A fossil champsosaur population from the high Arctic: Implications for Late Cretaceous paleotemperatures

Abstract During the Late Cretaceous, Axel Heiberg Island of the high Canadian Arctic supported a sizable population of champsosaurs, a basal archosauromorph, amongst a community including turtles and a variety of freshwater fishes. Here we report that a large portion of the available champsosaur fossil assemblage is comprised of elements from subadults. This dominance of subadults is similar to that seen from low latitude sites and suggests that the champsosaur population was a well-established facet of the ecological community. Because of the sensitivity of juveniles to ice formation, the make-up of the Arctic champsosaur population further indicates that the Late Cretaceous (Coniacian–Turonian) saw an interval of extreme warmth and low seasonality. The Coniacian–Turonian date makes these choristoderes amongst the earliest in North America, apart from the Jurassic Cteniogenys and a single limb bone from the mid-Cretaceous.