Paleontology and geology
Cretaceous rocks are well exposed in a belt along the southeastern border of Oklahoma. Shallow seas covered much of western and southeastern Oklahoma during this time interval, and limestones and shales formed from the sediments deposited on the seafloor. Fossils of oysters, giant ammonites, sand dollars and shark teeth can be found in these rocks. Early Cretaceous rocks formed from river and delta plain deposits also contain fossils, including those of small mammals discovered in southeastern Oklahoma. In contrast, similar deposits formed during the Late Cretaceous are known to contain bones from the giant sauropod Sauroposeidon, a dinosaur related to Brachiosaurus.