Jaws may be nature’s version of a plowshares-to-swords program: They seem to have originally evolved to help fish breathe better.
When our vertebrate ancestors debuted about 520 million years ago, they didn’t take the world by storm. Inches long and jawless, they grabbed helpless worms with their lips, much as a toothless, armless man might eat a hot dog. Only when fish developed jaws 460 million years ago did Earth see serious predation. As soon as jaws evolved, there was a revolution, says Jon Mallatt, a zoologist at Washington State University. You got all these giant-jawed vertebrates that were at the top of the food chain and eating really big things--just mean, nasty carnivores all of a sudden. And one of these groups gave rise to the land vertebrates. So jaws were a big event. Without them we wouldn’t be here.
Paleontologists have believed that jaws evolved precisely because they ...
