Every now and again palaeontologists come across a fossil so weird it takes decades of detective work to finally understand its relationship to other organisms. The 275-million-year-old Helicoprion is one of these enigmas.

The first glimpses of this shark-like animal came from the Gascoyne Region in Western Australia; a partial tooth whorl with 14 preserved teeth.

The fossil was subsequently shipped to England and examined by esteemed palaeontologist Henry Woodward. In 1886 he officially named it Edestus davisii, after its discoverer, Mr Davis. Thirteen years later, Russian geologist Alexander Karpinsky described a new type of shark-like fish from the Ural Mountains in Russia and named it Helicoprion bessonowi. He noted that the Gascoyne fossil did not quite fit the description of Edestus but closely matched his Helicoprion so he renamed it Helicoprion davisii.

Over the next century several interpretations of the position and function of the whorl were put forward. Some thought it was a tail like that of a seahorse while others regarded it as a defensive weapon embedded in the skin of a weird looking shark. Most however viewed it as a tooth-whorl of some sort and therefore part of the mouth.

Additional discoveries over the last few decades from various parts of the world have confirmed its long-suspected identity as a tooth whorl and more specifically part of the lower jaw. Helicoprion is currently regarded as most closely related to ratfishes which themselves are cousins of sharks and rays. It would have been a scary looking animal, big as a white shark with a chainsaw-like dentition.