File:Helicoprion tooth whorl.jpg

English: Helicoprion sp. - fossil shark tooth whorl from the Permian of Idaho, USA. (public display, FHPR L2003-2, Utah Field House of Natural History, Vernal, Utah, USA)

This remarkable fossil is a symphyseal tooth whorl from the lower jaw of an edestoid shark. It is in fossiliferous limestone of the Permian-aged Phosphoria Formation in Idaho. Sharks have a cartilaginous skeleton and mineralized, phosphatic teeth (as are all vertebrate teeth). Helicoprion is undoubtedly the strangest shark in geologic history (see reconstructions elsewhere in this photo album).

Some paleontologists have interpreted the tooth whorl of this shark as part of a coiled lower jaw that may have been whipped outward and back to capture fish prey. Although intriguing, this type of reconstruction is almost certainly incorrect. Instead of an external lower tooth whorl, the tooth whorl was likely internal. The latter interpretation is based on well-preserved specimens with soft-part preservation from Idaho Phosphoria Formation concretions.

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From museum signage: This stunning fossil is a shark tooth-whorl. A whorl is a spiral of teeth that Helicoprion sharks evolved 250 million years ago. This species of early shark may have been more than 10 feet long and used its unusual teeth to injure and disable prey.

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Classification: Animalia, Chordata, Vertebrata, Chondrichthyes, Elasmobranchii, Eugeneodontida, Edestoidea, Agassizodontidae/Helicoprionidae

Stratigraphy: Phosphoria Formation (a.k.a. Park City Formation), Roadian Stage to Wordian Stage, mid-Permian

Locality: unrecorded/undisclosed site in Idaho (likely southeastern Idaho), USA