A new taxon of hybodontiform (Chondrichthyes, Elasmobranchii, Hybodontiformes) from the Late Triassic of Arizona, U.S.A., and its biostratigraphic importance within the Chinle Formation

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Elasmobranchs are excellent candidates for biostratigraphy, with distinctive dentitions and wide distributions over a long period of time. However, the high variation in tooth shapes present within some groups of chondrichthyans makes disentangling species variation from higher levels of taxonomy difficult. Here, we describe a sample of over 250 isolated tooth crowns of a new taxon of hybodontiform from a productive microvertebrate site from the Sonsela Member of the Chinle Formation, Arizona, U.S.A. This sample is assigned to a new taxon, Lonchidion minimorsus sp. nov., which possesses teeth that are mesiodistally twice as long as they are labiolingually wide, include no or small lateral cusps, have a low to moderately defined labial peg consistent with other members of Lonchidion, and lack ornamentation apart from the common occurrence of two or three lingually oriented cristae. Anatomical variation is present within the sample, mainly relating to the presence and/or size of the cusplets and labial peg, number of cristae, and the angle of the distal edge of the principal (= center) cusp. Three-dimensional geometric morphometrics show variation in one population and we hope that in the future further populations or species can be compared. Lonchidion minimorsus sp. nov. increases diversity of the genus Lonchidion and fills a stratigraphic gap in the recognized distribution of chondrichthyans from the Upper Triassic of the western U.S.A. Together, the stratigraphic sequence of Lonchidion appears useful for biostratigraphic correlation of localities within and across the Chinle Formation and Dockum Group in the southwestern U.S.A.

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