Researchers on an expedition in Tibet recently discovered the oldest big cat fossil ever found, filling a significant gap in the fossil record.
The skull from the new species, named Panthera blytheae, is described today in the Proceedings of the Royal Society B: Biological Sciences. The research, led by Jack Tseng, a Ph.D. student at the University of Southern California at the time of the discovery and now a postdoctoral fellow at the Museum, suggests that big cats have a deeper evolutionary origin than previously expected based on the existing fossil record.
Life reconstruction of Panthera blytheae based on skull CT data; illustrated by Mauricio Antón.
DNA evidence and "molecular clock" age estimation techniques had suggested that "big cats"—the Pantherinae subfamily, including lions, jaguars, tigers, leopards, snow leopards, and clouded leopards—diverged from their nearest evolutionary cousins, Felinae (which includes cougars, lynxes, and domestic cats), about 10.8 million years ago.
However, the oldest fossils of big cats previously found are tooth fragments uncovered at Laetoli in Tanzania, dating to just 3.6 million years ago.
Using magnetostratigraphy—dating fossils based on the distinctive patterns of reversals in the Earth’s magnetic field, which are recorded in layers of rock—Tseng and his team were able to estimate the age of the new fossil skull at around 4.4 million years old.
Images of the holotype specimen and reconstructed facial bones based on CT data; Figure 1 from the paper.
The find not only challenges previous suppositions about the origins of big cats, it also helps place that evolution in a geographical context. The discovery occurred in a region that overlaps the majority of current big cat habitats, and suggests that the group evolved in central Asia and spread outward, rather than originating in Africa as previously inferred from the known fossil record.
In addition, recent estimates suggested that species within the genusPanthera (lions, tigers, leopards, jaguars, and snow leopards) did not begin to diversify until 3.72 million years ago, which the new find disproves because the new species of Panthera is much older than that.
“This research provides an elegant example of the continuing value of exploration in understudied regions of our planet, and of integrative interdisciplinary and international research,” said John Flynn, Frick Curator of Fossil Mammals in the Museum’s Division of Paleontology and Tseng’s postdoctoral supervisor, who was not an author on the paper. “New discoveries like this well-dated fossil ‘big cat’ can transform our understanding of the geographic origins and age of key groups of mammals, as well as the environmental context for their early histories and diversification.”
Tseng, his wife Juan Liu, and Gary Takeuchi of the Natural History Museum of Los Angeles County, discovered the skull in 2010 while scouting in the remote border region between Pakistan and China—an area that takes a bumpy seven-day car ride to reach from Beijing. Liu found more than 100 bones that were likely deposited by a river eroding out of a cliff. There, below fossil antelope limbs and jaws, was the crushed—but largely complete—remains of the cat skull.
For the past three years, Tseng and his team have used detailed anatomical studies to determine that the skull does, in fact, represent a new species, and combined it with DNA and geological information to determine its place in time and cat (felid) evolution. They plan to return soon to the site where they found the skull in order to search for more specimens.
Read more about the field expedition in an article by Tseng in Slate.