Horses and rhinos likely originated in the Indian subcontinent, over 54 million years ago, according to a new study.
Working at the edge of a coal mine in India, researchers at the Johns Hopkins University and colleagues have filled in a major gap in science’s understanding of the evolution of a group of animals that includes horses and rhinos.
The group likely originated on the subcontinent when it was still an island headed swiftly for collision with Asia, the researchers said.
Modern horses, rhinos and tapirs belong to a biological group, or order, called Perissodactyla. Also known as “odd-toed ungulates”, animals in the order have, as their name implies, an uneven number of toes on their hind feet.
Though paleontologists had found remains of Perissodactyla from as far back as the beginnings of the Eocene epoch, about 56 million years ago, their earlier evolution remained a mystery, said Ken Rose, a professor of functional anatomy and evolution at Johns Hopkins.
In 2001, Prof. Rose and Indian colleagues began exploring Eocene sediments in western India. In an open-pit coal mine northeast of Mumbai, they uncovered a rich vein of ancient bones. The mine yielded what Prof. Rose said was a treasure trove of teeth and bones.
More than 200 fossils turned out to belong to an animal dubbed Cambaytherium thewissi , about which little was known.
In 1990, researchers at the Stony Brook University suggested that several groups of mammals that appear at the beginning of the Eocene, including primates and odd and even-toed ungulates, might have evolved in India while it was isolated. Cambaytherium is the first concrete evidence to support that idea, Prof. Rose said.