Fossils in India support new hypotheses for the origin of ungulate mammals, including horses

Historical discoveries involving more than 350 fossils will become a crucial landmark for the origin of the horse, rhino and tapir, following a 15-year study.

The research, just published in Journal of Vertebrate Paleontology, describes a fossil family that illuminates the origin of the perissodactyls, the group of odd-toed ungulates that includes horses.

It provides insights into the controversial question of where these ungulates evolved, concluding that they arose in or near present-day India.

The study, which involved many years of demanding fieldwork, puts together a nearly complete picture of the skeletal anatomy of Cambaytherium, an extinct cousin of perissodactyls that lived on the Indian subcontinent nearly 55 million years ago.

The results describe a sheep-sized animal with moderate running ability and intermediate characteristics between specialized perissodactyls and their more generalized mammalian predecessors.

By comparing its bones to many other living and extinct mammals, Cambaytherium was found to represent a more primitive evolutionary stage than any known perissodactyl, supporting the group’s origin in or near India before they dispersed to other continents when it formed. the terrestrial connection with Asia.

The article was selected for publication as part of the prestigious Society of Vertebrate Paleontology memoir series, a special annual publication that provides a deeper analysis of the most significant vertebrate fossils.

Cambaytherium, first described in 2005, is the most primitive member of an extinct group that branched out shortly before the evolution of the perissodactyls, providing scientists with unique clues to the group’s ancient origins and evolution.

“The modern orders Artiodactyla (even ungulates), Perissodactyla and Primates suddenly appeared in the early Eocene around 56 million years ago in the Northern Hemisphere, but their geographical origin has remained a mystery,” explained Professor Ken Rose. emeritus of Johns Hopkins University and lead author of the study.

Rose was fascinated by a new hypothesis which suggested that perissodactyls may have evolved in isolation in India. At that time, India was an island continent drifting north, but later collided with Asia to form a continuous continental mass.

“In 1990, Krause and Maas proposed that these orders may have evolved in India during its northward drift from Madagascar, dispersing across the northern continents when India collided with Asia,” he noted.

Armed with this new hypothesis, Rose and colleagues secured funding from the National Geographic Society to explore India for rare age-corrected fossil rocks that could provide critical evidence for the origin of perissodactyls and other mammal groups.

The first trip to Rajasthan in 2001 had little success, only finding a few fish bones.

“The following year our Indian colleague, Rajendra Rana, continued to explore the lignite mines to the south and came across the Vastan mine in Gujarat.”

This new mine turned out to be much more promising.

“In 2004 our team was able to return to the mine, where our Belgian collaborator Thierry Smith found the first mammalian fossils, including Cambaytherium.”

Encouraged, the team returned to the mines and collected fossil bones from Cambaytherium and many other vertebrates, despite the harsh conditions.

“The heat, constant noise, and coal dust in the lignite mines were difficult, basically trying to work hundreds of feet near the bottom of the open cast lignite mines that are actively mined 24/7.” Rose said.

After many years of hard field work, the team can finally shed light on a mammal mystery.

Despite the abundance of perissodactyls in the Northern Hemisphere, Cambaytherium suggests that the group probably evolved in isolation in or near India during the Paleocene (66-56 million years ago), before dispersing to other continents when the terrestrial connection with Asia was formed.

Funding used to support field and laboratory research was provided by the National Geographic Society, the LSB Leakey Foundation and the US National Science Foundation.