Date of Award
Master of Science (MS)
Joseph J.W. Sertich
David J. Varricchio
Western North America preserves a spectacular record of Late Cretaceous environments and biotas along the eastern Laramidian shore of the Western Interior Seaway. The Kaiparowits Formation of Grand Staircase-Escalante National Monument (GSENM), Utah preserves a diverse assemblage of archosaur eggshell, complementing the high skeletal biodiversity of the formation. Along with the Kaiparowits, several paracontemporaneous Laramidian formations collectively form the Western Interior Basin (WIB) system, including: the Dinosaur Park Formation of Alberta; the Two Medicine Formation of Montana; and the Fruitland Formation of New Mexico. These formations provide a unique, 2 Ma-long window on Campanian ecosystems across different paleoenvironments and depositional settings. Radial thin sectioning and scanning electron microscopy facilitated characterization and identification the Kaiparowits eggshell assemblage, revealing a high oodiversity consisting of nine archosaur ootaxa (Portituberoolithus warnerensis, Continuoolithus canadensis, Prismatoolithus levis, Prismatoolithus oosp., Spheroolithus albertensis, Spheroolithus choteauensis, cf. Macroelongatoolithus carlylei, unassigned krokolithidae) including Stillatuberoolithus storrsi oogen. et oosp. nov. Comparison with other eggshell assemblages preserved in the WIB reveals that Laramidian dinosaur eggshell assemblages are geographically and temporally consistent through the Santonian–Maastrichtian across different paleoenvironments and depositional settings.
Stillatuberoolithus storrsi is described from two partial eggs and 29 eggshell fragments and represents the first Laevisoolithid (small-bodied avian or non-avian theropod) eggshell from North America, extending the geographic range of this oofamily. The eggs are small (~17 mm diameter) and ornamented, with a two-layer microstructure and branching pores. The macroevolutionary transition of avians from non-avian theropod dinosaurs is characterized by a diverse assemblage of taxa displaying a mosaic of transitional morphological and behavioral features. The study of dinosaur eggs has revealed a similar mosaic pattern in reproductive behavior and eggshell features, a characteristic exemplified by Stillatuberoolithus storrsi. The suite of features preserved in this ootaxon is unique among theropod eggs and is also among the smallest Mesozoic eggs described, increasing the diversity of eggs that characterize the non-avian to avian theropod transition. This study adds to the growing wealth of paleobiological data preserved within GSENM and is a reminder that conserving public lands is deeply beneficial.
Oser, Sara Elizabeth, "Campanian ooassemblages Within the Western Interior Basin: Eggshell from the Upper Cretaceous Kaiparowits Formation of Grand Staircase-Escalante National Monument, UT" (2018). Museum and Field Studies Graduate Theses & Dissertations. 3.