If you placed a tiger next to a lion, it would be ridiculously easy to say which was which. If you placed their skeletons next to each other, the task would be far more difficult. Stripped of their distinctive coats, the 37 species of cats look much the same as each other. Some are big, others small, but their bones share similar proportions and features. Even experts have a tough time telling them apart.
So, when fossil-hunters find the remains of a new prehistoric cat, they can take a long time to work out what they just dug up.
That certainly happened to Jack Tseng from the American Museum of Natural History in New York. In 2010, he travelled to Tibet with his wife and other palaeontologists, and discovered a large collection of fossils. Among the bones were the skull of a large cat and several fragments of jaws and teeth. “We spent the next three years trying to find out what this thing was.”
They now know that they have found the oldest ever specimen of a big cat, one that resolves a curious conflict about when and where these iconic animals evolved.
The term “big cat” has been defined in many different ways, based on size, roaring ability and evolutionary history. Currently, the term refers to the pantherines—a seven-strong group that includes the lion, tiger, leopard, jaguar, snow leopard, clouded leopard, and Sunda clouded leopard.
The new cat skull didn’t match any of these living species. Instead, it’s an extinct member, closely related to the living snow leopard but slightly smaller. Tseng named it Panthera blytheae*.
P.blytheae lived on the Tibetan Plateau—a dry, open expanse of land that’s punctuated by steep cliffs. It’s known as the “Roof of the World”. There, P.blytheae would have hunted large prey like horses, antelopes, and sheep, probably pursuing them across the crags as snow leopards do today.
Big cat fossils are very rare, and the oldest ones were just 3.8 million years old and came from Africa. But when geneticists compared the DNA of modern big cats, they shifted the group’s origins in both space and time. They suggested that the last common ancestor of the living pantherines lived in Asia around 6.4 million years ago, and the whole lineage split off from the rest of the cat family tree 10.8 million years ago.
“There were no fossils even approaching that age anywhere in the world,” says Tseng. Genes and bones seemed to tell completely different stories, separated by at least 2.6 million years if not longer.
But P.blytheae fills the gap almost perfectly. The youngest remains of this new cat are 4.1 million years old, and the oldest are 6 million years old. “It fits nicely in that slot where we didn’t have anything before,” says Tseng.
“New informative fossils are always welcome,” says Stephen O’Brien, who led the last gene-based reconstruction of cat evolution. “Our molecular estimates are always dependent on accurate fossil dates to help calibrate our time estimates.”
The team have now built a new family tree for the big cats, using both physical traits form their bones and DNA where possible. They included all seven living members, three extinct ones (P.blythae, the big cave lion and the even bigger American lion) and two outliers (the puma and ocelot).
This new tree firmly anchors the origin of the big cats in central Asia. It also says that the group is even older than previously thought, diverging from other cats 18.7 million years ago.
The clouded leopards then split off from the other pantherines 16.4 million years ago, and moved into Southeast Asia. The remaining lineages diverged into two main branches around 10.2 million years ago. One spread into the rest of southern and eastern Asia, and gave rise to P.blytheae, the snow leopard and the tiger. The other spread west into the Middle East, Africa and the Americas, giving rise to the lion, leopard, jaguar, cave lion and American lion.
But these dates are far from precise. For example, the team’s tree suggests that the clouded leopards diverged from the other big cats around 16.4 million years ago, but the real date could be anywhere from 8.4 to 27.7 million years ago. (The confidence intervals are wide.)
The only way to narrow down these estimates is to find more fossils, and that’s what Tseng wants to do. Note that P.blytheae is the oldest big cat specimen, but it’s not the earliest big cat. It arose well after the group started diversifying. Tseng suspects that more primitive felines have already been found, and are sitting around in museum collections waiting to be described.
“The big issue is whether palaeontologists can actually recognise them when they see them,” he says. “Cats are notoriously similar to each other, and they’re probably even more similar at the beginning of the cat lineage.” A careful trawl of museum specimens may be in order. Perhaps curiosity will fill the cats.
* Finally, why P.blytheae? In 2011, Tseng presented his Tibetan specimens at a ball that several museum trustees had attended. One of them, Paul Haaga Jr., was excited enough that he decided to sponsor the project. “When we got the paper done, we asked him whether they wanted to name the cat,” says Tseng. “He said his daughter Blythe is really into cats, and had a snow leopard toy when she was small.” The new animal was a sister species to the living snow leopard. Everything fit, and Panthera blytheae was christened.
Blythe herself found out on Monday night, when she went home to Los Angeles to visit her parents. The news was a 30th-birthday gift. “They are known for off-the-wall, philanthropy-oriented gift-giving,” she says. “I don’t think they realized how significant the research outcomes would be so in many ways it’s a wonderful surprise for all of us.”
Reference: Tseng, Wang, Slater, Takeuchi, Li, Liu & Xie. 2013. Himalayan fossils of the oldest known Pantherine establish ancient origin of big cats. Proc Roy Soc B http://dx.doi.org/10.1098/rspb.2013.2686
More on cats: