>>No, not the dinosaur-killer asteroid, although it was the perfect size and stroke at the right time.

If you look at bird intelligence, it's not at all clear that the dinosaurs were a cognitive dead end - they were just a branch of the family terminated by outside events. I say 'family' as there are proteins and cellular mechanisms conserved all the way from bacteria to current multicell animals such as ourselves.

But agreed that the incorporation of mitochondria was a spectacularly unlikely event.