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11/13/2013

Tibetan fossil find rewrites big cat evolutionary history

Big cat

 

Left, an artist's reconstruction of Panthera blytheae based on skull CT data. Right, images of the fossilized skull of the big cat discovered in Tibet; the find pushes back the age of the oldest known pantherine fossil by 2 million years. (illustration credit: Mauricio Antón.) 

 

 

Like so many fields these days, when it came to the evolutionary history of big cats, the paleontology people and the molecular people did not agree.

The earliest recorded fossil of a pantherine -- the group that includes lions, tigers, jaguars, leopards, snow leopards, and clouded leopards -- was a 3.8 million-year-old fragmented jawbone found in Africa. 

But DNA analysis of living big cats suggested that pantherines were much older and from a different continent. It indicated the big cat lineage diverged 11 million years ago and then split into different species 6 million years ago, and that all this happened in Asia.

Big cat history was a big fat mystery (sorry).

"We really don't know a lot about where they came from, in terms of both their geographical and evolutionary origins," says Jack Tseng, a postdoctoral fellow at the American Natural History Museum and a paleobiologist. 

All this despite their outsized reputations.

"These big cats are among the most charistmatic animals, not only for science but also for conservation and in the popular imagination. There are only seven living big cat species, and several of them are critically endangered."

Then, Tseng and a group of researchers were on a field mission in a basin of the Himalayas. University of Alberta researcher Juan Liu -- who also happens to be Tseng's wife -- discovered a broken jaw fragment. The team began digging in that location. Quickly, they discovered an intact skull. 

It was obvious the skull belonged to a carnivore. 

"We knew it was cat. But didn’t really know how old it was," says Tseng.

Only two years later, after extensive testing, did they discover the animal was 4.4 million years old, substantially older than the previous oldest-known big cat fossil, the one from Africa. 

Subsequent digs in 2012 would turn up more fossils that were nearly 6 million years old. In all, they found seven specimens from three different individuals. The research is published this week in Proceedings of the Royal Society B.

Based on comparisons to living cats, this ancient pantherine -- which was named Panthera blytheae after the daughter of generous donors to the museum -- is a relative of the modern snow leopard. It was slightly smaller, and probably ate antelope and other herbivores of the region (whose limb bones turned up in the dig in large quantities). 

The discovery still leaves huge gaps in scientists' knowledge of the big-cat evolutionary tree. Will an 11-million-year old ancestor to big cats be uncovered eventually?

In the meantime, Tseng says that knowledge that big cats originated in Asia could be used to help conservation efforts. "If you can narrow down a geographic region of where these big cats come from, that’s the type of region you need to conserve," he says.

Kate Allen is the Star's science and technology reporter. Find her on Twitter at @katecallen.

 

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