Class Mammalia

Grey Seal -Halichoerus grypus-, female slapping fin on a male seal's rear, Helgoland, Schleswig-Holstein, Germany
Wilfried Martin/Imagebroker/Getty Images

The Class Mammalia is comprised of animals known as mammals.


Mammals represent a wide range of shapes, sizes and colors.

One characteristic of all mammals is that they have hair. This is more obvious in some animals, such as seals, who often have visible fur, than in others, like whales, whose hair has sometimes disappeared by the time they are born.

Speaking of birth, just about all mammals (except the platypus and echidna) give birth to live young, and they all nurse their young.

Mammals are also endotherms, commonly known as "warm-blooded."


  • Kingdom: Animalia
  • Phylum: Chordata
  • Class: Mammalia

Habitat and Distribution:

Mammals are distributed worldwide, in a variety of habitats. Marine mammals range from coastal areas (e.g., the manatee) to the pelagic zone (e.g., whales), with some, such as sea turtles and seals, even venturing into the deep sea to feed.


Most mammals have teeth, although some, like the baleen whales, do not. Since mammals range widely in habitat and food preferences, they have a wide range in feeding styles and preferences.

In marine mammals, whales feed using teeth or baleen, and on a variety of prey, including small fish, crustaceans and sometimes other marine mammals. Pinnipeds feed using teeth, usually eating fish and crustaceans. Sirenians also have teeth, although they also use the power of their strong lips when grasping and ripping aquatic vegetation.


Mammals reproduce sexually and have internal fertilization. All marine mammals are placental mammals, meaning they give birth to live young, and the unborn young are nourished in the mother's uterus by an organ called the placenta.

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Kennedy, Jennifer. "Class Mammalia." ThoughtCo, Aug. 26, 2020, Kennedy, Jennifer. (2020, August 26). Class Mammalia. Retrieved from Kennedy, Jennifer. "Class Mammalia." ThoughtCo. (accessed January 22, 2021).