Large numbers of dinosaur fossils have been discovered in deposits on Alaska's North Slope, a region that today experiences an extremely cold, arctic climate. One hundred million years ago, when those dinosaurs were alive, the environment of the North Slope was already inhospitable, especially during the winter when it experienced several months of total darkness. How did the dinosaurs survive the wintertime? Paleontologists have proposed that one of the most common North Slope dinosaurs, the elephant-sized edmontosaur (Edmontosaurus), survived the winter by migrating south to more hospitable regions. Several arguments support the migration hypothesis.

First, the edmontosaur's diet supports the migration hypothesis. Edmontosaurs fed exclusively on plants. Since there would have been no plants growing during the cold and dark North Slope winter, it appears that the edmontosaur must have left for at least part of the year and migrated to more temperate zones to find food.

Second, many edmontosaur skeletons have been unearthed from the same site. This suggests that edmontosaurs lived in herds. Many modern-day migratory animals, such as caribou and buffalo, live and migrate in herds as well. Moving in herds helps animals coordinate their migration. The finding that edmontosaurs lived in herds further supports the migration hypothesis.

Finally, edmontosaurs were physically capable of migrating long distances. To reach more hospitable regions, the edmontosaur had to migrate about 1,600 kilometers southward. To make such a journey, the edmontosaur needed to move at about five kilometers per hour for several weeks, which it certainly could do. These animals could run very fast, reaching speeds up to 45 kilometers per hour. It could have easily used its locomotive power to move to warmer climates during the harsh arctic winters.