The largest animal on Earth swims through the depths of the oceans, but 50 million years ago whales walked on earth on all fours.
A professor at Northeast Ohio Medical University reveals that the massive creatures are the descendants of an ancient “little deer,” known as the Indohyus.
By researching the evolution of cetaceans, which includes the hippopotamus to whales, Hans Thewissen discovered a 47-million-year-old fossil in Pakistan that featured a thick, fox-sized animal with an elongated body and tail.
The bones glued in a layer of mud reflect the characteristics of today’s whales – a bone over the space of the middle ear 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 of avoiding predators, which eventually led them to move from land to a completely aquatic lifestyle. .
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The largest animal on Earth swims through the depths of the oceans, but 50 million years ago whales floated on all fours. A professor at Northeast Ohio Medical University reveals that the massive creatures are the descendants of an ancient “little deer” known as Indohyus.
From Darwin, scientists knew that whales descended from mammals that once roamed the land, but which had remained a mystery.
However, the missing link was pulled together when Thewissen and his team discovered the fossil from Pakistan.
It was cemented in a layer of mud stone found in the Kasmir region of India, which contained hundreds of bones from an Indohyus.
Scientists describe the skeleton as “a fox-sized mammal that looked like a miniature deer.”
Through the study of cetacean evolution, which includes the hippopotamus to the whales, Hans Thewissen discovered that a 47 million-year-old fossil in Pakistan was that of a stuffed animal with an elongated body and tail.
The bones glued in a layer of mud reflect the characteristics of modern whales – a bone over the middle ear space and skull structure
Following a deeper analysis, the researchers found similarities between the skull and ears of both Indohyus and whales.
They determined that the bones of Indohyus’ skeleton had a thick outer layer, much thicker than other mammals of this size.
This feature is often seen in mammals that are slow aquatic limousines, such as the hippopotamus today.
“We think they were in the water and waiting to drink prey, like crocodiles,” Thewissen told Discovery Magazine.
Indohyus’ aquatic habits are further confirmed by the chemical composition of their teeth, which revealed oxygen isotope ratios similar to those of aquatic animals – all indicating that the creature spends much of its time in water.
Thewissen and his team also established that Indohyus entered the water as a hippopotamus in search of food and as a means of avoiding predators, which eventually led to the transition from land to a complete lifestyle. aquatic.
Prior to these discoveries, it was hypothesized that whales descended from carnivorous ancestors who moved to an aquatic lifestyle to celebrate fish living in the ocean.
The fossilized skull also had a bone over the middle ear area, which is also found in cetaceans.
And the eye sockets were placed towards the top of Indohyus’s head – just like the placement of a whale’s eyes.
Thewissen’s team also looked at Indohyus’s teeth to find out what he ate.
The levels of different isotopes of carbon and oxygen in the enamel of the teeth of land-dwelling animals differ from those in aquatic animals due to the different isotope compositions in the food and water they ingest.
Indohyus teeth have higher levels of the carbon-13 isotope than is typical of Eocene water-feeding whales, suggesting that they feed 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 this in the future.
Another clue to how Indohyus lived can be found in the bones of his limbs, which were thickened and heavy in the same way that hippopotamuses are.
This suggests that the animal was a ford, with heavy bones to prevent it from floating.
Based on this evidence, Thewissen suggests that whale ancestors arrived in the water as a mechanism to avoid predators and did not develop a specific aquatic feeding behavior until much later.
Paleontologist Jonathan Geisler, of Georgia Southern University in Statesboro, had previously identified a link between raeloids and whales, but his evidence was based on only small fragments of teeth. This new work solidifies the connection, he says.
“What is 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 fish consumption,” says Geisler.
The first ancestors of whales appeared 42 million to 48 million years ago, which Thewissen describes as resembling sea lions.
Then came the Baleen whales, about 41 million years ago, which included ancestors with humps and blue whales.
These were followed by toothed whales about seven million years later, which still swim the oceans to this day.