Browsing by Subject "Kayenta Formation"
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Item Observations on the osteology of scutellosaurus lawleri Colbert, 1981 (Ornithischia: Thyreophora) on the basis on new specimens from the Lower Jurassic Kayenta Formation of Arizona(2016-05) Breeden, Benjamin Thomas, III; Rowe, Timothy, 1953-; Bell, Christopher J; Martindale, Rowan CScutellosaurus lawleri is a basal thyreophoran dinosaur from the Lower Jurassic Kayenta Formation, and it is the most abundantly known ornithischian dinosaur from the Lower Jurassic of North America. Despite its abundance in the fossil record, certain aspects of its anatomy have remained poorly understood due to the incomplete nature of the holotype, paratype, and referred specimens. I report here nearly 30 new specimens of Scutellosaurus lawleri collected along the Adeii Eechii Cliffs of northern Arizona between 1997 and 2000 by field parties from The University of Texas at Austin. Among this new material are two disarticulated associated skeletons, each preserving anatomy that is poorly known or not previously reported for the taxon, including the nasal, maxilla, lacrimal, postorbital, quadratojugal, squamosal, opisthotic, scapula, and ilium. These specimens have both been compressed taphonomically, making their removal from the surrounding matrix in their field jackets difficult without risk of damage to the fossil bone, so the specimens were CT scanned to aid with preparation. A phylogenetic analysis supports the position of Scutellosaurus lawleri as the basalmost member of Thyreophora. New autapomorphies identified include six premaxillary teeth, narrow and elongate frontals, a humerus substantially longer than the scapula, and neural spines of the proximal caudal vertebrae that are greater than 50% taller than the centra.Item The osteology of Sarahsaurus aurifontanalis and geochemical observations of the dinosaurs from the type quarry of Sarahsaurus (Kayenta Formation), Coconino County, Arizona(2013-05) Marsh, Adam Douglas; Rowe, Timothy, 1953-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.