Some of the talk in the status feed reminded me of something.
Did any of you ever see this book by Dougal Dixon?
I think a lot of the ideas are pretty interesting. He constructs the biosphere of an Earth 50 million years in the future, long after our human mass-extinction event (yes, humans are absent. Extinct? Probably!) All the animals present are descended from surviving "generalists" that evolved to fill interesting niches, like rodents, antelopes and birds. All of the major continents bar Antarctica and South America are connected thanks to continental drift.
There are other speculative evolution universes, but I think After Man may be one of the most comprehensive. What are your favorites?