Big Picture

Mammals are four-limbed endothermic vertebrates. Mammals are characterized by how they warm and cool themselves, by how they eat and digest food, by the structure of their lungs, heart and brain, and by their means of locomotion. Mammals can be herbivores, carnivores, or omnivores depending on their diet.

Key Terms

Mammal: A class of endothermic vertebrates that have four limbs and produce amniotic eggs.

Mammary Glands: The glands that produce milk after the birth of an offspring and carried by female mammals.

Lactation: The production of milk for offspring.

Alveoli: Air sacs in mammalian lungs that improve the efficiency of gas exchange.

Neocortex: Covering on the mammalian brain.

Cerebrum: Most forward region of the brain and is particularly pronounced in mammals. It is responsible for memory and learning

Arboreal: Animal that lives in trees.


Mammals are a very diverse group, yet they share many traits that set them apart from other types of animals.

  • Females have mammary glands to produce milk for feeding their young.
  • Milk is a nutritious fluid that contains disease-fighting molecules as well as all the nutrients a baby mammal needs. The production of milk is called lactation
  • Mammals have fur or hair. It helps insulate the animals and keep them warm.
  • Whiskers are specialized strands of hair that help animals sense
    their surroundings.
  • Have sweat glands that produce sweat, which helps cool the body when it evaporates.
  • Lungs contain millions of alveoli that provide a very large surface area for gas exchange.
  • Mammalian lungs are adapted to meet the high oxygen demands of cellular respiration required to maintain body heat.
  • The contraction and relaxation of a diaphragm, which is the large muscle below the lungs, helps move air in and out of the lungs.
  • Mammals have four-chambered heart that improves oxygen delivery
    to the rest of the body.
  • The neocortex plays an important role in complex brain functions.
  • Mammals have four types of teeth: incisors, canines, premolars, and molars. They help mammals digest their food.
Image Credit: 3D rendered mouth copyright Zoltan Pataki, 2010, used under license from

Structure and Function

How Mammals Stay Warm

  • Cells of mammals have more mitochondria than cells of other animals. The extra mitochondria help keep the metabolic rate high, which help generate heat.
  • Shivering occurs when many muscles contract a little bit. This generates a small outburst of heat. Each muscle that contracts produces a small amount of heat.

How Mammals Stay Cool

  • Dilation (widening) of blood vessels means more blood flow toward the surface of skin. The skin warms up, and that heat can be given off to the environment.
  • Sweating cools the body down when the wet sweat evaporates from the surface of the body.



Structure and Function (cont.)

  • Fur or hair also helps insulate the body.
  • There is a fatty layer under the skin, which also helps to insulate the body.
  • Panting, which is like sweating, cools the body down due to the evaporation of water from the body sur-face.

Eating and Digesting Food

  • Food provides the energy to maintain a high metabolic rate
  • Mammals have diverse diets. Mammals may be herbivores, carnivores, or omnivores. Most mammals are generalists and eat a diverse variety of species, but some like koalas and pandas feed on only one species.
  • Herbivore: Only eats plants. Herbivorous species include rabbits and mice.
  • Carnivore: Only eats meat. Carnivorous species include hyenas and wolves.
  • Omnivore: Eat both plant and meat. Omnivorous species include humans and rats.
  • Herbivores have more complicated digestive systems than carnivores or omnivores do. Herbivores must digest plant tissue and carbohydrates like cellulose, which are much harder and take much longer to digest.

Mammalian Brain and Intelligence

  • Mammals have large and complex brains. The cerebrum is especially large.
  • The larger the area of the neocortex, the more complex and sophisticated the brain.
  • Mammals, on the whole, are very intelligent and given the size of the cerebrum have an incredible capacity to learn.
Image Credit: Bourrichon, Public Domain

Social Living in Mammals

  • Many mammals live in societies, which give the individual mammal, as well as the group, many benefits.
  • Security: Social living helps conceal individual animals and makes the group more threatening.
  • Efficiency: Social living allows mammals to hunt or forage for food together, which is often more effective than doing so alone.
  • Education: Social living allows young mammals to learn from many different individuals.


  • Mammals tend to be very mobile and have a more upright posture.
  • Limbs may be specialized for the type of movement mammals use, such as running, jumping, and flying.
  • Arboreal animals have adaptations like tails, long arms, and stick pads on their fingers to help them climb trees.