Figure 8. Range chart of Arctocyonia (extinct) + Artiodactyla (extant), Mesonychia (extinct), and Archaeoceti (extinct) + Mysticeti/Odontoceti (both extant). Spectra of reasonable likelihoods (0.05 less than or equal to L less than or equal to 1.00) for the time of origin of Mesonychia from Arctocyonia + Artiodactyla and the time of origin of Archaeoceti from Mesonychia, are shown in the context of condylarthran, artiodactyl, and cetacean phylogeny (phylogenetic relationships follow Van Valen 1966, 1971, 1978; Rose 1996; Geisler and O'Leary 1997; and others). From a paleontological point of view the origin of Cetacea is constrained by fossils to lie within the interval from 49.5 to about 51.6 Ma (early Eocene). From a neontological point of view the divergence time of Cetacea and Artiodactyla is constrained by fossils to lie within the interval from 63 to about 66.7 Ma (early Paleocene to latest Cretaceous).