214 The Nature of Dinosaurs
times as much per pound of body weight as do reptile predators. By studying the fossil record, Bakker found that the ratio of predators to herbivores in dinosaur ecosystems matched
what would be expected of a warm-blooded ecosystem.
Dinosaurs had to have been warm-blooded. Their bones, relative numbers, and locations proved it.
He studied the legs of zoo animals, comparing leg structure to how they moved. Did a
chicken’s leg bend differently than a zebra’s? How did those differences relate to the different activity of each animal? How did form dictate function for each animal, and how did
function dictate form? What did the shape of a dinosaur’s joints and the size of its bones say
about how it must have moved and functioned? He tried to account for this motion and the
implied probable muscle masses to control and move each bone in his drawings.
He compared leg bone size, shape, and density for hundreds of modern animals with
those of dinosaurs. He found that dinosaur leg bones closely matched the bone structure of
running mammals—not those who sprint for 10 seconds when alarmed, but those who regularly run for 20 minutes.
Dinosaurs were runners. Their structure proved it. That also meant that they were agile. No sluggish, clumsy oaf would be a natural runner.
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