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 from the Late Cambrian period to the Early Ordovician^3-6. Although initially interpreted as an agnathan fish^2,3 that predated other representatives⁷, 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 arthropods⁶, although this interpretation has also been refuted¹². 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.