Fossils Found in India Offer Clues to Equid Evolution

Scientists have unearthed an ancient “uncle” to equids in India, pointing to the evolutionary origins of horses.

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Fossils Found in India Offer Clues to Equid Evolution
Life reconstruction of Cambaytherium | Photo: Courtesy Dr. Kenneth Rose
More than 50 million years ago, the earliest equids appeared in what is now Asia and North America. But their appearance, along with that of other hooved mammals with an odd number of toes (essentially, rhinos and tapirs)—was “abrupt” and, for paleontologists, difficult to explain. How these animals appeared on earth’s mainland, shortly after a prehistoric period of global warming, long remained a mystery.

Enter Uncle Cambaytherium. From India.

Although scientists still haven’t found the grandfather of all perissodactyls—“odd-toed” ungulates like horses—one international group has recently discovered and described a critical clue: their “uncle,” so to speak. Hundreds of Cambaytherium fossils, excavated from Indian lignite (brown coal) mines, provide evidence that the Cambaytherium and perissodactyls probably descended from the same common line. And that strongly suggests that equids could have evolved from a mammal that once roamed the great “island” of modern-day India before the land mass rammed into the continent of Asia 55 million years ago, said Kenneth Rose, PhD, emeritus professor at Johns Hopkins University, in Baltimore, Maryland.

Once entirely surrounded by ocean, the land that’s now India drifted slowly northward up from Madagascar over millions of years, Rose said. Completely isolated, the land mass harbored evolving mammals that had little or no contact with land-roaming species elsewhere in the world during most of that time. Cambaytherium was one of those, he said. Although it wasn’t a direct ancestor of horses (or rhinos or tapirs), it was what researchers call a “sister taxon”—meaning it was essentially a sibling species to the ancestor they wanted to find

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Passionate about horses and science from the time she was riding her first Shetland Pony in Texas, Christa Lesté-Lasserre writes about scientific research that contributes to a better understanding of all equids. After undergrad studies in science, journalism, and literature, she received a master’s degree in creative writing. Now based in France, she aims to present the most fascinating aspect of equine science: the story it creates. Follow Lesté-Lasserre on Twitter @christalestelas.

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