THERE IS NO FREE LUNCH: THE JAWS AND TOOTH WHORLS OF EDESTUS HEINRICHI FORM STREAMLINED GRASPING-CUTTING TOOLS

The precise location of the unique dentition within the jaws of Edestus has long been the focus of much conjecture in the literature. Artistic reconstructions typically show the upper tooth whorl curling forward and upward with the lower tooth whorl curling forward and downward out from the mouth. The tooth whorls were thought to be used by Edestus to ram into and slice prey. The head of Edestus heinrichi was reconstructed using X-rays and CT scans of the fossil FMNH PF2204 from the Logan Quarry shale. The upper and lower tooth whorls are clearly identified along with several cartilages of the chondrocranium and jaws: parts of the dorsal and ventral chondrocranium; nasals; rostral; left and right palatoquadrates (upper jaws); and left and right Meckel’s cartilages (lower jaws). Some cartilages could not be completely distinguished due to the compacted state of the fossil. The quadratomandibular joint has dual articulations perpendicular to each other, characteristic of Cladodont level sharks, but appears to have a more restricted motion than other forms. However the palatoquadrate-cranial articulation appears to have more freedom of motion and may have been the primary contributor to mouth opening. A reexamination of Edestus heinrichi reveals that the tooth whorls are rigidly contained between cartilages and functioned as effective grasping and piercing tools for disabling soft-bodied prey before engulfing them. In contrast to previous depictions of this enigmatic chondrichthyan, the tooth whorls curve inward towards the throat presenting an externally streamlined profile of the jaws. The occlusal surfaces of the upper and lower tooth whorls also appear to be parallel when the jaws were nearly closed.