Histology of the first fish

THE first description of Anatolepis Bockelie & Fortey was from early Ordovician sediments of Ny Friesland, Spitsbergen(1,2), but the genus is now known from many localities in North America and Greenland, ranging in age hom the Late Cambrian period to the Early Ordovician(3-6). Although initially interpreted as an agnathan fish(2,3) that predated other representatives(7), this has been widely disputed because the available histological data were unconvincing(6,8-10) and the scales fell outside the known morphological range of other accepted early vertebrates(9-11). Further doubt was cast upon the vertebrate affinity of Anatolepis when specimens from East Greenland were interpreted as the cuticular fragments of aglaspid arthropods(6), although this interpretation has also been refuted(12). Here we report on the morphology and histology of large collections of Anatolepis, and demonstrate the presence of dentine, a tissue unique to vertebrates, confirming that the taxon is both a vertebrate and the oldest known fish.