2. Dolphins can swim up to 260 m. below the surface of the ocean, although they are mainly shallow divers.

3. Dolphins can stay up to 15 minutes under water, however they usually stay only a few minutes diving.

4. Dolphins use a technique called echolocation to find food and navigate.

5. Dolphins are social beings which live in groups and cooperate among each other for activities like getting food and calf rising.

6. There are 32 species of ocean dolphins and 5 species of river dolphins.

7. The largest dolphin is the “killer whale” (orca), which can grow to 6.1 meters long.

8. The most known dolphin is the “bottlenose dolphin” which can grow to 2.5-2.8 meters.

9. Dolphins are warm-blooded and their internal temperature is around 36 degrees. To conserve this temperature they are surrounded by a thick layer of fat called “blubber” just below the skin.

10. The average botllenose dolphin brain weighs 1500-1600 grams, while average human brain weighs 1200-1300 grs. This is not a conclusive evidence of dolphin intelligence as many other factors might be the cause of intelligence according to scientists.

11. Dolphins can make a unique signature whistle that may help individual dolphins recognize each other or perform any other kind of communication still unknown.

12. Bottlenose dolphins can swim 5 to 12 kilometers per hour, although they can reach up to 32 km/h

Dolphins may look like fish, but they’re mammals that have adapted over the years to water. There are a number of differences caused by living in water instead of on land. For instance, dolphins and other cetaceans have no hair whatsoever, with the exception of a few follicles on their lower jaws and snouts.

Dolphin Senses

Probably the most peculiar difference between land mammals and dolphins is the way they vocalize. Most mammals have a larynx or a similar structure that allows them to vocalize using throat vibrations and exhaled air. Dolphins and other cetaceans are no different; but they’re specially adapted to make extremely high-pitched sounds used for echolocation as well as more human-pitched sounds used for ordinary communication with others in their pod.

In addition, dolphins have extremely sharp hearing, and much better vision than one might expect of an animal that uses echolocation as its primary means of sensing the world. Dolphins can see limited colors, and even have limited binocular vision like a primate. They do not possess much of a sense of smell, however.

One of the most interesting differences between cetaceans and fish is in their swimming method. Fish swim by wiggling left and right, and if you watch crocodiles and snakes you’ll see the same motion. But because dolphins were descended from mammals with a quite different skeletal structure, they use up and down strokes to swim.
Today you can still see some of the remnants of terrestrial mammals in the dolphin’s skeletal structure. For instance, they have forelimbs, but they’re adapted into flippers with shortened arm bones and no fingers. Hind limbs can sometimes be found as vestigial skeletal remains, much like tails can still be found vestigially on some humans. Most cetaceans, including dolphins, still have a pelvis, which is entirely absent from fish.

Unlike other mammals, a dolphin’s hind quarters are much, much more developed than its front musculature; the flippers are only to steer, while the tail provides most of the force of motion. Dolphins have also developed horizontal flukes on their tail to make propulsion more efficient, and they’ve developed a dorsal fin just like fish. External parts that get in the way of a dolphin’s streamlined shape, like the genitalia or the ears, have been entirely lost, turning into internal organs instead.

Breathing

Dolphins, like other mammals, breathe air instead of water, and thus use lungs instead of gills. A dolphin that cannot surface also cannot breathe, and thus will drown; this is why dolphins caught in fishing nets are given such a poor chance of survival. Unlike most fish, dolphins are very much creatures of the surface of the ocean.

Like whales and other cetaceans, dolphins respire through a blowhole in the tops of their heads, breathing in air when they break the surface of the water. Unlike humans, dolphins do not breathe reflexively; instead, they have to remember to breathe. An unconscious dolphin is likely to be a dead dolphin. Though when actively swimming they must breathe fairly often, dolphins can hold their breath for fifteen minutes or more.