After living on land for a long time, can you return to the ocean to live a "carefree" life?

Produced by: Science Popularization China

Author: Blue Ocean Team

Producer: China Science Expo

During this period, the "From Fish to Man" research conducted by the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences and other institutions has overturned most people's cognition. Some netizens joked that it is no wonder that everyone wants to paddle in the water and go ashore every day, it turns out that it is caused by genes. Current research shows that the evolution from fish to humans takes nearly 500 million years. However, about 260 million years ago, some mammals did the opposite and returned to the ocean from land.

Mammals returning to the ocean

Some scientists believe that these "maverick" "returnees" were descended from otters, while others believe they were bears. Regardless of their ancestry, these mammals have basically adapted to marine life.

Their bodies gradually became longer, and their feet used for walking on land became flippers suitable for moving in fluids, and finally shortened to fins. However, they still retained the basic characteristics of mammals: body hair and mammary glands, and maintained a constant body temperature.

So, who are these mysterious and brave “returnees”?

Marine mammals can be divided into two main groups: pinnipeds (seals, walruses and sea lions) and cetaceans (whales and dolphins).

Descendants of Carnivores: Pinnipeds

Pinnipeds are descendants of carnivores, eating fish and sometimes cuttlefish, squid and octopus. They are not as good at swimming as cetaceans and do not give birth to their young in the water. Some pinnipeds take care of their young for a very short time. The mother will leave the young after 3 weeks of birth, leaving them to practice swimming and hunting independently. The limbs of pinnipeds are blade-like flippers supported by long toe bones. Pinnipeds live in groups.

Pinnipeds

(Photo source: Veer Gallery)

Seals mainly live in the Antarctic and Arctic, where the climate is harsh. The elephant seal is a giant seal that is 6.5 meters long and weighs up to 3 tons. Male seals gather many female seals together as their "harem".

The bearded seal (Erignathus barbatus), also called the Square Flipper Seal, is a medium-sized pinniped that lives in and around the Arctic Ocean.

(Photo source: Veer Gallery)

Walruses are large pinnipeds that are closely related to sea lions and have two incisors that grow into tusks. Sea lions crawl on all fours on land faster than seals and have external ears that are different from seals. Sea lions are more numerous in the Southern Hemisphere, but are rare in the North Pacific Ocean. During the breeding season, sea lions gather in groups.

Walrus Cow

(Photo source: Veer Gallery)

Pinnipeds are distributed in almost every ocean, but due to extensive hunting by humans for their skins and fat, some species are on the verge of extinction. For example, the monk seals in the Mediterranean are almost completely extinct.

Hawaiian monk seal resting on the beach

(Photo source: Veer Gallery)

A branch of prehistoric ungulates: cetaceans

Whales are a group of prehistoric ungulates that returned to the ocean to survive. Now they can no longer live on land, and mating, reproduction, and caring for their young are all done in water.

All whales have a cone-shaped body with a horizontal caudal fin (tail) at the end. Their hind legs have completely degenerated, while their front legs have evolved into fins. They have nostrils on the top of their heads, and exhaust gases are expelled through openings called blowholes. Whales can dive to depths of hundreds of meters and hold their breath for up to an hour. Some whales can emit ultrasonic waves to communicate with each other and detect prey.

Cetaceans can be divided into two main groups: baleen whales and toothed whales.

The baleen whales, which include humpback whales and warm whales, have no teeth but have horny gums, or baleen, which they use to filter seawater to pick out fish and shrimp.

Humpback Key

(Photo source: Veer Gallery)

The toothed whale suborder includes dolphins (including killer whales), hook-billed whales and sperm whales. They all have dozens of identical conical teeth, which they use to hunt squid and other fish. They live in all oceans, and some species live in fresh water.

Striped dolphin jumping

(Photo source: Veer Gallery)

There are more than 40 species of dolphins, which like to live in groups and communicate with each other using language. Scientists are currently working to decipher their language. As a social animal, dolphins will take the initiative to help injured or sick companions.

Dolphin jumping out of the water

(Photo source: Veer Gallery)

Sperm whales can dive to a depth of 1,000 meters to catch giant squid. The digested residue gradually accumulates in their stomachs and forms ambergris, which is widely used in the perfume industry.

Four sperm whales living in bright blue waters

(Photo source: Veer Gallery)

Conclusion

There is no shortage of miracles of life in nature. In the process of species evolution, there are not only the evolution from aquatic to terrestrial, but also the return of land mammals to the ocean. Here, let's imagine boldly, if you can choose, would you stay on land or choose to swim freely in the ocean?

Editor: Ying Yike