Temporal range: Early Carboniferous
Sphenacanthus is an extinct genus of a chondrichtyan xenacanthiform that belongs to the Sphenacanthidae family and lived during the Carboniferous periodo 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 was discovered in Carboniferous terrains of Scotland (Visén Oil Shale Groups), in the United Kingdom, in ancient fresh water systems, a habitat that also is known in the Paraná Basin in Brazil (Rio do Rasto Formation). Another findings, like those of the Puertollano Bason in Spain suggests that also it lived in zones of marine influence, in brackish waters. It shared its environment with other primitive sharks, including to Xenacanthus of one meter in length and the similar species, Tristychius arcuatus. It is possible that Sphenacanthus may have preyed on its smaller relatives.
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