Mammals are a group of vertebrate animals. Examples of mammals include rats, cats, dogs, deer, monkeys, apes, bats, whales, dolphins, and humans
Mammals are distinguished from other vertebrate animals by several unique features. All mammals produce and secrete milk from mammary glands to feed their offspring. They also have hair on their bodies, although some mammalian groups have less hair than others. Hair or fur helps mammals survive in cold climates by insulating their bodies.
Mammals are a diverse group of animals that includes between 5,000 and 5,500 species adapted to live in a wide variety of environments. The vast majority of mammal species live on land, although some, such as otters, seals, and dolphins, live in freshwater and ocean habitats. Bats are mammals that are capable of flying.
Mammals are arguably one of the most successful groups of vertebrate animals. Evolutionary adaptations have allowed mammals to survive in places like the cold polar zones and alpine mountain habitats where few other vertebrate animals can live. The success of mammals in colonizing the earth is perhaps best illustrated by one particular species capable of altering its environment on a global scale: the human.
The remainder of this unit will focus on marine mammals—mammals that live in or near the ocean. There are 128 known species of marine mammals. Marine mammals include whales, sirenians, pinnipeds, the marine otter, the sea otter, and the polar bear. Figure 6.3 shows some examples of marine mammals. There are also several groups of marine mammals that have gone extinct. These include marine sloths, marine bears, and an entire order of hippo-like mammals called desmostylians.
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