November 13, 2013
New Species Of Big Cat Discovered In Tibet Fills Evolutionary Gap
[ Watch the Video: Fossil Skull Of Ancient Big Cat Unearthed In Tibet ]
The evolution of big cats has been nearly as mysterious as the cats themselves, but a new discovery will likely lead anthropologists to a better understanding of when and where big cats originated.
During a 2010 paleontological dig in Tibet, a husband-and-wife team who were part of a larger expedition discovered the fossilized partial remains of what appeared to be a type of cat. University of Southern California (USC) graduate Z. Jack Tseng and his wife Juan Liu made the discovery in the Zanda Basin near the border of Pakistan and China.
Tseng, who now works with the American Museum of Natural History (AMNH) in New York, said the discovery was a surprise. In a Smithsonian Magazine blog, Tseng explained that the team had been driving trail after trail in the Tibetan “badlands” before discovering a patch of fossils protruding from the ground on one particular hillside.
“In the little concentration of fossils, there were lots of limb bones from antelopes and horses obscuring everything else,” said Tseng. “It wasn’t until we started lifting things up, one by one, that we saw the top of a skull, and we thought, from the shape, that it looked something like a cat.”
FILLING THE GAP
And after a few years of analysis, Tseng and his colleagues have published a paper today in the Proceedings of the Royal Society B explaining that this cat fossil is no ordinary cat, rather a totally new species, which has been described as Panthera blytheae by the team. This discovery also represents the oldest known “big cat,” a group that includes lions, tigers, leopards, etc., ever found and by a pretty significant margin. Of all the felines, the big cats were the first to split off into their own group from a common ancestor. As such, big cats are vital in the understanding of cat evolution.
Previously, the oldest big cat fossil ever found came from Africa and placed the group at about 3.8 million years old. However, some theories, based on geographical patterns and genetic data, suggest that Asian cats originated much earlier, at least six million years ago.
Theories can now be considered fact now that Tseng and his team have made and shared their exciting discovery. This new cat species fills the massive gap that existed within the fossil record and places the evolution of the big cat to around the Late Miocene-Early Pliocene.
“This find suggests that big cats have a deeper evolutionary origin than previously suspected,” Tseng said in a USC statement.
The new DNA evidence suggests these big-cats diverged from their nearest evolutionary cousins, Felinae, which includes cougars, lynxes, domestic cats, etc., about 6.37 million years ago.
In order to date the fossil, Tseng and colleagues relied on a technique called magnetostratigraphy. This method requires analysis of the magnetic orientation of the rocks around the site of the discovery and compare it to known reversals of the Earth’s magnetic field. However, this technique can only provide a rough estimate of an item’s actual age – in this case between 4.10 and 5.95 million years old.
So even if the fossil is at the latest point of 4.10 million years old, it is still nearly a half-million years older than the previous discovery.
But the researchers were not happy with just this conclusion, so they dug deeper. This discovery, said Tseng, suggests that big cats branched off from smaller cats much farther back than previously thought. The team compared the skull of P. blytheae to fossils from other extinct big cats, the anatomy of living cat species, and DNA samples taken from both living and some more recently extinct Ice Age-era species (cave lions). With this evidence in hand, the team was able to build a new evolutionary family tree for all big cats.
Using known rates of anatomical changes over time and the observed anatomy of P. blytheae, the team estimated that the earliest big cats branched off from the Felinae subfamily between 10 and 11 million years ago.
The new discovery also helps researchers answer an old question in evolutionary geology. In previous research, DNA analysis of all living big cats and fossils from various sites around the world had indicated that the most likely common ancestor of big cats originated in Asia. However, the oldest known specimens were only found in Africa, leaving some skeptical of the Asia link.
Tseng’s discovery, however, provides the first direct evidence that central Asia was indeed the ancestral home of big cats, at least as far back as the fossil record currently goes.
ANATOMY OF A KILLER
The team acknowledged that based on the fossil remains, it is difficult to describe a lot about the behavior and lifestyle of P. blytheae, but the team was able to draw some conclusions based on skull anatomy.
“It’s not a huge cat, like a lion or a tiger, but closer to a leopard,” Tseng said.
Tseng speculated that the habitat of the cat was very similar to what we see today on the Tibetan plateau. The area today is home to snow leopards, and like these cats, Tseng said it is likely P. blytheae did not hunt on the open plains, but rather on cliffs and in valleys. Evidence in tooth wear patterns suggests similarities to the snow leopard. The rear teeth, which appeared sharp, were likely used for cutting soft tissue; the front teeth were heavily worn, suggesting they were used to pry open carcasses and picking meat off the bones.
STILL NOT COMPLETE
Tseng and colleagues plan to return to Tibet to hunt for more evidence. Tseng noted that while the current fossil represents the earliest of its kind, it is not the final piece of the puzzle in the evolution of big cats. He maintains that it cannot be the oldest big-cat fossil out there.
“The gap still isn’t completely filled yet,” he said. “We need to find older big cats to put the picture together.”
"It points us to look for more ancestral big cats in the Miocene rocks of central Asia," Tseng, a National Geographic Young Explorer grantee, told NatGeo’s Jennifer Holland in an interview.
He added that the timeline of big-cat evolution has more than just historical significance.
The more that can discovered about the successes of ancient big cats and their prey in ever-changing environments, the better equipped scientists will be in predicting how today’s big cats will respond to change, said Tseng.
Among the many coauthors of this study from several colleges and institutions, perhaps Tseng's closest colleague is his wife Juan Liu, of the University of Alberta and the Chinese Academy of Sciences (CAS).
The research was funded by National Basic Research Program of China, the Chinese Academy of Sciences, the National Science Foundation, the American Museum of Natural History, the Smithsonian Institution (National Museum of Natural History), and the National Geographic Society.