The first epoch of the Neogene period, extending from the end of the Oligocene, about 23 million years ago, to the start of the Pliocene, roughly 5 million years ago. It saw the radiation of several modern mammal groups, including the ruminants (deer, cattle, and antelopes), certain rodents (beavers, porcupines, and cavies) and the apes. Cooling of the climate during the Oligocene resulted in a continuing shift to deciduous hardwood species, such as oak and maple, at the expense of conifers during the Miocene.