- Jan 2014
Diversity did fall but as far as we know, only in Laramidia. (It is possible that extinctions--involving the last local lambeosaurs, nodosaurs and T. latus--occurred by mid Hell Creek time c 67 Ma or so instead of the start.) Things may have been different in Europe and Asia however. The Udurchukan may predate the Hell Creek but not by very much, and it had numerous lambeosaurs (wheareas in Laramidia only a single genus was still present in the early-late Maastrichtian.) Europe also had lambeosaurs such as Blasisaurus. They might've persisted to the end.Dinosaur and Pterosaur speciation was falling by the K-Pg anyway, pterosaurs lungs were taking their last breaths even before being filled with ash. Ornithischian species in North America had fallen sharply, maybe not the total number of individuals, but, in very general terms, not much more than herds of Triceratops and Edmontosaurs, some others of course. So I think that if any did survive, they were, for unknown reasons, already on their way out, no matter if conditions were improving, and while perhaps able to carry on for a few thousand years, or maybe only a few generations, were the dinosaur living dead.
I don't think the dinosaurs were doomed to extinction just because diversity plunged before the end. This had happened before e.g. around the time of the Cenomanian-Turonian transgression. I note the last Laramidian ornithiscians, Triceratops, Ankylosaurus and Edmontosaurus, were quite sizeable, which to my mind argues against deterioration of the physical environment.
Btw as for pterosaurs, they were doing OK in the Javelina environment and elsewhere like Romania IIRC.
Or ammonoids.Off course huge numbers of other animals died out, the marine reptiles probably due to a lack of plankton causing a loss of sufficient fish for them.
Dinosaurs in fact endured quite a lot including transgressions, cold spells, Morokweng, Manson etc before Chicxulub finally proved too much.But it is interesting to play with the idea of just how much of the late Cretaceous fauna was dependent on a few species, but vast numbers of individuals, of hadrosaurs and ceratopsians. It seemed even without volcanoes and asteroids to have been a fragile world.