Why Did Nonavian Dinosaurs Become Extinct?

Data from diverse sources indicate that the Late Cretaceous (100 to 65 million years ago) climate was milder than today’s because of shallow seas covering the continents. At the end of the Cretaceous, the geological record shows that these seaways retreated from the continents back into the major ocean basins. No one knows why. Over a period of about 100,000 years, while the seas pulled back, climates around the world became dramatically more extreme: warmer days, cooler nights; hotter summers, colder winters. Perhaps nonavian dinosaurs (that is, all the dinosaurs except those belonging to the Ave, or bird, family) could not tolerate these extreme temperature changes and became extinct.

If true, though, why did cold-blooded animals, such as snakes, lizards, turtles, and crocodiles survive the freezing winters and torrid summers? Those animals are at the mercy of the climate to maintain a livable body temperature. It’s hard to understand why they would not be affected, whereas nonavian dinosaurs were left too crippled to cope, especially if some dinosaurs were warm-blooded. Critics also point out that the shallow seaways had retreated from and advanced on the continents numerous times during the Mesozoic, SO why did the nonavian dinosaurs survive the climatic changes associated with the earlier fluctuations but not with this one? Although initially appealing, the hypothesis of a simple climatic change related to sea levels is insufficient to explain all the data.

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