Abstract
A new genus and species of Ptychodontiform elasmobranch, Paraptychodus washitaensis n. gen. et n. sp. is described on the basis of 13 teeth from the Middle Albian Duck Creek Formation of the Washita Group in north central Texas, USA. This material is significant as it demonstrates an intermediate tooth form between the Lonchidiidae and Ptychodus with regard to occlusal ornamentation of the crown and tooth root morphology; the new taxon represents the earliest member of the family Ptychodontidae in North America. Analysis of dental characters and stratigraphic occurrences within the family suggests that P. washitaensis is a basal taxon and is the most recent ancestor of Ptychodus. Morphological trends of derived species of Ptychodus demonstrate continuous specialization in tooth crown morphologies. The diagnosis of P. washitaensis from the upper Albian of Texas adjusts the stratigraphic distribution of the genus Ptychodus to lower Cenomanian through lower Campanian.
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