Late Cretaceous Vertebrate Fossils from the North Slope of Alaska and Implications for Dinosaur Ecology

Abstract

Skeletal remains of ceratopsian dinosaurs and a turtle, a dinosaur footprint, and tooth marks of a small carnivorous reptile on a freshwater clam show that the terrestrial vertebrate fauna of the Late Cretaceous of the North Slope of Alaska was moderately diverse in the Late Cretaceous. Paleobotanical evidence suggests that the climate was cool temperate and that mean annual temperature decreased through the Late Cretaceous. Winter temperatures were likely to have been below freezing for at least short intervals. Dinosaurs either could have overwintered on the North Slope or migrated. Modern high-latitude herbivores survive severe winters on poor-quality forage, despite the food requirements suggested by their metabolism. So long as freezing conditions were not long or severe enough for dinosaurs to sustain tissue damage, the reptiles are likely to have been able to survive the Late Cretaceous high-latitude winters, whether they were endotherms or ectotherms, because forage was richer and temperatures milder than the conditions faced by modern, highlatitude herbivores. Alternatively, the dinosaurs could have migrated with the sun line, possibly as far as the Cretaceous Arctic Circle, a distance of < 2100 km, easily traveled by moving at a rate of 1 kmlhr for 12 hrslday. Climatic data are not sufficiently precise to estimate the severity or length of freezing conditions and whether such conditions could have required migration.