Climate is one of the factors that determines where different species of plants and animals can live, so paleontologists look for clues to a location's ancient climate in the types of fossil plants and animals they find there. For example, no modern crocodile species lives in a climate with long periods of freezing temperatures, so scientists hypothesize that ancient crocodiles had the same requirement for year round warmth. That leads them to consider the 110-million-year-old crocodile fossils from the Washington, D.C. to be part of a large body of circumstantial evidence that temperatures there were warm year round during the Early Cretaceous. Similarly, coal beds and fossil trees in the Arctic Slope of Alaska are among the many clues that Alaskan temperatures were very warm during the Late Cretaceous.
