There had to be a combination of factors at play for removing a species as successful as the dinosaurs... currently we know of three (asteroid, loss of plant eater diversity and the Deccan eruptions) who knows a fourth one may also be there. The analogy here is with the extinction of trolobites..it took nature 3 extinction events to completely wipe them out...but if birds have survived as the not so glamorous descendents of dinosaurs, the kt extinction event was not so successful after all...
