THE OCCURRENCE OF THE MARINE ELASMOBRANCH BRACHYRHIZODUS SP. FROM A SANTONIAN NONMARINE LOCALITY, BRYCE CANYON NATIONAL PARK, UTAH

Brachyrhizodus sp. has been recovered by screen washing of Utah Museum of Natural History Vertebrate Paleontology (UMNH VP) Locality 1156 in Bryce Canyon National Park, southwestern Utah. The large tooth has an unworn, smooth crown, and rectangular form readily distinguishing it from the crested, freshwater ray teeth that typify Upper Cretaceous terrestrial microvertebrate sites in southern Utah. The locality is in the John Henry Member of the Straight Cliffs Formation (Upper Cretaceous, Santonian) and the fauna from the locality is entirely nonmarine and includes terrestrial mammals (e.g. Dakotamys sp., ?Varalphadon sp.) and fresh water Cyprididae ostracodes (Mongolocypris sp., Timiriaseyia sp., Altanicypris sp. and a likely new genus of Talicyprideinae). The composition of the ostracode fauna bears close resemblance to the talicyprid dominated faunas described from the Upper Cretaceous (Campanian-Maastrichtian) of Mongolia. Brachyrhizodus has been previously reported from marine Campanian-Maastrichtian localities in Texas and New Jersey, and the Cretaceous of Georgia. This early occurrence of Brachyrhizodus, the only specimen of this taxon ever recovered from the Cretaceous Western Interior, in nonmarine rocks is puzzling. The coastal floodplains of the John Henry Member were not far from the ocean at this time; nonetheless, this occurrence suggests that Brachyrhizodus was able to travel some distance up stream into fresh waters.