A new study challenges the long-held belief that dinosaurs were already declining before the asteroid impact 66 million years ago. University College London researchers suggest that the apparent decline of these dinosaurs before the impact might be an illusion created by a patchy fossil record.

The dinosaurs were not in decline before the asteroid hit, a new study finds. Instead, poor fossilization conditions and unexposed late Cretaceous rock layers mean they're either not preserved or hard to find.