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Animal Groups and Their Coverings Mammals live on land, breathe with lungs and have fur or hair covering their bodies. Most have 4 legs, or 2 legs and 2 arms. They give birth to live young (with the exception of monotremes). They feed their young on milk produced by mammary glands and are warm-blooded. Mammals are the only animals that have hair. It grows from the outer layer of the skin. A dense covering of hair is often called fur or wool and insulates. Glands in the skin release oils which help to keep the fur waterproof and protects against rain and cold. Some mammals don’t need the protection of a furry coat e.g. elephants, rhinos and hippos have only a sparse covering of hair over their thick, leathery skins and whales and dolphins contain a layer of blubber under their skin that insulates, although they still possess some sensory bristle hairs around their mouths. Fish live in water, breathe with gills, have skin covered with scales, have fins, lay soft eggs and are cold-blooded. They are covered in a flexible layer of overlapping scales embedded in the inner layer of skin. They are also protected by mucous slime that is secreted from glands in the skin, which lubricates it and helps it to swim. Sharks and Manta rays have a different type of scale from most fish. Scales are small and tooth-like and extend into their mouth where they serve as teeth. Young amphibians live in water, adults live on land. The young breathe with gills while adults breathe with lungs. They have moist, scale-less skin, have 4 legs, lay soft eggs and are cold-blooded. Most amphibians have naked skins that lack scales, feathers or fur, but the outer layer of the skin may be tough and horny. The skin contains mucous glands that secrete slime to lubricate the skin and prevent water logging. It must be kept moist as it can also be used for respiration. Reptiles mainly live on land. They breathe with lungs, have scaly skin, lay eggs with leathery shells, are cold-blooded and can have 4 legs or zero (snakes). The skin of reptiles contains no sweat glands and if they are in an exposed environment, can dry out. They possess a protective layer of horny scales that helps prevent water loss from their body. Often the outer layer of skin is renewed and the old layer is shed. Birds live on the land, breathe with lungs and have feathers covering their bodies. They have 2 legs and 2 wings and most can fly. They lay eggs with hard shells and they are warm-blooded. They possess a covering of feathers on their body and scales over the exposed skin of their legs. Other functions associated with some skin coverings include: ο camouflage for protection against predators ο recognition signal to mates or members of the same population ο flight (contour feathers) ο sensory organs (whiskers) ο protection against harmful UV rays from the sun ο waterproofing