For years, paleontologists have argued about why hard skeletons, those containing hydroxyapatite, arose in the first place. For those who believed that skeletons began with jaws, backbones, or body armor, conodonts provide an “inconvenient tooth,” if you will. The first hard hydroxyapatite-containing body parts were teeth. Hard bones arose not to protect animals, but to eat them. With this, the fish-eat-fish world really began in earnest. First, big fish ate little fish; then, an arms race began. Little fish developed armor, big fish obtained bigger jaws to crack the armor, and so on. Teeth
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