Mammals are one of the five animal classes (mammals, reptiles, amphibians, fish, birds). Mammals are all warm-blooded, have fur or hair, breathe air through lungs, give birth to live young, and nurse them with mother’s milk. Some of these animals belong to a group called marine mammals because they spend all or most of their time in the sea and depend on the sea for food.
If you call marine mammals fat they won’t be offended. After all, their streamlined bodies need blubber for insulation against the cold. If they go underwater, they will come up again. But don’t hold your breath, because marine mammals can hold theirs for a long time. They store oxygen in their blood and muscle, and actually have more blood than land mammals so they can store more oxygen. Also, a marine mammal can direct more blood to its heart and lungs. It can even slow its heartbeat to conserve oxygen.
Meet the four types of marine mammals:
• Hi! Scientists call us pinnipeds. But you can just call us flipper-footed. Our order includes sea lions, walruses, and seals. We regularly come out of the ocean to rest, breed, and give birth to pups.
• Welcome to the cetacean club. Cetus is Latin for whale. But our group of marine mammals also includes dolphins and porpoises. To get a membership card you need to have a streamlined, hairless body (most of us had a little hair before we were born), no hind limbs, a horizontal tail fin, and a blowhole on top of your head for breathing.
• I’m a fissiped. That’s a fancy way of saying paw-footed. “Wait!” you exclaim. “A polar bear is a marine mammal?” Yessirree! It sounds strange, but since I depend mostly on the ocean for food, and spend my life on the sea ice, I am grouped with whales and such. Now I’ll admit that like my fellow fissiped, the sea otter, I don’t go out into the open ocean. Otter and I spend most of our time near shore. He likes to forage for sea urchins in the kelp beds. I like to wait for tasty seals on the sea ice.
• Our little group is sirenia. If you ever saw dugongs and manatees like me moving slowly and grazing on sea grasses, you would understand why we’re often referred to as sea cows. Sadly, we lost a member of our group. Steller’s sea cow was first discovered in 1741. But this close relative of the dugong was hunted to extinction just 27 years later. We like warm tropical waters. Our bodies, flippers, and tails are rounded. And we have large, flat molar teeth for grinding our food.
