Allosaurus

Utah designated Allosaurus fragilis as its state fossil in 1988. The choice reflected the state's extraordinary Jurassic fossil record. The Cleveland-Lloyd Dinosaur Quarry in Emery County has yielded more than 60 individual Allosaurus specimens, more than any other site on Earth. Allosaurus was the dominant large predator of the Morrison Formation, the geological layer that stretches across much of the American West and is especially rich in Utah.

Allosaurus was a large bipedal predator with a massive skull, short arms ending in three curved claws, and powerful hind legs built for speed. Adults typically reached about 28 feet in length. The skull was built with large openings that reduced its weight without losing strength, allowing it to absorb impact forces during feeding. A bony ridge above each eye gave it a distinctive look.

Scientists think Allosaurus hunted large prey including Stegosaurus and long-necked sauropods. One hypothesis holds that it drove its upper jaw downward into prey like a hatchet rather than biting with full clamping force. Allosaurus lived from about 155 to 145 million years ago during the Late Jurassic and was the top predator in the ecosystem that produced the Morrison Formation.

The Cleveland-Lloyd Dinosaur Quarry had been producing Allosaurus fossils since the early 20th century, and the Bureau of Land Management designated it a National Natural Landmark in 1966. By 1988, the quarry had already yielded more Allosaurus individuals than any other site in the world, giving Utah a clear claim to the species.

Utah designated Allosaurus fragilis as its official state fossil in 1988, the same year Colorado named Stegosaurus and South Dakota named Triceratops. The concentration of specimens at Cleveland-Lloyd, and the ongoing scientific attention the quarry drew, made Allosaurus the natural symbol of the state's Jurassic heritage.

The Cleveland-Lloyd Dinosaur Quarry in Emery County, about 30 miles south of Price, is the most significant Allosaurus site in the world. The quarry has produced more than 12,000 individual fossil bones from at least 70 dinosaurs, the majority of them Allosaurus. Why so many predators ended up in one place is still debated. Theories include a predator trap similar to the La Brea Tar Pits, seasonal drought, and contaminated water that attracted and killed animals over thousands of years.

The Natural History Museum of Utah in Salt Lake City holds a major collection of Morrison Formation dinosaurs including articulated Allosaurus specimens. The Morrison Formation outcrops broadly across eastern and central Utah, and Allosaurus bones have turned up at multiple localities beyond Cleveland-Lloyd, including areas near Dinosaur National Monument in the northeastern corner of the state.