A diverse assemblage of tanystropheid archosauromorphs from the continental interior of Late Triassic Pangea includes a new taxon (Akidostropheus oligos gen. et sp. nov.)

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Abstract
The upper Blue Mesa Member of the Chinle Formation at Petrified Forest National Park, Arizona, U.S.A., contains a remarkable diversity of Triassic vertebrate fossils. The locality PFV 456 includes hundreds of bones of the long-necked archosauromorph clade Tanystropheidae. Using cervical vertebrae morphotypes as a metric for diversity, there are three distinct taxa of tanystropheids present at the locality, including aff. Tanystropheus and a novel taxon, described here and named as a new genus and species, Akidostropheus oligos, recognizable by its autapomorphic spike emanating dorsally from the neural spine that may be a defensive structure. This new taxon is also present at locality PFV 396 and the nearby possibly contemporaneous MNA 207/UCMP A269 (the Placerias and Downs quarries) near St. Johns, Arizona. This unexpected diversity of tanystropheid archosauromorphs indicates that semi-tropical nonmarine ecosystems may have provided opportunities for speciation and niche partitioning in Triassic vertebrates and provides valuable three-dimensional anatomical data for a group that is often characterized by two-dimensional preservation.

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