adaptive radiation
After a mass extinction, many habitats are no longer inhabited by organisms because they have gone extinct. With new habitats available, some species will adapt to the new environments. Evolutionary processes act rapidly during these times. Many new species evolve to fill those available habitats. The process in which many new species evolve in a short period of time to fill available niches is called adaptive radiation . At the end of this period of rapid evolution, the life forms do not look much like the ones that were around before the mass extinction. One example came after the extinction of the dinosaurs. Mammals underwent adaptive radiation and became the dominant life form. Although they lived in the habitats the dinosaurs had lived in, they didn't look much like the dinosaurs.