 And "S. tchadensis" does indicate that the last common ancestor of humans and chimpanzees is unlikely to closely resemble extant chimpanzees, as had been previously supposed by some paleontologists.Sediment isotope analysis of cosmogenic atoms in the fossil yielded an age of about 7 million years.In this case, however, the fossils were found exposed in loose sand; co-discoverer Beauvilain cautions that such sediment can be easily moved by the wind, unlike packed earth, making the date of 7 million years less certain.