Utah in the Age of Dinosaurs
Dinosaurs lived during the Mesozoic Era (252 to 66 million years ago), often called the “Age of Dinosaurs.” The Mesozoic Era is divided into three time periods, the Triassic, Jurassic, and Cretaceous. The Utah Geological Survey recognizes the presence of over 27 sequential, non-overlapping dinosaur faunas spanning 165 million years from the Mesozoic Era. These faunas range from the very first North American dinosaur-bearing strata in the Upper Triassic Chinle Formation, through Utah’s real “Jurassic Park” in the Upper Jurassic Morrison Formation, to the uppermost Cretaceous North Horn Formation which has a lone example of Tyrannosaurus and a record of the extinction of the dinosaurs.
Use the arrows to scroll through each Mesozoic period’s rock units and paleoenvironments.
Select each Mesozoic period below to read about the rock units and paleoenvironments.
252 TO 201 MILLION YEARS AGO
The first of the three periods of the Mesozoic is the Triassic Period. Many animal groups, including dinosaurs, first evolved during this time period. However, this time was dominated by animals that were not dinosaurs. Instead, the most common and ecologically important animals were reptiles such as the crocodile-like Phytosaurs.
The Triassic rocks of southern and eastern Utah consist mainly of two formations: the Early to Middle Triassic-age (250–240 million years ago) Moenkopi Formation and the Late Triassic-age (225–210 million years ago) Chinle Formation. These rocks are found around St. George, Zion National Park, and Grand Staircase-Escalante National Monument. They are also found in and around many other Utah national parks and monuments including Glen Canyon National Recreation Area, Capitol Reef National Park, the San Rafael Swell, Bears Ears National Monument, Canyonlands National Park, Arches National Park, and Dinosaur National Monument.
The Moenkopi Formation does not preserve many body fossils (bones of the skeleton) but does have many tracksites that give us a glimpse of what animals may have been around during this time. To the west and north, an ocean lapped onto Utah with many marine fossils including some gigantic marine reptiles like the school bus-sized Shonisaurus popularis found at Berlin-Ichthyosaur State Park in Nevada. The Late Triassic Chinle Formation, on the other hand, is one of the most fossil-rich rock units in all of Utah. The Chinle is especially famous for its fossil logs found in places like Petrified Forest National Park in Arizona and the Wolverine Petrified Forest in the southern Circle Cliffs of Utah. Historically, the Chinle Formation in Utah did not receive as much scientific attention as regions in the southern part of the Colorado Plateau, but this has changed over the last twenty years. Several research groups including the Utah Geological Survey, Brigham Young University, University of Utah, St. George Dinosaur Discovery Site, Appalachian State University, Virginia Tech, Yale University, and others have greatly expanded our knowledge of Utah’s Triassic fossil record.
201 TO 145 MILLION YEARS AGO
During the Early and Middle Jurassic, Utah was mostly desert. Periodically, sea level would rise and invade this sand dune-covered landscape. The rock exposed in the great sandstone cliffs of Zion National Park and Arches National Park comprises fossil sand dunes. Dinosaur footprints are known from many Lower and Middle Jurassic sites in Utah, but only one dinosaur, Seitaad ruessi, has been described from these desert rocks. Marine reptiles have been found in Jurassic marine rocks near Dinosaur National Monument.
Utah’s most well-known dinosaur fossils are Late Jurassic in age. They are found mainly in a rock unit known as the Morrison Formation which dates to approximately 150 million years ago. Dinosaur fossils from the Morrison Formation are displayed in Utah at the Dinosaur National Monument quarry in northeastern Utah and at the Cleveland-Lloyd Dinosaur Quarry in east-central Utah. Allosaurus, Utah’s state fossil, was a carnivorous theropod found in abundance at the Cleveland-Lloyd Dinosaur Quarry.
145 TO 66 MILLION YEARS AGO
Early Cretaceous dinosaur fossils are found in Utah in the Cedar Mountain Formation, which dates to about 142 to 98 million years ago. This rock unit overlies the famous dinosaur-bearing Late Jurassic-age Morrison Formation, but represents vastly more time and contains several entirely different faunas or groups of dinosaurs. These rocks represent a time when North America was connected to Europe followed by a period when rising sea levels led to the isolation of North America from the rest of the world. Towards the end of the Early Cretaceous the first land connections with Asia were established and the first flowering plants originated. UGS paleontologists have been focusing their research on the Cedar Mountain Formation for over twenty years and have published numerous scientific papers detailing their findings.
Utah is also famous for its Late Cretaceous dinosaurs, especially those that have been found over the past two decades in Grand Staircase-Escalante National Monument of southern Utah. The region has the most continuous record of Late Cretaceous dinosaurs in the world and many important discoveries have been and are still being made there. Ages of the Upper Cretaceous strata are well established from radiometric dating and from marine layers of the fossiliferous Mancos Group, which is as much as a mile thick in eastern Utah.
Farther north, the North Horn Formation of central Utah contains dinosaurs such as Tyrannosaurus and Torosaurus that lived about 65 million years ago, at the end of the “Age of Dinosaurs.”
Explore Utah’s Dinosaurs
Scroll through the database of Utah’s dinosaurs to learn more about specific species, discoveries, and find additional resources. For specific age information, use the Geological Society of America’s geologic time scale. Click the images to view the gallery for each dinosaur. Filter by age using the drop-down or use the search bar to filter the database by any field. Example search terms include: ceratopsian, Late Cretaceous, Morrison Formation, Apatosaurus.