Text 11
HOW THE DINOSAURS DIED Part 2 cold-blooded, like a large dinosaur, you'd better live on a very predictable and warm planet. Otherwise, when the weather changes, your species may be out of luck! Warm-blooded animals do pay a price for their extra energy and versatility. Though they needn't spend all day keeping their temperature under control, they must eat a lot more to produce their bodies' internal energy. An enormous brontosaurus couldn't have eaten enough in a whole day of chewing up ferns to keep itself warm. That's why warm-blooded animals tend to be a lot smaller than the brontosaurus. Something as large as an elephant, for example, must spend up to 18 hours each day eating — that's how much energy it takes to keep that giant creature warm! Actually, scientists now believe that some dinosaurs did become warm-blooded. Not all at once, of course; it would have taken many millions of years and many tiny changes for this transformation to occur. It's possible that even the large dinosaurs were moving in this same direction. We can only guess, but we think the smaller dinosaurs may have turned into warm-blooded, feathered animals. Yes, that's right, birds! The fossil record and other evidence tells us this really may have happened. What better way to escape the frigid weather!
Warm-blooded animals, like ourselves, produce a lot of energy from the food we eat. That's why we can live as comfortably in snowy climates as we can in the tropics. Dinosaurs and other cold-blooded animals can't do this, however. Most of their body heat comes from outside, from the sun or warm waters. Modern reptiles, like alligators, lizards, and snakes, spent most of their energy keeping their body temperatures at the right level. The lesson is that if you want to be
|
