PALEOCENE EPOCH

also spelled Palaeocene Epoch, major worldwide division of Early Tertiary rocks and time that began 66.4 million years ago and ended 57.8 million years ago. The earliest division of the Tertiary Period, it precedes the Eocene Epoch and follows the Cretaceous Period. Because marine rocks of the Paleocene Epoch are limited in occurrence, much of the information about the Paleocene comes from terrestrial deposits. Subdivisions of the Paleocene vary from region to region; in Europe, for example, at least three stages of the Paleocene are recognizedthe Danian, the Montian, and the Thanetian. In North America, especially in the San Juan River basin of New Mexico and southern Colorado, where Paleocene continental deposits are well developed and sequences are based on mammalian evolution, local names (such as the Puercan, the Torrejonian, and the Tiffanian) were assigned to the various stages. The Paleocene record of North America affords the most complete picture of Paleocene life and environments; elsewhere, Paleocene animals, especially mammals, are lacking, rare, or of late Paleocene age. Late Paleocene faunas are known from the regions of Cernay, France; Gashato, Mongolia; and the Chico River region of Patagonian Argentina. The Paleocene of North America was characterized by a general warming trend in climatic conditions, with little or no frost; seasonal variations probably consisted of alternations of dry and wet seasons. Among the most prominent features of Paleocene vertebrate faunas are the complete absence of dinosaurs and other reptilian groups that were dominant during the Cretaceous and the rapid proliferation and evolution of the mammals. Paleocene mammals include representatives of many groups or orders that are still extant, although the Paleocene forms are mostly archaic or highly specialized. In terms of proportions and relative abundance, however, Paleocene faunas are dominated by mammals that have no living representatives. Paleocene mammalian faunas include Cretaceous species such as opossum-like marsupials and, especially, the archaic and unusual multituberculates, herbivorous animals that had teeth very similar in some respects to those of the later, more advanced rodents. The condylarths, very important elements of Paleocene faunas, include forms that were trending toward herbivorousness while still retaining primitive traits of their insectivore-carnivore progenitors. Primates became more abundant in the middle Paleocene and displayed characteristics intermediate between the insectivores and lemurs, especially in terms of dental anatomy. Late in the Paleocene, mammalian evolution showed a trend toward larger forms and more varied assemblages. The primitive mammalian carnivores, the creodonts, appear late in the Paleocene, as do large herbivores, ancestral rodents, and the first tarsioid primates. The Gashato fauna from Mongolia contains the remains of the earliest-known hare, Eurymylus, and among Paleocene mammals from South America are many early representatives of animals that dominated later Tertiary faunas in the region.