Specimens of Allosaurus

There have been a number of potential species assigned to the carnosaurian dinosaur genus Allosaurus since its description in 1877 by Othniel Charles Marsh, but only a handful are still regarded as valid. Allosaurus was originally described from material from the Upper Jurassic Morrison Formation of the western United States of America; the type species A. fragilis became one of the best-known species of dinosaur.

The genus Allosaurus was part of the Marsh/Cope "Bone Wars" of the late 19th century, and its taxonomy became increasingly confused due to the competition, with several genera and species named by Cope and Marsh now regarded as synonyms of Allosaurus or A. fragilis. Since the description of Allosaurus, scientists have proposed additional species from such far-flung locales as Portugal, Siberia, and Tanzania, but only the one non-US species of Allosaurus is currently considered valid.

The issue of synonyms is complicated by the type specimen of Allosaurus fragillis (catalogue number YPM 1930) being extremely fragmentary, consisting of a few incomplete vertebrae, limb bone fragments, rib fragments, and a tooth. Because of this, several scientists have noted that the type specimen, and thus the genus Allosaurus itself or at least the species A. fragillis, is technically a nomen dubium ("dubious name", based on a specimen too incomplete to compare to other specimens or to classify). In an attempt to fix this situation, Gregory S. Paul and Kenneth Carpenter (2010) submitted a petition to the ICZN to have the name A. fragillis officially transferred to the more complete specimen USNM4734 (as a neotype). This request is currently pending review.

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