The largest animal on Earth swims through the depths of the oceans, but 50 million years ago whales walked the earth on four legs.
A professor at Northeast Ohio Medical University states that the giant creatures are descendants of an ancient ‘little deer,’ called Indohyus.
Through a study of cetacean evolution, which includes hippopotamus to whales, Hans Thewissen discovered a 47-million-year-old fossil in Pakistan that contained a stocky animal, the size of a fox with a body and a long tail.
The bones stuck in a layer of mud reflect the features of modern whales – a bone above the width of the middle ear and the structure of the skull.
Thewissen and his team concluded that Indohyus was wading in the water as a hippopotamus in search of food and as a way to avoid predators, which led them to move from land to a water-filled 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 says the giant creatures are descended from an ancient ‘little deer,’ called Indohyus
From Darwin, scientists know that whales come from mammals that once walked on land, but were still a mystery.
However, the missing link was tied together when Thewissen and his team discovered the fossil in Pakistan.
Its cement was found in a layer of mudstone found in the Kasmir region of India containing hundreds of bones from Indohyus.
The scientists refer to the skeleton as a fox-sized mammal that looked something like a small deer. ‘
Through a cetacean evolution researcher, which introduces hippopotamus to whales, Hans Thewissen discovered that Hans Thewissen in Pakistan was a stocked animal with a long body and tail.
The bones stuck in a layer of mud mirror the features of modern whales – a bone above the width of the middle ear and the structure of the skull.
After a more in-depth study, researchers found the similarities between the skull and ears of both Indohyus and whales.
They concluded that the skeletal bones of Indohyus had a thick outer covering, much thicker than in other mammals of this size.
This character is often seen in mammals that are slow-wading birds, such as the hippopotamus today.
‘We think they sat in the water and waited for prey to drink, like jars,’ Thewissen told Discovery Magazine.
Indohyus water habits are further determined by the chemical composition of the teeth, which showed isotope oxygen ratios similar to those of aquatic animals – all indicating that the creature spends much of its time in water.
Thewissen and his team also concluded that Indohyus floated in the water as a hippopotamus in search of food and as a way to avoid predators, which eventually led him to move from land to a water-filled lifestyle.
Prior to these conclusions, it was thought that whales were descended from carnivorous ancestors who moved to an aquatic lifestyle to feast on fish that lived in the ocean.
The fossil skull also had a bone above the middle ear area, which is also found in cetaceans.
And the eye sockets sat towards the top of Indohyus’ head – just like the eyes of a whale.
Thewissen’s team also checked Indohyus ’teeth, to find out what they would eat.
The levels of carbon isotopes and oxygen in the tooth enamel of land-dwelling animals differ from those of aquatic animals due to the different isotope compositions in the food and the water they absorb.
Indohyus teeth have higher levels of the isotope carbon-13 than normal for Eocene-seeking whales, suggesting that it would eat land-based plants.
‘We’d like to know more about what he ate,’ said Thewissen. Isotopes found in the teeth indicate that it was not underwater vegetation. We will explore that in the future. ‘
Another idea is how Indohyus lived in his limb bones, which were thick and heavy in the same way as a hippo.
This gives the impression that the animal was a wolf, with heavy bones to stop it from sailing.
Based on this evidence, Thewissen suggests that ancestors introduced whales into the water as a way to avoid predators, and did not develop specific water-feeding behavior until much later.
Palaeontologist Jonathan Geisler, of the University of South Georgia in the Statesboro, had previously identified a link between raoellids and whales, but his evidence was based on only small fragments of teeth. This new work reinforces the connection, he says.
‘What’s really important about these fossils is that they seem to confirm the idea that the ancestor of semi-aquatic cetaceans came before he developed teeth that were unique to eating fish,’ 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 next Baleen whales, about 41 million years ago, which introduced the ancestors of humpbacks and blue whales.
Toothed whales were followed about seven million years later, which still swim in the oceans today.