Generally speaking, mammals are well suited to life on land, which is their playground, but there are some mammals that are specialized groups suited to the marine environment, such as whales, sea otters, sea lions, seals, manatees, and so on. They have adapted to marine life, generally possessing a fusiform or streamlined body shape, but are still thermostats, breathing through their lungs and retaining mammalian characteristics.
Seals share the same life characteristics as sea lions and walruses*** in that they generally live in the ocean and feed on fish. But there are times when they come to the shore to rest and raise their children; they all have streamlined bodies with thick blubber under their skins to protect them from the cold water; and all their flippers can be used as paddles in the water. Among other things, sea lions and fur seals are still close relatives. The difference between them and seals is that sea lions and fur seals are able to walk on land because their flippers can face forward, whereas seals cannot. In addition, having pinky-like ears is a trait that seals lack.
In fact, sea lions can be called "masters of memorization. U.S. marine biologists Colleen Kashjak and Ronald Schuttman, in 1991, a female sea lion named "Leo" for the more complex letters and numbers of the memory test, 10 years later, they were surprised to find that, in the absence of any prompting, the sea lion can use its extraordinary memory to deal with these "tricks" with ease. The sea lion was surprised to find that without any prompting, the sea lion was able to use its exceptional memory to easily deal with these "tricks". There is also a particularly interesting thing is that the U.S. Special Forces in a well-trained sea lions, once in a minute will sink to the bottom of the rocket up, and people as long as to give it a little squid and fish for the "payment", it will be happy to meet.
The walrus, as its name implies, is the elephant of the sea, and is found in the Pacific and Atlantic Oceans. Its carapace is huge and ugly, its skin is rough and wrinkled, its eyes are narrowed and its canines protrude out of its mouth. Walrus is a good swimmer in the ocean, and its performance in the water is much more sensitive than on land. In order to adapt to the sea life, the walrus also has the ability to change body color.
The sea otter is a "new" member of the species that entered the sea about 10,000 years ago. It has a small, round head with very distinct whiskers and small ears hidden in its fur, making it look like a large mouse. The sea otter spends about half of its day grooming its fur. Grooming not only keeps the fur tidy, but also promotes the secretion of sebaceous glands, making the fur form an insulating barrier in the water. Sea otters also use tools, often taking stones from the sea floor and placing them on their chests as anvils, on which they crack the hard shells of mussels and then feed on them.
The sea otter is similar in appearance to the dugong (also known as the mermaid), with a spindle-shaped body. It differs from the dugong in the shape of its tail: the manatee's tail is fan-shaped, while the dugong's is flat and forked. The manatee has a diurnal habit, sleeping in the deep sea during the day and going out to feed at night. It is the only herbivorous mammal in the ocean, and it eats a surprisingly large amount of food, as it eats 5 to 10 percent of its own body weight in water plants every day. But you don't have to worry about indigestion! Its intestines are up to 30 meters long, which facilitates the slow digestion and absorption of the food it eats. Interestingly, the manatee eats grass like a roll of carpet, a piece of the past, it is really a veritable water "weeder".