The Cenozoic Radiation of Mammals

Abstract

One of the major features of the continental Cenozoic faunas of South America is the presence of native lineages of mammals, most of with have no counterpart in living faunas. In this chapter we study the ichnologic record of South American mammals during the Cenozoic and review their potential producers. We also analyze chronologic and geographic changes on the composition of the mammalian ichnofaunas and compare them with those of body fossils. Finally, we consider the paleoenvionmental distribution of mammalian footprints and their paleoecological significance. The Eocene and Oligocene ichnologic assemblages mostly represent forms of uncertain affinity, including small caviomorph rodents or typothere notoungulates, medium-size undetermined tetradactyl mammals, small toxodontid notoungulates or macraucheniid litopterns, large toxodontid notoungulates, and large dinomyids caviomorph rodents. Among the Miocene assemblages are recorded for the first time footprints assigned to ground sloth, macrauqueniiid and proterotheriid litopterns, caviid caviomorph rodents and hegetotheriid notoungulates. The Late Miocene-Pliocene and Late Pleistocene assemblages include footprints of both native South American mammals and North American lineages arrived as part of the Great American Biotic Interchange. Footprints of native South American lineages recorded for the first time include a variety of ground sloths, glyptodonts, hydrochoerid caviomorph rodents, and carnivorous marsupials. The North American lienages are equids, gomphotheriids, camelids, cervids, and several carnivoran taxa such as felids, mustelids, and bears. The ichnologic records of these unique lineages provide valuable paleobiological information on locomotion capacity, serve as proxy for body size, and are useful tools for paleocommunities analysis and paleoenvironmental interpretations. Some remarkable cases are the locomotion capacity of megatheres discussed based on the record of their trackways, and the record of peculiar rodent-like footprints that could expand the record of caviomorph rodents to the Early Eocene.