Purgatorius is the genus of the four extinct species believed to be the earliest example of a primate or a proto-primate, a primatomorph precursor to the Plesiadapiformes, dating to as old as 66 million years ago. The earliest primates likely descended from a small, nocturnal, insectivorous mammal. The tree shrews and colugos are the closest living relatives to primates. The tree shrew is used as a living model for what the earliest primates, or primate predecessors