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Platypus

The platypus is a semi-aquatic endemic to eastern Australia and Tasmania. Together with the four species of echidna, it is one of the five species of monotremes, the only mammals that lay eggs instead of giving birth to live young. It is the sole living representative of its family and genus, though a number of related species have been found in the fossil record.

The unique appearance of this egg-laying, duck-billed mammal baffled naturalists when it was first discovered, with some considering it an elaborate fraud. It is one of the few venomous mammals; male platypuses have a spur on the hind foot that delivers a poison capable of causing severe pain to humans.

Description

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. The platypus uses its tail for storage of fat reserves, an adaptation it shares with the Tasmanian devil. It has webbed feet and a large, rubbery snout; these are features that appear closer to those of a duck than to those of any known mammal. The webbing is more significant on the front feet and is folded back when walking on land. Unlike a bird’s beak, the snout of the platypus is a sensory organ with the mouth on the underside. 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. Platypuses have been heard to make a low growl when disturbed.

Weight varies considerably from 1.54 lb (700g) to 5.3 lb (2.4kg) with males being larger than females: males average 20 in(50cm) total length while females average 17 in(43 cm). There is 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.
The platypus has an average body temperature of 88″“90 °F (31-32°C) rather than the 100 °F(°C ) typical of mammals. Research suggests this has been a gradual adaptation to harsh environmental conditions.

Modern platypus young have three-cusped molars, which they lose before or just after leaving the breeding burrow. The platypus jaw is constructed differently from that of other mammals, and the jaw opening muscle is different. 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. However, the external opening of the ear still lies at the base of the jaw.

Venom

The male platypus has venomous ankle spurs, which produce a cocktail of venom. They are composed largely of defense-like proteins, which is unique to the platypus. Although powerful enough to kill smaller animals, the venom is not lethal to humans, but does produce intense pain. Information obtained from case histories and evidence indicates that the pain developed can persists for days or even months. The venom appears to have a different function from those produced by non-mammalian species: its effects are non-life threatening but nevertheless powerful enough to seriously impair the victim. Since only males produce venom and production rises during the breeding season it is theorized that it is used as an offensive weapon to assert dominance during this period.

Electrolocation

Monotremes are the only mammals known to have a sense of electroreception: they locate their prey in part by detecting electric fields generated by muscular contractions. The platypus’ electroreception is the most sensitive of any monotreme.

The platypus feeds by digging in the bottom of streams with its bill. The electroreceptors could be used to distinguish animate and inanimate objects in this situation. Experiments have shown that the platypus will even react to an “artificial shrimp” if a small electrical current is passed through it.

Ecology and behavior

The platypus is an excellent swimmer and spends much of its time in the water chasing for food. When swimming, it can be distinguished from other Australian mammals by the absence of visible ears. Uniquely among mammals it propels itself when swimming by alternate rowing motion with the front two feet; although all four feet of the platypus are webbed, the hind feet do not assist in swimming, but are used for steering in combination with the tail. It utilizes cheek pouches to carry prey to the surface where they are eaten. The platypus needs to eat about 20% of its own weight each day. This requires the platypus to spend an average of 12 hours each day looking for food. 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.

Reproduction

The species exhibits a single breeding season, with mating occurring between June and October, with some local variation taking place in populations throughout the extent of its range. Females are thought likely to become sexually mature in their second year, with breeding confirmed to still take place in animals over nine years old.

Outside the mating season, the platypus lives in a simple ground burrow whose entrance is about 1 ft(30 cm) above the water level. After mating, the female constructs a deeper, more elaborate burrow up to 66 ft(20m) long and blocked with plugs at intervals (which may act as a safeguard against rising waters or predators, or as a method of regulating humidity and temperature). The male takes no part in caring for its young, and retreats to its yearlong 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 looks for bedding material. This material is dragged to the nest by tucking it underneath her curled tail.

The female platypus has a pair of ovaries but only the left one is functional. It lays one to three (usually two) small, leathery eggs. After laying her eggs, the female curls around them. The incubation period is separated into three parts. 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. There are grooves on her abdomen that form pools of milk, allowing the young to lap it up. After they hatch, the offspring are suckled for three to four months. Initially yhe mother will only leave the burrow for short periods of time. When doing so, she creates a number of thin soil plugs along the length of burrow possibly to protect the young from predators. 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.

Conservation status

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, is less well known and it has probably declined in numbers, although still being considered as common over most of its current range. The species was extensively hunted for its fur until the early years of the 20th century and, although protected throughout Australia in 1905. The platypus does not appear to be in immediate danger of extinction thanks to conservation measures, but it could be impacted by habitat disruption caused by dams, irrigation, pollution, netting and trapping.

Platypus


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