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 had a heterodont dentition and mandibles relatively long and deeper.

[8] 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.

[7] It shared its environment with other primitive sharks, including to Xenacanthus of one meter in length and the similar species, Tristychius arcuatus.