Paleontology and geology
During the Cretaceous, western Maryland was above sea level. To the southeast, Cretaceous seas advanced and retreated across the coastal plain numerous times, providing habitats that ranged from terrestrial to deep continental shelf. Fossil leaves of magnolias and other plants have been found in sediments formed in terrestrial environments, and clams, oysters, snails, ammonites, and brachiopods are common fossils in the marine deposits. Dinosaurs also lived in the humid forests and swamps of Maryland’s low-lying areas. Fossil footprints, teeth, or bones of at least twelve species of dinosaurs have been discovered in Mesozoic sediments in eastern or central parts of the state. Astrodon was the first dinosaur found in Maryland, as well as the first sauropod described from North America, and has been designated as the State Dinosaur.