Stethacanthus

“	This must be the most preposterous shark ever!	”
– Sea Monsters, Dangerous Seas

Stethacanthus, colloquially known as the ironing board shark, was a small, primitive shark-like Holocephalian from the Devonian. It was unique for its flat dorsal fin which resembled an ironing board.

Creature attributes

Physical appearance and biology

Stethacanthus was a small, primitive shark-like Holocephalian. It looked similar to some of the shark species that would evolve later, like Hybodus, but unlike them, its dorsal fin was thick and flat at the tip and was shaped like an ironing board, hence the colloquial name.

Near its fluke and near its fins were draping lines of skin which ranged in size. The lines near its fins were long whilst the ones near its fluke were short.

Behaviour and traits

Stethacanthus was a solitary hunter that preyed upon small animals like the amphibian Hynerpeton and the heavily armoured Bothriolepis. However, during its time, there were larger and far more dangerous predators and Stethacanthus was often preyed upon itself. Large fish like Hyneria and Dunkleosteus had the shark on its menu.

The shark's most striking feature was its flat dorsal fin. As the fin was only featured in the males, it was probably used for courtship and possibly intimidation.

In Sea Monsters

Dangerous Seas

A male Stethacanthus is the first to be attracted by Nigel's bait and makes an attempt to strike at it. But as it circles the Shark cage with plans of another attack, it quickly swims away upon sensing a Dunkleosteus.

In Walking with Monsters

Water Dwellers

At the beginning of the third act of the episode, it is seen chasing a Hynerpeton. But it is soon devoured by a Hyneria and the shark's prey escapes onto dry land.

Gallery

Behind the scenes

Stethacanthus closeup — The official artwork of *Stethacanthus*.

Stethacanthus' model is actually that of a modified Hybodus.

In both Sea Monsters and Walking with Monsters, Stethacanthus is identified as an "ironing board shark" and a "primitive shark" respectively. The directors likely thought describing the species of shark in both series was unnecessary, so they left it out, though despite this, Stethacanthus' name is seen online and in The Complete Guide to Prehistoric Life.