Purgatorius

Purgatorius is an extinct genus of eutherian mammal from the early Paleocene epoch of western North America. It is typically believed to be the earliest example of a primate or protoprimate (a primatomorph precursor to the Plesiadapiformes), dating to nearly as old as 66 million years ago.

The first remains (P. unio and P. ceratops) were reported in 1965, from what is now eastern Montana's Tullock Formation (early Paleocene, Puercan). P. unio is from Purgatory Hill (hence the animal's name) in deposits believed to be about 63 million years old, and P. ceratops is a single worn tooth from Harbicht Hill in the lower Paleocene section of the Hell Creek Formation. Both locations are in McCone County, Montana. Harbicht Hill was once thought to be late Cretaceous, but it is now clear that it represents Paleocene channels with time-averaged fossil assemblages. Several more Montanan Purgatorius species have been named since the initial discovery, though fossils are still limited to teeth, jaw fragments, and a few ankle bones. Two Purgatorius species were also named from the Ravenscrag Formation of Saskatchewan, and an undetermined species is known from Corral Bluffs in Colorado.

Purgatorius is thought to have been rat-sized (6 in (15 cm) long and 1.3 ounces (about 37 grams)) and a diurnal insectivore. In life, it would have resembled a squirrel or a tree shrew (most likely the latter, given that tree shrews are one of the closest living relatives of primates, and Purgatorius is considered to be the progenitor to primates). The oldest remains of Purgatorius date back to 65.946–65.912 million years ago, or between 105 thousand to 139 thousand years after the K-Pg boundary.