Sinemurian (Early Jurassic) Ammonite from Longzi, Southern Tibet, China and Its Biostratigraphic Significance

Recently, we discovered the typical Epophioceras sp. ammonite fauna in the Early Jurassic Ridang formation from Longzi, Tibet. As far as perspective of ammonite fauna is concerned, it can be compared with the Obtusum zone in European. The age is the Sinemurian of the Early Jurassic. In the lowest Jurassic times the ammonite fauna shows a differentiation into two biogeographical unites. The Tethyan realm is characterized by a variety of phylloceratids and lytoceratids. Typical elements of boreal realm, on the other hand, are the amaltheids. The Sinemurian Stage is well-known worldwide by the abundance of large-sized Arietitinae (Arietites, Coroniceras), and differentiation of biogeography is not pronounced until Pliensbachian. This study was supported by the Natural Science Foundation of China (No. 42293280) and Key laboratory of Palaeobiology and Petroleum stratigraphy foundation (20231102).