Horses, rhinos originated on Asian subcontinent: Study

Washington: Working at the edge of a coal mine in Gujarat, a team of Johns Hopkins researchers and colleagues has discovered a treasure trove of fossils that suggest that the ancestor of horses and rhinos originated on the Asian subcontinent when it was still an island.

Modern horses, rhinos and tapirs belong to a biological group called Perissodactyla - animals that have an uneven number of toes on their hind feet and a distinctive digestive system.

The coal mine yielded over 200 fossils that turned out to belong to an animal dubbed Cambaytherium Thewissi about which little has been known.

The researchers dated the fossils to about 54.5 million years old, making them slightly younger than the oldest known Perissodactyla remains.

But it provides a window into what a common ancestor of all Perissodactyla would have looked like."Many of Cambaytherium's features like the teeth, the number of sacral vertebrae and the bones of the hands and feet, are intermediate between Perissodactyla and more primitive animals. This is the closest thing we have found to a common ancestor of the Perissodactyla order," said Ken Rose, professor of functional anatomy and evolution at Johns Hopkins University's school of medicine.

Cambaytherium and other finds from the coal mine also provide tantalising clues about India's separation from Madagascar, lonely migration and eventual collision with the continent of Asia as the Earth's plates shifted, Rose added.

In 1990, two researchers David Krause and Mary Maas of Stony Brook University published a paper suggesting that several groups of mammals that appear at the beginning of the Eocene Period, including primates, might have evolved in India while they were isolated.

Cambaytherium is the first concrete evidence to support that idea, Rose noted. Around Cambaytherium's time, we think India was an island, but it also had primates and a rodent similar to those living in Europe at the time.

"One possible explanation is that India passed close by the Arabian Peninsula or the Horn of Africa and there was a land bridge that allowed the animals to migrate. But Cambaytherium is unique and suggests that India was indeed isolated for a while," Rose suggested.

The research appeared in the online journal Nature Communications.