The Cretaceous Period was the last period of the Mesozoic Era dating back 145 to 66 million years ago. This period ended with the mass extinction of the dinosaurs. A time when dinosaurs dominated the earth with a total of 37 species living in Canada, including the infamous Tyrannosaurus, the aptly named Albertosaurus, and Edmontosaurus. Canada not only featured dinosaurs but also marine reptiles, crocodiles, fish, birds, and small mammals. The climate was typically warmer and more humid due to volcanic activity and greenhouse gases in the atmosphere. It was so warm, lush plant life grew in the Arctic Circle. Canada was a lush tropical forest! With the earth’s sea levels about 200 meters higher than today, North America was divided by a giant inland sea known as the Western Interior Seaway that connected the Arctic Ocean and the Gulf of Mexico.