A paleohistological study of the prearticular teeth of Gyrodus circularis revels several dental peculiarities. Firstly, the teeth are inserted in deep bony alveolae. Secondly the walls of the pulp cavity are overlain by spheritic dentine with odontocytes embedded in the peripheral areas of the dentine core. The bony tissues are cellular and they are crossed by osteoblastic canalicles of Williamson. Bone alveolae and osteoblastic canalicles support a phylogenetic relationship between Pycnodontidae and Gyrodidae. Until paleohistological studies are performed on other gyrodid taxa, the spheritic dentine and the odontocytes would appear to constitute an autapomorphy of Gyrodus circularis.