Jurassic Dinosaurs of Utah

The Morrison Formation

Allosaurus, Utah’s State Fossil, was the dominant predator of North America during the Late Jurassic. It is known from numerous skeletons, ranging from 10 to 40 feet in length, from the Cleveland-Lloyd Dinosaur Quarry in east-central Utah. Mounted skeletons, cast from Cleveland-Lloyd Allosaurs, are displayed in over three dozen museums around the world. With sharper teeth and a more graceful build, Allosaurus rivals Tyrannosaurus rex as the supreme meat-eater of the Mesozoic.

Apatosaurus is the correct name for the dinosaur better known as BrontosaurusApatosaurus is probably the most commonly known, but not the most common of the four-footed, long-necked sauropod dinosaurs. This heavily built quadrupedal giant of the Jurassic Period weighed more than 30 tons, or as much as six average elephants. With lengths approaching 90 feet, the Apatosaurus was a giant in the Age of Dinosaurs.

Barosaurus was a slender, long-necked, long-tailed sauropod. Because of its graceful anatomy, some paleontologists have argued that this sauropod could stand on its hind legs and reach high into the trees for food, perhaps to heights of 50-60 feet. A skeleton from Dinosaur National Monument was mounted in the standing position was recently unveiled at the American Museum of Natural History in New York. However, recent studies of its skull and neck suggest that with its close relatives Apatosaurus and DiplodocusBarosaurus spent most of its time grazing low growing plants.

Brachiosaurus was the largest and heaviest dinosaur known from the Morrison Formation of Utah. This supergiant weighed as much as 80 tons, or the combined weights of 15 large elephants. Ultrasauros, a supergiant from the Morrison Formation of Colorado was a giant specimen of Brachiosaurus, and may have weighed as much as 100 tons. Brachiosaurus is the giraffe-necked sauropod, with tall front legs and a long neck designed to reach far above the ground. Bones of this Late Jurassic giant have also been found in eastern Africa.

Camarasaurus was the most common dinosaur of the Jurassic Period. Even with their relatively short neck and tail, this sauropod reached lengths of 50 feet and weighed as much as 25 tons. The spoon-like teeth chopped coarse vegetation (primarily conifers, cycads, and ferns), their principal food.

Camptosaurus was a medium-sized, bipedal herbivore of the Late Jurassic that weighed up to 1,000 pounds and reached lengths up to 23 feet. This ornithopod was ancestral to many of the highly successful plant-eating dinosaurs of the Cretaceous, such as the duckbills and Iguanodon.

Ceratosaurus was a large but slender predator of the Late Jurassic. With a strange horn on the top of the head between the eyes, this active meat-eater may have engaged in head-butting combat. Like Brachiosaurus, bones of Ceratosaurus have also been found in eastern Africa.

Dryosaurus is a common, small ornithopod first found at Dinosaur National Monument.

Diplodocus, the “double-beam” dinosaur named for unusual support structures beneath its tail, was a long and slender relative ofApatosaurus. Several nearly complete skeletons have been found at Dinosaur National Monument. Casts of Diplodocus skeletons, averaging 87 feet in length, were sent to museums around the world by Andrew Carnegie in the early part of this century, including the Vernal Field House of Natural History.

Dystrophaeus is the rarest, oldest, and first-discovered sauropod dinosaur in western North America. Its bones were found by the Macomb Expedition to southern Utah in 1857. Because of its stratigraphic position at the bottom of the Morrison Formation (Tidwell Member), this dinosaur may be ancestral to some or all of the other North American sauropods of the Late Jurassic Morrison Formation.

Marshosaurus is another small, rare theropod. It reached lengths up to 16 feet and was named after O.C. Marsh, a famous paleontologist from the 1800s.

Stegosaurus, the plated dinosaur, was one of the major plant-eaters of the Jurassic Period. Most paleontologists believe its triangular bony plates were set in two rows along the backbone in a staggered arrangement. The function of the plates is controversial. Perhaps they were for protection, but some paleontologists think that they may have collected solar radiation for thermal regulation. Even though it is the state dinosaur of Colorado, it is common in Utah.

Stokesosaurus was a rare carnivorous dinosaur reaching lengths of 13 feet, and was named for a prominent Utah geologist, the late Dr. William Lee Stokes. Its bones and braincase anatomy indicate that it may be an ancestor of the giganticTyrannosaurus that lived 85 million years later at the end of the Cretaceous Period.

Torvosaurus is the largest Jurassic theropod known in Utah. Reaching nearly the size of Tyrannosaurus, it was able to terrorize even the giant sauropods. Although rare it is known from a couple of sites.