Research On Dinosaur Fauna And Contemporary Sedimentary Environment In Bayan Mandahu,Inner Mongolia

The Bayan Mandahu area is located in the west of the Inner Mongolia Plateau, and is administratively attributed to Urad Houqi, Bayannur. A large number of dinosaur fossils were collected from this area. Most of the fossils are from the Upper Cretaceous Wulansuhai Formation. The Wulansuhai Formation lithologically consists of brownish red sandstones and siltstones, as well as pink sandy limestones. The Bayan Mandahu area has been recognized as the hot spot of dinosaur research, owing to the discovery of numerous genera and species in the last two decades, such as the famous dromaeosaurid Linheraptor exquisitus. 16 genera and 12 species in the Dinosauria are found in this area. The dinosaur fauna in the Bayan Mandahu area is very similar to that in Bayn Dzak(Djadokhta Formation), ?mn?govi, Mongolia, with the shared Protoceratops, Pinacosaurus, Oviraptor, and Velociraptor. In addition, the Bayan Mandahu area has also yielded some endemic dinosaur taxa, including Linheraptor exquisitus, Linhenykus monodactylus, and Linhevenator tani.The red sandstones, calcareous mudstones, and limestones of the Upper Cretaceous Wulansuhai Formation constitute the dinosaur-bearing beds in the Bayan Mandahu area, showing a unique depositional environment. This paper focuses on the study of the sedimentary environment and lithofacies-paleogeographic characters of the Wulansuhai Formation. The sedimentary system in the formation is mainly referred to highly meandering stream deposits, aeolian dune deposits, and lake-delta deposits. Judged from paleoenvironmental characters of the Mongolian Plateau, the Bayan Mandahu area and neighboring ?mn?govi of Mongolia are probably ascribed to the same sedimentary basin in the Late Cretaceous. The basin is limited south and north by the Lang Mountains and the southeast region of the Altai Mountains, respectively, and has a geographic centre near the border between China and Mongolia.The Late Cretaceous dinosaur fossils in the Bayan Mandahu area are preserved in aeolian sandstones, as well as sandtones, limestones, and mudstones of the lake-delta depositional system, especially the first sediments. These specimens are rich in quantity and species, and are preserved almost in situ. Most of them are articulated, and could be ascribed to different growth stages. Interestingly, some dinosaur individuals were abruptly buried during the march in life. This taphonomic condition indicates that these animals were buried after the sudden environmental change. The dune movements of ancient sandstorms led to the formation of aeolian sandstones and mass deaths of the dinosaur fauna.