What Are Some Mammal Characteristics?

Each group or class of animals has characteristics or physical features that help in grouping it scientifically. Mammals are a large and varied class of animals that range from tiny mice to massive blue whales. As different as the animals in the Mammalia class can be, they share several common traits.

  1. Unique Bones

    • Bone structure is one indication of mammalian lineage that is used by science. Mammals, unlike all other classes of animal, have three inner-ear bones: the malleus, incus and stapes. The bones are used in sequence to transmit the vibrations of noise to cochlea. The other distinct bone structure of mammals is a lower jaw that is just one bone. The jaws of non-mammals comprise more than one bone.

    Milk for the Young

    • In most other groups of animals that care for their young, food from foraging or hunting is brought to the young. With all mammals, the females have specialized glands that produce milk as nutrition. Almost all mammals have external teats through which the young suckle milk from these mammary glands. The only mammals that do not have teats are the platypus and the echidna, which sweat the milk onto their bodies for the young to lick off.

    Hair

    • Mammals are also different in what covers their bodies. At some point in their lives, all mammals have some hair on their bodies. This is distinctly mammalian, as all birds have feathers, reptiles and fish have scales, and arthropods have exoskeletons. Mammalian hair grows out of small pits in the skin called follicles, with the hair's root below the skin. The part of the hair above the skin is called the shaft.

    Live Birth

    • With the exception of the platypus and echidna, which lay eggs, all mammals give birth to live young. All animals start life in an egg, and are either incubated internally and born live, or the egg is laid and the young hatch out. Other animal classes have live births, but it is most common in mammals.