A skull from the new species Panthera blytheae -- a distant relative of modern snow leopards -- was found by a team led by Jack Tseng, a postdoctoral fellow at the American Museum of Natural History in New York.
"This find suggests that big cats have a deeper evolutionary origin than previously suspected," said Tseng, who at the time of the discovery was a doctoral student at the University of Southern California.
DNA evidence suggests that the so-called "big cats" -- the Pantherinae subfamily including lions, jaguars, tigers, leopards, snow leopards, and clouded leopards -- split off from their nearest evolutionary cousins, Felinae (which includes cougars, lynxes, and domestic cats) about 6.37 million years ago.
However, the oldest fossils of big cats found to date had been tooth fragments uncovered in Tanzania dating to just 3.6 million years ago.
Tseng and his colleagues say they've been able to estimate the age of the fossil skull at between 4.1 and 5.95 million years old.
The fossil find was made in a region that overlaps the majority of current big cat habitats, suggesting the group evolved in central Asia and spread outward, the researchers said.