ARCTIC FAUNAS

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Ectotherms , by prediction and by observation of extant examples, do not do well in extreme cold. Late Cretaceous faunas are now known from a number of locations in Alaska and other Arctic areas that were laid down when mean annual temperatures ranged between 2 and 8 degrees C. These deposits are notable for the almost complete absence of ectotherms such as the crocodyliform champsosaurs that are normally abundant in comparable North American faunas from warmer climates. However, these deposits contain large numbers of dinosaurs - hadrosaurs , ceratopians and theropods . If these were also ectotherms , the question becomes “how did they manage to survive so well when other ectotherms did not?” One postulated explanation is that they migrated during the coldest times, but the presence of neonates and many juveniles suggests that this did not happen, and indeed, migration is not generally considered a viable option for ectotherms due to metabolic restrictions on the long-term activity levels needed for migration. A more likely explanation for the presence of dinosaurs in this environment is that they were endotherms and thus able to cope better with the extremes of temperature, possibly by hibernating, or by some adaptation against freezing.

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