The osteology of Sarahsaurus aurifontanalis and geochemical observations of the dinosaurs from the type quarry of Sarahsaurus (Kayenta Formation), Coconino County, Arizona
Sarahsaurus aurifontanalis is the most recent sauropodomorph dinosaur to be discovered and named from the Early Jurassic of North America. The dinosaur is represented by a mostly complete and articulated holotype specimen that preserves a unique manual phalangeal count of 2-3-4-2-2 and accessory pubic foramen adjacent to the obturator foramen. The holotype of Sarahsaurus comprises a braincase and isolated cranial elements, but the skull previously referred to this taxon, MCZ 8893, can only be provisionally referred to Sarahsaurus until additional crania are found associated with postcranial material. Sarahsaurus comes from the middle third of the Kayenta Formation, which is considered to be Early Jurassic in age despite the absence of a radiometric date from that unit. A new technique used to obtain a U-Pb radiometric date from the type quarry of Sarahsaurus in the Kayenta Formation was influenced by secondary uranium enrichment in the open system of the fossil bone. That suggests that uranium within the Kayenta Formation may be the result of the movement of groundwater during the Laramide orogeny in the Late Cretaceous and Early Eocene, and lends support to the hypothesis that the uplift of the Colorado Plateau began relatively early in Late Cretaceous to the Eocene.