Geologic period: Devonian
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Stethacanthus's dramatic dorsal fin has been described as looking like an anvil or an ironing board, but in fact it was a highly specialized fin with special denticles along the top. Denticles are common on sharks' skin, but on Stethacanthus the denticles on top of the fin and on the shark's head were much larger and were clearly were specialized for some purpose...
Scientists suggest the fin was used for mating displays or as a means of making the 24-inch shark appear more fearsome to predators.
Did you know?
No fossils remains of a female Stethacanthus -- identifiable by the lack of claspers -- has been found.