Helicoprion: The Spiral Toothed Shark Explained

Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and phylogeny in fossil Helicoprion

Authors:

1. Leif Tapanila (a,b)
2. Jesse Pruitt (b,c)
3. Alan Pradel (d)
4. Cheryl D. Wilga (e)
5. Jason B. Ramsay (e)
6. Robert Schlader (c)
7. Dominique A. Didier (f)

Affiliations:

a. Department of Geosciences, Idaho State University, Pocatello, ID 83209, USA

b. Division of Earth Sciences, Idaho Museum of Natural History, Pocatello, ID 83209, USA

c. Idaho Virtualization Lab, Idaho Museum of Natural History, Pocatello, ID 83209, USA

d. Department of Vertebrate Paleontology, American Museum of Natural History, New York, NY 10024, USA

e. Department of Biological Sciences, University of Rhode Island, Kingston, RI 02881, USA

f. Department of Biology, Millersville University, Millersville, PA 17551, USA

Abstract:

New CT scans of the spiral-tooth fossil, Helicoprion, resolve a longstanding mystery concerning the form and phylogeny of this ancient cartilaginous fish. We present the first three-dimensional images that show the tooth whorl occupying the entire mandibular arch, and which is supported along the midline of the lower jaw. Several characters of the upper jaw show that it articulated with the neurocranium in two places and that the hyomandibula was not part of the jaw suspension. These features identify Helicoprion as a member of the stem holocephalan group Euchondrocephali. Our reconstruction illustrates novel adaptations, such as lateral cartilage to buttress the tooth whorl, which accommodated the unusual trait of continuous addition and retention of teeth in a predatory chondrichthyan. Helicoprion exemplifies the climax of stem holocephalan diversification and body size in Late Palaeozoic seas, a role dominated today by sharks and rays.

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