A new report details how researchers have found gnawing teeth marks on the bones of Cretaceous dinosaurs and marine reptiles. The dinosaur femur and rib bones demonstrate opposing pairs of teeth marks which would indicate that they belonged to a group of rodent-like mammals. The nature of the bite marks suggests that the small mammals were not scavenging meat but were gnawing the bones to supplement their diet with calcium and protein.

Dr Longrich, the author of the report, believes these teeth impressions dating from  75 million years ago are the oldest known mammalian gnawing marks. During the reign of the dinosaurs all mammals that existed were small. It was only with the extinction of the dinosaurs 65 million years ago that the mammals could flourish and occupy the vacant ecological niche.