Northernmost occurrences of plesiosaurs and turtles in the Upper Cretaceous of Eurasia

Abstract

Here we describe the first findings of reptile remains in the Upper Cretaceous marine strata of Siberia, which represent the northernmost occurrences of plesiosaurians, ?mosasaurids and turtles in the Cretaceous of Eurasia (66–72° N palaeolatitudes). The specimens come from the upper Cenomanian, Turonian and Coniacian of the Pyasina River basin, Santonian and Maastrichtian of the Tanama River and upper Santonian–lower Campanian of the Kheta River. They include remains of polycotylid and elasmosaurid plesiosaurians, as well as indeterminate small and osteologically immature plesiosaurians, indicating a somewhat typical Late Cretaceous plesiosaurian assemblage at the Arctic Polar Circle and implying that these shallow-water regions possibly used by plesiosaurians as a birth and nursery areas during the polar summer. In addition to plesiosaurian remains, a partial carinate ?mosasaurid tooth, and two turtle shell fragments, assigned to either non-marine Macrobaenidae or to marine Chelonioidea, and to non-marine Testudinoidea, are discovered, providing first direct evidence for the presence of these reptile groups in the Late Cretaceous of Northern Siberia. The findings of turtles are the northern most records of this group in the Cenomanian and Coniacian of Eurasia, which parallels previous records from the upper Cenomanian of Arctic Canada, and further supports warm climate conditions during the Cretaceous Greenhouse at high latitudes. Therefore, the Cenomanian–Turonian Boundary Event associated to the climate warming and to the beginning of the Cretaceous thermal maximum is well-recognized in Northern Siberia showing an expression of this “global” event over the Arctic region.