More has been published about the extinction of dinosaurs at the K-T boundary than any other group of organisms. Excluding a few controversial claims, it is agreed that all non-avian dinosaurs went extinct at the K-T boundary. The dinosaur fossil record has been interpreted to show both a decline in diversity and no decline in diversity during the last few million years of the Cretaceous, and it may be that the quality of the dinosaur fossil record is simply not good enough to permit researchers to distinguish between the choices.[54] Since there is no evidence that late Maastrichtian nonavian dinosaurs could burrow, swim or dive, they were unable to shelter themselves from the worst parts of any environmental stress that occurred at the K-T boundary. It is possible that small dinosaurs (other than birds) did survive, but they would have been deprived of food as both herbivorous dinosaurs would have found plant material scarce, and carnivores would have quickly found prey to be in short supply.[35] The growing consensus about the endothermy of dinosaurs (see dinosaur physiology) helps to understand their full extinction in contrast with their close relatives, the crocodilians. Cold-blooded crocodiles have very limited needs of food (they can survive several months without eating) while warm-blooded animals of similar size need much more food in order to sustain their faster metabolism. Thus, under the circumstancies of food chain disruption above mentioned, non-avian dinosaurs died [55] while some crocodiles survived. In this context, the survival of other endothermic animals, such as some birds and mammals, could be due, among other

Adapted from Dinosaurs: The Very Latest Information and Hands-On Activities From the Museum of the Rockies, by Liza Charlesworth and Bonnie Sachatello-Sawyer. A Scholastic Professional Book. The last dinosaurs died approximately 65 million years ago. Although the cause of their extinction is still a mystery, climatic change, diseases, changing plant communities, and geologic events could all have played a role. Lately, dinosaur extinction theories have been the subject of much debate and controversy. A recent explanation, supported by many scientists, suggests that dinosaurs died out soon after a huge meteorite crashed to Earth near the Gulf of Mexico. A giant meteorite, they reason, could have landed with an impact that kicked up enough dust and debris to block out sunlight for a long time — leading to a deadly chain of events. Without the sun, all the plants died; without the plants, all the plant-eaters died; and without the plant-eaters, all the meat-eaters died. Sounds reasonable. But there is one problem with this theory: Paleontologists have not yet been able to find dinosaur skeletons in rocks dating to the period of impact. Some evidence even seems to indicate that all the dinosaurs had died before the meteorite hit. What is the answer? As paleontologists search for clues to support their theories, they agree to disagree.