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 of the 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 has a sense of electrolocation, which it uses to detect prey in water while its eyes, ears and nostrils are closed. It is one of the few species of venomous mammals, as the male platypus has a spur on each hind foot that delivers an extremely painful venom.
The unusual appearance of this egg-laying, duck-billed, beaver-tailed 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, and has appeared on stamps and currency.
The platypus was hunted for its fur, but since 1912 it has been a legally protected species in all states where it is found. Captive breeding programs have had slight success, and it is vulnerable to pollution, bycatching and climate change. 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.
Taxonomy and naming
Australian Aboriginal people have referred to the platypus in various ways depending on Australian indigenous languages and dialects. Among the names found: boondaburra, mallingong, tambreet, watjarang (names in Yass, Murrumbidgee, and Tumut), tohunbuck (region of Goomburra, Darling Downs), dulaiwarrung or dulai warrung (Woiwurrung language, Wurundjeri, Victoria), djanbang (Bundjalung, Queensland), djumulung (Yuin language, Yuin, New South Wales), maluŋgaŋ (ngunnawal language, Ngunnawal, Australian Capital Territory), biladurang, wamul, dyiimalung, oornie, dungidany (Wiradjuri language, Wiradjuri, Victoria, New South Wales), oonah, etc. The name chosen and approved in Palawa kani (reconstructed Tasmanian language) is larila.
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—because it arrived in England via the Indian Ocean—that it might have been created by Chinese sailors. It was thought somebody had sewn a duck's beak onto the body of a beaver-like animal. Shaw used a pair of scissors to check for stitches.
The common name "platypus" means 'flat-foot', deriving from the Greek word (),πλατύπους , Henry George Liddell, Robert Scott, A Greek-English Lexicon, on Perseus from ( 'broad, wide, flat')πλατύς , A Greek-English Lexicon, on Perseus and ( 'foot').πούς , A Greek-English Lexicon, on Perseus 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 a 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.
Various dictionaries list "platypuses" or simply "platypus" as the plural. 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 European settlers called it by many names, such as "watermole", "duckbill", and "duckmole". Occasionally it is specifically called the "duck-billed platypus". There is no official term for platypus young, but the term "platypup" sees unofficial use, as does "puggle".
The scientific name Ornithorhynchus anatinus literally means 'duck-like bird-snout', deriving its genus name from the Greek root ( ornith or órnīs 'bird') and the word ( 'snout', 'beak'). Its species name is derived from Latin ('duck-like') from 'duck'. The platypus is the sole living representative or monotypic taxon of its family (Ornithorhynchidae).
Description
Most of the platypus' small streamlined body is covered with short, dense, brown fur that traps a layer of insulating air to keep the animal warm, both in and out of water. The fur coat is waterproof and consists of flattened guard hairs and curvy underfur hairs. It is one of the most densely furred mammals, behind only otters. It is also biofluorescent and glows cyan and green when under ultraviolet light; this may serve to camouflage it in low lighting from UV-sensitive predators. It is also unique among mammal in having hair pigmentation melanosomes that are hollow. The duck-like bill consists of a long snout and lower jaw which is covered in soft skin. The nostrils are located near the tip of the snout's dorsal surface, while the eyes and ears are just behind the snout in a groove which closes underwater. It has cheek pouches for storing food. The platypus's wide, flat tail is compared to a beaver's but is furry rather than scaly; it stores fat reserves and can act as a rudder during swimming. The legs are short and have a sprawling stance. Webbing is more significant on the front feet. While walking on land, the feet are folded up in knuckle-walking to protect the webbing.
The platypus has an interclavicle in the shoulder girdle, a trait which they share in common with reptiles. As in many other aquatic and semiaquatic vertebrates, the bones show osteosclerosis, increasing their density to reduce buoyancy. Adult platypuses lack teeth and instead have heavily keratinised food-grinding pads. Young platypuses have one premolar tooth and two molars on each maxillae, and three molars on the dentaries. The first upper and third lower cheek teeth have only one major cusp, while the rest have two. They lose their teeth around the time they leave their natal burrow.
The platypus lacks a functional stomach, due to the lack of genes necessary for creating and secreting pepsin proteases. However, the platypus's digestive tract has a pouch-like section that assists with nutrient absorption in the intestines.
Male platypuses have an average length of and weight of , while females are smaller with an average length of and weight of . The species follows Bergmann's rule, with individuals being larger the farther south they are, due to colder climates; there are local variations, however. The platypus has an average body temperature of about , lower than the 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.
The platypus has a single opening, called a cloaca, for both the reproductive and waste systems. The male platypus has penile spines and an asymmetrical glans penis that is larger on the left side. The female has two ovaries, with the right one being non-functional, and teats are absent.
Senses
Monotremes are the only mammals (apart from the Guiana dolphin) known to have a sense of electroreception. The platypus relies on electrolocation when feeding, as the eyes, ears, and nose are closed while underwater. Digging in the bottom of streams with its bill, its electroreceptors detect tiny electric currents generated by the muscular contractions of its prey. Experiments have shown the platypus will even react to an "artificial shrimp" if a small electric current is passed through it.
The 40,000 electroreceptors are arranged in rows in the skin of the bill from front to back, 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 as 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 array 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 via the timing difference between electrical and mechanical pressure sensations. 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 in open water.
The eyes of the platypus have basal traits also found in lungfish and amphibians, such as scleral cartilage, double cones, and droplets. The platypus's eyes are small and shut under water, though several features indicate its ancestors relied on vision. As with other aquatic mammals, the eye has a flattened cornea and surrounding lens, while the posterior surface of the lens is sharply inclined. 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 wetter habitats is intermediate between the other two monotremes.
The ears of the platypus are adapted for hearing while out of water. As in all true mammals, it has three middle ear bones, though the cochlea lacks spirals, but is described as "well organised". Within the cochlea, there are rows of inner and outer hair cells. As in placental mammals, the outer hair cells of the platypus are adapted for hearing high frequencies, suggesting it is an ancestral mammalian trait. However it also possesses more rows of inner hair cells. The olfactory (smelling) systems of the platypus and the echidna independently evolved from an ancestor with less advanced smelling. The main olfactory bulb of the platypus lacks the complex layers of the echidna, while both the piriform cortex and flaps (lamella) are simpler. Monotremes differ from placental mammals in that their mitral cells are distributed throughout the outer plexiform layer of the olfactory bulb rather than packed as a monolayer.
Venom