Pollen compilations in North America track spruce, oak, pine, maple, and other species in a cinematic series of diagrams showing these changes over the past 18,000 years.
An expansion of dry shortgrass prairie in the rain shadow of the Rocky Mountains may have put tallgrass grazers such as horses and camels at a disadvantage compared with bison.
One extreme example is the spread of the prickly sculpin across the Continental Divide in British Columbia.
Pollen is one of the most important tools of correlation in terrestrial settings, and it is often used to extend knowledge from well-dated sequences to less clear situations.
Fossil pollen is particularly useful because it is almost indestructible when trapped in lake and bog sediments.
Expansion of some environments, such as vast dry steppe grasslands, were favourable areas for bison, horses, antelopes, and their predators.
Some species with modern relatives, including the woolly mammoth and woolly rhinoceros, were clearly adapted to the cold tundra regions because of their heavy fur.