Whales belong to the ocean, right? It may be true today, but cetaceans (whales, dolphins, porpoises) are actually from four-legged mammals that once lived on Earth. New research published in Current Biology reports the discovery in Peru of a brand new species of ancestral whale that rode land and sea, offering a glimpse of the strange course of our mammal friends.
We could think of them as two-legged, smooth ocean swimmers struggling to survive even in the Thames, but the whales are native to artiodactyls – land mammals inhabited more than 50 years ago.
Originally, the ancestors of whales resembled small deer with four toes, each ending in a small hoof. A fossilized "missing link" discovered in India suggests that the last whale precursors were put in the water in times of danger, but arrived on land to give birth and eat. They would spend a lot of time wading in shallow waters, looking for aquatic vegetation and invertebrates, and possibly small fish and amphibians.
The oldest prehistoric whale fossils date from 53 million years ago and have been found in sites in the northern Indian Himalayas and present-day Pakistan. The fossil record tells the story of a gradual transition from the wading pool to mostly living in deeper waters, like otters or beavers, while maintaining the ability to walk on land.
A trip to the sea
About 42 million years ago, and still worthy of the earth, the new discovery Peregocetus pacificus Go on an epic journey to the other side of the world. At the time of the Middle Eocene (about 48 to 38 million years ago), Africa and South America were half as far apart, but it is still an impressive swim for an animal less than three meters long that was not completely adapted to marine life.
The hind limbs of 42,6m P. pacificus were not much shorter than his forelegs, and he had tiny hooves on each toe and finger, suggesting that he was still quite capable of hoisting himself out of the water and out of trot on the mainland. However, other features of the skeleton suggest that it was well suited to aquatic life. For example, the bones of his hind legs had ridges to which ligaments and tendons would be attached, suggesting webbed feet. The bones of his beaver-like tail bear signs that he has been used as a powerful auxiliary to swimming, although there is no evidence as to whether or not he had a tail stroke such as whales. today.
P. pacificus was carnivorous, as demonstrated by his sharp teeth in scissors. He probably ate big bony fish, as many whales do today. P. pacificushowever, has teeth that resemble those of modern carnivores, with canines, premolars and molars with complex cusps. The exclusively aquatic cetaceans of today all have a row of many, simple, tooth-like, and do not chew their prey, but merely grab it and swallow it whole.
Over the millennia, the pelvic bones have been decoupled from the spine to allow more efficient swimming, while the increased duration in floating water to mitigate gravity has reduced the allocation of scalable resources to strong legs. and bearing. The forelegs turned into fins, while the more and more rudimentary hind limbs narrowed and disappeared.
Modern whales have, of course, returned to the oceans from which the distant ancestors of the first terrestrial mammals originated. There are only tiny remains of bone attached to the basin in some species, an anatomical echo of the adventures of their ancestors. But who can say where they will go in 50 million years?
This article is republished from The Conversation by Jan Hoole, Lecturer in Biology at Keele University, under Creative Commons license. Read the original article.
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