Exhibit Spotlight: Allosaurus fragilis

Let’s check out Utah’s state fossil, Allosaurus. We have a bunch of these guys in the park, so it’s an important one to know at any time. Allosaurus fossils have taught us more about dinosaurs in general than almost any other dinosaur. These fossils represent a nearly complete set of growth stages from possible egg-bound embryos to full adulthood. The great number of fossils from a wide variety of circumstances helps scientists study these animals as both individuals (Big Al, from Wyoming, has a whole life history) and populations.
  • Abundant fossils do carry some scientific drawbacks, however. The variable condition of these finds and differences between Allosaurus individuals have led scientists to apply well over a dozen names to these bones over the past century. Antrodemus, Labrosaurus, and Epantarias are all old synonyms for what we now call Allosaurus. Currently science recognizes three Allosaurus species, with a fourth known informally. These include A. fragilis, A. europaeus, A. lucasi, and A. “jimmadseni.” Work remains underway in regards to Allosaurus “jimmadseni,” named for a former Utah state paleontologist and Allosaurus expert Jim Madsen. Its jawline did not turn down at the back, giving it more of a “poker face” than the gruff frown of it’s A. fragilis cousins. This jawline variation might be due to individual differences, but “jimmadseni” might also be older. A. europaeus is distinguished more by where it lived than physical differences, and might be the same as A. fragilis. A. lucasi shows differences in the construction of its snout, but it is known from only 2 well-preserved but incomplete skeletons from southwestern Colorado.
  • The situation of the continents during the Jurassic allowed Allosaurus to roam over most of the northern hemisphere. At that time, North America, Europe, and Asia remained joined as the supercontinent Laurasia after the breakup of Pangea. Though many scientists currently consider the European Allosaurus its own species, the differences between the two counterparts are few and subtle.
  • More Allosaurus fossils have been found at Cleveland-Lloyd Dinosaur Quarry, near Price, Utah, than anywhere else in the world. This quarry helped catapult Utah to international fame in paleontological circles, leading the state legislature to adopt Allosaurus as a state symbol.
  • Skin impressions from a juvenile Allosaurus discovered in Wyoming show that even at a young age, Allosaurus had scales, not the downy feathers pictured in some modern books.
  • Allosaurus may have hunted in packs, which might explain why it occurs more often than other meat-eating dinosaurs in its time and area. Because behavior does not fossilize, scientists cannot say for sure if they had a social structure or coordinated pack behaviors, what form those behaviors might have taken, or even if they definitely traveled in groups at all.
  • The Eccles Dinosaur Park has more representations of Allosaurus than any other dinosaur here at the park. The next time you visit, look them on the courtyard, next to the iguana house, in the cave on the northeast corner, in the oak grove on the west side, in the museum, and check out the genuine fossils in the lab (ask a lab worker or staff member for a closer look).


Marsh, O. C. (1877). ART. LIII.–Notice of New Dinosaurian Reptiles from the Jurassic formation. American Journal of Science and Arts (1820-1879), 14(84), 514.

Mateus, O., Walen, A., & Antunes, M. T. (2006). The Large Theropod Fauna of the Lourinha Formation (Portugal) and Its Similarity to That of the Morrison Formation, with a Description of a New Species of Allosaurus. Paleontology and Geology of the Upper Jurassic Morrison Formation: Bulletin 36, 36, 123.

Dalman, S. (2014). Osteology of a large allosauroid theropod from the Upper Jurassic (Tithonian) Morrison Formation of Colorado, USA. Volumina Jurassica, 12(2), 159-180.

Hirsch, K. F., Stadtman, K. L., Miller, W. E., & Madsen Jr, J. H. (1989). Upper Jurassic dinosaur egg from Utah. Science, 243(4899), 1711.

Pinegar, R. T., Loewen, M. A., Cloward, K. C., Hunter, R. J., & Weege, C. J. (2003, January). A Juvenile Allosaur with Preserved Integument from the Basal Morrison Formation of Central Wyoming. In Journal of Vertebrate Paleontology (Vol. 23, pp. 87A-88A).