Researchers at Johns Hopkins University in Baltimore say fossils found in an Indian coal mine are pointing to a common ancestor for today’s horses, rhinos and tapirs.
The animals in question are members of an order called Perissodactyla or odd-toed ungulates because they happen to have an odd number of toes on their rear feet.
The findings come from an analysis of a huge bounty of various teeth and bones discovered in an open-pit coal mine located just north-east of Mumbai, India.
The number of fossils was so large and varied that researchers had to take them back home so that they could sort through all of them in their own laboratories.
After examining and sorting the collection, the group found about 200 fossils belonging to an extinct and mysterious ancestor named Cabaytherius thewisse, an animal that could be the missing link in the evolution of the Perissodactyla group.
The Hopkins research team, writing in the online journal Nature Communications, says the mammals likely evolved on the Indian tectonic plate millions of years ago, long before it collided with the Eurasian plate.
To date, the oldest Perissodactyla fossils discovered go back to the Eocene epoch, about 55 to 56 million years ago. These new samples from India are about 54.5 million years old.
Research team leader Ken Rose, a professor of functional anatomy and evolution at the Johns Hopkins School of Medicine, says because the fossils are slightly younger that previous samples,
“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 says. “This is the closest thing we’ve found to a common ancestor of the Perissodactyla order.”
Rose said the fossil collection gathered from the Indian coal mine also offers some provocative geological information about the ancient shifting of Earth’s tectonic plates.
“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,” Rose says. “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.”
Scientists speculate the Indian plate eventually crashed into the Asian continent about 55 to 60 million years ago.