Classifying Ocean Animals

Long ago, the ancestors of whales lived on land. They breathed air and walked on legs. Over millions of years, their bodies changed and they moved into the ocean for good. But whales are still mammals, just like you. They breathe air with lungs, so they must swim up to the surface to take a breath. They are warm-blooded, which means their bodies stay warm even in cold water. And mother whales feed their babies milk. So even though a whale looks like a giant fish, it is not a fish at all. Fish breathe underwater with gills and have scales. Whales breathe air and give milk to their babies.

Toothed whales are a big family of ocean animals. Dolphins, porpoises, killer whales, sperm whales, narwhals, and beluga whales all belong to it. These whales have teeth, and they use them to grab their food. They eat squid, fish, and sometimes other sea mammals. Toothed whales are some of the smartest animals on Earth. They like to live together in groups and can learn from each other. Remember, whales are not fish. They are marine mammals. They breathe air with lungs, they are warm-blooded, and mother whales feed their babies milk. A fish breathes with gills and has scales instead.

A backbone helps us sort animals. Those with one are vertebrates; those without one are invertebrates. Around 95 in every 100 kinds of animal belong to the second group. Sponges have very simple bodies. They stay in one place and collect tiny food pieces by filtering water. Soft, wobbly jellyfish have no bones. Their group is called cnidarians. Octopuses, crabs, and starfish also belong with the ocean's invertebrates.

Your backbone makes you a vertebrate. Fish, frogs, reptiles, birds, and mammals all have backbones. Earth's earliest vertebrates were fish. Fish live in water and use gills to breathe. Most also have scales. Mammals use lungs for breathing, and mothers produce milk for their young. Whales and dolphins are ocean mammals. Swimming does not make them fish: they use lungs and feed their young milk. To begin sorting a sea animal, check for a backbone. Then ask whether it uses gills or lungs.

Mammals have backbones and make heat inside their bodies to stay warm. Their temperature is usually fairly steady, though it can change. Most have fur or hair, and mothers produce milk for their young. People, dogs, cats, and bats belong to this group. Whales, dolphins, seals, and sea otters are marine mammals. They need air for their lungs, so they must breathe above water. Their bodies keep warm in cold seas, and their young get milk.