|MadSci Network: Evolution|
David: The short answer to your question is no. Back in the 1970's Dr. Ralph Bakker and others began to question the accepted idea that dinosaurs were cold-blooded. Modern reptiles are poikilotherms (meaning they cannot regulate their body temperature by altering their metabolism) and so it had been assumed that all ancient reptiles were poikilotherms as well. Poikilotherms CAN regulate their body temperature using behavior, which is why reptiles sun themselves on cool sunny days - they are warming up. However, dinosaurs were different from modern reptiles, and similar to modern mammals and birds, in ways that suggested they might have been homeotherms, or animals that use metabolism as well as behavior to regulate body temperature. First of all, dinosaur fossils are found in rocks that were near the poles when the dinosaurs were alive, but other reptiles that lived during the time of the dinosaurs are not preserved in these deposits. Among large animals, only homeotherms can live near the poles. Second, mammals and birds have a different kind of bone than modern reptiles; they have spongy areas in their bones where blood cells were made, but modern reptile bone is denser. Dinosaur bone has these spongy areas. Third, poikilotherms live at a slower pace than homeotherms; they don't use as much energy. Small mammals and small birds eat a lot--they have to just to keep their fast metabolism burning. Small reptiles don't eat a lot; they can go weeks without food. In an ecology with poikilothermic predators, the predators can be relatively common, because they don't eat much. Large homeothermic predators are rare, because they would eat everything in sight keeping their hot metabolisms going if there were too many of them. If you look at dinosaur fossil faunas, the large predators are as rare as you would expect if they were mammals or birds. By contrast, ancient large non-dinosaur reptile predators were as common as you would expect if they were poikilotherms like modern reptile predators. These are just three of the pieces of evidence that led scientists studying the ecology of dinosaurs to think that at least some groups of dinosaurs were warm-blooded. If you want more information about this, there is a good 4-part series of videos published by PBS called "Dinosaurs!" Each video is an hour long, and they are accurate and fun. Another good source of information is the National Museum of Natural History, which is part of the Smithsonian Institution: http://www.nmnh.si.edu/ departments/paleo.html/ David Kopaska-Merkel Geological Survey of Alabama P.O. Box 869999 Tuscaloosa AL 35486-6999 (205) 349-2852 fax (205) 349-2861 www.gsa.state.al.us
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