42 Facts About Allosaurus


The name "Allosaurus" means "different lizard" alluding to its unique concave vertebrae.

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The bulk of Allosaurus remains have come from North America's Morrison Formation, with material known from Portugal.

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Discovery and early study of Allosaurus is complicated by the multiplicity of names coined during the Bone Wars of the late 19th century.

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Allosaurus itself is based on YPM 1930, a small collection of fragmentary bones including parts of three vertebrae, a rib fragment, a tooth, a toe bone, and, most useful for later discussions, the shaft of the right humerus .

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Allosaurus came to the conclusion that the tail vertebra named Antrodemus by Leidy was indistinguishable from those of Allosaurus, and Antrodemus thus should be the preferred name because, as the older name, it had priority.

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Antrodemus became the accepted name for this familiar genus for over 50 years, until James Henry Madsen published on the Cleveland-Lloyd specimens and concluded that Allosaurus should be used because Antrodemus was based on material with poor, if any, diagnostic features and locality information .

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The quarry is notable for the predominance of Allosaurus remains, the condition of the specimens, and the lack of scientific resolution on how it came to be.

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Regardless of the actual cause, the great quantity of well-preserved Allosaurus remains has allowed this genus to be known in detail, making it among the best-known theropods.

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Six species of Allosaurus have been named: A amplus, A atrox, A europaeus, the type species A fragilis, A jimmadseni and A lucasi.

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Issue of species and potential synonyms is complicated by the type specimen of Allosaurus fragilis being extremely fragmentary, consisting of a few incomplete vertebrae, limb bone fragments, rib fragments, and a tooth.

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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 ilium, and ankle and foot bones.

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The referral was not accepted in the most recent review of basal tetanurans, and Allosaurus medius was simply listed as a dubious species of theropod.

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Allosaurus valens is a new combination for Antrodemus valens used by Friedrich von Huene in 1932; Antrodemus valens itself may pertain to Allosaurus fragilis, as Gilmore suggested in 1920.

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Allosaurus later decided it warranted its own genus, Labrosaurus, but this has not been accepted, and A lucaris is regarded as another specimen of A fragilis.

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Allosaurus lucaris, is known mostly from vertebrae, sharing characters with Allosaurus.

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Allosaurus meriani was a new combination by George Olshevsky for Megalosaurus meriani Greppin, 1870, based on a tooth from the Late Jurassic of Switzerland.

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However, it was considered indeterminate beyond Dinosauria by Chure, and Mickey Mortimer believes that the synonymy of Apatodon with Allosaurus was due to correspondence to Ralph Molnar by John McIntosh, whereby the latter reportedly found a paper saying that Othniel Charles Marsh admitted that the Apatodon holotype was actually an allosaurid dorsal vertebra.

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Smith, in his 1998 analysis of variation, concluded that S maximus was not different enough from Allosaurus to be a separate genus, but did warrant its own species, A maximus.

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Labrosaurus stechowi, described in 1920 by Janensch based on isolated Ceratosaurus-like teeth from the Tendaguru beds of Tanzania, was listed by Donald F Glut as a species of Allosaurus, is considered a dubious ceratosaurian related to Ceratosaurus.

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An astragalus thought to belong to a species of Allosaurus was found at Cape Paterson, Victoria in Early Cretaceous beds in southeastern Australia.

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Allosaurus was a typical large theropod, having a massive skull on a short neck, a long, slightly sloping tail, and reduced forelimbs.

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Skull and teeth of Allosaurus were modestly proportioned for a theropod of its size.

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Allosaurus had nine vertebrae in the neck, 14 in the back, and five in the sacrum supporting the hips.

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Forelimbs of Allosaurus were short in comparison to the hindlimbs and had three fingers per hand, tipped with large, strongly curved and pointed claws.

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Allosaurus was an allosaurid, a member of a family of large theropods within the larger group Carnosauria.

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This, along with the use of Antrodemus for Allosaurus during the same period, is a point that needs to be remembered when searching for information on Allosaurus in publications that predate James Madsen's 1976 monograph.

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Typical theropods that were thought to be related to Allosaurus included Indosaurus, Piatnitzkysaurus, Piveteausaurus, Yangchuanosaurus, Acrocanthosaurus, Chilantaisaurus, Compsosuchus, Stokesosaurus, and Szechuanosaurus.

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However, as Gregory Paul noted in 1988, Allosaurus was probably not a predator of fully grown sauropods, unless it hunted in packs, as it had a modestly sized skull and relatively small teeth, and was greatly outweighed by contemporaneous sauropods.

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The authors suggested that Allosaurus used its skull like a machete against prey, attacking open-mouthed, slashing flesh with its teeth, and tearing it away without splintering bones, unlike Tyrannosaurus, which is thought to have been capable of damaging bones.

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The original authors noted that Allosaurus itself has no modern equivalent, that the tooth row is well-suited to such an attack, and that articulations in the skull cited by their detractors as problematic actually helped protect the palate and lessen stress.

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When compared with Tyrannosaurus and the therizinosaurid Erlikosaurus in the same study, it was found that Allosaurus had a wider gape than either; the animal was capable of opening its jaws to a 92-degree angle at maximum.

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Biomechanical study published in 2013 by Eric Snively and colleagues found that Allosaurus had an unusually low attachment point on the skull for the longissimus capitis superficialis neck muscle compared to other theropods such as Tyrannosaurus.

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An alternate hypothesis by Pahl and Ruedas in 2021 suggested instead that Allosaurus subsisted primarily on carrion produced by giant sauropods, based on ecological modelling.

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Brain of Allosaurus, as interpreted from spiral CT scanning of an endocast, was more consistent with crocodilian brains than those of the other living archosaurs, birds.

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Allosaurus was one of only two theropods examined in the study to exhibit a tendon avulsion, and in both cases the avulsion occurred on the forelimb.

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The lack of such a bias in the examined Allosaurus fossils indicates an origin for the stress fractures from a source other than running.

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The abundance of stress fractures and avulsion injuries in Allosaurus provide evidence for "very active" predation-based rather than scavenging diets.

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An apparent subadult male Allosaurus fragilis was reported to have extensive pathologies, with a total of fourteen separate injuries.

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Allosaurus is commonly found at the same sites as Apatosaurus, Camarasaurus, Diplodocus, and Stegosaurus.

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The Late Jurassic formations of Portugal where Allosaurus is present are interpreted as having been similar to the Morrison, but with a stronger marine influence.

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Allosaurus coexisted with fellow large theropods Ceratosaurus and Torvosaurus in both the United States and Portugal.

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Allosaurus was itself a potential food item to other carnivores, as illustrated by an Allosaurus pubic foot marked by the teeth of another theropod, probably Ceratosaurus or Torvosaurus.

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