Lead author Stephen Chester said, "The textbook that he is currently using in his biological anthropology courses still has an illustration of Purgatorius walking on the ground. Hopefully this study will change what students are learning about earliest primate evolution and will place Purgatorius in the trees where it rightfully belongs. The ankle bones have diagnostic features for mobility that are only present in those of primates and their close relatives today and these unique features would have allowed an animal such as Purgatorius to rotate and adjust its feet accordingly to grab branches while moving through trees. In contrast, ground-dwelling mammals lack these features and are better suited for propelling themselves forward in a more restricted, fore-and-aft motion."
The research provides the oldest fossil evidence that arboreality played a key role in primate evolution. Researchers said, "It implies that the divergence of primates from other mammals was not a dramatic event. Rather, primates developed subtle changes that made for easier navigation and better access to food in the trees."