Sphenacanthus is an extinct genus of a chondrichtyan xenacanthiform that belongs to the family and lived from the Late Devonian, through Carboniferous until the Late Permian period in Scotland, Spain, Russia and Brazil. It lived 359 million years ago, and probably it was one of the first member of the elasmobranchians, the lineage that leads to the modern sharks. Sphenacanthus probably hunts small fishes and, unlike their modern-day relatives, its inhabited fresh water lagoons. Sphenacanthus had seven fins, two in the upper part and five in the underside, and it have a heterodont dentition and mandibles relatively long and deeper. Sphenacanthus serrulatus is still only known from incomplete neurocranial remains and associated dermal material. These suggest that it was a relatively large s