18 animals.
One very big family.

Almost every one of these is a mammal: they breathe air, they feed their babies milk, and every single one went back into the sea long after their ancestors had walked out of it. Then there is the whale shark, which does none of that — and is the fastest way we know to show you the difference.

8

Whales

4

Seals

2

Sea Lions

1

Walruses

2

Otters & Manatees

1

Sharks