platypus, are the only mammals known to possess electroreception, with the exception of the Guiana dolphin. The platypus, however, boasts the most sensitive electroreception among monotremes. Interestingly, when hunting, the platypus relies neither on sight nor smell. Instead, it closes its eyes, ears, and nose when diving. By digging into the stream bed with its bill, it uses its electroreceptors to pick up on the minute electric currents produced by the muscular contractions of its prey. This remarkable ability allows it to differentiate between living and non-living objects. Experiments have revealed that the platypus will even respond to an “artificial shrimp” if a small electric current is applied to it.

Eyes

Recent investigations propose that the ocular structures of the platypus exhibit greater resemblance to those of Pacific hagfish or Northern Hemisphere lampreys rather than to the eyes of most tetrapods. Notably, the platypus’s eyes possess double cones, a feature uncommon among mammals.

Despite the diminutive size of the platypus’s eyes and their limited use underwater, various characteristics suggest that vision was once paramount to its forebears. The corneal surface and the adjoining surface of the lens are flat, whereas the posterior surface of the lens is markedly curved. This configuration parallels the ocular structures of other aquatic mammals such as otters and sea lions. A temporal concentration of retinal ganglion cells, crucial for binocular vision, hints at a vestigial predatory function, albeit the visual acuity is inadequate for such pursuits. The limited acuity is in line with low cortical magnification, a small lateral geniculate nucleus, and a large optic tectum, implying that the visual midbrain assumes a more significant role than the visual cortex, akin to certain rodents.

These attributes indicate that the platypus has adapted to an aquatic and nocturnal existence, prioritising its electrosensory system at the expense of its visual capabilities. This adaptation stands in stark contrast to the short-beaked echidna, which inhabits arid environments and possesses a scant number of electroreceptors. Conversely, the long-beaked echidna, which resides in more humid habitats, exhibits an intermediate number of electroreceptors, bridging the gap between the other two monotreme species.

The electroreceptors are organised in rostrocaudal rows within the skin of the bill, whereas mechanoreceptors responsible for touch are spread evenly across the bill. The electrosensory area of the cerebral cortex is located in the tactile somatosensory region, and some cortical cells receive input from both electroreceptors and mechanoreceptors. This suggests that the platypus perceives electric fields similarly to how it feels physical touches. These receptors dominate the somatotopic map of the platypus brain, much like how human hands dominate the Penfield homunculus map.

The platypus can discern the direction of an electric source, possibly by comparing the differences in signal strength across the electroreceptors. This ability is further enhanced by the characteristic side-to-side motion of its head during hunting. Additionally, it may be able to gauge the distance of moving prey by noting the time lag between their electrical and mechanical pressure pulses.

The ability of monotremes to use electrolocation for hunting in murky waters might be linked to their tooth loss. The extinct Obdurodon, which was also electroreceptive, differed from the modern platypus in that it foraged pelagically, near the ocean surface.

Distribution, Ecology, and Behaviour

The platypus thrives in small streams and rivers spanning a vast range from the chilly highlands of Tasmania and the Australian Alps to the lush tropical rainforests along the coast of Queensland, stretching as far north as the base of the Cape York Peninsula.

Inland distribution remains somewhat enigmatic. Once thought extinct on the South Australian mainland, the last confirmed sighting occurred in Renmark in 1975. During the 1980s, John Wamsley initiated a platypus breeding programme at Warrawong Sanctuary, which has since closed. However, in 2017, there were unconfirmed sightings downstream from the sanctuary, and in October 2020, a nesting platypus was captured on film within the recently reopened sanctuary.

On Kangaroo Island, a population introduced in the 1920s is estimated to comprise around 150 individuals in the Rocky River area of Flinders Chase National Park. The devastating bushfires of the 2019–20 season ravaged large portions of the island, severely affecting wildlife. Nevertheless, recovery efforts by the SA Department for Environment and Water have led to habitat restoration, with sightings reported by April 2020.

The platypus has vanished from the main Murray–Darling Basin, likely due to deteriorating water quality from land clearing and irrigation, although it persists in Victoria’s Goulburn River. Its presence along coastal river systems is erratic: absent in some relatively pristine rivers yet found in some quite degraded ones, like the lower Maribyrnong.

In captivity, platypuses can live up to 30 years, while wild individuals have been recaptured at 24 years of age. Adult mortality rates in the wild seem to be low. Natural predators include snakes, water rats, goannas, hawks, owls, and eagles. In Northern Australia, low platypus numbers might be attributed to crocodile predation. The introduction of red foxes in 1845 for sport hunting may have impacted mainland populations. Typically nocturnal and crepuscular, the platypus can also be active on cloudy days. Its habitat spans rivers and the riparian zone, where it finds both prey and riverbanks for burrowing.

An adept swimmer, the platypus spends much of its time in water, foraging for food. It swims uniquely among mammals, using alternate strokes of its front feet while the webbed hind feet are tucked against the body, aiding steering along with the tail. Remarkably, it maintains a relatively low body temperature of about 32 °C while foraging in water as cold as 5 °C. Dives typically last around 30 seconds, with a maximum aerobic dive limit of 40 seconds, and 10 to 20 seconds spent at the surface between dives.

The platypus rests in a short, straight burrow in the riverbank, about 30 cm above water level, with its oval entrance often concealed under a tangle of roots. It may sleep up to 14 hours a day after spending half a day diving.

Diet

The platypus sustains itself on a diet comprising annelid worms, insect larvae, freshwater shrimp, and yabbies (crayfish). These agile hunters utilize their distinctive snouts to excavate these prey items from the riverbed or capture them whilst navigating through the water. Once caught, the platypus stores its prey in cheek-pouches and brings it to the surface before consuming it.

Interestingly, the platypus needs to consume a substantial amount of food, approximately 20% of its body weight each day. This voracious appetite necessitates that the platypus dedicates around 12 hours a day to foraging for sustenance.

Reproduction of the Platypus

Platypus undergoe a unique reproductive process. The breeding season of this species spans from June to October, although this period can vary slightly depending on the locality. Research has identified both resident and transient platypuses, indicating a polygynous mating system. Females usually reach sexual maturity in their second year, with some continuing to breed up to nine years of age or more. Males, on the other hand, do not participate in nesting activities and reside in their own burrows throughout the year.

Post-mating, the female constructs an intricate nesting burrow, which can extend up to 20 meters (about 65 feet) in length. She gathers fallen leaves and reeds, tucking them under her curled tail to carry to the burrow. These materials are used to soften the tunnel floor and provide bedding for the nest.

Interestingly, the female platypus has two ovaries, but only the left one is functional. She lays between one to three small, leathery eggs, typically two, which are about 11 mm in diameter and somewhat rounder compared to bird eggs. These eggs undergo a development period of approximately 28 days within the uterus, followed by around 10 days of external incubation. This differs significantly from a chicken egg, which spends roughly one day in the reproductive tract and 21 days incubating externally.

The female wraps herself around the incubating eggs, which develop in three distinct phases. Initially, the embryo lacks functional organs and relies entirely on the yolk sac for nourishment. As development progresses, digits form, and finally, an egg tooth appears. Historically, European naturalists were skeptical about the egg-laying nature of the platypus, but this was conclusively demonstrated by William Hay Caldwell in 1884.

In most mammals, zygotes undergo holoblastic cleavage, where the egg splits completely into multiple cells. However, monotremes like the platypus, as well as reptiles and birds, experience meroblastic cleavage. In this process, the ovum does not divide entirely, and the cells at the edge of the yolk remain connected to the egg’s cytoplasm. This connection facilitates the exchange of waste and nutrients between the yolk and the embryo.

Newly hatched platypuses, known as “puggles,” are particularly vulnerable, being blind and hairless. They are nourished by their mother’s milk, which is essential for their growth and development. Unlike most mammals, the platypus lacks teats. Instead, milk is secreted through pores in the skin and pools in grooves on the mother’s abdomen, from which the young lap it up.

During the incubation and weaning periods, the mother initially leaves the burrow only briefly to forage. She creates thin soil plugs along the burrow’s length, possibly to protect her young from predators. These plugs also help squeeze water from her fur as she returns, keeping the burrow dry. After about five weeks, the mother begins to spend more time away from the burrow, and by four months, the young are ready to emerge.

Platypuses are born with teeth, but these are lost at a very early stage, leaving behind horny plates used for grinding food. This unique reproductive strategy underscores the remarkable adaptations of the platypus to its environment.

Evolution of the Platypus

The platypus, along with other monotremes such as echidnas, has often been misunderstood throughout history. During the 19th century, myths perpetuated the notion that monotremes were ‘inferior’ or quasi-reptilian creatures. These misconceptions lingered until more refined research debunked them. In 1947, William King Gregory proposed that marsupials and placental mammals diverged earlier, with monotremes branching off subsequently. However, modern research and fossil evidence have painted a different picture. Monotremes, including the platypus, are actually the remnants of an early split in the mammalian lineage, with marsupials and placental mammals diverging later.

Molecular clock estimates and fossil records suggest that platypuses separated from echidnas between 19 and 48 million years ago. The oldest known fossil of a modern platypus dates back to approximately 100,000 years ago, from the Quaternary period. Earlier extinct monotremes such as Teinolophos and Steropodon from the Cretaceous period were initially thought to be closely related to the modern platypus but are now considered more basal taxa. The fossilised jawbone of Steropodon, discovered in New South Wales, features three molar teeth, unlike the toothless adult platypus of today. These molar teeth were initially believed to be tribosphenic, supporting Gregory’s theory, but further research revealed they evolved through a different process.

The Teinolophos fossil, dated at around 110 million years old, is the oldest mammal fossil discovered in Australia. Unlike modern platypuses and echidnas, Teinolophos did not possess a beak. In 2024, fossils of early platypus relatives from the Late Cretaceous (Cenomanian) period, including Opalios and Dharragarra, were unearthed from the same strata as Steropodon. Dharragarra might be the oldest member of the platypus lineage, retaining the same dental formula found in Cenozoic relatives.

Other fossil relatives, such as Monotrematum and Patagorhynchus, dating from the latest Cretaceous (Maastrichtian) and mid-Paleocene periods in Argentina, suggest that some monotremes managed to migrate from Australia to South America when the continents were connected via Antarctica. These fossils are also considered potential members of the platypus lineage. The closest fossil relative of the platypus, Obdurodon, dating from the late Oligocene to the Miocene in Australia, closely resembled the modern platypus but retained molar teeth.

A fossilised tooth of the giant platypus Obdurodon tharalkooschild suggests that the animal, which lived between 5 and 15 million years ago, measured about 1.3 metres long, making it the largest known platypus. The enigma of tooth loss in the modern platypus, which retained a distinctive lower molar tooth row for over 95 million years, was resolved by recent studies. These suggest that the loss occurred around the Plio-Pleistocene era (approximately 2.5 million years ago) when the rakali, a large semiaquatic rodent, migrated to Australia from New Guinea. The competition with rakalis for hard-bodied prey like crayfish and mussels may have driven the platypus to lose its teeth and develop horny pads, allowing it to specialize in softer-bodied prey, thus avoiding direct competition.

Status and Threats

The platypus maintains a distribution largely unchanged from before European settlement, save for its disappearance in South Australia. Despite this, human activities have fragmented and altered its habitat. Although exact historical population figures are elusive, it is widely believed that platypus numbers have dwindled. As of 1998, the species was still generally regarded as common within its existing range. Historically, the platypus faced significant hunting pressure for its fur until the early 1900s. Legal protections commenced in Victoria in 1890 and extended nationwide by 1912. Nonetheless, until around 1950, platypuses continued to drown in inland fishing nets.

In 2016, the International Union for Conservation of Nature (IUCN) upgraded the platypus to “near threatened” status. Despite legal protections, it is only listed as endangered in South Australia under the National Parks and Wildlife Act 1972. A recommendation in November 2020 proposed categorising the platypus as vulnerable across all states, with Victoria officially adopting this status under the Flora and Fauna Guarantee Act 1988 on 10 January 2021.

Habitat Destruction

While the platypus is not on the brink of extinction, it faces significant threats from habitat disruption due to dams, irrigation, pollution, netting, and trapping. Reduced water flow and levels from droughts and water extraction for various uses also pose risks. The IUCN’s 2016 assessment on the Red List notes a 30 percent decline in platypus numbers since European settlement. Although listed as endangered in South Australia, the species lacks protection under the federal Environmental Protection and Biodiversity Conservation (EPBC) Act.

Concerns have long existed that the decline in platypus populations may be more severe than estimated. In January 2020, researchers from the University of New South Wales warned that the species faces extinction risks due to water resource extraction, land clearing, climate change, and severe drought. Projections indicated a potential 47–66% reduction in abundance and a 22–32% decline in metapopulation occupancy over the next 50 years, leading to local extinctions across 40% of the range. Climate change could exacerbate these declines, with a 51–73% reduction in abundance and a 36–56% decline in metapopulation occupancy by 2070. The study highlighted the need for national conservation efforts, including more surveys, threat mitigation, and better river management to preserve platypus habitats. Co-author Gilad Bino expressed concerns that 2016 baseline estimates might be overly optimistic, suggesting population numbers could already be halved.

A 2020 report by the University of New South Wales, funded by the Australian Conservation Foundation in collaboration with the World Wildlife Fund Australia and the Humane Society International Australia, revealed a 22 percent reduction in platypus habitat over the past 30 years. The report recommended listing the platypus as a threatened species under the EPBC Act, with the steepest population declines observed in New South Wales, particularly within the Murray-Darling Basin.

Disease

Platypuses generally exhibit few diseases in the wild; however, there has been concern since 2008 about the impact of a fungal disease, mucormycosis, caused by Mucor amphibiorum in Tasmania. This disease, unique to Tasmanian platypuses, results in skin lesions or ulcers on various body parts, potentially leading to death from secondary infections or impaired thermoregulation and foraging. The Department of Primary Industries and Water’s Biodiversity Conservation Branch, in collaboration with NRM North and researchers from the University of Tasmania, has been investigating the disease’s impact, transmission, and spread among Tasmanian platypuses.

Wildlife Sanctuaries

The world was first introduced to the enigmatic platypus back in 1939, courtesy of an article published by National Geographic Magazine. This piece delved into the intricate efforts to study and rear this peculiar creature in captivity. The endeavour of raising platypuses is notoriously challenging, with only a handful of young successfully nurtured since then. Noteworthy among these successes are the efforts at Healesville Sanctuary in Victoria.

At the forefront of these pioneering efforts was David Fleay, who ingeniously devised a “platypusary”—a replica stream housed within a tank—at Healesville Sanctuary. Remarkably, this setup saw its first breeding success in 1943. In a rather unfortunate turn of events in 1972, Fleay stumbled upon a deceased baby platypus, estimated to be around 50 days old, which was presumed to have been born in captivity at his wildlife park in Burleigh Heads on the Gold Coast, Queensland.

Healesville continued to achieve breeding milestones, with successful attempts in 1998 and again in 2000, both involving a similar stream tank setup. Since 2008, the sanctuary has seen regular breeding of platypuses, including instances where second-generation animals (those born in captivity) have themselves reproduced in captivity. Taronga Zoo in Sydney also made headlines in 2003 with the birth of twins, and again in 2006 with another successful breeding attempt.

Captivity

As of 2019, you would find the only platypuses outside Australia residing in the San Diego Zoo Safari Park, located in California, USA. Prior to this, three attempts were made to introduce these fascinating creatures to the Bronx Zoo—in 1922, 1947, and 1958. Out of these, the 1947 endeavour saw two of the three platypuses, affectionately named Penelope and Cecil, survive for over eighteen months, marking a somewhat bittersweet success.

Human Interactions

Historically, Aboriginal Australians hunted the platypus, especially valuing their fatty tails for their nutritional benefits. Post-colonisation, Europeans pursued platypuses for their fur from the late 19th century until 1912, when such activities were outlawed. European scientists also captured and killed these creatures or took their eggs, driven by both scientific curiosity and the desire to outdo their international peers.

Cultural References

In Aboriginal Australian Dreamtime lore, the platypus often appears. Some tribes believed it to be a crossbreed between a duck and a water rat. One tale from the upper Darling River region tells of various animal groups vying for the platypus’s allegiance. However, the platypus chose to remain unaffiliated, preferring to be friends with all groups rather than belonging to one. Another story from the same region narrates the adventure of a young duck who, after being kidnapped by a water-rat named Biggoon, returned home to lay two eggs that hatched into peculiar furry creatures. These creatures, along with their mother, were subsequently banished to the mountains.

For some Aboriginal clans, the platypus serves as a totem, which is a natural object, plant, or animal inherited by clan members as a spiritual emblem. The Wadi Wadi people, residing along the Murray River, hold the platypus in high regard and actively work to protect and conserve it due to its cultural significance.

The platypus is also a potent symbol of Australian identity. During the 1940s, live platypuses were gifted to allies in WWII to foster goodwill and morale. Over the years, the platypus has been adopted as a mascot for various events: Syd the platypus for the Sydney 2000 Summer Olympics, Expo Oz for World Expo 88 in Brisbane, and Hexley for Apple’s Darwin operating system.

Since the introduction of decimal currency in Australia in 1966, the 20-cent coin has featured a platypus design by Stuart Devlin. The animal has also graced numerous Australian postage stamps, including the 2015 “Native Animals” series and the 2016 “Australian Animals Monotremes” series.

In popular culture, the American animated series “Phineas and Ferb” features a pet platypus named Perry, who leads a double life as a secret agent. The creators chose a platypus due to its unique appearance and relative underrepresentation in media. Interestingly, the character’s theme song borrows from the Wikipedia description of the platypus, specifically the phrase “semiaquatic egg-laying mammal.” Fans and critics alike have warmly received Perry, and real platypuses exhibit a similar cyan hue under ultraviolet light.