Name means: Strange Reptile


Species: fragilis, lucasi, europaeus, “jimmadseni”

Range: Late Jurassic (Tithonian, 150-145 MYA) of Utah, Wyoming, Colorado, Portugal, Spain, possibly France, Russia, Japan

Size estimate: 30-35 ft length, 5 tons

Discovery: Othniel Charles Marsh, 1877

Classification: dinosauria, saurischia, therapoda, tetanurae, allosauroidea


Thanks to plentiful fossil finds, scientists know more about Allosaurus than the average dinosaur. We have fossils for nearly every stage of growth—from fully grown adults to a possible embryo still in its egg, and nearly every stage in between. Fossils tell us features of its crocodile-like brain, its scaly skin, and even diseases it may have suffered. Since many of these finds occurred in Utah, the state legislature voted to make it Utah’s official state fossil. The Cleveland-Lloyd Dinosaur Quarry near Price has added hundreds of fossils to our knowledge of this animal.


Allosaurus lived alongside some of the most famous dinosaurs. It preyed upon Stegosaurus, Apatosaurus, Diplodocus, and possibly even Brachiosaurus. It also competed with the other large carnivores of the time: Torvosaurus and Ceratosaurus. Scientists aren’t sure why, but it far outnumbered these other two theropod types. Perhaps it lived in areas more likely to preserve its fossils. Or maybe it hatched more eggs or cared for its young longer. Some scientists even think it hunted in packs. Allosaurs also adapted to a wide variety of locales. Their fossils also occur in Portugal, France, and possibly Russia.

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