Which fossil has been found in north america and western europe

As for the best places for paleontology, it really depends on the group of animals and time period you're interested in. The US we have a great Cretaceous record partially because the Rocky Mountains were rising and depositing new rock as the relatives of T. rex were tromping around. But our record around the world is getting better and China is really becoming the center of a lot of crazy dinosaur discovery. But there isn't a great record in China for the early evolution of mammals after the extinction of the dinosaurs.