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Why Bigger Isnt Better

Part of the Dinosaurs: Ancient Fossils, New Discoveries exhibition.

The bigger an animal gets, the harder its muscles must work just to support its weight. As a result, enormously large animals, including T. rex, have more trouble getting around than you might imagine.The news is even worse for some of the imaginary giants that populate our fairy tales and films. A giant could never have climbed down a beanstalk, for instance. And King Kong couldn't have climbed up the stairs--much less the Empire State Building!

Which Is (Relatively) Stronger?

An Indian elephant can drag a load of tree trunks weighing a ton--roughly one-quarter the animal's weight--but an African dung beetle may spend its life rolling balls of dung 50 times its own weight. Elephants--and large tyrannosaurs--are very strong in absolute terms, but in relative terms, the tiny dung beetle is stronger.

Muscles at Work

Muscles are made of long cells called fibers packed together like drinking straws in a box. Contraction of those fibers allows you to move about, and to do nearly everything else your body does. The bodies of most living vertebrates--animals with backbones--regardless of size, are between 40 and 50 percent muscle. Because they share a common ancestor, all vertebrates have similar muscle tissue; under a microscope, it's hard to tell the muscle of a crocodile from that of a mouse or an elephant. Such similarities lead scientists to think that the muscles of living animals hold clues to the muscles of dinosaurs. All muscles, regardless of size, get their strength from cross-sectional area--not length or overall volume. The muscles of large animals alive today are bigger than those of small animals, but in large animals the ratio of cross section to volume is relatively smaller. So bigger is stronger, but not as much stronger as sheer size would suggest.