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 representatives 7 , this has been widely disputed because the available histological data were unconvincing 6,8–10 and the scales fell outside the known morpho-logical 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.