My man-in-the-street thinking is that the extinction of the dinosaurs was a gradual thing after the asteroid impact. The survivors of the asteroid impact were left with radiation contaminated air, water, and vegetation. In addition to breathing the contaminated air, the herbivores perished from consuming the contaminated vegetation and water, the carnivores perished from consuming the contaminated water and their contaminated prey. The contamination was likely also spread through herd migrations, and ultimately the contamination rendered the dinosaurs sterile, whereby they just stopped reproducing. I'm a science fiction junkie. ?