Fig. 7 in Morphology and histology of dorsal spines of the xenacanthid shark Orthacanthus platypternus from the Lower Permian of Texas, USA: Palaeobiological and palaeoenvironmental implications

Fig. 7. Cross-section of dorsal spine of Orthacanthus platypternus (Cope, 1884), Lower Permian, Craddock Bone Bed, Texas, USA; specimen HMNS-J7 non-denticulated region) showing color-banding in centrifugal trabecular dentine and growth lines in lamellar dentine. A. General view (posterior side of spine towards the top of the figure). B, C. Details of periphery showing pairs of growth lines (marked by arrows) in the centrifugal lamellar dentine. D. Detail of interglobular spaces within the centripetal lamellar dentine (arrows denote interglobular spaces).