Mammalia (Mammals)

A. Organized Body made of one or more cells066_Internal_anatomy_of_a_cat.jpg
Mammals are multi-cellular like all animals. Mammals are vertebrates, which means they have a spine. They are different from other vertebrates because they have hair and give milk to their babies from mammary glands. Mammals also have a four-chambered heart in their circulatory system, a one-way digestive system, and a complex nervous system. Humans are mammals! Even though most mammals live on land, some live in water, like whales and dolphins, which still have lungs. Some can fly, like bats!

(Picture at right: internal body parts of a cat)

B. Obtain and Use energylionJudaheat2.jpgCows_head_eating_grass.JPG
Mammals need a lot of energy, because they are warm-blooded and need energy to stay warm, as well as to move! Mammals get their energy from the food they eat. Mammals eat all kinds of food. Some, like deer, mice and horses, are herbivores (eat only plants). Some, like wolves, otters, and seals, are carnivores (eat only meat). Humans and bears are omnivores, which means we eat both plants and animals.

Right: A cow is an herbivore (eats plants) and a lion is a carnivore (eats meat)

C. Reproducecat_birth.jpgplatypus-11.jpgKangaroo_and_joey05.jpg
Mammals have internal fertilization, which means they must mate. Most mammals grow their babies in the placenta and then give birth. Some mammals, like kangaroos and opossum, are marsupials, which means their offspring are born very young, and then climb into their mothers' pouches to develop more. A few mammals lay eggs, like the platypus or the echidna. They are called "monotremes."
Above: Kangaroo = marsupial.....................Platypus with newly hatched babies.....................Cat giving birth

D. Grow and Develop baby_mice.jpg
Some mammals are born really developed, and can move around easily on their own, like horses and deer. Most mammals need to develop more after birth, however. For example, dogs and cats are blind, and mice are born both blind and hairless. All mammals must grow and develop before they can reproduce. Humans go through puberty as their main development.
Picture to right: Newborn baby mice who haven't developed fur or opened eyes yet.

E. Respond to Stimulibat-echolocation.jpg
Mammals have complex brains and nervous systems. Our main senses are the senses of touch, taste, smell, sight, and hearing. Some mammals have really strong senses, like dogs can hear high pitched sounds and smell very well. Bats use echolocation and dolphins use sonar to navigate. Mammals use their senses to find food and water, and interact with each other, among other things. (Right: bat echolocation; below: the Mythbusters show an elephant responding to a mouse.)

Mammals adapt to changing environments in lots of ways. Many mammals have to adapt to cold winters, which they do by hibernating (bears), growing thinker coats (dogs and wolves), and even changing colors (the Arctic Hare changes from brown to white to blend in with snow)! Mammals also adapt to drought, like the zebras and elephants in Africa, which migrate to follow the water.

F. Exchange gases with environmentStripedDolphin.jpg
Mammals all have internal lungs which allow the mammal to absorb oxygen from the air and release carbon dioxide back into the air. Mammals need oxygen to run cellular respiration. Carbon dioxide is the waste product of this chemical reaction. Even mammals who live in water, like dolphins and whales, must breathe air. These mammals have a blow hole on top of their heads, and even though they can stay under water for a long time, they must come back up to the surface every so often to breathe.

Resources (first one is Tiger textbook)
1. National Geographic Society; Biggs, Alton, et al. Life Science. New York: Glencoe McGraw-Hill, 2002.

2. "Mammal." Wikipedia. 9 Feb. 2009. <>.

3. "What is a Monotreme?" DLTK's Growing Together. 8 Feb. 2009. <>.