Trinacromerum marine reptiles, artwork. Dating from the Late Cretaceous, these marine reptiles are shown swimming in the ocean that covered what is now Manitoba, Canada. One is in the foreground, and one in the background. Across bottom are a Champsosaurus marine reptile and an ammonoid cephalopod (the subclass that includes ammonites). None of these animals are dinosaurs. Manitoba is mostly devoid of dinosaur fossils, since dinosaurs were found on land and Manitoba was covered by the eastern Interior Seaway for the vast majority of the Mesozoic.