Rowan bio professor helps trace evolution of horses, more via fossils

Joining with researchers from Johns Hopkins University and elsewhere, Dr. Luke Holbrook, professor of Biological Sciences at Rowan University, assisted in tracing the evolution of a group of animals via fossils that indicate the ancestor of today’s horses, rhinos and tapirs originated in India while it was still an island. Their work was reported recently in the online journal Nature Communications.

“This research provided the first evidence that India might have been a geological Noah’s Ark. During the time it was drifting in isolation, some groups of mammals might have originated or evolved there after India connected with Asia and later may have moved through the rest of Asia and into the Northern Hemisphere,” Holbrook said.

In India

Working at the edge of a coal mine in India, a team of Johns Hopkins researchers and colleagues filled in a major gap in science’s understanding of the evolution of Perissodactyla, which includes modern-day horses, rhinos and tapirs. 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, said Dr. Ken Rose, a professor of functional anatomy and evolution at the Johns Hopkins University School of Medicine.

Rose and his research team for years have been excavating mammal fossils in the Bighorn Basin of Wyoming. 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 during the last decade.

Treasure trove

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 said, 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 said. 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 said.

“This work was important for understanding where this very familiar and important group of mammals came from and tells us something about the early diversification on mammals in general,” Holbrook said. The research was the first to show that the group evolved from mammals that had five “fingers” and “toes.”

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 said. But, he added, “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 said. “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.”

Good fortune

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 said. His team has now found other mines in the area to continue digging.

Rose invited Holbrook into the project about a year ago. An expert on Perissodactyls, Holbrook contributed to the analysis of where the new fossils fit into the tree of life.

“They have a very rich fossil record that goes back 56 million years ago. So they were much more diverse in the past. They often figure prominently in the stories of evolution,” Holbrook said of Perissodactyls.  He and Rose were the lead authors of the paper.

In addition to Holbrook and Rose,  other  authors on the study were 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, awarded to Holbrook in 2002) and the Wadia Institute of Himalayan Geology.