Mosasaur - Extinct, giant marine lizard of the Cretaceous period. Natural Selection - The process of an organism better adapted to an environment being more successful in reproduction than less adapted organisms. Paleontologist - A scientist who studies fossils and the history of life. Paleontology - The scientific study of fossils and the history of life. Panthalassa - The single, gigantic ocean that existed when Pangaea was assembled.
Petrification is the process by which organic material turns to stone.
Quadruped - An animal that walks on four limbs. Radioactive Clock - A means of measuring geologic time by the radioactive decay of unstable atoms. Reptile - A tetrapod with scaly skin that lays an amniotic egg. Saline - Consisting of or containing salt. Sauropods - large herbivorous dinosaurs.