KEY POINTS:
In the search for a missing evolutionary link to modern whales, scientists have come up with an unlikely land cousin - a racoon-sized creature with the body of a small deer.
Prior molecular studies have proposed the hippo as the closest land relative of today's whales, but researchers reporting in the journal Nature on Wednesday suggest a four-footed creature from India known as Indohyus, which probably hid in water in times of danger.
Scientists have long known that whales had ancestors that walked on land. Now a team lead by Hans Thewissen of Northeastern Ohio Universities Colleges of Medicine and Pharmacy have pieced together a series of intermediate fossils that trace the whale's evolutionary journey from land to sea.
Thewissen and his team studied the structure and composition of hundreds of fossils of Indohyus, which is part of the larger group known as raoellids. Raoellids lived at about the same time as the earliest whales - about 50 million years ago.
Thewissen's team found key similarities in the skull and ear that suggest a link to cetaceans, a family that includes whales, dolphins and porpoises.
Indohyus, for example, had an outside layer that was much thicker than similarly sized mammals.
This is something typically seen in slow-wading mammals. They found further evidence in the chemical make-up of Indohyus' teeth, which resembled those of other aquatic animals.
This suggests the small, stocky Indohyus spent a lot of time in the water.
Scientists had assumed whales descended from land-dwelling carnivores, and made their way to sea to feed on fish.
"Clearly, this is not the case. Indohyus is a plant eater, and clearly is aquatic," Thewissen said in a statement.
The researchers believe Indohyus gradually spent more time in the water, either for protection or while feeding, and the dietary shift came later.
"Cetaceans originated from an Indohyus-like ancestor and switched to a diet of aquatic prey," the researchers wrote.
Theories about the evolution of whales have been evolving themselves, and it may take years before there is a consensus.
- REUTERS
