Marine mammals are a diverse group of 120 species of mammal that are primarily ocean-dwelling or depend on the ocean for
food and include:
cetaceans (whales, dolphins, and porpoises)
sirenians (manatees and dugong)
pinnipeds (true seals, eared seals and walrus)
otters (the sea otter and marine otter).
The polar bear, while not fully aquatic, is also usually considered a marine mammal because it lives on sea ice for most or all of the year. It
spends a large portion of its time in a marine environment, albeit a frozen one. When it does swim in the open sea it is extremely proficient and
has been shown to cover 74 km in a day. For these reasons, some scientists regard it as a marine mammal.You can discover the laser pen pointer with light is so interesting.
Marine mammals evolved from land dwelling ancestors and share several adaptive features for life at sea such as generally large size,
hydrodynamic body shapes, modified appendages and various thermoregulatory adaptations. Whales are the largest mammals ever. Different
species are, however, adapted to marine life to varying degrees. The most fully adapted are the cetaceans and the sirenians, which cannot live
Despite the fact that marine mammals are highly recognizable charismatic megafauna, many populations are vulnerable or endangered due to
a history of commercial use for blubber, meat, ivory and fur. Most species are currently in protection from commercial use.
Since mammals originally evolved on land, their spines are optimized for running, allowing for up-and-down but only little sideways motion.
Therefore, marine mammals typically swim by moving their spine up and down. By contrast, fish normally swim by moving their spine
sideways. For this reason, fish mostly have vertical caudal (tail) fins, while marine mammals have horizontal caudal fins
Some of the primary differences between marine mammals and other marine life are:
- Marine mammals breathe air, while most other marine animals extract oxygen from water.
- Marine mammals have hair. Cetaceans have little or no hair, usually a very few bristles retained around the head or mouth. All members
of the Carnivora have a coat of fur or hair, but it is far thicker and more important for thermoregulation in sea otters and polar bears than
inseals or sea lions. Thick layers of fur contribute to drag while swimming, and slow down a swimming mammal, giving it a
disadvantage in speed.
- Marine mammals have thick layers of blubber used to insulate their bodies and prevent heat loss. Sea otters and polar bears are
exceptions, relying more on fur and behavior to stave off hypothermia.
- Marine mammals give birth. Most marine mammals give birth to one calf or pup at a time.
- Marine mammals feed off milk as young. Maternal care is extremely important to the survival of offspring that need to develop a thick
insulating layer of blubber. The milk from the mammary glands of marine mammals often exceeds 40-50% fat content to support the
development of blubber.
- Marine mammals maintain a high internal body temperature. Unlike most other marine life, marine mammals carefully maintain a core
temperature much higher than their environment. Blubber, thick coats of fur, bubbles of air between skin and water,countercurrent
exchange, and behaviors such as hauling out, are all adaptations that aid marine mammals in retention of body heat.