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. The Tertiary was a time of recovery. Obviously, the aquatic environment acted as a great climatic buffer. Amphibians, especially anurans, rebounded, as did lizards and snakes. Mammals rapidly filled the new niches available from decline of the large reptiles, and birds speciated rapidly, much like teleosts.