...For the first few million years after an extinction the speciation rate actually falls. "That suggests to us a sort of wounded biosphere. Extinction events don't just remove organisms from an ecosystem, leaving lots of opportunity for new species to diversify. Instead, what we think happens is that the niches themselves collapse, so you won't have new organisms emerging to occupy them. The niches themselves don't exist any more," says [James] Kirchner.-- from Post-human Earth
Eventually, though, evolution wins the day, and after a few tens of millions of years biodiversity rebounds. Sometimes, as after the Ordovician mass extinction 440 million years ago, the new regime looks a lot like the old one. But more often a new world emerges. "You're not re-establishing the old chessboard, you're designing a whole new game," says [Doug] Erwin.