Scientists have reached a consensus that cetaceans are not the ancestors of terrestrial mammals, they are actually descendants of terrestrial mammals. From its structural characteristics, it can be seen:
The forelimbs of cetaceans are very similar to those of land mammals, and the forelimb bones of cetaceans are almost identical to those of human palms; when cetaceans swim, their spines move vertically up and down, which is very similar to that of cats and dogs on land mammals running.
In addition, cetaceans also breathe air through their lungs and surface every once in a while, and some cetaceans still use their pelvis to breed offspring like land mammals. So when did cetaceans enter the ocean?
329 years ago, biologist John first hypothesized that whales are not fish, but mammals, and in the early 1880s, scientist Henry further refined the above hypothesis, whales retain many of the same characteristics as land mammals, whales are descendants of land mammals, not the ancestors of land mammals.
At the same time, scientist Ferrauer believed that whales and ungulates must have a direct connection; Darwin, the proposer of evolution, expressed his view in the late 1850s that cetaceans were actually descendants of ancient bears, but they were widely criticized by public opinion, and he had to withdraw his conclusions.
In 1900, biologists Alberthard and Charles proposed that cetaceans were direct descendants of a long-disappeared carnivorous schizoodontis; subsequently, marine biologist Matthew proposed that the ancestors of cetaceans may have been primitive insectivores.
Modern ideas about the origin of cetaceans were formed around 1990, when scientists Weiling and Sare proposed that whales have teeth characteristics and similarities to those of the middle claw, an extinct, hoofed carnivore that resembles a wolf in appearance.
Like whales, the middle-clawed beast has unique triangular teeth, and its slender snout and other features are very similar to those of whales. For these reasons, Verin and Sare believe that the ancestors of cetaceans were middle-clawed beasts.
At the beginning of the 21st century, scientists found a fossil of a whale in Pakistan, and through the study of ancient whales in Pakistan, it was found that the ancestors of whales were not middle claws, but originated from even ungulates, and cattle, camels, hippos and other creatures are distant relatives.
This cloven-ungulates, which bucked the middle-clawed beasts many years ago and moved from land into the ocean, was a relatively primitive cloven-ungulate carnivore that also retained many of the features of even-ungulates that modern even-ungulates have lost.
Scientists have found that early ungulate mammals were carnivorous or scavengers, while today's even-hoofed or odd-hoofed animals have evolved to become vegetarians, but whales have retained their ancestors' carnivorous characteristics.
Whales are thermostatic creatures that need to obtain high calories from food to survive in the cold deep sea, so they retain their carnivorous properties.
In the mid-1980s, American paleontologist Vincent determined that cetaceans were closestly related to hippos by comparing the DNA of several animals.
Scientists have found that about 60 million years ago, hippos and whales shared the same ancestors that lived in the sea. But one population of this creature eventually entered the ocean to become whales, while the other became carbon beasts, and the direct descendants of carbon beasts were hippos.
The picture comes from the Network, and the intrusion must be deleted.