Helicoprion is an extinct genus of large shark-like cartilaginous fish that lived from the Early to the Middle Permian, about 290-270 million years ago. Helicoprion is a member of the Eugeneodontiformes, an extinct order of cartilaginous fish within the clade Holocephali, a group today represented only by chimaeras. It is also the type genus of the Helicoprionidae, a family of eugeneodonts characterised by distinctive tooth structures called tooth whorls. Helicoprion was first named in 1899 by Alexander Karpinsky on the basis of fossils discovered in Russia and Australia, the generic name meaning "spiral saw". Although numerous species were subsequently assigned to the genus, only H. bessonowi, H. davisii, and H. ergassaminon are recognized following a 2013 revision. The three species are distinguished by the shape and spacing of their tooth crowns. Helicoprion is mainly known from its fused, spiral-shaped tooth whorls, which account for almost all documented fossils of the taxon. The position and function of these structures was long debated, but studies based on specimens preserving jaw cartilage indicate that they were positioned in the lower jaw and were specialised for grasping and slicing soft-bodied prey such as cephalopods. The whorl may also have aided in shelling or extracting the bodies of nautiloids and ammonoids. Based on the skeletal anatomy of smaller eugeneodonts, Helicoprion is estimated to have reached lengths between 5 and 12 m (16 and 39 ft), with a general external appearance possibly comparable to that of tunas, swordfish, or mackerel sharks. Fossils of Helicoprion are known from marine deposits worldwide, indicating that it was pelagic and had a cosmopolitan distribution. The highest concentrations of these come from Idaho and Russia, which used to be covered by deep inland seas where Helicoprion may have congregated.
Research history
The first known specimen of Helicoprion consists of a partial tooth whorl preserving 15 teeth, 14 of which are visible. It was discovered in Western Australia in a tributary of the Gascoyne River by a gold prospector named Mr. Davis, his first name being unknown. Now housed in the Western Australian Museum under the catalogue WAMAG 9080, the fossil was not found in situ, thus its precise stratigraphic origin remains uncertain. In 1884, Irish meteorologist Robert Henry Scott forwarded to British paleontologist Henry Woodward a letter written by a reverend from Fremantle, accompanied by a photograph of the find. Because of its incomplete condition, Woodward identified the fossil as being very similar to those of the cartilaginous fish Edestus, a genus first described by American paleontologist Joseph Leidy in 1855. Wishing to examine the fossil directly, Woodward persuaded Scott to write to his sister, Lady Barker, to obtain the loan of the specimen from the same reverend. After an extended correspondence, Irish geologist Edward Hardman, then on assignment in the Kimberley region, was tasked with bringing the fossil back to England upon his return. In a 1886 publication, Woodward finally described the specimen as representing a new species of Edestus, which he named Edestus davisii in honor of its discoverer.
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