Utah State Fossil - Allosaurus

In 1988 the Utah state legislature designated Allosaurus as the Utah state fossil. In addition the Utahraptor was designated as the official state dinosaur in 2018.

Allosaurus was an iconic, meat-eating dinosaur that was one of the top predators during the Late Jurassic period. It grew up to 39 feet long, with a mouthful of serrated teeth, and curved claws up to 8 inches in length. It likely preyed upon the large, sauropod dinosaurs such Diplodocus that shared its environment. It also frequently battled Stegosaurus, as bite marks matching Allosaurus have been found on fossil Stegosaurus bones, a puncture wound matching a Stegosaurus tail spike has been found on an Allosaurus vertebra. It’s theorized that Allosaurus hunted in packs to take down much larger prey.

Allosaurus fragilis skeleton from Utah.
Allosaurus fragilis skeleton from Utah.


Allosaurus is the most common dinosaur found in the Morrison Formation that is exposed in Eastern Utah as well as neighboring Colorado and Wyoming. The Cleveland-Lloyd Dinosaur quarry located at the Jurassic National Monument in Utah has yielded the bones of 46 individual Allosaurus. It’s believed that the quarry represents a “predator trap” similar to how the La Brea Tar Pits in California frequently trapped predatory mammals.

Allosaurus Fragilis Reconstruction by Fred Wierum  Creative Commons License
Allosaurus Fragilis Reconstruction by Fred Wierum Creative Commons License


Another fearsome theropod dinosaur found discovered in Utah, the Utahraptor was named the official state dinosaur in 2018. Initially it was proposed that Utahraptor would replace Allosaurus as the state’s official fossil, but it was decided to make it the state dinosaur instead. Unlike Allosaurus which lived during the Late Jurassic, Utahraptor lived during the Early Cretaceous and its fossils are found in the Cedar Mountain Formation. Utahraptor is the largest-known member of the family Dromaeosauridae, dinosaurs commonly referred to as raptors. It reached 19 feet in length and its sickle-shaped claws have been found over 9 inches in length.

Claw of a Utahraptor, on display at the BYU Museum of Paleontology.
Claw of a Utahraptor, on display at the BYU Museum of Paleontology.


In 2001 a 9-ton block of sandstone containing the bones of at least seven individual Utahraptors was discovered in Eastern Utah. These seven individuals represent at least one adult, four juveniles and at least one hatchling. The block of sandstone was removed in a single piece and is currently under preparation at the Museum of Ancient Life at Thanksgiving Point, Utah. It is estimated that it will still take another decade to completely remove the fossils from the hard limestone. Check out the Utahraptor project for more information.


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