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It is the 'missing link' that shows horses and rhinos were once related.

Experts have uncovered a fossil from an ancient relative of the animals that lived 54.5 million years ago in what is now India. 

The discovery also sheds new light on how India shifted over time.

Modern horses, rhinos and tapirs belong to a biological group lived 54.5 million years ago in what is now India, and cam from this create, Cambaytherium thewiss

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 and a distinctive digestive system. 

Working at the edge of a coal mine in India, a team of Johns Hopkins researchers 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. 

That group likely originated on the subcontinent when it was still an island headed swiftly for collision with Asia, the researchers report Nov. 20 in the online journal Nature Communications.

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, says Ken Rose of Johns Hopkins University School of Medicine.

'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.' 

An open-pit coal mine northeast of Mumbai yielded what Rose says was a treasure trove of teeth and bones, with more than 200 fossils turned out to belong to an animal dubbed Cambaytherium thewissi, about which little had been known. 

Modern horses, rhinos (pictured) and tapirs belong to a biological group, or order, called Perissodactyla.

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. 

Cambaytheri 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 says. 

In 1990, two researchers, David Krause and Mary Maas of Stony Brook University, published a paper suggesting 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, Rose says.