Utah in the Age of Dinosaurs

Dinosaurs lived only during the Mesozoic Era, which is often called the “Age of Dinosaurs.” Utah has perhaps the best Mesozoic rock record in the world.

The Mesozoic Era (252 to 66 million years ago) is divided into three time periods:

Cretaceous Period

66 to 145 million years ago

Jurassic Period

145 to 201 million years ago

Triassic Period

201 to 252 million years ago

Survey Notes 47-3 Megablock

A reconstruction of the Stikes dinosaur death trap. Adult and juvenile Utahraptor dinosaurs attack an iguanodont dinosaur trapped in quicksand. By Julius Costonyi.

Cretaceous Period

A geologist examines a sequence of Early Cretaceous-aged paleosols (ancient soils) in the Yellow Cat Member of the Cedar Mountain Formation. Many dinosaur fossils are found in these rocks, and the study of paleosols can provide valuable information about the environments in which these dinosaurs lived. Poison Strip area, east of Arches National Park, Grand County, Utah. Photographer: Don DeBlieux

Early Cretaceous dinosaur fossils are found in Utah in the Cedar Mountain Formation, which dates to about 125 to 98 million years ago. This rock unit overlies the Morrison Formation, but represents more time and contains several entirely different faunas or groups of dinosaurs. These rocks represent a time when North America was connected to Europe before flowering plants, a period when rising sea levels led to the isolation of North America from the rest of the world, and finally a time when the first land connections with Asia were established and flowering plants had come into their own. The Cedar Mountain Formation is the basis of considerable research by UGS paleontologists.

Late Cretaceous dinosaurs such as Tyrannosaurus and Torosaurus lived about 65 million years ago at the end of the age of dinosaurs. Cretaceous dinosaur sites are found in great abundance in Montana and Alberta, Canada, and are also found in the North Horn Formation of central Utah. Farther south in the Grand Staircase – Escalante National Monument the most continuous record of Cretaceous dinosaurs in the world has now been recognized and research is just beginning to bring these many undescribed Utah dinosaurs to light.

Photo caption: A geologist examines a sequence of Early Cretaceous-aged paleosols (ancient soils) in the Yellow Cat Member of the Cedar Mountain Formation. Many dinosaur fossils are found in these rocks, and the study of paleosols can provide valuable information about the environments in which these dinosaurs lived. Poison Strip area, east of Arches National Park, Grand County, Utah. Photographer: Don DeBlieux

Early Cretaceous Dinosaurs Found in Utah


Acrocanthosaurus

Acrocanthosaurus was a giant carnivore of the Early Cretaceous that was nearly as large asTyrannosaurus which lived at the end of the Cretaceous Period. With enormous teeth adapted for cutting flesh, this predator ruled the world in which it lived. It is known from the middle part of the Cedar Mountain Formation in the area around the San Rafael Swell.

Animantarx

Animantarx is a small armored nodosaurid ankylosaur only about 10 feet long. It was first discovered by University of Utah radiological technician Ramal Jones near where his wife Carol discovered the first specimen of Eolambia. He performed a detailed survey of the low-level radiation levels across the area as he knew the bones there were slightly radioactive. Finding a spot that was slightly radioactive, he said, “Dig here,” and, lo and behold, the first dinosaur ever discovered solely by technology was found. The dinosaur was named Animantarx ramaljonesi in his honor and joined Eolambia caroljonesa among Utah’s newest dinosaurs in 1999.

Deinonychus

Deinonychus is the best known of the Dromaeosaurids, “raptors.” It is known from skeletal remains from Montana and Oklahoma. In Utah, it is only known from teeth collected in the middle part of the Cedar Mountain Formation in the area near the Colorado River near Dewey Bridge.

Eolambia

Eolambia is the oldest duckbilled dinosaur in the world. It is a link to Iguanodon as it still has a spike on its thumb. Its direct ancestors are from Asia and its presence in the uppermost part of the Cedar Mountain Formation helps date the origins of Alaska and the first migration of Asian dinosaurs into North America about 100 million years ago. This bipedal plant-eater reached about 30 feet long and is the best known dinosaur of this time interval. It is known from the San Rafael Swell area, where it occurs with early dome-headed pachycephalosaurs, horned dinosaurs, and tyrannosaurs based on fossil teeth. Many new dinosaurs await discovery here.

Gastonia

Gastonia is an armored dinosaur known as an ankylosaur. It had a low slung tank-like body covered by armor with rows of spines sticking up above and to the sides off its shoulders. It also had triangular blades running down each side of its tail. Probably the best protected of all the armored dinosaurs, it was probably nearly immune to attacks by Utahraptor. It is common in the basal Cedar Mountain Formation around Arches National Park. There are at least four other kinds of ankylosaur known from the Cedar Mountain Formation, making the Early Cretaceous the Age of Ankylosaurs.

Iguanodon

Iguanodon, the ancestor of the duckbilled dinosaurs, has been found in Utah, Europe, and Asia. Named in 1825, it was only the second identified dinosaur. This bipedal plant-eater had a peculiar spike on its hand, a modification of the thumb, that from earlier skeletons was thought to be a horn from its head. It weighed a ton or more and measured up to 25 feet in length. It is reported from the basal Cedar Mountain Formation near Arches National Park.

Nedcolbertia

Nedcolbertia is a small, lightly built, predatory dinosaur. It was first described from the basal Cedar Mountain Formation near Arches National Park. Like many new Cedar Mountain discoveries it is only known in Utah; however, scientists in England now think they have discovered it there as well. It might be an ancestor to the ostrich-mimic dinosaurs.

Pleurocoelus

Pleurocoelus is a poorly known sauropod dinosaur that is probably related to Brachiosaurus. A partial skeleton was excavated from east-central Utah by the University of Utah and other fossils referred to this animal have been found throughout the middle part of the Cedar Mountain Formation. Many of these new discoveries may turn out to be new unnamed relatives of Pleurocoelus. In fact, although none have been named yet, lots of new sauropod dinosaurs have been discovered in the Cedar Mountain Formation, telling scientists that not so many sauropods went extinct at the end of the Jurassic Period.

Sauropelta

Sauropelta was one of the largest of the armored dinosaurs, ranging up to 30–35 feet long. It was a nodosaurid ankylosaur. Its large neck and shoulder spines were probably used for defense. It has been found in the middle Cedar Mountain Formation near Moab, Utah. Recently, an even larger related species was found south of Price, Utah, that has not been named yet.

Tenontosaurus

Tenontosaurus was the most common large bipedal to quadrupedal plant-eater from the later part of the Early Cretaceous of North America. Unlike other large ornithopods, this 12 ton beast had four toes on its hind feet, indicating that it is more closely related to primitive types like Dryosaurus. It is thought that following the extinction of Iguanodon in North America, a primitive ornithopod evolved to fill that role in the ecosystem. Tenontosaurus was later replaced by more advanced ornithopods like Eolambia that migrated into North America from Asia. It is known from the middle and upper part of the Cedar Mountain Formation in the area around the San Rafael Swell.

Utahraptor

Utahraptor, one of Utah’s more famous new dinosaurs and named the state dinosaur in 2018, was a sickle-clawed predator that may have hunted in packs. Weighing perhaps half a ton, this agile meat-eater was the real-life version of the ferocious oversized Velociraptor portrayed in the movie Jurassic ParkUtahraptor bones have been found in the basal Cedar Mountain Formation around Arches National Park. A mounted skeleton is on display at the College of Eastern Utah Prehistoric Museum in Price, Utah.

Late Cretaceous Dinosaurs Found in Utah

Alamosaurus

Alamosaurus, a large quadrupedal herbivore, was perhaps the only sauropod dinosaur in North America at the time of the great dinosaur extinction 65 million years ago. Named for Ojo Alamo (Cottonwood Spring) of New Mexico (not the Alamo in San Antonio, Texas), Alamosaurus has also been found on the Wasatch Plateau of central Utah, where its bones are associated with Tyrannosaurus and Torosaurus.

Torosaurus

Torosaurus was a three-horned ceratopsian dinosaur that was widespread in North America at the end of the Cretaceous Period. As large as an elephant, its enormous frill was modified from the bones in the rear part of the skull, giving it a skull over 10 feet long (the largest of any land-living animal). Its three horns served to protect the front of the body, making even Tyrannosaurus think twice about attacking a healthy adult.

Tyrannosaurus

Tyrannosaurus, the most famous of the carnivorous dinosaurs, weighed up to 7 tons. Its serrated, banana-sized teeth were used to crush the flesh and bone of its prey. With a massive head and jaws that measured more than 5 feet in length, and a body length of up to 50 feet, adult tyrannosaurs were the largest of the predatory dinosaurs. They were also the last, living only at the very end of the Cretaceous Period, 65 million years ago.

Parasaurolophus

Parasaurolophus was a large bipedal to quadrupedal herbivore best known for its large trombone-shaped crest. This hollow crest is thought to have been used as a resonating chamber for making low-frequency sounds for communicating with others of its kind. The crest may also have been used for display or for giving it an improved sense of smell.

Struthiomimus

Struthiomimus was a lightly built, toothless, carnivorous dinosaur. Its name means ostrich mimic as it was built very much like an ostrich and was also built for high-speed running. The identification of Struthiomimus in the Kaiparowits Formation of the Grand StaircaseEscalante National Monument was originally used to correlate these rocks with the North Horn Formation, but continued research in the area utilizing microvertebrate fossils and pollen has shown that these rocks are as much as 10 million years older.

Troodon

Troodon is a small meat-eating dinosaur so far recognized in the Kaiparowits Formation only by its distinctive teeth. Most of the dinosaurs known from the Grand Staircase–Escalante National Monument are known only from their teeth found by wet screen washing of fossiliferous rock. The study of dinosaurs in the monument is still in its early stages and many new dinosaurs await discovery. Troodon had a small killing claw on its hind foot, which might have been independently developed. This is the most intelligent dinosaur yet discovered based on the size of its brain.