Dougal Dixon's alternative evolutions demand to be better known than they are. The New Dinosaur's is the weakest of the three. It is less inspired than After Man and Man After Man.
The book suffers a bit from Dixon beating the drum of convergent evolution too loudly, so that we get a dinosaur giraffe, dinosaur panda, dinosaur whale and even dinosaur koala bear. That is fair enough but there could have been more completely novel dinosaur variants. Probably his least interesting book of fictional evolutionary history, but they are all well worth reading.