This book begins with the premise that humankind has self-destructed. 50 million years go by. What might the world look like? Assume that most of the large mammals have been wiped out, but some smaller ones have survived (rabbits, shrews, squirrels). How might these animals evolve to fill available niches?
The book then covers the planet by each region, giving illustrations of possible creatures that might exist there. It’s a wealth of material for anyone writing either a science fiction novel set on another planet (or very distant future earth) or a fantasy novel with fantastic creatures. The creatures are thought through as far as their ecological niches, what they evolved from, what their natural predators would be, etc.
Sadly, now that I’ve possibly gotten you excited about this book, I have to report that it is out of print, and very expensive on the secondary market. In fact, when I hopped onto Amazon to check it out, Amazon, which sold me this book some years ago, put a message on my screen saying they would like to buy it back from me. Sorry, Amazon, I’m keeping my prize. But if you’re an SFF writer and can scare up a copy of this somewhere, it’s a great resource.