![]() ![]() The giants of the earth today, blue whales, eat low on the food chain-plankton and shrimplike krill. It's a much more efficient use of energy to eat plants than it is to eat the animals that eat plants. Colinvaux drew on research that showed, in keeping with the second law of thermodynamics, that energy is lost with each step you take up the food chain. Paul Colinvaux, a well-known ecologist, asked and answered the same question in his 1978 book Why Big Fierce Animals Are Rare. rex must have been quite different than it is, say, for lions on the Serengeti Plain today. rexes to keep the species alive for the millions of years we know it endured. When you apply to dinosaurs estimates based on the number and size of modern mammal predators, as University of Indiana paleontologist Jim Farlow has done, the figures don't work. But you've also got to keep enough of your kind around to prevent quick extinction. You've got to keep your population down so you don't use up the available food. i suspect dinosaurs benefitted from the heat retained by their mass as well. Some scientists have suggested that tyrannosaurs could have become so big only by sea turtles are thought of as cold blooded, but their mass enables them to retain a consistently high body temperature. rex was huge, bigger than almost every preceding carnivore, and far bigger than the meat-eating mammals that replaced it. Primitive animals aren't specialized in their behavior and can tolerate a wider range of environments. To Phil's thinking, big animals and primitive animals are the best adapted to surviving hard times, at least in the short term. The weather was becoming more and more harsh at the end of the Cretaceous. ![]() rex and its contemporaries, the last dinosaurs, were giants. rex might have come along.Ĭanadian paleontologist Phil Currie has a different idea about why T. If dinosaurs had lasted longer, a killer even bigger than T. But when the dinosaurs vanished at the end of the Cretaceous period 65 million years ago, mammals started getting larger until there were giant mammals, bigger than elephants, in some groups in the Eocene (56 million to 34 million years ago). Mammals were no bigger than house cats all through dinosaur times. It might have taken a truly catastrophic event to wipe out the last dinosaurs, and the last dinosaurs, big and litde, seem to have disappeared at about the same time. Nearly everything that ever lived is dead. That doesn't mean big animals are more susceptible to extinction. Throughout the geologic record we see trends toward bigger animals and then the extinction of those big animals. Those that grow huge are more limited in the kind and amount of food and the extent of habitat they need, and so are more apt to go extinct than small animals. Those that do eat a lot of different things seem able to adapt to change more readily. And paleontologists have thought for a while that as the herbivores got bigger, the carnivores did, too.Įach group of animals seems to start out small and get bigger over time. So I'll rephrase the question: Why were the last dinosaurs so big? Well, maybe it's because the seaway in the middle of North America was drying out and there was more space for bigger animals to browse. The herding duckbills and horned dinosaurs were almost as hefty. rex wasn't the only giant dinosaur of its day. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |