Formerly, the older geological period of the Cenozoic era (compare quaternary). It began about 65 million years ago, following the Cretaceous period, and extended to the beginning of the Quaternary, 2.58 million years ago. The Tertiary period was characterized by the rise of the modern mammals and the development of shrubs, grasses, and other flowering plants. It is no longer officially recognized as a division of geological time, having been replaced by the Palaeogene and Neogene periods.