Whales and dolphins are mammals. Being a mammal, dolphins share many characteristics with humans. Yet, unlike humans who live on land, dolphins are born in a different way in the sea. Dolphins were born with tail out first while humans were born with head out first. It takes a mother dolphin 11 months in general to give birth to a baby dolphin.

When the baby dolphin comes out from the mother, mother and aunts will help him get to the surface for the first breath.

Baby dolphins depend on their mother's milk as food, just like human babies. So, they have to stay closely to their mother until they are around three years old. They can live with friends and move further away from mother and aunts when they know how to catch fishes and protect themselves.

Appearance
Dolphins and humans are similar in skeletal structure to a certain extent. Both have spine. Dolphins' flippers are like human hands with "fingers".

There is no bone at the dorsal fin or tail. Though dolphins do not have legs, they have a pair of regressed pelvis bone which was once used to connect to their legs long time ago.

Dolphins swim with their tails moving up and down to speed up.

Dolphins’ skin is smooth like rubber.

Body Temperature
Dolphins are warm-blooded animals. Their body temperature is almost the same in winter and summer.

The way dolphin breathe
Dolphins breathe with lungs and have to come to the water surface to breath in fresh air once in a few minutes.
Next time when you visit whales or dolphins, listen carefully. You will hear them breathe with a "fop" when you see them. That "fop" is from the blowhole at the top of their head. Their blowhole is like human nose but it closes before they dive. This can prevent water from getting into their lungs.

Pilot whale surfacing to breathe

Blue whale surfacing to breathe

Echolocaton
Living in the sea, dolphins use the lump of fat at their forehead, called melon fat, to emit sounds. The sounds will bounce back to help the dolphin sense their surroundings, including shape and size of the objects. This ability is called "echolocation".