It was originally thought that the first platypus specimens that were sent to England, were nothing more than an elaborate hoax. This was a fairly logical reaction to an animal that would seem impossible because it had a muzzle like a duck's bill, a tail like a beaver and which laid eggs but suckled its young. All of these attributes seemed contradictory to the knowledge scientists had in those days. But since then a lot of investigation has been done in order to find out more about this 'hoax' of a creature.
The platypus is roughly half the size of a household cat. The adult male's average length is about 50cm and its weight is approximately 1.7kg. The female, however, is smaller and will reach an average length of 44cm and weigh about 0.9kg. This difference in size and weight between the males and the females is called sexual dimorphism. See the table below for more information about the size of platypuses.
The platypus has a thick covering of waterproof hair over all of its body, apart from on its feet and its bill. The outer hair is dark brown on its back and yellowish on its underside. Under this outer hair, which is long and coarse, there is a fine, dense under-fur which has a similar feel to wool and ranges in colour from grey to dark brown.
The tail of the platypus is mainly made up of a fatty tissue that is used to store energy supplies, which the animal can use when there is a shortage of food, such as in the winter months. The top is covered by coarse hairs, whereas underneath there is only a sparse growth of hair. The platypus's tail differs from that of a beaver's both in it's shape and the purpose it is used for. The beaver's tail is flatter, broader and covered in special scales, and it is used to help the animal propel itself through the water. The platypus, on the other hand, uses its tail only for steering while swimming.
The platypus's body is flat, streamlined, and has short legs. The front feet are webbed, which make the platypus ideally suited for swimming. This it does by alternatively kicking its front legs in order to propel it through the water, and the hind legs, which are only partially webbed, acting as steering rudders. These webbed feet could be the reason why the platypus is called a platypus. This is because the webbed feet may give the impression that the platypus is flat-footed, which is what platypus means.
When out of the water and moving around the webbing is folded under the animal's feet, in order to prevent damage occurring and to uncover broad nails, which are ideally suited for digging. On each of the hind legs of the male there is a 1.5cm long horny spur on the ankle. The spur is hollow and is linked to a poison gland in the thigh by a duct. Juvenile females also have a rudimentary version of this spur, which is lost within their first year.
The platypus has a flexible, duck-like bill, which is soft, flat and rubbery, and is very sensitive to touch. This is due to its large supply of nerves. The platypus uses its bill in order to search for food and to find its way around when it is submerged. The top of the bill is a blue-grey colour and slightly back its tip are two nostril holes. The positioning of these allow it to breathe while the rest of its body is submerged. The lower bill, which is a pale pink or mottled colour on its underside, is smaller than the upper bill. At the back of the bill is the frontal shield that stretches slightly up and over the forehead. It is unknown as to what its purpose its.
Since the platypus does not have any teeth it has to grind its food using grinding pads that can be found on the upper and lower surfaces inside its mouth. The lower bill is held in place by two elongated dentary bones. This structure can be found in all mammals, whereas other vertebrates, e.g. reptiles, have a lower jaw which is made up of several pairs of bones.
There are two grooves situated on either side of the platypus's head, just behind the bill. These contain the eyes and the ear openings. The platypus has no external ear lobes. When diving, the platypus closes both its ears and eyes. This means it has to rely on other organs for finding its way about underwater, hence the sensitivity of its bill. However, when on land it has the use of its eyes which are very acute over long distances. But because of their location it is unable to see what is literally 'under its nose'.
It has been reported that the platypus is capable of making noises. These include a growl that is similar to the one a puppy would make and a noise that is comparable with that of a brooding hen. They are believed to be used when the animal is in danger.
http://www.platypus.org.uk/details.html