Females usually lay two eggs at a time, but sometimes they lay one egg or three, which are about 1and 1/7 cm in diameter. Platypuses lay small, leathery eggs similar to those of reptiles, which are slightly rounder than bird eggs. Finally, the fifth recorded instance included the female and male circling one another in tight circles. The fourth documented the female swimming underneath the male and surfacing behind him. The third recorded the female swimming beneath the male upside down, while rubbing his abdomen. The second included the female swimming to the male and rubbing his side. The first involves the male resting on the water, and the female swimming over to him and resting her muzzle on his. There have been about five different recorded courtship methods. During mating, the male curls his tail beneath the female, and lays his chest on the female’s back. Platypus are usually solitary animals, but during courtship, bodily contact between the pair is increased. Few platypuses have been seen mating, but courtship has been recorded to involve the male chasing and circling the female and biting her tail. A male will mate with any number of females during this time, for the platypus does not form life-long mates. The breeding season is in the late winter to early spring, which in Australia is August to November. The platypus’ behavior before mating is complex but relatively undocumented. The other is primitive and underdeveloped, and does not produce eggs. Although the platypus has two separate ovaries, only the left one is functional. Their paired ovaries resemble those of birds and reptiles. The female reproductive system, on the other hand, differs from other placental mammals. One exception is that their testicles are inside their body, near their kidneys. The male platypus reproductive structure is much like that of other mammals. The venom can be lethal to dogs and smaller domestic animals. The poison is not lethal to humans but produces excruciating pain and swelling that may last for several months. The male platypus has venomous ankle spurs, used in vicious territorial battles and fights over mates. It also has a reptile-like gait, with legs that are on the sides of rather than underneath the body. The platypus has extra bones in the shoulder girdle, including an interclavicle, which is not found in other mammals.
However, the external opening of the ear still lies at the base of the jaw. As in all true mammals, the tiny bones that conduct sound to the inner ear are fully incorporated into the skull, rather than lying in the jaw as in cynodonts and other pre-mammalian synapsids. The platypus jaw is constructed somewhat differently from that of other mammals, and the jaw opening muscle is different. Modern platypus young have tribosphenic (three-cusped) molars, which are one of the hallmarks of mammals adults are toothless. Platypus Image provided by Classroom Clip Art ( ) There is substantial variation in average size from one region to another, though oddly this pattern does not seem to follow any particular climatic rule. Males are around one-third larger than females. Weight varies considerably between less than a kilogram (two pounds) and over two kilograms (just under four and one half pounds) with body length ranging from 30 to 40 cm (nearly 1 ' to 1'3 "), and tail length from 10 to 15 cm (4" to 6") for males and 8 to 13 cm (3" to 5") for females. It has webbed feet and a large, rubbery snout that are more reminiscent of a duck's features than those of any known mammal. The body and the broad, flat tail of the platypus are covered with brown fur.
The extent to which this is a characteristic of monotremes, as opposed to an adaptation on the part of the small number of surviving species to harsh environmental conditions, is uncertain. The platypus' metabolic rate is remarkably low compared to other mammals, with a body temperature averaging 32? C (90? F) rather than the 38?C (100.4?F) typical of placental mammals.
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