Mammals are a group of vertebrates (animals that have a backbone). Certain characteristics separate them from all other animals: mammals breathe air through lungs, give birth to live young, produce milk for their young, are warm-blooded, and have hair or fur. They also have relatively large brains and a variety of tooth sizes and shapes.

A Group of Walruses

A Manatee

Marine mammals have adapted to life in the ocean. More than 100 mammals depend on the ocean for most or all of their life needs. Marine mammals have all the characteristics of mammals, but they have different appearances and survival strategies.

Marine mammals are divided into three orders: Carnivora, Sirenia and Cetacea. Within the order Carnivora are the pinnipeds (seals, sea lions, walruses), the sea otter, and the polar bear. Polar bears are closely related to bears like the grizzly, but are considered marine mammals since they have adopted a marine lifestyle. The order Sirenia is composed of manatees and dugongs (or sea cows), and the order Cetacea includes whales, dolphins, and porpoises.

On the right is a picture of a humpback whale breaching, or jumping out of the water. Actually, this animal is feeding and has just taken a mouthful of fish, probably herring in southeast Alaska. The water drains out of the back of the mouth, leaving the fish behind to be swallowed. Breaching allows gravity to help drain the water.

A humpback whale breaching.