Science /Weird Science
Elaine Kasmer
What Horses and Rhinos Have in Common: An Ancestor in India
Who
knew that horses and rhinos were on the same branch of the evolutionary
tree? Actually, scientists have known for a long time that those two
types of animals, along with tapirs, are part of a biological group
known as perissodactyls or odd-toed ungulates.
But now an international research team has found fossils in India that
appear to point to the common ancestor of all living perissodactyls.
They didn't find the
ancestor itself. Instead, they found the fossils of a creature known as
Cambaytherium thewissi. Over the course of the past decade, they dug up
more than 200 Cambaytherium bones — including teeth, vertebrae and foot
bones — in an open-pit coal mine in India's Gujarat state, northeast of
Mumbai.
Those bones allowed the researchers to flesh out their picture of Cambaytherium. In this week's issue of the journal Nature Communications, they report that the creature's primitive, tapir-like characteristics are a close match for the earliest perissodactyls.
"What we have found is
essentially the cousin of all the living perissodactyls," said Ken Rose,
a professor of functional anatomy and evolution at the Johns Hopkins
University School of Medicine.
When Cambaytherium
walked the earth, about 54.5 million years ago, India was a huge island
drifting between Madagascar and Asia. How did it get there? The
researchers can't say for sure, but Rose speculates that during an even
earlier era, animals migrated over a land bridge that linked up with the
Horn of Africa or the Arabian Peninsula.
Once the land bridge
disappeared, the resulting isolation set up the evolutionary conditions
for one lineage to give rise to Cambaytherium as well as its
perissodactyl cousins. "What we're reporting is actually a remnant of
the probable ancestral group," Rose told NBC News.
Rose hopes that fossils found in future coal-mine digs will contribute to a clearer picture.
In addition to Rose, the authors of "Early Eocene Fossils Suggest That the Mammalian Order Perissodactyla Originated in India"
include Luke Holbrook, Rajendra Rana, Kishor Kumar, Katrina Jones,
Heather Ahrens, Pieter Missiaen, Ashok Sahni and Thierry Smith.
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