Orthacanthus buxieri fossil. Orthacanthus is an extinct genus of freshwater shark-like cartilaginous fish. Members of the genus had a long spine growing from the back of their skull and a very long dorsal fin, which ran all along its back, making the shark look more like an eel. There is also evidence of cannibalism in the diet of Orthacanthus and of filial cannibalism where adults preyed upon juveniles. This fossil dates to the Lower Permian period, 290 million years ago. Found in Buxieres-les-Mines, Allier, France.