Though huge variation exists in mammals, there are a few physical traits that unite them.
1) Mammals are covered with body hair (with the exception of marine mammals like dolphins and whales who have traded the benefits of body hair for better aerodynamics for traveling in water). Hair is important for keeping mammals warm in cold climates, protecting them from sunburn and scratches, and used to warn off others, like when a dog raises the hair on its neck. Sometimes hair is adapted as a protective tool like the spines on a porcupine or the shield on an armadillo or pangolin. Hairs can be used to feel for things, like the whiskers on a cat or sea lion or act as camouflage to blend into the mammal’s habitat.
2) Mammals have 3 middle ear bones called the malleus (hammer), incus (anvil), and stapes (stirrup). They greatly improve a mammal’s hearing, which allows a better ability to communicate. Specifically, when sound waves hit the eardrum, these small bones transmit the vibrations from the eardrum (tympanic membrane) to the inner ear.
3) Female mammals have mammary glands that make milk to feed their young. The milk is full of fat and protein that helps young grow and develop, giving them a good start toward surviving to adulthood.
4) Mothers (and sometimes fathers) will protect young from predators and often live with them even after they are finished nursing to allow them to learn how to hunt, survive predation or be in a social group.
About Mammals - Traits and Classification
About Mammals: React and React
Mammal Traits – Multiple Choice Test
Mammals of the World Giant Poster
Structure and Function in Mammals - Mini-Poster
Structures and Functions in Mammals (Bobcat) - Matching Activity
