BEIJING, Sept. 25 (Xinhuanet) -- The hardest part of human body is the enamel, the protective coating of teeth made almost entirely of calcium.
But a new study of fish fossils suggest that this specialized material once served a very different function: to toughen some bones and scales of ancient fish.
According to the study published online Wednesday by the journal Nature, scientists examined the fossils of ancient fishes and DNA of a range of creatures living today.
While enamel coats the teeth of almost all tetrapods (four-limbed creatures) and lobe-finned fish such as coelacanths and living fish have it on scale, ancient exceptions are found.
One ancient fish called Psaroepis, living in seas between 410 million and 415 million years ago, had enamel in its scales and its skull, but not its teeth.
And specimens of Andreolepis, which lived around the same time as Psarolepis, have been found with enamel on their scales but not on bones in the skull.
Study authors concluded that "Enamel originated on the scales, before colonizing the dermal bones and finally the teeth."
(Agencies)
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