Earliest primate fossils documented, shed light on rise of mammals They are estimated to be 65.9 million years old, about 1,05,000 to 1,39,000 years after the mass extinction event. Scientists have documented the earliest-known fossil evidence of primates, an advance which sheds light on how life on land recovered after the extinction event 66 million years ago that wiped out the dinosaurs and led to the rise of mammals. The researchers, including those from the University of Washington in the US, analysed several fossils of Purgatorius -- the oldest genus in a group of the earliest-known primates called plesiadapiforms. According to the study, published in the journal Royal Society Open Science, these ancient mammals were small-bodied and ate specialised diets of insects and fruits that varied by species.