Science, Tech, Math › Animals & Nature Purgatorius Share Flipboard Email Print Purgatorius (Nobu Tamura). Animals & Nature Dinosaurs Prehistoric Mammals Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated March 07, 2017 Name: Purgatorius (after Purgatory Hill in Montana); pronounced PER-gah-TORE-ee-us Habitat: Woodlands of North America Historical Period: Late Cretaceous (65 million years ago) Size and Weight: About six inches long and a few ounces Diet: Probably omnivorous Distinguishing Characteristics: Small size; primate-like teeth; ankle bones adapted to climbing trees About Purgatorius Most of the prehistoric mammals of the late Cretaceous period looked pretty much the same--small, quivering, mouse-sized creatures that spent most of their lives high up in trees, the better to avoid rampaging raptors and tyrannosaurs. On closer examination, though, especially of their teeth, it's clear that these mammals were each specialized in their own distinct way. What set Purgatorius apart from the the rest of the rat pack is that it possessed distinctly primate-like teeth, leading to speculation that this tiny creature may have been directly ancestral to modern-day chimps, rhesus monkeys, and humans--all of whom had the chance to evolve only after the dinosaurs went extinct and opened up some valuable breathing room for other types of animals. The trouble is, not all paleontologists agree that Purgatorius was a direct (or even distant) precursor of primates; rather, it may have been an early example of the closely related group of mammals known as "plesiadapids," after the most famous member of this family, Plesiadapis. What we do know about Purgatorius is that it lived high up in trees (as we can infer from the structure of its ankles), and that it managed to straddle the K/T Extinction Event: fossils of Purgatorius have been discovered dating both to the late Cretaceous period and the early Paleocene epoch, a few million years later. Most likely, this mammal's arboreal habits helped rescue it from oblivion, making accessible a new source of food (nuts and seeds) at a time when most non-tree-climbing dinosaurs were starving to death on the ground.