Two Cut-marked Bones from Dikika, Ethiopia (image) California Academy of Sciences Share Print E-Mail Caption These two bones from Dikika, which have been dated to roughly 3.4 million years ago, provide the oldest known evidence of stone tool use among human ancestors. Both of the cut-marked bones came from mammals -- one is a rib fragment from a cow-sized mammal, and the other is a femur shaft fragment from a goat-sized mammal. Both bones are marred by cut, scrape, and percussion marks. Credit Dikika Research Project, California Academy of Sciences Usage Restrictions With credit to the Dikika Research Project, California Academy of Sciences Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.