The Cretaceous Period of North America had several distinct phases. For approximately the first third to the first half of the period, conditions were generally similar to the Late Jurassic. Toward the middle of the Cretaceous, rising sea levels driven by the ongoing breakup of Pangaea submerged the shallow lowlands of the center of the continent, while the western margin was thrust up into a volcanic mountain range similar to the Andes as it overrode oceanic crust. North America was like two continents at this time—a narrow western landmass and a broader eastern landmass—with the Western Interior Seaway between them. Near the end of the Cretaceous, the seas retreated and the Rockies began to push up. North America was close to its current position and shape.
The dinosaurs of the Early Cretaceous, before the Seaway, are a mix of Jurassic-like holdovers and newer forms. The long, low Diplodocus-like sauropods and the plated stegosaurs went extinct, while ankylosaurs and ornithopods diversified. Sickle-clawed theropods became significant small carnivores. We don’t know much about the dinosaurs that lived in North America during the height of the Seaway, although there are many fossils of marine reptiles and pterosaurs in the marine rocks. Therefore, it is not clear how the Early Cretaceous dinosaurs transitioned to the dinosaurs known from near the end of the Cretaceous, which were much different.
The dinosaurs of the last 10 million years of the Cretaceous in North America are some of the best known in the world. They include tyrannosaurs such as Tyrannosaurus, diverse small theropods, ankylosaurs, bone-headed pachycephalosaurs, horned and frilled ceratopsians such as Triceratops, and “duckbilled” hadrosaurs. Sauropod dinosaurs seem to have gone extinct in North America around the time of the Seaway, to be reintroduced a few million years before the end of the Cretaceous. The new faunas may have something to do with the introduction and spread of flowering plants.
The end of the Cretaceous is famously marked by a major extinction that killed off all dinosaurs except birds, many groups of early birds, pterosaurs, marine reptiles, shelled squid-like ammonites, and many other groups. This extinction is attributed to an impact in the Yucatan.
Life and Death in the Cretaceous
Meet the Dinosaurs
Cretaceous Dinosaurs in Parks
Cretaceous (145 to 66 Ma) dinosaur fossils in the NPS are geographically more scattered than the Triassic and Jurassic examples. In recent years, Alaska’s parks have become significant for tracks, especially at Denali National Park and Preserve, where hadrosaur tracks are abundant. Bryce Canyon National Park (Utah), has a notable record of microfossils from early Late Cretaceous rocks that have otherwise yielded few dinosaur fossils. Several parks have records of dinosaurs that lived near the Western Interior Seaway, a continental sea that submerged much of North America from the Gulf Coast to the Canadian Arctic between approximately 100 and 70 Ma. Significant discoveries have been made in the rocks deposited just before the advance of the seaway at Arches National Park (Utah), and Dinosaur National Monument (Colorado and Utah), including skulls of the sauropod Abydosaurus at Dinosaur National Monument. The most extensive Cretaceous dinosaur fossil record comes from Big Bend National Park (Texas), where rocks from the Late Cretaceous hold fossils similar to those from southern Canada, Montana, and nearby areas. At Big Bend, there were tyrannosaurs, horned dinosaurs, hadrosaurs, the giant sauropod Alamosaurus, and others, many of which we’ve only learned about in the past few decades.
Find Your Park
National Natural Landmarks—Cretaceous Dinosaurs
Part 3: Cretaceous Period This video is the last in a series about the dinosaur story. Learn about the Cretaceous Period. By the end of this period, 66 million years ago, dinosaurs will be extinct. _ The Telling the Dinosaur Story series explores the fascinating time of dinosaurs as told through various National Natural Landmarks (NNLs) in and along the Rocky Mountain Front. Learn more about NNLs at nps.gov/nnlandmarks
- 7 minutes, 49 seconds
Bridger Fossil Area National Natural Landmark, Montana—[NNL Listing]
Cloverly Formation Site National Natural Landmark, Montana—[NNL Listing]
Dinosaur Valley State Park National Natural Landmark, Texas—[NNL Listing]
Garden of the Gods National Natural Landmark, Colorado—[NNL Listing]
Hell Creek Fossil Area National Natural Landmark, Montana—[NNL Listing]
Morrison-Golden Fossil Areas National Natural Landmark, Colorado—[NNL Listing]
Roxborough State Park National Natural Landmark, Colorado—[NNL Listing]
Valley of Fire National Natural Landmark, Nevada—[NNL Listing]
West Bijou Site National Natural Landmark, Colorado—[NNL Listing]
National Historic Landmarks
Edward Drinker Cope House National Historic Landmark, Pennsylvania
Hadrosaurus Foulkii Leidy Site National Historic Landmark, New Jersey
Othniel Charles Marsh House National Historic Landmark, Connecticut
Site Index and Credits
Age of Dinosaurs (2021)
Text by Justin Tweet (AGI). Contributors: Vincent Santucci (GRD), Adam Marsh (PEFO), ReBecca Hunt-Foster (DINO), Don Corrick (BIBE). Project Lead / Web Development, Jim Wood (GRD).
Tweet, J.S. and V.L. Santucci. 2018. An Inventory of Non-Avian Dinosaurs from National Park Service Areas. in Lucas, S.G. and Sullivan, R.M., (eds.), Fossil Record 6. New Mexico Museum of Natural History and Science Bulletin 79: 703-730. https://irma.nps.gov/DataStore/Reference/Profile/2257153
Santucci, V.L., A. Marsh, W. Parker, D. Chure, and D. Corrick, 2018. “Age of Reptiles”: Uncovering the Mesozoic Fossil Record in three Intermountain national parks. IMR Crossroads. Spring 2018, p. 4-11. https://irma.nps.gov/DataStore/Reference/Profile/2253529
Last updated: July 8, 2022