Platypus - biology.

Platypus - biology. I INTRODUCTION Platypus (Greek platys, "broad"; pous, "foot"), also called duckbill, a semiaquatic, egg-laying mammal native to Tasmania and southern and eastern Australia. Egglaying mammals are called monotremes; aside from the platypus, the only monotremes that exist are the echidnas. All other mammals give birth to live young. In outward appearance, the platypus is best known for its ducklike bill and webbed feet. II PHYSICAL CHARACTERISTICS The bill of the platypus is the most conspicuous feature of its small head and measures about 6 cm (about 2.5 in) long and 5 cm (2 in) wide. The bill is actually an elongated snout covered with soft, moist, leathery skin. It contains specialized sense organs called electroreceptors that can sense weak electric fields. Using its bill, the platypus stirs up mud at the bottom of rivers or lakes to detect and uncover the insects, worms, or snails on which it feeds. Platypuses also eat frogs, small fish, and crustaceans. The platypus lacks external ears. Eye and ear openings are located in grooves on each side of the head. The grooves close over, as do the flaps over the nostrils, when the animal is submerged, obstructing vision, hearing, and the sense of smell. Young platypuses have rudimentary teeth; in adults the teeth are replaced by a few horny plates. A cheek pouch, used for storing food during foraging, is present in each side of the mouth. The head of the platypus is joined directly to the body without an apparent neck. The body is 30 to 45 cm (12 to 18 in) long. The platypus has a thick, woolly coat that is typically dark brown above and reddish brown and gray below. The tail, flattened like that of a beaver and covered with fur, measures 10 to 15 cm (4 to 6 in) in length. As in most aquatic mammals, the legs of the platypus are short. All four feet are webbed, but the webbing on the front feet extends beyond the sides of the five toes and the ends of the claws, forming fan-shaped paddles. Unlike most aquatic mammals, the platypus propels itself mainly with its front feet rather than with its hind feet. Adult males have a hollow, horny spur on the inner side of each hind foot. The spur connects to a gland at its base containing a venomous secretion that the animal may use to defend itself. The platypus is one of only a few venomous mammals. III BEHAVIOR Platypuses are shy animals and seldom observed, even in areas where they abound. They are active only during the early morning and late evening. The call of the platypus is a low throaty growl. They are excellent swimmers and divers and live in long, winding burrows, which are usually dug by the females in the banks of rivers or streams. The burrows are blocked with earth in several places as fortification against intruders and flooding. IV REPRODUCTION AND LIFE SPAN Platypuses breed in the spring. About two weeks after mating, the female lays one to three eggs. The nest, lined with leaves and grass, is in a chamber at the end of a burrow. Only the female occupies the breeding burrow. The eggs are incubated for about ten days, and then the young hatch, naked, blind, and helpless. The female uses its tail to clasp the young to its abdomen, enabling them to nurse. Nursing ends at about four months of age, when the young emerge from the nest and begin to feed themselves. The life span of platypuses in the wild is uncertain, but one zoo animal lived for 17 years. Platypuses cannot be legally hunted or maintained as pets. Scientific classification: The platypus makes up the family Ornithorhynchidae in the order Monotremata. It is classified as Ornithorhynchus anatinus. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.