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Sea Mammals or Marine Mammals
Sea mammals or marine mammals includes diverse group of various (around 120) species of mammals. All these species either lives at sea or depends on the ocean for food. These mammal species include:
- Sirenians (Dugong and Manatees),
- Cetaceans (Dolphin, Whales, and Porpoises),
Pinniped (Walrus, True Seals, and Eared Seals),
- several Otters (the Sea Otter and Marine Otter), and
- Polar Bear
The polar bear is generally included in marine mammals. Marine mammals are mainly evolved from land dwelling ancestors, but now have adapted several things for life at sea such as hydrodynamic body shapes, thermoregulatory adaptations and, modified appendages. The most adapted are cetaceans and the sirenians. They spend all their life under water, while the other species spend some time on land.
Marine mammals are highly charismatic megafauna, but now many are endangered due to their commercial uses. They were abused for fur, meat, blubber and ivory. Now a day they are protected from the commercial misuse.
As the mammals have spines, they are optimized for running. They can move up and down, but have little motion sideways. Mammals swim with their spine up and down, while deep sea fish swim by moving their spine sideways. Because of which, mammals have horizontal caudal fins, while fish have vertical caudal fins.
There are many differences between sea mammals and other sea life, which are given below:
- The marine mammals breathe air, whereas the other sea animals takes oxygen from water.
- Marine mammals have thick layer of blubber, which helps them to prevent heat loss. Exceptions to these are the sea otters and polar bears, which depends on fur and behavior to stay away from hypothermia.
- Marine mammals give birth to young lives and the female produces milk to feed them. They give birth to one calf or pup at a time. The milk from marine mammals generally exceeds 40-50% fat content which helps the young to develop the blubber.
- Unlike other marine lives, marine mammals maintain a high internal body temperature. The thick blubber, countercurrent exchange, fur and the air bubbles between skin and water helps them to maintain the high body temperature.
- Dislike other sea lives; marine mammals have hairs on their body. The cetaceans have little bristles around the head or mouth. Some cetaceans don't have hairs. However, every member of carnivora has fur or hairs. But the thickness of hairs is much in polar bears and sea otters than the sea lions. The coat of hair helps the polar bears and sea otters for thermoregulation. However these hairs also give disadvantage to the mammals, as it slows down their swimming.