Marine Reptiles and Climates of the Jurassic and Cretaceous of Siberia

Resumo

All current data on the Jurassic and Cretaceous climates of Siberia based on isotope, paleontological, and lithological proxies are summarized. The late Pliensbachian cooling episode, early Toarcian warming, promptly replaced by long-term Middle Jurassic cooling at the end of the Toarcian, and a long-term warm interval in the Late Jurassic are clearly recorded. From the end of the Ryazanian, a gradual cooling episode began, which apparently continued throughout the Early Cretaceous except for a brief warming episode in the early Aptian. At the beginning of the Late Cretaceous, the climate became warmer; the peak of warming is recorded at the Cenomanian–Turonian boundary. Then, the middle–late Turonian was marked by a relatively cold episode. Later, in the Coniacian–Campanian, the climate warmed again, but at the end of the Campanian another cooling episode occurred. New findings of marine reptiles are described from the Toarcian, Kimmeridgian, Volgian, and Santonian-Campanian deposits of north of Eastern Siberia. All existing records of marine reptiles known from the Jurassic and Cretaceous of Siberia are revised, and all the findings (from 51 localities) are positioned in relation to paleolatitudes. It is established that the majority of occurrences of these fossils were within the polar paleolatitudes (70°–87°). We found no direct correlation between climate fluctuations and the distribution of these organisms. Taking into account the newest data showing that representatives of the majority of Jurassic and Cretaceous large groups of marines reptiles were able to maintain a more or less constant body temperature and were also able to undertake large-scale seasonal migrations, it is reasonable to be cautious in interpreting the presence of remains of these animals as indicators of a warm climate.