Why couldn't dinosaurs return after mass extinction?

Dinosaurs, in fact, never went "extinct". They simply came to be known as the birds of today- the avian dinosaurs. They had evolved to try to again take over the top predator niche with the terror birds, but that failed. They didn't return. read more

In case you're asking why dinosaurs didn't evolve back into their massive dino-sizes, it's because the environment didn't allow them to. After the mass extinction event (The massive meteor) wiped out most of the dinosaurs, not all the dinosaurs were killed by the impact, what did kill them almost entirely was a 'Nuclear Winter'. read more

As I understand it, pterosaurs died out before the end Cretaceous extinction event, they were out competed by early bird species, so they went extinct before the non avian dinosaurs, and thus could not have survived the Cretaceous extinction event. read more