It kinda makes sense that diversity and extinction would go together. in stable conditions I suspect that evolution would find some optimal players that would dominate the world because they are better adapted to it. this would lower diversity.

Then when things are shifting, species start going extinct, but this opens different shaped gaps as things are shifting which opens opportunities for different species to evolve w/o too much competition as much has died. None of the competition is very aligned with the shifting enviornment, thus many competitors can get a foothold even when they themselves are not so well adapted.

then as things shift more, new forms get a foot hold, meanwhile the once dominant species are simply dying off in the new mismatched world.

This suggests (perversely) that the human-caused mass extinction could eventually yield such evolutions? not sure, our even is going to be much much faster than anything except the asteroid.