Mesozoic Era (252 million years ago to 66 million years ago)
Dinosaurs appeared and disappeared during the Mesozoic Era, which lasted 186 million years and encompasses three periods: the Cretaceous, Jurassic, and Triassic. During the first part of the era, much of the surface in Kansas was being eroded. If dinosaurs lived in Kansas then, they weren't preserved. Later, seas covered much of the state. Because the land was under water, not many dinosaur fossils have been found, but bones from giant swimming and gliding reptiles have been recovered in western Kansas chalk. The few incomplete dinosaur fossils found are likely from animals that died, floated out to sea, and sank.
Cretaceous Period (145 million years ago to 66 million years ago)
Seas covered western and central Kansas during the late Cretaceous Period. Fossilized marine rocks found at the surface include the Greenhorn Limestone in central Kansas and the Niobrara Chalk to the west. The Greenhorn Limestone consists of chalky limestone beds alternating with thicker beds of grayish shale. Near the top of the Greenhorn is a limestone bed called Fencepost limestone. Because timber was scarce in this part of the state, limestone was used extensively by early settlers for buildings and fenceposts. The Niobrara Chalk beds, which were deposited in the deeper part of the Cretaceous ocean, are known for the awe-inspiring chalk remnants such as Castle Rock and Monument Rocks in Gove County. Fossils of marine reptiles such as plesiosaurs and mosasaurs have been found in the Niobrara. Dakota Formation sandstones, the remains of beach sands and sediments dumped by rivers draining into the Cretaceous seas, formed in central Kansas during this period. Igneous kimberlite pipes erupted toward the surface in eastern Kansas. Mass extinction occurred at the end of this period.
Jurassic Period (201 million years ago to 145 million years ago)
Shale and sandstone deposited during this period are found underground in western Kansas. Fossils from this period have not been found in Kansas.
Triassic Period (252 million years ago to 201 million years ago)
Triassic rocks have not been found in Kansas.