DESCRIPTION OF A PREVIOUSLY UNKNOWN PHOSPHATIZED OPHIUROID GENUS AND SPECIES FROM THE LOWER TRIASSIC VIRGIN LIMESTONE MEMBER, MOENKOPI FORMATION, WESTERN UNITED STATES

A new genus and species of ophiuroid is described in a single fossiliferous packstone from the Lower Triassic Virgin Limestone Member of the Moenkopi Formation at the Lost Cabin Springs locality in southern Nevada. The ophiuroid fragments were most abundant within the > 250 µm fraction of sample LC-18-34 in the upper half of the Virgin Limestone. Energy-dispersive X-ray spectra (EDS) analysis indicates these fragments are composed of calcium phosphate, which is an uncommon style of preservation for ophiuroids. The phosphatization led to exceptional preservation of diagnostic microstructures and allowed for acid-extraction and 3D imaging of the fossils. The extracted skeletal elements are comprised of arm plates, vertebrae, radial shields, oral and genital plates. Bayesian phylogenetic analysis suggests that the new ophiuroid holds a position at the base of the Ophintegrida, one of the two extant Ophiuroidea superorders. The existence of near-coeval but more derived ophiuroids implies that the new taxon from the Virgin Limestone Member is a representative of an ancestral lineage surviving the end-Permian mass extinction. Further work on this and other Lower Triassic sections may yield additional fossils that are unusually preserved, contributing to a more complete picture of diversity during the recovery from the end-Permian mass extinction.