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BackgroundThe popular theropod dinosaur, Allosaurus fragilis, is known from numerous specimens discovered in Late Jurassic sediments across Montana, Utah, and Wyoming. Unlike many Allosaurus specimens, this isolated individual was discovered as an isolated, associated skeleton near Shell, WY in 2004 and preserves 65 cranial and postcranial elements.This specimen exhibits a unique combination of large body size with sub -adult characteristics. Features such as lack of fusion between elements commonly fused in adults, such as the neural arches of the dorsal vertebrae, pubic boots, cranial elements, and pectoral girdle, suggest that this individual was not fully grown. Additionally, the number of alveoli in the dentaries and maxillae are higher than in "adult" individuals of Allosaurus (Madsen 1976). Despite these indications that the individual was not fully grown, it was comparable in body size to other, large "adult" Allosaurus specimens. Furthermore, this specimen exhibits variation described by Carpenter (2010) as not being associated with age, including on the skull elements such as the lacrimal.

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