What Are Characteristics of Animals in the Mammal Class?

Animals that are part of the mammal class have backbones like birds, amphibians, reptiles and fish. They are also warm-blooded like birds. However, several characteristics, some based on external structure and physical appearance and others based on internal body workings and structure as well as reproduction function, are unique to mammals.

  1. Characteristics Of All Mammals

    • Mammal females produce milk from modified sweat glands known as mammary glands to feed their young. All mammals are covered with hair to some degree; even marine mammals such as newborn whales and dolphins have mustaches. Mammals' lower jaws are a single bone, unlike with other vertebrates. The bones of the inner ear, the stirrup, anvil and hammer, are exclusive to mammals. In mammals, one main artery leaves the heart. Mammals also have a diaphragm, a muscle sheet that separates the body into two sections.

    Defining But Not Necessary Characteristics

    • Toothed mammals have two sets of teeth, one upper and one lower, unlike reptiles and fish that can have many replaceable sets. Also, mammal teeth are heterodontic, meaning they have different shapes. Mammal nostrils do not lead directly into the mouth, allowing mammals to breathe while chewing food. Mammals are endothermic, meaning they have internal heating and cooling. The optimum temperature varies by species, as well as the effectiveness of the temperature control.

    Monotremes

    • Monotremes are egg-laying mammals. There are only five species of this mammal sub-class in the world, the duck-billed platypus and four types of echidnas. All are found in New Guinea, Australia and Tazmania. Like other mammals, they have three ear bones, hair, single-bone jaws. Despite laying eggs, they also produce milk to feed their young. Monotremes have no teeth in their specialized snouts or beaks.

    Marsupials

    • Members of the marsupial mammal sub-class are pouched animals. They give live birth but the gestation time is very short, between eight and 40 days. The newborns, essentially still embryos, climb from the birth canal to the mammary glands and cling on, developing from there. Marsupials share characteristics with other mammals like being covered with hair. Examples of marsupials include the kangaroos, wallabies and koalas of Australia and the opossum of North America.

    Placental Mammals

    • The placental mammal sub-class is comprised of mostly rodents and bats but also includes whales, elephants, cats, dogs, sheep, cattle, horses and humans. The placenta is an organ attached to the female mammal's uterus wall. It nourishes the unborn young, fueled by the mother's bloodstream, and protects them from attacks from the mother's immune system. Gestation periods range from 18 days to 625 days. Smaller animals have shorter pregnancies than larger animals.