Only small & unspecialized vertebrates survives the major mass extinctions.
By the late cretaceous birds dominated small organism niches in the dinosaur world. In that time frame:
1. Birds were the smallest theropoda. Small non-avian unspecialized theropods like saltopus or Procomsognathus [who could have possibly survived the cretaceous event, like they survived the Triassic] were long gone.
2. The only sauropods left were titanosaurs, which were all huge. Ornithiscians pushed them away from smaller niches, but being a titan dependent on a lot of food is a sure way to go extinct during climate change.
3. Ornithischian, the most dominant and diverse dinosaur family in the cretaceous, did not fill many small animal niches, their smallest member at the time was the size of a large chicken, which is too big/needs too much food to survive an major extinction event [especially when you consider dinosaur metabolism].
4. Pterosaurs are not dinosaurs but late cretaceous birds took many of their niches, only highly specialized pterosaurs remained. Some were HUGE.
It seems Ornithiscians doomed the sauropods, and birds doomed other theropods, Ornithiscians & pterosaurs.
Mammals survived because they filled the same niche small therapsids filled [burrowing scavengers], and reptiles along with amphibians, have filled the same niches [and still do] which have seen them through most mass extinctions. It seems birds doomed other dinosaurs. Thoughts?