Cenozoic Mammalian Herbivores From the Americas: Reconstructing Ancient Diets and Terrestrial Communities

▪ Abstract Herbivory first evolved in terrestrial mammals during the late Cretaceous, ∼100 million years ago (Mya). Of the ∼35 ordinal-level clades of extinct or extant eutherian mammals from the New World, ∼24 have been adapted to herbivory in one form or another. Dental adaptations for specialized terrestrial browsing are first recognized during the early Cenozoic (Paleocene-Eocene). Mammalian herbivores adapted for grazing did not become widespread in the New World until the middle Cenozoic; it seems that this adaptation and the spread of grasslands occurred during the late Oligocene (30 Mya) in South America ∼10 million years earlier than in North America (20 Mya). Carbon isotopic evidence from fossil herbivore teeth indicates that C3 plants predominated until the late Miocene (∼8 Mya). Thereafter, C3 and C4 terrestrial communities diversified. Late Pleistocene extinctions ∼10,000 years ago decimated the diversity of mammalian herbivores, particularly those of larger body size.