This great blog post demonstrates exactly why mammals are cooler than dinosaurs (yes, I did just write that!). We (currently) live alongside some amazing examples of evolution such as the sea otter, the blue whale, the pygmy fairy armadillo and the hedgehog, but look further back and you find some truely awe-inspiring animals. This list is a great summary of some of the wierd and wonderful, though I might have added Nurolagus rex. This giant Minorcan lagomorph (relative of the rabbit) lived about 4 million years ago and weighed in at an estimated 12 kg. Ok. So not quite T-rex sized, but that is still a big rabbit-like animal!
Dinosaurs are great. They dominated the world for over 170 million years, and one line has survived to the present day as birds. But they’re hardly the be-all and end-all of prehistory. In the wake of the mass extinction that wiped out the non-avian dinosaurs, prehistoric mammals proliferated into a variety of astounding forms that were just as fantastic as those of the dinosaurs they succeeded. Instead of letting them be persistently overshadowed by dinosaurs, it’s time to give fossil mammals their due.
http://www.tor.com/blogs/2015/01/ten-fossil-mammals-as-awesome-as-any-dinosaur