Today's hoofed animals are vegetarian, but in the Indian subcontinent at that time there was a group of animals with strange hooves, such as the Indian pig Indohyus, this deer-like guy may live at the water's edge, if in danger jump into the water to swim and escape. Its eyes grow on the upper part of the head, a physiological structure that allows the Indian pig to look down at the ground for food, while it is convenient to observe the surrounding situation, and at the same time, it is convenient to expose the top of the head to the water when diving and escaping. The ancestors of cetaceans may be close relatives of the Indochoan beasts.
Left: Indian beast, right: raccoon. Although the appearance does not have a bit of a "whale-like", the auditory bulla formed by the ectotympanic bone of the Indian pig's ear forms a special shape, other than it, which is only found in ancient cetaceans and modern cetaceans | Akrasia25 / Wikimedia Commons
About 50 million years ago, the world's first whales, and the protagonists of our story today: the Bucky whale Pakicetus appeared. Although it is a whale, I believe that the first reaction of most people when they see it is: "Isn't this just a big dog with a long face?" ”。 Indeed, the whale at this time was not at all fish-like, with four legs and a long tail.
Pakistani whale skeleton model | Kevin Guertin / Wikimedia Commons
The 1997 discovery of the Bucky whale fossil in Pakistan by American paleontologist Philip D. Kingridge is, in the eyes of laymen like me, a strange-looking "big-tailed wolf". However, the paleontologist's eyes are shiny, the fossil skull of bucky whale exposes its origins, and it actually has the same structure as the living whale with a protruding ear bulge!
Pakistani whale skull model | James St. John / Wikimedia Commons
Subsequently, some fossils of Bucky whales were discovered, and after research, paleontologists found that the body of Bucky whales had begun to change to suitable for aquatic life, the original hooves had become webbed feet, more suitable for swimming in the water; and their ears began to shrink to reduce the resistance caused by swimming; the mouth became longer to facilitate the predation of fish in the water.
The whale family tree makes you eat a whale
In the time of Bucky whale life, the Earth was in a relatively warm and humid period. Its homeland was once spread through streams and swamps, and the food in the water was relatively abundant, which made bucky whales "like fish", becoming more and more like fish, and their successors began to conquer the oceans from generation to generation.
The chocobo whale Ambulutus looks like a crocodile and may live a crocodile-like life, ambushing animals that come to drink water in the water; Rodhocetus' tail and limbs become more like a paddle, able to move more flexibly in the water, and may live a life similar to that of seals; the appearance of the Dragon King Whale Basilosaurus indicates that cetaceans are beginning to covet the throne of the apex of the marine ecological niche; The Leviathan whale Livyatan descends into the ocean as if a tyrant. Let all the sea creatures tremble and live under its rule...
Archaeocetei (Archaeocetei) from different geological periods | Conty / Wikimedia Commons
It was once widely believed that the ancestors of cetaceans were relatively close to carnivores, and even speculated that the ancestors of cetaceans were an animal that was relatively close to bears. Darwin wrote in On the Origin of Species that bears have been observed in North America swimming with their mouths wide open, fishing for insects in the water, much like whales (filter-eating plankton).
Living marine mammals include cetaceans, sea lions, walruses, seals, manatees and dugongs. Although they all evolved a streamlined body type and swimming flippers, they are very cute in appearance, but the taxonomic relationship is far apart: seals, sea lions and walruses belong to the carnivorous pinniped suborder, and are more closely related to cats and dogs, while the ancestors of manatees and dugongs are related to elephants. The whale family is more likely to make you eat a whale, they are members of the order Cloven, and they are quite close to hippos. Whales, once listed separately as cetaceans, are now "downgraded" to the order Cetacean and placed under the order "under the order" of the order Cetacean.
Ancient whale restoration map, here are the Dragon King Cetaceae Basilosauridae, the Chocoboc family Ambulocetidae, the protoceritidae, the Bucky Cetaceae Pakicetidae, the Remingtonocetidae | Ana Claudia Rocha e Charbel Niño / Wikimedia Commons
Trivia
The order Cetartiodactyla was once known as cesar-hoofed order Cetartiodactyla, but was later abolished because the name emphasized the particularity of the whale, and only when "whale" and "other even-hoofed" flowers bloomed two flowers, each with a branch, the name that juxtaposed "whale" and "other even-hoofed order" could be established, although the whale looked completely different from the aniu a sheep, but it actually did not have that much particularity, and it was one of the many branches of the even-hoofed family
。
The "fawn", which once searched for food deep in the dense forest and among the fallen leaves, has become the world's largest animal after tens of millions of years, so surprising that the interesting thing about the exploration of the evolutionary history of life is that there are always unexpected truths.