Here's a LiveScience story by Heather Whipps, about the discovery of chimpanzee nutcracking stones dating back to 4300 years ago:
Though there were no chimpanzee remains at the settlement, testing by archaeologists revealed the tool-laden camp was most likely used by the Great Ape. The stones were much bigger than anything a human could use comfortably and bore the residue of nuts that modern chimpanzees like to snack on.
"This is the only case of any prehistoric, non-human Great Ape tool use ever discovered," [archaeologist Julio] Mercader told LiveScience.
That's very cool. The news piece claims that this is great vindication for the idea that chimpanzees developed this ability without exposure to humans. That is, some people had argued that chimpanzees might have been "acculturated" to crack nuts by watching nearby people. Personally, I never thought there was much to that idea, since nutcracking is so widespread among chimpanzees and clearly learned by chimps with minimal or no human contact.
The most interesting part to me is the possibility that archaeologists will develop a search strategy for stone tools older than flaked stone tool manufacture.