Over the years, scientists have proposed a number of theories as to why dinosaurs suddenly became extinct about 65 million years ago. A. Many explanations for dinosaur extinction have been proposed, but most of them are either called into question by known facts or are merely unsupported hypotheses. B. Focusing on dinosaurs misses the point that the extinction, at about the same time, of the shelled squidlike creatures that dominated the Mesozoic seas was far more scientifically significant. C. Computerized climate models of global temperature fluctuations support the theory that a huge rock from space hit the Yucatan Peninsula in Mexico about 65 million years ago. D. Although mammals and dinosaurs appeared at about the same time in the Late Triassic, the K-T event, which marked the end of the dinosaurs, apparently had relatively little impact on mammals. E. Any satisfactory explanation of the mass extinction of dinosaurs must take into account the fact that the disappearance of the dinosaurs was part of a global mass extinction. F. A huge bolide striking Earth would have created conditions in which most plants would have died, thus explaining the mass extinction of organisms – including dinosaurs – further up the food chain.