A new procolophonid from the Upper Triassic of Texas, with a description of tooth replacement and implantation

ABSTRACT

A new procolophonid, Libognathus sheddi, gen. et sp. nov. is reported from the Cooper Canyon Formation (Dockum Group; Upper Triassic: lower Norian) near Post, Texas. This is the first published description of an unequivocal procolophonid from the Upper Triassic of the southwestern United States. Some of the distinctive characters of Libognathus are the deep dentary, large anteriorly directed foramen on the lateral dentary surface, and the forward projecting coronoid. Libognathus provides a good example of tooth replacement and implantation, which are poorly known in procolophonids. The implantation is protothecodont, with the teeth set in sockets and firmly anchored by spongy bone of attachment. The stages of replacement are of the typical reptilian pattern. Libognathus is closely related to Hypsognathus from the Passaic Formation (Norian) of New Jersey, and correlative strata in Connecticut and Nova Scotia.