This is the heart of the winter season - the time of year that the Northern Hemisphere of planet earth is in the grip of the coldest weather of the year. It is characterized by the shortest daylight and longest night of December 21 - the winter solstice, marking when the north pole is at its furthest tilt away from the sun. The earth had a similar tilt during the reign of the dinosaurs, and polar regions during the Cretaceous Period were subjected to alternating seasons of long days and short days resulting from the tilt combined with the journey around the sun, just as we experience today. However, the entire global climate of the Cretaceous was warmer than today, and the polar chill was less extreme. Dinosaurs inhabiting polar regions experienced a cool-down during winter months, but not nearly as cold as now.
Dinosaurs living above the Arctic Circle, or below the Antarctic Circle in the southern hemisphere, encountered an environment similar to the wet, lush yet cool rain forests of the "Pacific Northwest" region of modern North America. During the winter months, the main issue for polar dinosaurs was lack of sunlight: they would have been plunged into weeks of darkness when the sun dropped below the horizon. The sun wouldn't rise again until spring, similar to current-day northern Alaska and Siberia.
Dinosaurs did populate what is now the north slope of Alaska, and northern Alaska was in nearly the same latitude then as now: fossils found from above the Arctic Circle represent dinosaurs that actually lived above the Arctic Circle millions of years ago.
Pictured above is a midday scene from the north slope of Alaska, as it would have looked in December, 70 million years ago. Midday in December would be the heart of a dark winter's night. However, the Troodon seen here are well adapted for the long night, protected from chilled air by dense feathered plumage, and possessing especially large eyes that accommodated hunting at night. The teeth of Troodon were uniquely adapted for a mixed diet of meat and foliage - perfect for a lifestyle that required flexibility in a widely changing, seasonal environment.
