(Reuters) - Along the banks of the Kalambo River in Zambia near Africa's second-highest waterfall, archaeologists have excavated two logs of the large-fruited bushwillow tree that were notched, shaped and joined nearly half a million years ago.

These artifacts, researchers said on Wednesday, represent the oldest-known example of humans - in this case a species that preceded our own - building wooden structures, a milestone in technological achievement that indicates that our forerunners displayed more ingenuity than previously thought.

The logs, modified using stone tools, appear to have been part of a framework for a structure, a conclusion that contradicts the notion humans at that time simply roamed the landscape hunting and gathering resources.

"The framework could have supported a walkway or platform raised above the seasonally wet surroundings. A platform could have multiple purposes including storage of firewood, tools, food and as a foundation on which to place a hut," said archaeologist Larry Barham of the University of Liverpool in England, lead author of the study published in the journal Nature. "Not only did the working of trees require considerable skill, the right tools and planning, the effort involved suggests that the makers were staying in the location for extended periods whereas