Well, I'd still like to make sure we are both on the same wavelength when we discuss evolution. As I said before, there are a LOT of false assumptions here on what evolution is. If you think it is "survival of the fittest" then that is not evolution, for example.
But as far as God "guiding" evolution, then I don't think anyone can say. Yes, God caused the beginning of the universe, including the millions of galaxies, and millions upon millions of stars. He also, and it blows my mind thinking about this, designed the DN/RNA of all plants and animal species. Whether or not he gave a nudge to some mutations or not, I don't know. And no-one else does either.
As to the 'why' of some of the extinctions, I don't know that either. If dinosaurs were in fact wiped off the planet by the results of a huge asteroid, which sounds quite likely, no-one knows yet. And no-one knows why, either. Maybe God got tired of dinosaurs?
But if you believe in God, then you believe he is somewhere in all this. But he isn't going to pass down the manual that goes with the 'machine', so there are a lot of questions that simply cannot be answered.
Which is as it should be. After all, he is God.