There is a distinct and sudden lack of large dinosaur fossils dating to 60 million years ago. you have to understand how evolution works. They couldn't have simply evolved into everything else because there has to be species linking them, showing the gradual progression from T-rex to deer (or whatever animal/dino combo you wish). They didn't all one day just magically transform into horses and elephants.

P.S. X-men, while very entertaining, gives a terribly false view of the workings of evolution.