Early Cretaceous Dinosaurs of Utah

Cedar Mountain Formation

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 is a small armored nodosaurid ankylosaur only about 10 ft 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 low 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 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 is the oldest duckbilled dinosaur in the world. It is a link to Iguanodon as it still has a spike on its thumb. It’s 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 is 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 is an armored dinosaur known as an ankylosaur. It had a low slung tank-like body cover by armor with rows of spines sticking up above and to the sides off its shoulders. It also has 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, 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.

Nedcolbertia is a small lightly built predatory dinosaur. It was first described from the basal Cedar Mountain Formation near Arches. 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 is a poorly known sauropod dinosaur that is probably related to Brachiosaurus. A partial skeleton has been 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 was one of the very largest of the armored dinosaurs ranging up to 30-35 ft 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, a even larger related species was found south of Price, Utah that has not been named yet.

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 1-2 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, one of Utah’s more famous new dinosaurs, was a sickle-clawed predator that may have hunted in packs. Weighing perhaps a half ton, this agile meat-eater personifies the ferocious oversized Velociraptor portrayed in the movie Jurassic Park. Several Utahraptors 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, UT.