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Tweet: Common ancestor of horses, rhinos, and tapirs originated in India, fossils show.
EMBARGOED: FOR RELEASE NOV. 20, 2014 AT 5:00 A.M. EDT
Fast Facts:
 Newly described fossils suggest an ancient relative of horses and rhinos lived 54.5 million years
ago in what’s now India.
 Finding sheds light on the evolution of this group of animals.
OUT OF INDIA
--Fossils suggest ancestor of horses and rhinos originated on the Asian subcontinent while it was still an
island
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.
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. 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, Ph.D., a professor of functional anatomy and
evolution at the Johns Hopkins University School of Medicine.
Rose and his research team have for years been excavating mammal fossils in the Bighorn Basin of
Wyoming, but in 2001 he and Indian colleagues began exploring Eocene sediments in Western India
because it had been proposed that perissodactyls and some other mammal groups might have
originated there. In an open-pit coal mine northeast of Mumbai, they uncovered a rich vein of ancient
bones. Rose says he and his collaborators obtained funding from the National Geographic Society to
send a research team to the mine site at Gujarat in the far Western part of India for two weeks at a time
once every year or two over the last decade.
The mine yielded what Rose says was a treasure trove of teeth and bones for the researchers to comb
through back in their home laboratories. Of these, more than 200 fossils turned out to belong to an
animal dubbed Cambaytherium thewissi, about which little had been known. 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. “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.”
Cambaytherium 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. But, he
adds, “It’s not a simple story.”
“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,” he 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.”
Rose said his team was “very fortunate that we discovered the site and that the mining company
allowed us to work there,” although he added, “it was frustrating to knowing that countless fossils were
being chewed up by heavy mining equipment.” When coal extraction was finished, the miners covered
the site, he says. His team has now found other mines in the area to continue digging.
Other authors on the study were Luke T. Holbrook of Rowan University, Rajendra S. Rana of Garhwal
University, Kishor Kumar of the Wadia Institute of Himalayan Geology, Katrina E. Jones and Heather E.
Ahrens of Johns Hopkins University, Pieter Missiaen of Ghent University, Ashok Sahni of Panjab
University and Thierry Smith of the Royal Belgian Institute of Natural Sciences.
This study was funded by the National Geographic Society (grants 6868-00, 7938-05, 8356-07, 8710-09,
8958-11 and 9240-12), the Belgian Science Policy Office (project BR/121/A3/PALEURAFRICA), the
National Science Foundation (grant number DEB-0211976) and the Wadia Institute of Himalayan
Geology.
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Caption: An artist’s depiction of Cambaytherium thewissi
Credit: Elaine Kasmer