NO SIGNIFICANT NONMARINE CARNIAN-NORIAN (LATE TRIASSIC) EXTINCTION EVENT: EVIDENCE FROM PETRIFIED FOREST NATIONAL PARK

Petrified Forest National Park (PEFO) is located in northeastern Arizona and it preserves an unparalled sequence of latest Carnian-early Norian (Upper Triassic) nonmarine strata. This rock sequence is principally comprised of three members of the Petrified Forest Formation (Chinle Group) which are in ascending order: (1) Blue Mesa Member (Adamanian: latest Carnian); (2) Sonsela Member (Revueltian: early-middle Norian); and (3) Painted Desert Member (Revueltian: early-middle Norian). The Blue Mesa and Painted Desert Members are highly fossiliferous and the Sonsela contains a more limited fauna. Paleontologists have studied these faunas for more than 80 years. This sequence contains no temporally significant break or major change in paleoenvironment, virtually continuous outcrop and faunas that are stratigraphically superposed within a limited geographic area. Thus, Upper Triassic strata at PEFO provide the best location in the world to study nonmarine events associated with tetrapods at the putative Carnian-Norian extinction event. Phytosaurs are the most common fossils throughout the sequence and they exhibit only a generic-level turnover at the Carnian-Norian boundary (Rutiodon is replaced by Pseudopalatus) and the number of species is unchanged. Aetosaurs are the next most common tetrapods. One genus becomes extinct (Stagonolepis), two undergo species level turnover (Desmatosuchus, Typothorax) and one is unaffected (Paratypothorax). One of the two late Carnian genera of metoposaurs becomes extinct (Buettneria), but the other (Apachesaurus) continues into the Norian. Dinosaurs at PEFO show generic turnover, but the number of taxa (a large and small theropod and one ornithischian) is unchanged. Among sphenosuchians, Hesperosuchus continues across the boundary, although the ?sphenosuchian Parrishia does becomes extinct. The taxonomically-challenged rauisuchians apparently display no extinctions. Other enigmatic taxa such as Vancleavea display no extinction across the boundary. Clearly data from PEFO are not consistent with a major extinction at the Carnian-Norian boundary among nonmarine tetrapods as has been hypothesized by a number of workers. We conclude that there was no major extinction at this time and that the apparent event is probably the result of the combined correlation effect.