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Helicoprion (shark) mystery solved (free pdf)

From: Ben Creisler

OK--it's non-dino but how the weird spiral teeth worked in the shark
Helicoprion has been a major mystery in paleontology:

PDF is free!

Leif Tapanila, Jesse Pruitt, Alan Pradel, Cheryl D. Wilga, Jason B.
Ramsay, Robert Schlader, and Dominique A. Didier (2013)
Jaws for a spiral-tooth whorl: CT images reveal novel adaptation and
phylogeny in fossil Helicoprion.
Biology Letters  9(2) 20130057
doi: 10.1098/rsbl.2013.0057

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