The largest animal on Earth swims across the depths of the oceans, but 50 million years ago whales roamed the earth on all fours.
A professor at Northeast Ohio Medical University reveals that the massive creatures are descendants of an ancient “little deer” known as Indohyus.
By researching the evolution of cetaceans, which includes the hippopotamus in whales, Hans Thewissen discovered in Pakistan a 47 million-year-old fossil featuring a thick-sized animal with an elongated body and tail.
The bones stuck in a layer of mud reflect the characteristics of current whales: a bone over the middle ear space and the structure of the skull.
Thewissen and his team also determined that Indohyus entered the water as a hippopotamus in search of food and as a means to avoid predators, which eventually led them to move from land to a totally healthy lifestyle. aquatic.
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The largest animal on Earth swims through the depths of the oceans, but 50 million years ago whales walked on the surface on all fours. A professor at Northeast Ohio Medical University reveals that the massive creatures are descendants of an ancient “little deer” known as Indohyus
Since Darwin, scientists have known that whales descended from mammals that once walked on land, but that had been a mystery.
However, the missing link came together when Thewissen and his team discovered the fossil in Pakistan.
It was cemented in a layer of clay stone found in the Kasmir region of India with hundreds of bones from an Indohyus.
Scientists describe the skeleton as “a mammal the size of a fox that looked like a miniature deer.”
Through cetacean evolution researcher, which includes the hippopotamus in whales, Hans Thewissen discovered that a 47-million-year-old fossil in Pakistan was that of a robust animal with an elongated body and tail.
The bones stuck in a layer of mud reflect the characteristics of today’s whales: a bone over the middle ear space and the structure of the skull
After a deeper analysis, the researchers discovered similarities between the skull and ears of both the Idohyus and the whales.
They determined that the bones of the Indohyus skeleton had a thick outer layer, much thicker than in other mammals of this size.
This feature is often seen in slow-moving aquatic wader mammals, such as the hippopotamus.
“We think they sat in the water and waited to drink prey, much like crocodiles,” Thewissen told Discovery magazine.
Indohyus’ aquatic habits are further confirmed by the chemical composition of his teeth, which revealed oxygen isotope proportions similar to those of aquatic animals, suggesting that the creature spends much of its time. time in the water.
Thewissen and his team also determined that Indohyus waded into the water as a hippopotamus in search of food and as a means to avoid predators, which eventually led to the change of land to a totally aquatic lifestyle.
Prior to these discoveries, the hypothesis was raised that whales descended from carnivorous ancestors who moved to an aquatic lifestyle to enjoy fish that live in the ocean.
The fossilized skull also had a bone over the middle ear space, which is also found in cetaceans.
And the eye cavities were located towards the top of the Idohyus’s head, as was the placement of the whale’s eyes.
Thewissen’s team also looked at Indohyus’s teeth to see what he was eating.
The levels of different isotopes of carbon and oxygen in the tooth enamel of animals living on land differ from those of aquatic animals due to the different isotope compositions contained in the food and water they ingest.
Indohyus teeth exhibit higher carbon-13 isotope levels than those typical of Eocene water-feeding whales, suggesting that they fed on terrestrial plants.
“We’d like to know in more detail what he ate,” Thewissen said. ‘The isotopes found in the teeth indicate that it was not submerged vegetation. We will study it in the future.
Another clue to how Indohyus lived can be found in the bones of the limbs, which were thickened and weighed in the same way that hippos do.
This suggests that the animal was a wader, with heavy bones that helped prevent it from floating.
Based on this evidence, Thewissen suggests that whale ancestors took water as a mechanism to avoid predators and did not develop a specific aquatic feeding behavior until much later.
Paleontologist Jonathan Geisler, of the University of South Georgia at Statesboro, had previously identified a link between raoelids and whales, but his evidence was based on only small fragments of teeth. This new job strengthens the bond, he says.
“What’s really important about these fossils is that they seem to confirm the hypothesis that the ancestor of cetaceans became semi-aquatic before evolving specialized teeth for eating fish,” says Geisler.
The first ancestors of whales emerged between 42 and 48 million years ago, which Thewissen describes as sea lions.
Then came the Baleen whales, about 41 million years ago, which included the ancestors of humpback whales and blue whales.
These were followed by toothed whales about seven million years later, which still swim in the oceans today.