Origin of the earliest amniota. Rapid evolutionary rate produced several important lines. Also from this stem arose the synapsid group that yielded the dominant predators of that time. Dinosaurs remain dominant but gradually decline in diversity and importance. Mammals radiate into several groups but are small in size and relatively unimportant.
Birds are virtually absent from the fossil record.
A cladogram at the bottom of this page summarizes these temporal and biological relationships. Labels for the above drawing. Dinosaurs remain dominant but gradually decline in diversity and importance. Mammals radiate into several important groups but remain small and unimportant. Birds remain virtually absent from the fossil record.