About 5.9 inches (15 centimeters) below the surface the team found an ancient jawbone fragment with three molars still intact.
Using several dating techniques, the team determined the fragment was definitely older than 397,000 years and perhaps older than 525,000 years.
The jawbone lacked several characteristic Neanderthal features, including distinctive chewing surfaces on the teeth that show up in Western Europe at that time. Instead, the fossil resembled the more primitive Homo erectus.
Back then, the cave may have been a hyena den, though the researchers can't say whether a hyena actually brought the human remains into its den.
Oldest specimen In the past, anthropologists assumed that Neanderthals were widespread throughout Europe, basing that assumption on Neanderthal fossils almost exclusively found in Western Europe, Roksandic said.
The new findings suggest that Neanderthals may not have evolved in this region of Southeastern Europe, at least during this time. Instead, during several ice ages, rising glaciers over the past eons cut off Western Europe from the rest of the continent, and this isolation likely contributed to the evolution of Neanderthals' distinctive features from the more primitive Homo erectus.