NEW DELHI: Horses and rhinos probably originated on the Indian subcontinent, some 54.5 million years ago according to a new study of fossils found in Gujarat. At that time, the subcontinent was an island inching its way towards a collision with the Eurasian landmass.
The study was carried out by a team of John Hopkins researchers and colleagues, and published on November 20 in the online journal Nature Communications.
Modern horses, rhinos and tapirs belong to a biological group, or order, called Perissodactyla. How and when this order evolved has been a mystery, although fossils from as far back as 56 million years ago have been discovered. This group has an uneven number of toes on their hind feet and a distinctive digestive system.
Ken Rose, a professor at the John Hopkins University School of Medicine and his Indian colleagues began exploring ancient sediments in Western India because it had been proposed that perissodactyls and some other mammal groups might have originated there, a John Hopkins press release said.
In an open-pit coal mine in Gujarat, they uncovered a rich vein of ancient bones. Rose says he and his collaborators obtained funding from the National Geographic Society to send a research team to the mine site at Gujarat for two weeks at a time once every year or two over the last decade.
The mine yielded what Rose says was a treasure trove of teeth and bones for the researchers to comb through back in their home laboratories. Of these, more than 200 fossils turned out to belong to an animal dubbed Cambaytherium thewissi, about which little had been known, the release said.
The researchers dated the fossils to about 54.5 million years old, making them slightly younger than the oldest known Perissodactyla remains, but, Rose says, 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," Rose said according to the release. "This is the closest thing we've found to a common ancestor of the Perissodactyla order," he added.
Cambaytherium and other finds from the Gujarat coal mine also provide tantalizing clues about India's separation from Madagascar, lonely migration, and eventual collision with the continent of Asia as the Earth's plates shifted, Rose said.
"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," he said, according to the release.