The Paleoenvironments of Tugrikin-Shireh (Gobi Desert, Mongolia) and Aspects of the Taphonomy and Paleoecology of Protoceratops (Dinosauria: Ornithishichia)

Abstract

Tugrikin-shireh, south-central Gobi Desert, Mongolia, consists of about 1.5 km of westand northwest-facing exposures that produce a rich vertebrate fauna dominated by the ornithischian dinosaur Protoceratops. The sandstones of Tugrik are thick-bedded (2-9 m) and are distinguished by large-scale (10's to 100's of meters in cross-section), high-angle (28-34 ?) trough-cross stratification. The axes of the cross stratification dip east-northeast. These and other sedimentary features indicate eolian deposition, driven by westerly winds. At Tugrik, bedding planes as well as inferred slip faces, are dominated by a complex calciteand iron-oxide-cemented ichnofauna. At least three different trace fossil types are preserved. A biologically active ecosystem is reflected by the vertebrate body fossil and invertebrate trace fossil assemblages. Protoceratops specimens are commonly found articulated and semi-articulated, and oriented parallel to the maximum dip direction of the sediments in which they are entombed. Limbs are commonly contracted and necks are pulled back, in poses indicative of dessication. In some cases, death probably occurred by suffocation during sand storms, but in other cases, by less dramatic processes. Turgik may constitute the basinward continuation of a nearby braid plain-to-eolian suite of depositional environments. Penecontemporaneous deposits in northern China reveal similar suites of environments, suggesting a uniform depositional response in the region to Late Cretaceous climates.