Dinosaur Diversity Information (image) Ohio University Caption This is a diagram illustrating the diversification of duck-billed and horned dinosaurs during the Late Cretaceous as a result of high ocean level and mountain uplift. The geologic time scale is to the left of the diagram, with horizontal green divisions representing the Campanian (lower) and Maastrichtian (upper) time periods. Silhouettes of North America demonstrating areas covered by ocean water during each of the time periods are to the right along with triangles designating the relative size of both the Western Interior Seaway and the Laramide mountain range. Finally, the fork within the duck-billed (black) and horned (grey) dinosaur family trees show the coinciding time (yellow bar) of a major split within each group. Credit Lindsay Zanno Usage Restrictions Lindsay Zanno Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.