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T-Rex as Scavenger | Warm-blooded vs. Cold-blooded


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Warm-blooded vs. Cold-blooded
It was once believed that all dinosaurs were cold-blooded, like present-day reptiles. But much of their structure and behavior was more like that of warm-blooded animals than modern reptiles.

Science began thinking of dinosaurs as cold-blooded because of the early identification of dinosaurs with lizards (witness their name "terrible lizards), which are cold-blooded. It is now understood that dinosaurs and lizards are not closely related. In fact, the descendants of dinosaurs are most likely birds, which are warm-blooded.

Because of the identification of dinosaurs as big lizards, they were depicted in lizard terms: they were thought to have the sprawling lizard stance and to be slow moving, as lizards weighing tons would be. Evidence, however, shows that many dinosaurs -- and not just the small ones -- were extremely active, moving at great speed. This level of activity argues a metabolism too high for a cold-blooded animal.

Cold-blooded animals do not function well in cold-climates, but dinosaur fossils have been found near the polar regions, in what were cold climates even during the Mesozoic. What were "cold-blooded" animals doing in such cold climates? There is no mystery if one assumes that these dinosaurs were warm-blooded. On the other hand, it has been argued that large warm-blooded dinosaurs would have suffered from heat overloads in the tropical climates where they are known to have lived. But the largest creatures in tropical climates today are not cold-blooded reptiles, but warm-blooded mammals, like the elephant.

Many dinosaurs had dense bone structure that is easily explained -- if these dinosaurs had the high metabolic rate of warm-blooded animals. Theropods walked upright, on two feet, like warm-blooded birds, and their bone structure was more like that of modern birds than reptiles.

There are, in fact, many puzzling characteristics of dinosaurs that are not mysterious -- if you assume they were warm-blooded.

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