older vs modern reconstructions
Helicoprion (“Spiral Saw”) was a long-lived genus of shark-like cartilaginous fish that first arose in the oceans of the late Carboniferous 280 million years ago, survived the Permian-Triassic Extinction Event, and eventually went extinct during the early Triassic, 225 million years ago.
The only fossils known are the teeth, which were arranged in a fantastic “tooth-whorl” strongly reminiscent of a circular saw. It was not until the discovery of the skull of a relative, Ornithoprion, that it was realized that the tooth-whorl was in the lower jaw. The tooth-whorl represented all of the teeth produced by that individual in the lower jaw, in that as the individual grew, with the older, smaller teeth being moved into the center of the whorl by the appearance of larger, newer teeth. Comparisons with other eugenodontids suggest that Helicoprion may have grown up to 10-15 ft (3-4 m) long.
The exact location of the tooth-whorl in the lower jaw is an open debate. Older reconstructions placed the whorl in the front of the lower jaw; however this would create drag, making the shark a less efficient swimmer, and turbulence, alerting prey of its approach. A more current and scientifically accepted reconstruction places the whorl deeper into the throat. This arrangement would be best suited for soft bodied prey.
Coloured modern reconstruction illustration  by Mary Parrish
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