Is a Dolphin a Mammal?

Is a dolphin a mammal? On this page you’ll find out the answer to this often-asked question! You’ll also learn an interesting fact about dolphins and hippos ...

Are Dolphins Mammals?

The answer is YES, a dolphin IS a mammal. Let’s find out why …

Although a dolphin looks more like a fish than a ‘typical’ mammal such as a dog or a cat, it has all the characteristics of a mammal. These include: having lungs for breathing air, having a backbone, and the female of the species giving birth to live young and feeding their young with milk.

Bottlenose Dolphin
A bottlenose dolphin surfs the wake of a research boat on the Banana River near the Kennedy Space Center

You’ll discover more about mammalian characteristics (i.e. what makes a mammal a mammal) shortly.

People get confused about dolphins because dolphins resemble large fish such as sharks. Instead of having arms and legs like land mammals, dolphins have fins. They live in the sea and in some rivers – environments that seem very unlike typical mammal habitats.

There's something fishy about this Great white shark! Unlike a dolphin, it breathes using gills, and doesn't have to come to the surface for air.

What is a dolphin?

Dolphins, along with whales and porpoises, are members of a group of mammals called Cetacea.

Members of this group are known as Cetaceans. They are mammals that have adapted to an aquatic lifestyle. Cetaceans are found throughout the world’s oceans (and in some freshwater river systems too). Although todays cetaceans are well adapted for living in the water, their ancestors lived on land.

These Orcas are Cetaceans, just like dolphins. Cetaceans are mammals that have adapted to life in the water.

The dolphin’s ancestors were hooved animals. All of the cetaceans are in the order (a group of related animals) Artiodactyla, or ‘even-toed ungulates’.

Other even-toed ungulates include cattle, giraffes, pigs, deer and … hippopotamuses.

Dolphins & Hippos

In fact, the closest living relative of the cetaceans (including the dolphin) is the hippopotamus!

Around 50 million years ago in the Indian subcontinent, even-toed ungulates began to adapt to an aquatic lifestyle. Over time they gradually evolved to become totally dependent on water, becoming the whales, dolphins and porpoises of today.

The dolphin's closest living relative on land is the hippo!

Why Are Dolphins Mammals?

A mammal is a member of the class Mammalia. You can tell that a dolphin is a mammal because it has a number of characteristics that are only found in mammals rather than in fish, or any other kind of animal.

Eurasian Wolf
This Gray Wolf is a member of Mammalia.

Mammalian characteristics include:

  • Being a vertebrate (i.e. having a backbone)
  • Being endothermic (i.e. being warm-blooded)
  • Giving birth to live young … although there are five mammals that lay eggs – they’re known as the monotremes.
  • Breathing air with lungs (dolphins don’t have gills like fish, and have to come to the surface of the water in order to breathe).
  • Females having mammary glands that produce milk for feeding their young.
  • Having hair or hair follicles (see below)

You can find out more about mammal characteristics here: What Is A Mammal?

Dolphins, Mammals and Hair

When people think of a ‘mammal’ they tend to think of a hairy animal. In fact, having hair – or at least, hair follicles – is one of the defining characteristics of a mammal. No other type of animal has hair.

(Hair follicles are the organs within a mammal’s skin that produce hair.)

Amazon Pink River Dolphin
Amazon Pink River Dolphin

Do Dolphins Have Hair?

Most dolphins don’t have hair. However, they do have hair follicles. Some scientists think that these act as sensory organs.

Some river dolphins do have small hairs on their snouts. Again, it is thought that these may provide sensory information to make up for the animals’ poor eyesight.

Is a Dolphin a Mammal: Conclusion

On this page you’ve discovered that dolphins ARE mammals. This is because dolphins have mammalian characteristics such as being warm blooded, and producing milk to feed their young.

You’ve also found out that dolphins are members of a group of animals called Cetacea, and that all Cetaceans are related to hooved animals.

Don’t forget that the closest living relative of the Cetaceans is the hippo!

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