Although dinosaurs are traditionally believed to be cold-blooded reptiles, such as crocodiles, lizards and sea turtles, evidences recently discovered have implied a picture on quite the opposite side. Scientists today are more readily to believe that there is a good chance for dinosaurs to be warm-blooded animals, like todays mammals and birds.<br> First, as demonstrated by a stony heart recently found in South Dakota in 1993 by a private fossil collector, dinosaurs could have evolved a heart adapted to warm-blood circulation. Although the fact that soft tissues usually decomposed before they could fossilize had left scientists searching in darkness for centuries, fossil organs could still be preserved under extreme circumstances such as rapid sediment on the seabed. Because today four-chambered heart is only found in warm-blooded animals, this fossil heart indicates the close relationship between dinosaurs and mammals.<br> Second, because cold-blooded animals such as reptiles couldnt maintain their body temperature constantly, they have to rely on the surrounding environment to adjust the body heat. Thus, if dinosaurs are cold-blooded, their huge body size would make it impossible to shift between basking and burrowing as often as todays lizards.<br> Third, for huge body animals to maximize their energy usage, they must maintain a constant body temperature. This is because metabolism is in fact a chemical process occurring in the body, which burns food in-take and releases energy supporting growth. For this chemical reaction to function optimally, keeping organs working at certain temperature is a necessity.
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