Tiny, tooth-sized fossils have just reshaped the story of our deepest ancestry. Paleontologists have discovered the southernmost remains ever found of Purgatorius—the earliest-known relative of all primates, including humans—in Colorado’s Denver Basin. Previously thought to be confined to Montana and parts of Canada, this shrew-sized, tree-dwelling mammal now appears to have spread southward soon after the asteroid impact that wiped out the dinosaurs.