Well, there is the fact that it's impossible. Once a species is extinct*, it is, by definition, gone. It has no living members left alive to continue its genetic lineage. read more
Dinosaurs didn’t get wiped out completely. Scientifically speaking, birds are true dinosaurs. A more accurate term to indicate all the extinct dinosaurs is “non-avian dinosaur”. No major extinction events have managed to wipe out all life on Earth. So life didn’t return because it has never gone absent in the first place. read more
As a matter of fact, more than just the dinosaurs died. Most things did. What we've got now are just the evolved descendants of the few survivors of that time. And what allowed them to survive is their smaller size and lesser food requirements. read more
Several groups of mammals most people have never heard of (like the triconodontids, spalacotheroids, dryolestids and multituberculates) perished right at or not long after the extinction event. Some groups of mammals did survive, but others were either wiped out or so reduced in diversity that, like the dinosaurs, they fell into extinction. read more