Arctic mosasaurs (Squamata, Mosasauridae) from the Upper Cretaceous of Russia

Abstract From the northern part of Chukotka Region (Russian Far East) and Nether-Polar Urals, one of the oldest and one of the most northerly occurrences of mosasaur remains in the world are recorded. The appearance of mosasaurs at high latitudes could be explained by the expansion of their habitat and an unusual balance of insolation. Polar day conditions could have been useful for marine predators such as mosasaurs because they could have hunted for prey at any time. During the Cretaceous, almost two months of complete darkness can be reconstructed for the territory of present-day Chukotka, and more than one month of twilight. It is highly unlikely that these large-sized animals with a high metabolic rate were capable of surviving in complete darkness. Seen in this light, mosasaur remains at both high and low latitudes can serve as indirect evidence of seasonal migrations.