Late Cretaceous Dinosaurs of Utah

The North Horn Formation

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 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 ft 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, 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 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.

The Kaiparowits Formation

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 display or for giving it an improved sense of smell.

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 Staircase – Escalante National Monument was originally used to correlate these rocks with the North Horn Formation, but continued research in area utilizing microvertebrate fossils and pollen has shown that these rocks are as much as 10 million years older.

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 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.