Pathologic tooth deformities in fossil and modern sharks related to jaw injuries

Dental abnormalities in a tiger shark Galeocerdo cuvier and in Carcharoides totuserratus are presented here again, along with some further ones in shark teeth. Comparisons are made with fossil and modern shark teeth abnormalities. A coalescent set of two Squalicorax pristodontus teeth is described. The gibbous shape of the crown is similar to that in S. kaupi, the preceding species of the same lineage. It therefore suggests that the differentiation of the most derived species S. pristodontus may have resulted from kaupi through size increase and development of jaws, becoming more spacious, with teeth getting broader mesio-distally. An abnormal Carcharocles megalodon tooth is described. We regard it as a left lateral tooth from the mandible, whose crown is much deformed. Its features suggest trauma resulting from a feeding accident, maybe through biting the very compact bones of its more likely common prey, Halianassa sirenians. The last case concerns an abnormal Negaprion tooth. The most remarkable differences apart from the normal teeth concern the crown, which is irregular in shape. It shows some torsion, which also occurs in the root. A well-marked notch occurs in the mesial side. The cusp is somewhat labially bent. Trauma on the tooth-forming tissues seems to be responsible for the abnormalities under study. As far as we could ascertain, no lemon-shark dental abnormalities have previously been described. Our results stress that tooth modifications resulting from injuries to the tooth-producing tissues occurred since long ago in similar ways as in extant sharks. Biting prey's hard skeletal parts seems as always the main cause for injuries.