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noun, plural: mammals

A taxonomic class that includes all mammals


Mammalia is a taxonomic class of the phylum Chordata. It includes all mammals, which are animals characterized by the following characteristics: a neocortex, three middle ear bones, a lower jaw made of a single bone, a hairy body covering, a thoracic diaphragm, a four-chambered heart, and females that are mostly viviparous.

Class Mammalia is divided into three subclasses: (1) Placentalia, (2) Marsupialia, and (3) Monotremata. Placentalia is a subclass that includes all the higher orders, including humans. These animals are characterized mainly by their foetus being attached to the uterus by a placenta. Marsupialia is a subclass that includes mammals characterized by the lack of placenta. As such, the young, which are born at an early stage of development, needs to be carried for a time and attached to the teats. The young is usually protected by a marsupial pouch. Monotremata is a subclass of mammals that includes Echidna and Ornithorhynchus species. The young of these animals are hatched like those of birds and are nourished by a watery secretion from the imperfectly developed mammae.

Monotremes, marsupials (e.g. kangaroos) and placentals (e.g. primates, elephants, dolphins, cattle, etc.) are examples of mammals. With the exception of the monotremes (which are oviparous), most female mammals are viviparous. Viviparous mammals give birth to live young and nourish their newborn with milk produced from their mammary glands. Mother monotremes do not have nipples; thus, they feed their young with milk through specialized ducts at their abdomen. In dayak fruit bats, males are the ones producing milk to nourish the young.

Word origin: Latin mamma ( breast)

Scientific classification:

  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia [Linnaeus, 1758]

See also:

Related term(s):