Dolphins are mammals although they live in the sea. They are members of a group of mammals called cetaceans or whales. Whales are divided into 2 groups. One group lacks teeth. Most large whales belong to this first group. Dolphins belong to the second group which has teeth.
Dolphins live mainly in warm, tropical seas in the open ocean, bays, and coral reefs. They join together in herds or groups. Sometimes as many as one million live together but they usually live in smaller herds. River dolphins can be seen in groups of only three or four.
Dolphins range in size from five feet to thirteen feet. They have black and white backs to help them blend into colorless deep seas. Their bellies are light-colored and help them avoid being seen by the sharks below. The light color blends with the sky-bright seas as the sharks look up at them.
The dolphin has a torpedo shape, long and thin. It can move quickly through the water as the flippers help it steer. The dolphin doesn't have bones. The fins keep the dolphin going in a straight line. Both the fin and flippers sense objects that may be in the way.
Strong muscles along the side of a dolphin move the tail up and down. Their skin is smooth and has no scales. A thick layer of blubber is under their skin. This layer keeps them warm. A dolphin's eyes move independently. One is located on each side of the head. They can see all around and straight ahead. They do not have a sense of smell.
Dolphins communicate with their voices and have good hearing. With these abilities they can catch food and speak with other dolphins. To find prey they make a clicking sound. The sound of this clicking bounces off anything in its path. The dolphins hear the echo of the clicking and know where prey is located. This method of finding prey is called echolocation.
Dolphins can also communicate with their friends by sounds. Certain sounds send different messages. Dolphins will go to help another dolphin if they hear a cry for aid. Each dolphin has its own specific sound. It can be identified by other dolphins. Being able to communicate well with others is a sign of great intelligence.
Dolphins swim between three and seven miles an hour. They can go as fast as twenty-two miles per hour. They usually dive from ten to one-hundred fifty feet to find food. A dive could last up to fifteen minutes.
The most common type of dolphin near the shore is the bottlenose dolphin. Their backs are grey and their underbellies white or pink. They grow to about eight feet. They weigh about two hundred pounds.
In summary, dolphins are mammals although they live in the sea. They are one of two groups of whales. Many larger whales belong to the group which has no teeth. Dolphins belong to the second group of whales and have teeth.
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