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All About Mammals

All About Mammals

Introduction: When one thinks of animals, chances are the first type that comes to mind would be a dog or a cat. Well, both of these creatures belong to a large group of animals called mammals. In order to be considered a mammal, an animal needs to:
have hair of some kind
produce milk

Hair can come in many different forms. Picturing a dog, some breeds have fur, which does not shed. Poodles are examples. Other breeds have hair, which sheds when the weather gets warmer. Golden retrievers are an example.

Milk is produced is mammary glands and is usually distributed via nipples. However, not all mammals have nipples. The platypus extrudes milk from the mammary glands and the young lap it directly off of the mother's fur.

Mammals can be classified further into how they deliver their young. The smallest group of mammals are called the monotremes. This group only includes two species, the echidna (see image left)and the platypus. These species are special because they actually lay eggs.

The second grouping of mammals is called the marsupials. These animals have a pouch in which the developing offspring live until they are ready to live in the world. In the kangaroo (the most common member of this group), the young exit the mother and then climb through her fur until they reach the pouch. They then climb inside of it and attach to a nipple to receive the milk. They stay inside of the pound for several months until they are ready to live on their own. As the image below shows, the young kangaroo (called a joey) still jumps inside its mother's pouch when danger is near.

The final group of mammals are called the placentals. These animals have a special layer of tissue inside the mother's body that nourishes and protects the developing fetus. The placenta acts as a barrier through which blood and other fluids can diffuse. After birth (which is live), the placenta is extruded from the mother's body. In some species, the mother or the young eat it in order to regain the nutrients it contains.

Another trait that all mammals share, but is not a distinguishing characteristic of the group is that they are all warm blooded. This means that they maintain a constant internal body temperature. The hair or fur all mammals have is an adaptation used to keep them warm even in the coldest climates. Being warm blooded is not only a mammal trait. Birds are also warm blooded.

Directions for this Lesson: Answer the practice questions and then watch the video to learn more about mammals.

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