Heterodontiformes

Heterodontiformes is an order of sharks in the superorder Galeomorphi. It includes the bullhead sharks (genus Heterodontus), and several extinct genera. The earliest known members of the group are from the Early Jurassic (Toarcian), around 175 million years ago. Several extinct genera are known from the Jurassic, with all except Paracestracion only known from isolated teeth. The teeth of heterodontiforms exhibit differentation, with the front teeth having well developed cusps to grasp prey, while the back teeth are flattened, and serve to crush hard shelled prey. They inhabit shallow littoral

Paracestracion is an extinct genus of heterodontiform sharks from Early Jurassic to Early Cretaceous-aged rocks of England, France, Germany and Luxembourg. The genus was first described in 1911 by Ernst Hermann Friedrich von Koken in Karl Alfred von Zittel.