Separate Evolutionary Origins of Teeth from Evidence in Fossil Jawed Vertebrates

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Science  21 Feb 2003:
Vol. 299, Issue 5610, pp. 1235-1236
DOI: 10.1126/science.1079623

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Placoderms are extinct jawed fishes of the class Placodermi and are basal among jawed vertebrates. It is generally thought that teeth are absent in placoderms and that the phylogenetic origin of teeth occurred after the evolution of jaws. However, we now report the presence of tooth rows in more derived placoderms, the arthrodires. New teeth are composed of gnathostome-type dentine and develop at specific locations. Hence, it appears that these placoderm teeth develop and are regulated as in other jawed vertebrates. Because tooth development occurs only in derived forms of placoderms, we suggest that teeth evolved at least twice, through a mechanism of convergent evolution.

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