The original post: /r/askscience by /u/Significant-Factor-9 on 2024-12-25 03:03:39.

Whenever you watch documentaries or read about the late Cretaceous it is always said that the dinosaurs were declining before the impact. Sometimes this is framed as the beginning of a minor extinction event, other times the implication is that the dinosaurs would have vanished with or without the asteroid. But it is never elaborated on. However looking on the surface it looks like the dinosaurs were just fine. Archosaurs still filled almost all megafauna niches on earth. Dinosaurs were still THE dominant land vertebrates and were even starting to encroach on aerial and aquatic niches. From what I’m seeing, the dinosaurs in the late Cretaceous were even more dominant, diverse and abundant than at other times of the Mesozoic. I don’t see why the dinosaurs couldn’t have kept this success up until today had the asteroid never hit. Does anyone know what is meant by this “decline”?