Adaptive radiation of mammals: Major stages

Several major stages are distinguished in the process of mammalian adaptive evolution. The first stage lasted from the Late Triassic to the end of the Early Cretaceous when mammals permeated the terrestrial vertebrate community like a network without competing with its principal members. During the second stage, the Late Cretaceous, many Mesozoic lineages became extinct and the onset of the Cenozoic radiation. The third stage includes the Cenozoic diversification of therian mammals, which occupied all the ecological niches of dinosaurs within a short period and gave rise to new ones. The number and diversity of mammalian adaptive niches are shown to increase in the course of their history.