Triassic Vertebrate Fossils in Arizona

The Triassic System in Arizona has yielded numerous world-class fossil specimens, including numerous type specimens. The oldest Triassic vertebrates from Arizona are footprints and (largely) temnospondyl bones from the Nonesian (Early Triassic: Spathian) Wupatki Member of the Moenkopi Formation. The Perovkan (early Anisian) faunas of the Holbrook Member of the Moenkopi Formation are exceptional in that they yield both bodyand trace fossils of Middle Triassic vertebrates and are almost certainly the best-known faunas of this age in the Americas. Vertebrate fossils of Late Triassic age in Arizona are overwhelmingly body fossils of temnospondyl amphibians and archosaurian reptiles, with trace fossils largely restricted to coprolites. Late Triassic faunas in Arizona include rich assemblages of Adamanian (Carnian) and Revueltian (early-mid Norian) age, with less noteworthy older (Otischalkian) assemblages. The Adamanian records of Arizona are spectacular, and include the “type” Adamanian assemblage in the Petrified Forest National Park, the world’s most diverse Late Triassic vertebrate fauna (that of the Placerias/Downs’ quarries), and other world-class records such as at Ward’s Terrace, the Blue Hills, and Stinking Springs Mountain. The late Adamanian (Lamyan) assemblage of the Sonsela Member promises to yield new and important information on the Adamanian-Revueltian transition. Revueltian records are nearly as impressive as those of the Adamanian, including extensive exposures in the vicinity of the Petrified Forest National Park and the best-known tetrapod assemblages from the Owl Rock Formation. The combination of an exceptionally rich record and outstanding exposures of sedimentary sections that allow the correlation of tetrapod faunas means that Arizona will remain a hotbed of research on Middle and Late Triassic vertebrates for the foreseeable future.