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Horse, Rhino Origins Tracked in India

Nov 21, 2014 04:04 PM EST

The evolution of odd-toed animals like horses and rhinos has long remained a mystery to researchers, despite previous discoveries of their remains, but a new study has tracked their origins in India, solving a piece of the puzzle.

The breakthrough came from a treasure trove of fossils belonging to what is believed to be an ancient ancestor of the group Perissodactyla.

Perissodactyla, made up of "odd-toed ungulates" such as horses and rhinos, likely originated on the subcontinent when it was still an island headed swiftly for collision with Asia. They are not only identified by the uneven number of toes on their hind feet, but also by their distinctive digestive system.

Fossils of Perissodactyla have been found as far back as the Eocene epoch 56 million years ago, and yet the details of the beginnings of their evolutionary history have eluded scientists. But in an open-pit coalmine northeast of Mumbai, a Johns Hopkins University-led team uncovered a rich deposit of ancient bones. Lead author Ken Rose and his colleagues decided to explore this area in western India after hearing word that perissodactyls and some other mammal groups might have originated there.

This fossil treasure trove revealed more than 200 teeth and bones belonging to a little-known animal dubbed Cambaytherium thewissi. Living about 54.5 million years, Cambaytherium may be slightly younger than the oldest known Perissodactyla remains, but according to Rose, it provides a picture of what a common ancestor of all Perissodactyla would have looked like, shedding light on their evolutionary history. (Scroll to read on...)

"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 explained in a statement. "This is the closest thing we've found to a common ancestor of the Perissodactyla order."

These findings, published in the journal Nature Communications, may have filled in a major gap in science's understanding of the evolution of a group of animals that includes today's horses and rhinos.

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