Teeth

Fossilized teeth are very resistant, often preserved when bones are not, and reflect the diet of the host organism, they are very valuable to archaeologists and paleontologists. Early fish such as the thelodonts had teeth for scales, suggesting that the origin of teeth was scales which were retained in the mouth. Fish as early as the Late Cambrian had dentine in their exoskeleton, which may have functioned in defense or for sensing their environment. Dentine can be as hard as the rest of teeth, and is composed of collagen fibres, reinforced with hydroxyapatite.

Decalcification removes the enamel from teeth and leaves only the organic interior intact, which comprises dentine and cementine. Enamel is quickly decalcified in acids, perhaps by dissolution by plant acids or via diagenetic solutions, or even the stomach of vertebrate predators. Enamel can also be lost by abrasion or spalling, and is lost before dentine or bone are destroyed by the fossilisation process. In such a case, the 'skeleton' of the teeth would consist of the dentine, with a hollow pulp cavity. Dentine, conversely, is destroyed by alkalis.