* Whales: These include the largest animals on Earth, like the blue whale, and smaller species like dolphins and porpoises.
* Dolphins: Highly intelligent and social animals, dolphins are found in all oceans.
* Porpoises: Smaller than dolphins, with a more blunt head, porpoises are often mistaken for dolphins.
* Seals: These are generally found in colder regions and can be divided into two main groups: harbor seals and true seals.
* Sea Lions: Similar to seals, but with external ear flaps and the ability to walk on land.
* Walruses: Large, tusked marine mammals found in the Arctic.
* Manatees: Large, herbivorous mammals often called "sea cows" found in warm, shallow waters.
* Dugongs: Close relatives of manatees, dugongs are found in the Indo-Pacific region.
What makes them mammals?
All these animals share the following mammalian characteristics:
* Warm-blooded: They maintain a constant internal body temperature.
* Breathe air: They have lungs and must surface to breathe.
* Give birth to live young: They don't lay eggs.
* Nurse their young: They produce milk to feed their offspring.
* Have hair (or fur): Though some species have very little hair, it is still present at some point in their life.