Palaeospinacids are known from both teeth and some Jurassic skeletons of Palaeospinax. Paraorthacodus has a worldwide fossil record dating back to the Lower Jurassic. Duffin & Ward (1993) attributed 15 species to this genus. North American species include: P. andersoni (CASE 1978) - Upper Cretaceous of Montana and P. clarkii (EASTMAN, 1901) - Late Palaeocene of Maryland.

The teeth from this clutching dentition are quite distinctive. A large central cusp is flanked by long, well defined, lateral cusplets — the cutting edge is rather complete. Enameloid ridges rise from the base of the crown on both labial and lingual faces. The root is broad and flat and protrudes lingually. Viewed labially, the root is rather high (an ontogenetic feature per Siverson (1997) and lingually, there is a central foramen and multiple tiny foramina. Viewed basally, there is a shallow median groove, which deepens labially and bears a large foramen. Laterally, there are additional but weaker transverse grooves opening on the lower labial face of the root.

Fig. 1 - Paraorthacodus clarkii lateral Lower Aquia Frm (Thanetian - Late Palaeocene) Maryland Grimsley Collection

Fig. 2 - Paraorthacodus clarkii lateral Lower Aquia Frm (Thanetian - Late Palaeocene) Maryland Grimsley Collection

References (also see Bibliography)

Duffin, C.J. & Ward, D.J., 1993. The Early Jurassic Palaeospinacid sharks of the Lyme Regis, southern England. Prof. Paper, 264: Elasmobranches et Stratigraphie, Belgian Geo. Survey. pp 53-102.
Siverson, M., 1997. Sharks from the mid-Cretaceous Gearle Siltstone, Southern Carnarvon Basin, Western Australia. Journal of Vertebrate Paleontology, 17(3):453-465.