Purgatorius is one of Earth’s earliest primates, living over 65 million years ago. The small mammal’s 65 million year old anklebones were found fossilized in Montana. Purgatorius is part of the plesiadapiform primates, whose fossils were dated to being made right after the non-avian dinosaurs became extinct. When the anklebones were closely studied, they showed that the Purgatorius lived in trees. This is significant because many researchers believed that primitive primates belonging to the plesiadapiforms were terrestrial. They were believed to have become tree dwelling in the later species. The discovery of the anklebones is substantial because paleontologists had only the animal’s teeth and jaws to study. The anklebones were found in the