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Scientists have assessed over 350 fossils of hoofed mammals — a group that includes horses, rhinos, and tapirs — and suggest that they may have originated in or near present day India.
The 15-year study , published in the Journal of Vertebrate Palaeontology , pieces together a nearly complete picture of the skeletal anatomy of hoofed mammals that lived on the Indian subcontinent almost 55 million years ago.
In the research, the scientists, including Kishor Kumar from Wadia Institute of Himalayan Geology in Uttarakhand, unearthed a sheep-sized animal with moderate running ability belonging to the now-extinct genus of mammals called Cambaytherium.
They said the animal possessed features that were intermediate between specialised hoofed mammals and their more generalised forerunners.
Comparing its bones with many other living and extinct mammals, revealed that this group of animals represents an evolutionary stage more primitive than any known hoofed mammal.
According to the scientists, the findings support origin for the group in or near India, which they believe was an island continent during this time period, drifting northwards and later colliding with the continent of Asia to form a continuous landmass.
They believe the group likely evolved in isolation in or near India 66-56 million years ago, before dispersing to other continents when the land connection with Asia formed.
“In 1990, Krause & Maas proposed that these (mammal) orders might have evolved in India, during its northward drift from Madagascar, dispersing across the northern continents when India collided with Asia,” said Ken Rose, lead author of the study from Johns Hopkins University in the U.S.
The researchers then explored India for rare fossil-bearing rocks of the correct age that might provide critical evidence for the origin of these groups of mammals. Their first trip to Rajasthan in 2001 bore little fruit, they said.
“Although we found only a few fish bones on that trip, the following year our Indian colleague, Rajendra Rana, continued exploring lignite mines to the south and came upon Vastan Mine in Gujarat,” Rose said.
This new mine proved much more promising, the scientists added. “In 2004 our team was able to return to the mine, where our Belgian collaborator Thierry Smith found the first mammal fossils, including Cambaytherium,” Rose said.
Despite challenging conditions, the researchers returned to the mines and collected fossilized bones of these ancient mammals.
“The heat, the constant noise and coal dust in the lignite mines were tough - basically trying to work hundreds of feet down near the bottom of open-pit lignite mines that are being actively mined 24/7,” Rose added.