Washington, May 21 (IANS): Scientists have found in east Africa stone tools dating back 3.3 million years -- long before the advent of modern humans and by far the oldest such artefacts yet discovered.

This is the first evidence that an even earlier group of proto-humans may have had the thinking abilities needed to figure out how to make sharp-edged tools. The tools have been found in northwestern Kenya.

"The tools shed light on an unexpected and previously unknown period of hominin behaviour and can tell us a lot about cognitive development in our ancestors that we can't understand from fossils alone," said lead author Sonia Harmand, of the Turkana Basin Institute at Stony Brook University in New York.

Hominins are a group of species that includes modern humans, Homo sapiens, and our closest evolutionary ancestors. Anthropologists long thought that our relatives in the genus Homo -- the line leading directly to Homo sapiens -- were the first to craft such stone tools.

But researchers have been uncovering tantalizing clues that some other, earlier species of hominin -- distant cousins, if you will -- might have figured it out.

The area from where the tools were discovered was at that time a partially wooded, shrubby environment. The tools could have been used for breaking open nuts or tubers, bashing open dead logs to get at insects inside, or maybe something not yet thought of.

The study appeared in the journal Nature.