I am a massive fan of speculative zoology. I adore the whole "what if the dinosaurs hadn't died out" ideas, and like many people of my generation I owned lots of books about dinosaurs many of which were written by
Dougal Dixon. Who, back in 1981 wrote "After Man: A Zoology of the Future". He also subsequently wrote "Man After Man", which is essentially full on Sci-Fi, though I have to say that Nemo Ramjet did the whole "the next 500 million years of human evolution" thing better in All Our Tomorrows" (seriously, read it, its freaking awesome, if not a little nightmarish in places). In 1988 "The New Dinosaurs", which I read before Jurassic Park came out. Sadly this is the one that doesn't stand up that well to the massive amount of stuff we've learnt about maniraptorans and the like since then.
Specworld is a very good modern version.
But its After Man, which was the first, and I think still the best. Not all of the future animals are particularly practical- I agree with
Tricia that tusks on a mole are just dumb. but the hypercarnivorous rats are a masterstroke.
But I mostly want to point out that Japan seems to have gone completely nuts for him. There was an hour-long program (sometime in the '80s by the looks of it) with some rather lovely stop-motion animals. I think it also talks a lot about other aspects of evolution, but I don't speak Japanese, so I have no idea exactly what they're talking about, but there's shots of the Galapagos and that kind of thing.
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And if that wasn't enough, someone made a cartoon sequence with all these animals in it. Which would be perfectly sane if that happy dancing bipedal baboon wasn't supposed to be the size of a Tyrannosaurus
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But what I most want is
this the "After Man" model kit. (It looks like there was more than one "After Man" cartoon based on that too. And yes, the Nightstalker, a flightless, blind, bipedal, killer bat, from Hawaii, really was supposed to be five feet tall. Call Roger Corman, I've got an idea for a film...