Mammals: Traits, Behavior & Grouping

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  • 0:01 Mammals
  • 0:50 General Traits
  • 2:02 Reproduction
  • 3:48 Grouping
  • 4:51 Lesson Summary
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Lesson Transcript
Instructor: Jayne Yenko

Jayne has taught health/nutrition and education at the college level and has a master's degree in education.

Ever wondered what the largest mammal on Earth was? Or what traits connect mammals together? In this lesson, you will discover the basic traits of mammals, some of their behavior, and how they are grouped by scientists. Read on!


Mammals live everywhere: on land, in the ocean like whales, some fly like bats. Different groups of mammals eat different foods, and they look different from each other, so what makes them mammals? The largest mammal in the ocean is the blue whale, which grows up to 108 feet in length (that's longer than an NBA basketball court). The largest mammal on land is the African elephant at 13 feet tall. The smallest mammal anywhere on Earth is the Kitti's hog-nosed bat. It is also called the bumblebee bat. It is only 1.2 inches long. How is the blue whale, who lives in the ocean, similar to the African elephant, who lives on land? And how are they similar to the bumblebee bat, who lives in the air?

General Traits

All mammals are warm-blooded so they are able to regulate their own body temperature, which enables them to live in a variety of environments, cold or hot or in between. Regulating body temperature requires a lot of food for energy, so mammals tend to eat enormous amounts of food.

All mammals have fur or hair. Hair or fur can take on a variety of forms, such as whiskers, spines or even horns. Hair provides insulation, protects the skin and serves as camouflage - like the cheetah's spots -and even provides sensory information - like a cat's whiskers do.

All mammals have backbones. All mammals except the echidna have teeth. Mammals have four limbs. In some mammals, such as whales and manatees, their limbs are fins and flippers.

All female mammals have mammary glands to produce milk to feed their young. Most female mammals have nipples to nurse their young.

Some mammals are meat eaters, such as mountain lions and lynx. Some eat meat and everything else, like raccoons and bears. Some are plant eaters, like elephants and deer.


There are three ways mammals reproduce. These are the placental mammals, marsupials and monotremes. The placental mammals give birth to live young. Placental mammals use the mother's blood supply to feed the infants during the long gestation. Gestation refers to the length of pregnancy. Elephants are pregnant for two years before they give birth to their babies.

Marsupials have pouches on their stomachs. They give birth to live young just as the placental mammals do, but they have shorter gestation times. The babies are born hairless and helpless. After they are born, they enter the mother's pouch. Once in the pouch, the babies continue to develop over weeks or months. Marsupials have a yolk-like placenta to nourish their infants. The only North American marsupial is the opossum. Other examples of marsupials are kangaroos and koalas.

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