True placentals may have originated in the Late Cretaceous around 90 MYA, but the earliest undisputed fossils are from the early Paleocene, 66 MYA, following the Cretaceous–Paleogene extinction event. The species "Protungulatum donnae" was thought to be a stem-ungulate known 1 meter above the Cretaceous-Paleogene boundary in the geological stratum that marks the Cretaceous–Paleogene extinction event and "Purgatorius", previously considered a stem-primate, appears no more than 300,000 years after the K-Pg boundary; both species, however, are now considered non-placental eutherians. The rapid appearance of placentals after the mass extinction at the end of the Cretaceous suggests that the group had already originated and undergone an initial diversification in the Late Cretaceous, as suggested by molecular clocks. The lineages leading to Xenarthra and Afrotheria probably originated around 90 MYA, and Boreoeutheria underwent an initial diversification around 70-80 MYA, producing the lineages that eventually would lead to modern primates, rodents, insectivores, artiodactyls, and carnivorans.