The largest animal on earth swims through the depths of the oceans, but 50 million years ago whales walked the land on four legs.
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 whales, which include hippos and whales, Hans Thewissen discovered a 47 million year old fossil in Pakistan with a squat, fox-sized animal with an elongated body and tail.
The bones, stuck in a layer of mud, reflect the characteristics of modern whales – a bone above the middle ear cavity and the structure of the skull.
Thewissen and his team also found that Indohyus waded like a hippopotamus in the water in search of food and as a means of avoiding predators, eventually leading them to move from land to a fully aquatic lifestyle.
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The largest animal on earth swims through the depths of the oceans, but 50 million years ago whales walked the surface on four legs. A professor at Northeast Ohio Medical University reveals that the massive creatures are descendants of an ancient “little deer” known as Indohyus
Scientists have known since Darwin that whales descended from mammals that once went ashore but remained a mystery.
The missing link, however, was put together when Thewissen and his team discovered the fossil in Pakistan.
It was cemented into a layer of mudstone found in the Kasmir region of India that contained hundreds of bones from an Indohyus.
Scientists describe the skeleton as “a mammal the size of a fox that looked something like a miniature deer”.
Through the researcher of the whale evolution, which also includes hippos and whales, Hans Thewissen discovered that a 47 million year old fossil in Pakistan was that of a stocky animal with an elongated body and tail
The bones, stuck in a layer of mud, reflect the characteristics of modern whales – a bone above the middle ear cavity and the structure of the skull
After deeper analysis, the researchers discovered similarities between the skulls and ears of both Indohyus and whales.
They found that the bones of the Indohyus skeleton had a thick outer layer that was much thicker than other mammals of this size.
This trait is common in mammals that are slow water waders, such as today’s hippopotamus.
“We think they were sitting in the water waiting for prey to be drunk, much like crocodiles,” Thewissen told Discovery Magazine.
Indohyus’ aquatic habits are further corroborated by the chemical makeup of their teeth, which revealed oxygen isotope ratios similar to those of aquatic animals – all of which suggests that the creature spends much of its time in the water.
Thewissen and his team also found that Indohyus waded like a hippopotamus in the water in search of food, avoiding predators, which eventually led them to migrate from land to a fully aquatic lifestyle
Prior to these findings, it was hypothesized that whales descended from carnivorous ancestors who adopted an aquatic lifestyle to delight in marine fish.
What is an Indohyus?
Indohyus’ existence could mark the point where some mammals gave up life on land to spend time in lakes, rivers, and oceans – before evolving into the giant marine animals we know today.
Its bones had a thick outer layer – a property normally seen in wadding like hippos, where the extra weight helps them cope with fast currents.
Scientists describe the skeleton as “a fox-sized mammal that looked something like a miniature deer”.
It has a narrow snout like a crocodile, an elongated body, and a long tail.
The fossilized skull also had a bone over the middle ear cavity, which is also found in whales.
And the eye sockets sat on top of the Indohyus’ head – just like the placement of a whale’s eyes.
Thewissen team also looked at Indohyus’s teeth to find out what it was eating.
The levels of various carbon and oxygen isotopes in the enamel of land animals differ from those in aquatic animals due to the different isotopic compositions in the food and in the water they ingest.
Indohyus’ teeth contain more carbon-13 isotopes than is typical of water-eating whales from the Eocene, suggesting that they were feeding on land-based plants instead.
“We want to know more precisely what it was eating,” said Thewissen. Isotopes found in the teeth indicate that it is not submerged vegetation. We will study that in the future. ‘
Another clue of how Indohyus lived is found in its limb bones, which were just as thickened and heavy as those of a hippopotamus.
This suggests that the animal was a wader with heavy bones to keep it from hovering.
Based on this evidence, Thewissen suggests that the ancestors of the whales went into the water as a predator avoidance mechanism and only developed specific aquatic feeding behavior much later.
Paleontologist Jonathan Geisler of Georgia Southern University in Statesboro had previously established a link between raoellids and whales, but his evidence was based only on small tooth fragments. This new job strengthens the connection, he says.
“What is really important about these fossils is that they seem to confirm the hypothesis that the ancestors of the whales became semi-aquatic before the development of teeth that specialize in eating fish,” says Geisler
The first ancestors of the whales emerged 42 to 48 million years ago, which Thewissen describes similarly as sea lions.
Then came baleen whales about 41 million years ago, including the ancestors of humpback whales and blue whales.
Toothed whales followed around seven million years later and still swim in the oceans today.