Mass extinctions led to low species diversity, dinosaur rule

Two of Earth’s five mass extinction events — times when more than half of the world’s species died — resulted in the survival of a low number of so-called ‘weedy’ species that spread their sameness across the world as the Earth recovered from these dramatic upheavals. The findings could shed light on modern high extinction rates and how biological communities may change in the future.
Paleontology News — ScienceDaily