page_title: Allosaurus
section_title: Synonyms
hierarchical_section_title: Allosaurus / Discovery and history / Synonyms
caption_attribution_description: Holotype material of Creosaurus atrox.
context_page_description: Allosaurus is a genus of carnivorous theropod dinosaur that lived 155 to 145 million years ago during the late Jurassic period. The name "Allosaurus" means "different lizard" alluding to its unique concave vertebrae. It is derived from the Greek ἄλλος and σαῦρος. The first fossil remains that could definitively be ascribed to this genus were described in 1877 by paleontologist Othniel Charles Marsh. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles.
  Allosaurus was a large bipedal predator. Its skull was large and equipped with dozens of sharp, serrated teeth. It averaged 9.5 metres in length, though fragmentary remains suggest it could have reached over 12 m. Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long and heavily muscled tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes 3 valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal.
context_section_description: Creosaurus, Epanterias, and Labrosaurus are regarded as junior synonyms of Allosaurus. Most of the species that are regarded as synonyms of A. fragilis, or that were misassigned to the genus, are obscure and were based on scrappy remains. One exception is Labrosaurus ferox, named in 1884 by Marsh for an oddly formed partial lower jaw, with a prominent gap in the tooth row at the tip of the jaw, and a rear section greatly expanded and turned down. Later researchers suggested that the bone was pathologic, showing an injury to the living animal, and that part of the unusual form of the rear of the bone was due to plaster reconstruction. It is now regarded as an example of A. fragilis.
  In his 1988 book Predatory Dinosaurs of the World, the freelance dinosaurologist Gregory Paul proposed that A. fragilis had tall pointed horns and a slender build compared to a postulated second species A. atrox, and was not a different sex due to rarity. Allosaurus atrox was originally named by Marsh in 1878 as the type species of its own genus, Creosaurus, and is based on YPM 1890, an assortment of bones including a couple of pieces of the skull, portions of nine tail vertebrae, two hip vertebrae, an illium, and ankle and foot bones. Although the idea of two common Morrison allosaur species was followed in some semi-technical and popular works, the 2000 thesis on Allosauridae noted that Charles Gilmore mistakenly reconstructed USNM 4734 as having a shorter skull than the specimens referred by Paul to atrox, refuting supposed differences between USNM 4734 and putative A. atrox specimens like DINO 2560, AMNH 600, and AMNH 666.
  "Allosaurus agilis", seen in Zittel, 1887, and Osborn, 1912, is a typographical error for A. fragilis. "Allosaurus ferox" is a typographical error by Marsh for A. fragilis in a figure caption for the partial skull YPM 1893, and YPM 1893 has been treated as a specimen of A fragilis. Likewise, "Labrosaurus fragilis" is a typographical error by Marsh (1896) for Labrosaurus ferox. "A. whitei" is a nomen nudum coined by Pickering in 1996 for the complete Allosaurus specimens that Paul referred to A. atrox.
  "Madsenius" was coined by David Lambert in 1990 Reportedly for remains from Dinosaur National Monument assigned to Allosaurus or Creosaurus (a synonym of Allosaurus), and was to be described by well-known paleontologist Bob Bakker as "Madsenius trux". However, "Madsenius" is now seen as yet another synonym of Allosaurus because Bakker's action was predicated upon the false assumption of USNM 4734 being distinct from long-snouted Allosaurus due to errors in Gilmore's (1920) reconstruction of USNM 4734.
  "Wyomingraptor" was informally coined by Robert Bakker for allosaurid remains from the Morrison Formation of the Late Jurassic. The remains unearthed are labeled as Allosaurus and are housed in the Tate Geological Museum. However, there has been no official description of the remains and "Wyomingraptor" has been dismissed a nomen nudum with the remains referable to Allosaurus.
caption: Holotype material of Creosaurus atrox
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