In DepthEvolution

How teeth got tough: enamel's evolutionary journey

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Science  25 Sep 2015:
Vol. 349, Issue 6255, pp. 1431
DOI: 10.1126/science.349.6255.1431

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The hardest bit of your body is the enamel coating your teeth. But new analyses of fish fossils, as well as genetic analyses of a living fish species, suggest that this specialized material once served a very different function: to toughen some bones and scales of ancient fish. Well-preserved fossils of an ancient fish called Psarolepis romeri reveal that this 20-centimeter-long mini-predator, which prowled the seas between 410 million and 415 million years ago, had enamel in its scales and its skull--but not its teeth. The findings bolster earlier suggestions that ancient fish had armored scales, and they point to a new scenario for exactly how enamel ended up on teeth. Previously, researchers had suggested that over millions of years of evolution, hardened structures such as external scales gradually migrated into the mouth and changed shape to become teeth. But the patchy distribution of enamel in Psarolepis may suggest a different scenario, in which the pattern of enamel production, rather than the shape and location of already-enameled structures, shifted over time.