Editing Allosaurus

{{mergefrom|Epanterias|discuss=Talk:Allosaurus#Proposal to merge Epanterias into Allosaurus|date=March 2025}}
{{Short description|Extinct genus of carnosaurian theropod dinosaur}}
{{Featured article}}
{{pp-move}}
{{Use American English|date=March 2024}}
{{Use mdy dates|date=January 2025}}
{{Automatic taxobox
| fossil_range = [[Late Jurassic]] ([[Kimmeridgian]] to [[Tithonian]]), {{Geological range|155|143.1}}
| image = Allosaurus SDNHM (1).jpg
| image_caption = Mounted ''A. fragilis'' skeleton cast, [[San Diego Natural History Museum]]
| image_upright = 1.15
| parent_authority = [[Othniel Marsh|Marsh]], [[1878 in paleontology|1878]]
| taxon = Allosaurus
| authority = Marsh, [[1877 in paleontology|1877]]
| type_species = {{extinct}}'''''Allosaurus fragilis'''''
| type_species_authority = Marsh, 1877
| subdivision_ranks = Other species
| subdivision_ref = 
| subdivision = *{{extinct}}'''''A. europaeus''''' <br/><small>[[Octávio Mateus|Mateus]] et al., [[2006 in paleontology|2006]]</small>
*{{extinct}}'''''A. jimmadseni''''' <br/><small>Chure & Loewen, [[2020 in archosaur paleontology|2020]]</small>
*{{extinct}}'''''A. anax''''' <br/><small>Danison et al., [[2024 in archosaur paleontology|2024]]</small>
| synonyms = {{collapsible list|bullets = true|title=<small>Genus synonymy</small>
|''[[Antrodemus]]''? <br/><small>[[Joseph Leidy|Leidy]], [[1870 in paleontology|1870]]</small>
|''[[Apatodon]]''? <br/><small>Marsh, [[1878 in paleontology|1878]]</small>
|''Creosaurus'' <br/><small>Marsh, [[1878 in paleontology|1878]]</small>
|''[[Epanterias]]''? <br/><small>[[Edward Drinker Cope|Cope]], 1878</small>
|''Labrosaurus'' <br/><small>Marsh, [[1879 in paleontology|1879]]</small>
|"Madsenius" <br/><small>[[Robert Bakker|Bakker]], [[1990 in paleontology|1990]]</small>
|"Wyomingraptor" <br/><small>Bakker, [[1997 in paleontology|1997]]</small>
}}
}}

'''''Allosaurus''''' ({{IPAc-en|ˌ|æ|l|ə|ˈ|s|ɔːr|ə|s}})<ref>{{cite Merriam-Webster|Allosaurus}}</ref><ref>{{cite Dictionary.com|Allosaurus}}</ref> is an extinct [[genus]] of large [[theropoda|theropod]] dinosaur that lived 155 to 145&nbsp;million years ago during the [[Late Jurassic]] [[Geologic time scale|period]] ([[Kimmeridgian]] to late [[Tithonian]] [[Geologic time scale|ages]]). The name "''Allosaurus''" means "different lizard", alluding to its unique (at the time of its discovery) concave [[Glossary of dinosaur anatomy#vertebrae|vertebrae]]. The first fossil remains that could definitively be ascribed to this [[genus]] were described in [[1877 in paleontology|1877]] by [[Othniel Charles Marsh]]. The genus has a very complicated [[Taxonomy (biology)|taxonomy]] and includes at least three 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 the [[Alcobaça Formation]] and [[Lourinhã Formation]] in Portugal with teeth known from Germany. It was known for over half of the 20th century as ''[[Antrodemus]]'', but a study of the abundant remains from the [[Cleveland-Lloyd Dinosaur Quarry]] returned the name "''Allosaurus''" to prominence. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles.

''Allosaurus'' was a large [[biped]]al predator for its time. Its skull was light, robust, and equipped with dozens of sharp, [[serrated]] teeth. It averaged {{convert|8.5|m|sp=us}} in length for ''A. fragilis'', with the largest specimens estimated as being {{convert|9.7|m|sp=us}} long. Relative to the large and powerful legs, its three-fingered hands were small and the body was balanced by a long, muscular tail. It is classified in the family [[Allosauridae]]. As the most abundant large predator of the Morrison Formation, ''Allosaurus'' was at the top of the food chain and probably preyed on large herbivorous dinosaurs such as [[ornithopod]]s, [[stegosaurid]]s, and [[sauropod]]s. It is also possible that it hunted other predators. Scientists have debated whether ''Allosaurus'' had cooperative [[social behavior]] and hunted in packs or was a solitary predator that form congregations, with evidence supporting either side.

==Discovery and history==

===Early discoveries and research===
{{multiple image
| direction         = vertical
| width             = 
| align             = left
| header            = 
| image1            = AMNH Allosaurus.jpg
| alt1              = 
| caption1          = Mounted ''A. fragilis'' specimen (AMNH 5753), posed as scavenging an ''[[Apatosaurus]]''
| image2            = Allosaurus4.jpg
| alt2              = 
| caption2          = AMNH 5753 in a [[Charles R. Knight]] life restoration (Outdated)
}}
The discovery and early study of ''Allosaurus'' is complicated by the multiplicity of names coined during the [[Bone Wars]] of the late 19th century. The first described [[fossil]] in this history was a bone obtained secondhand by [[Ferdinand Vandeveer Hayden]] in [[1869 in paleontology|1869]]. It came from [[Middle Park (Colorado basin)|Middle Park]], near [[Granby, Colorado]], probably from [[Morrison Formation]] rocks. The locals had identified such bones as "petrified horse hoofs". Hayden sent his specimen to [[Joseph Leidy]], who identified it as half of a tail vertebra and tentatively assigned it to the European dinosaur genus ''[[Poekilopleuron]]'' as ''Poicilopleuron''{{sic}} ''valens''.<ref name="JL70">{{cite journal |last=Leidy |first=Joseph |author-link=Joseph Leidy |year=1870 |title=Remarks on ''Poicilopleuron valens'', ''Clidastes intermedius'', ''Leiodon proriger'', ''Baptemys wyomingensis'', and ''Emys stevensonianus'' |journal=Proceedings of the Academy of Natural Sciences of Philadelphia |volume=22 |pages=3–4}}</ref> He later decided it deserved its own genus, ''Antrodemus''.<ref name=JL73>{{cite journal |last=Leidy |first=Joseph |year=1873 |title=Contribution to the extinct vertebrate fauna of the western territories |journal=Report of the U.S. Geological Survey of the Territories I |pages=14–358}}</ref>

''Allosaurus'' itself is [[Holotype|based on]] [[Peabody Museum of Natural History|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 (upper arm). [[Othniel Charles Marsh]] gave these remains the formal name ''Allosaurus fragilis'' in 1877. ''Allosaurus'' comes from the [[Ancient Greek|Greek]] words ''{{lang|grc-Latn|allos}}/{{lang|grc|αλλος}}'', meaning "strange" or "different", and ''{{lang|grc-Latn|sauros}}/{{lang|grc|σαυρος}}'', meaning "lizard" or "reptile".<ref>{{cite book|author=Liddell & Scott|year=1980|title=Greek–English Lexicon, Abridged Edition|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-910207-5|oclc=17396377|url=https://archive.org/details/lexicon00lidd}}</ref> It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery.<ref name="OCM77">{{cite journal |last=Marsh |first=Othniel Charles |author-link=Othniel Charles Marsh |year=1877 |title=Notice of new dinosaurian reptiles from the Jurassic formation |url=https://zenodo.org/record/1450040 |journal=American Journal of Science and Arts |volume=14 |issue=84 |pages=514–516 |bibcode=1877AmJS...14..514M |doi=10.2475/ajs.s3-14.84.514 |s2cid=130488291 |archive-date=April 20, 2021 |access-date=August 31, 2020 |archive-url=https://web.archive.org/web/20210420181422/https://zenodo.org/record/1450040 |url-status=live }}</ref><ref name=DMLomnipedia>{{cite web|url=http://www.dinosauria.com/dml/names/dinoa.htm |title=Dinosauria Translation and Pronunciation Guide A |access-date=September 11, 2007 |last=Creisler |first=Ben |date=July 7, 2003 |publisher=Dinosauria On-Line |archive-url=https://web.archive.org/web/20100105101204/http://www.dinosauria.com/dml/names/dinoa.htm |archive-date=January 5, 2010 |url-status=dead}}</ref> The species epithet ''fragilis'' is [[Latin]] for "fragile", referring to lightening features in the vertebrae. The bones were collected from the Morrison Formation of [[Garden Park, Colorado|Garden Park]], north of [[Cañon City, Colorado|Cañon City]].<ref name=OCM77/> O. C. Marsh and [[Edward Drinker Cope]], who were in scientific competition with each other, went on to coin several other genera based on similarly sparse material that would later figure in the taxonomy of ''Allosaurus''. These include Marsh's ''Creosaurus''<ref name=OCM78/> and ''Labrosaurus'',<ref name=OCM79>{{cite journal |last=Marsh |first=Othniel Charles |year=1879 |title=Principal characters of American Jurassic dinosaurs. Part II |journal=American Journal of Science |series=Series 3 |volume=17 |issue=97 |pages=86–92 |doi=10.2475/ajs.s3-17.97.86 |url=https://babel.hathitrust.org/cgi/imgsrv/download/pdf?id=hvd.32044107172876;orient=0;size=100;seq=5;attachment=0 |hdl=2027/hvd.32044107172876 |s2cid=219247096 |hdl-access=free |archive-date=November 9, 2021 |access-date=August 6, 2018 |archive-url=https://web.archive.org/web/20211109005146/https://babel.hathitrust.org/cgi/imgsrv/download/pdf?id=hvd.32044107172876;orient=0;size=100;seq=5;attachment=0 |url-status=live }}</ref> as well as Cope's ''Epanterias''.<ref name=EDC78/>

In their haste, Cope and Marsh did not always follow up on their discoveries (or, more commonly, those made by their subordinates). For example, after the discovery by [[Benjamin Franklin Mudge|Benjamin Mudge]] of the type specimen of ''Allosaurus'' in Colorado, Marsh elected to concentrate work in [[Wyoming]]. When work resumed at Garden Park in [[1883 in paleontology|1883]], M. P. Felch found an almost complete ''Allosaurus'' and several partial skeletons.<ref name=DBN85/> In addition, one of Cope's collectors, H. F. Hubbell, found a specimen in the [[Como Bluff]] area of Wyoming in [[1879 in paleontology|1879]], but apparently did not mention its completeness and Cope never unpacked it. Upon unpacking it in [[1903 in paleontology|1903]] (several years after Cope had died), it was found to be one of the most complete theropod specimens then known and the skeleton, now cataloged as AMNH 5753, was put on public view in [[1908 in paleontology|1908]].<ref name=NGD95>{{cite book |last1=Norell |first1=Mark A. |last2=Gaffney, Eric S. |last3=Dingus, Lowell |title=Discovering Dinosaurs in the American Museum of Natural History |publisher=Knopf |location=New York |year=1995 |pages=[https://archive.org/details/discoveringdinos00nore_0/page/112 112–113] |isbn=978-0-679-43386-6 |url=https://archive.org/details/discoveringdinos00nore_0/page/112 }}</ref> This is the well-known mount poised over a partial ''[[Apatosaurus]]'' skeleton as if [[Scavenger|scavenging]] it, illustrated as such in a painting by [[Charles R. Knight]]. Although notable as the first free-standing mount of a theropod dinosaur and often illustrated and photographed, it has never been scientifically described.<ref name=BBetal99>{{cite journal |last=Breithaupt |first=Brent H. |year=1999 |title=AMNH 5753: The world's first free-standing theropod skeleton |journal=Journal of Vertebrate Paleontology |volume=19 |issue= |page=33A | doi = 10.1080/02724634.1999.10011202}}</ref>

The multiplicity of early names complicated later research, with the situation compounded by the terse descriptions provided by Marsh and Cope. Even at the time, authors such as [[Samuel Wendell Williston]] suggested that too many names had been coined.<ref name=SWW78>{{cite journal |last=Williston |first=Samuel Wendell |year=1878 |title=American Jurassic dinosaurs |journal=Transactions of the Kansas Academy of Science |volume=6 |pages=42–46 |doi=10.2307/3623553 |jstor=3623553 }}</ref> For example, Williston pointed out in [[1901 in paleontology|1901]] that Marsh had never been able to adequately distinguish ''Allosaurus'' from ''Creosaurus''.<ref name=SWW01>{{cite journal |last=Williston |first=Samuel Wendell |year=1901 |title=The dinosaurian genus ''Creosaurus'', Marsh |journal=American Journal of Science |series=Series 4 |volume=11 |issue=62 |pages=111–114 |doi=10.2475/ajs.s4-11.62.111 |url=https://zenodo.org/record/1450114 |bibcode=1901AmJS...11..111W |archive-date=November 9, 2021 |access-date=June 28, 2019 |archive-url=https://web.archive.org/web/20211109012757/https://zenodo.org/record/1450114 |url-status=live }}</ref> The most influential early attempt to sort out the convoluted situation was produced by [[Charles W. Gilmore]] in [[1920 in paleontology|1920]]. He came to the conclusion that the tail vertebra named ''Antrodemus'' by Leidy was indistinguishable from those of ''Allosaurus'' and that ''Antrodemus'' should be the preferred name because, as the older name, it had priority.<ref name=CWG20/> ''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. For example, the [[geological formation]] that the single bone of ''Antrodemus'' came from is unknown.<ref name=JM76/> "''Antrodemus''" has been used informally for convenience when distinguishing between the skull Gilmore restored and the composite skull restored by Madsen.<ref name=DH98>{{cite journal |last=Henderson |first=Donald M. |year=1998 |title=Skull and tooth morphology as indicators of niche partitioning in sympatric Morrison Formation theropods |journal=Gaia |volume=15 |pages=219–266 |url=https://www.researchgate.net/publication/228687281}}</ref>

===Cleveland-Lloyd discoveries===
[[File:Allosaurus atrox Cleveland-Lloyd Quarry.jpg|thumb|''A. fragilis'' at the Cleveland-Lloyd Dinosaur Quarry museum, Utah]]
Although sporadic work at what became known as the [[Cleveland-Lloyd Dinosaur Quarry]] in [[Emery County, Utah|Emery County]], Utah, had taken place as early as [[1927 in paleontology|1927]] and the fossil site itself described by [[William Lee Stokes|William L. Stokes]] in [[1945 in paleontology|1945]],<ref name=WJS45>{{cite journal |last=Stokes |first=William L. |year=1945 |title=A new quarry for Jurassic dinosaurs |journal=Science |volume=101 |issue=2614 |pages=115–117 |doi=10.1126/science.101.2614.115-a |pmid=17799203|bibcode = 1945Sci...101..115S |s2cid=13589884 }}</ref> major operations did not begin there until [[1960 in paleontology|1960]]. Under a cooperative effort involving nearly 40&nbsp;institutions, thousands of bones were recovered between 1960 and [[1965 in paleontology|1965]], led by James Henry Madsen.<ref name="JM76"/> 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. The majority of bones belong to the large theropod ''Allosaurus fragilis'' (it is estimated that the remains of at least 46&nbsp;''A. fragilis'' have been found there, out of at a minimum 73&nbsp;dinosaurs) and the fossils found there are disarticulated and well-mixed. Nearly a dozen scientific papers have been written on the [[taphonomy]] of the site, suggesting numerous mutually exclusive explanations for how it may have formed. Suggestions have ranged from animals getting stuck in a bog, becoming trapped in deep mud, falling victim to drought-induced mortality around a waterhole, and getting trapped in a spring-fed pond or seep.<ref name="APHetal06">{{cite book |last1=Hunt |first1=Adrian P |last2=Lucas, Spencer G.|last3= Krainer, Karl|last4= Spielmann, Justin |year=2006 |chapter=The taphonomy of the [[Cleveland-Lloyd Dinosaur Quarry]], Upper Jurassic Morrison Formation, Utah: a re-evaluation |editor=Foster, John R. |editor2=Lucas, Spencer G. |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin, '''36''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |pages=57–65}}</ref> Regardless of the actual cause, the great quantity of well-preserved ''Allosaurus'' remains has allowed this genus to be known in great detail, making it among the best-known of all theropods. Skeletal remains from the quarry pertain to individuals of almost all ages and sizes, from less than {{convert|1|m|ft|abbr=off}}<ref name="LSCC03"/> to {{convert|12|m|ft|abbr=off}} long, and the disarticulation is an advantage for describing bones usually found fused.<ref name="JM76"/> Due to being one of Utah's two fossil quarries where numerous ''Allosaurus'' specimens have been discovered, ''Allosaurus'' was designated as the [[state fossil]] of Utah in [[1988 in paleontology|1988]].<ref name=statefossil>{{cite web|url=http://pioneer.utah.gov/research/utah_symbols/fossil.html |title=Utah Symbols&nbsp;– State Fossil |access-date=June 16, 2010 |publisher=Pioneer: Utah's Online Library, State of Utah |archive-url=https://web.archive.org/web/20100108021254/http://pioneer.utah.gov/research/utah_symbols/fossil.html |archive-date=January 8, 2010 |url-status=live}}</ref>

===Modern study===
The period since Madsen's monograph has been marked by a great expansion in studies dealing with topics concerning ''Allosaurus'' in life ([[paleobiology|paleobiological]] and [[paleoecology|paleoecological]] topics). Such studies have covered topics including skeletal variation,<ref name=DKS98>{{cite journal |doi=10.1080/02724634.1998.10011039 |last=Smith |first=David K. |year=1998 |title=A morphometric analysis of ''Allosaurus'' |journal=Journal of Vertebrate Paleontology |volume=18 |issue=1 |pages=126–142|bibcode=1998JVPal..18..126S }}</ref> growth,<ref name=PBetal06>{{cite journal |last1=Bybee |first1=Paul J. |year=2006 |title=Sizing the Jurassic theropod dinosaur ''Allosaurus'': Assessing growth strategy and evolution of ontogenetic scaling of limbs |journal=Journal of Morphology |volume=267 |issue=3 |pages=347–359 |doi=10.1002/jmor.10406 |pmid=16380967 |last2=Lee |first2=AH |last3=Lamm |first3=ET|s2cid=35111050 }}</ref><ref name=FC06>{{cite book |last1=Foster |first1=John R. |last2=Chure, Daniel J. |year=2006 |chapter=Hindlimb allometry in the Late Jurassic theropod dinosaur ''Allosaurus'', with comments on its abundance and distribution |editor=Foster, John R. |editor2=Lucas, Spencer G. |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin, '''36''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |pages=119–122}}</ref> skull construction,<ref name="ERetal01">{{cite journal |last1=Rayfield |first1=Emily J. |last2=Norman |first2=DB |author-link2=David B. Norman |last3=Horner |first3=CC |last4=Horner |first4=JR |author-link4=Jack Horner (paleontologist) |last5=Smith |first5=PM |last6=Thomason |first6=JJ |last7=Upchurch |first7=P |year=2001 |title=Cranial design and function in a large theropod dinosaur |journal=Nature |volume=409 |issue=6823 |pages=1033–1037 |bibcode=2001Natur.409.1033R |doi=10.1038/35059070 |pmid=11234010 |s2cid=4396729}}</ref> hunting methods,<ref name=BB98>{{cite journal |last=Bakker |first=Robert T. |year=1998 |title=Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues |journal=Gaia |volume=15 |pages=145–158|issn=0871-5424 |url=https://www.researchgate.net/publication/40662858}}</ref> the brain,<ref name=SWR99>{{cite journal |last=Rogers |first=Scott W. |year=1999 |title=''Allosaurus'', crocodiles, and birds: Evolutionary clues from spiral computed tomography of an endocast |journal=The Anatomical Record |volume=257 |issue=5 |pages=163–173 |doi=10.1002/(SICI)1097-0185(19991015)257:5<162::AID-AR5>3.0.CO;2-W | pmid = 10597341|doi-access=free }}</ref> and the possibility of gregarious living and parental care.<ref name=RTB97>{{cite book |last=Bakker |first=Robert T. |year=1997 |editor=Wolberg, Donald L. |editor2=Sump, Edmund |editor3=Rosenberg, Gary D. |chapter=Raptor Family values: Allosaur parents brought giant carcasses into their lair to feed their young |title=Dinofest International, Proceedings of a Symposium Held at Arizona State University |publisher=Academy of Natural Sciences |location=Philadelphia |pages=51–63|isbn=978-0-935868-94-4}}</ref> Reanalysis of old material (particularly of large 'allosaur' specimens),<ref name=GSP88/><ref name=DJC95>{{cite book |last=Chure |first=Daniel J. |year=1995 |chapter=A reassessment of the gigantic theropod ''Saurophagus maximus'' from the Morrison Formation (Upper Jurassic) of Oklahoma, USA |editor=Ailing Sun |editor2=Yuangqing Wang |title=Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers |publisher=China Ocean Press |location=Beijing |pages=103–106| isbn=978-7-5027-3898-3}}</ref> new discoveries in Portugal,<ref name=PMetal99>{{cite journal|last1=Pérez-Moreno |first1=B.P. |year=1999 |title=On the presence of ''Allosaurus fragilis'' (Theropoda: Carnosauria) in the Upper Jurassic of Portugal: First evidence of an intercontinental dinosaur species |journal=Journal of the Geological Society |volume=156 |issue=3 |pages=449–452 |doi=10.1144/gsjgs.156.3.0449 |url=http://correio.fc.ul.pt/~cmsilva/Artigos/CMS034.pdf |last2=Chure |first2=D. J. |last3=Pires |first3=C. |last4=Marques Da Silva |first4=C. |last5=Dos Santos |first5=V. |last6=Dantas |first6=P. |last7=Povoas |first7=L. |last8=Cachao |first8=M. |last9=Sanz |first9=J. L. |url-status=dead |archive-url=https://web.archive.org/web/20071025123324/http://correio.fc.ul.pt/~cmsilva/Artigos/CMS034.pdf |archive-date=October 25, 2007 |bibcode=1999JGSoc.156..449P |s2cid=130952546 }}</ref> and several very complete new specimens<ref name=DJC00b/><ref name=BB96>{{cite book |last=Breithaupt |first=Brent |year=1996 |chapter=The discovery of a nearly complete ''Allosaurus'' from the Jurassic Morrison Formation, eastern Bighorn Basin, Wyoming |editor=Brown, C.E. |editor2=Kirkwood, S.C. |editor3=Miller, T.S. |title=Forty-Seventh Annual Field Conference Guidebook |pages=309–313 |publisher=Wyoming Geological Association |location=Casper, Wyoming |oclc=36004754}}</ref><ref name=BigAlTwo>{{cite web |url=http://geo-sciences.com/howequarry.htm |archive-url=https://web.archive.org/web/20071203133129/http://geo-sciences.com/howequarry.htm |archive-date=December 3, 2007 |title=Howe Dinosaur Quarry&nbsp;– Wyoming's Jurassic Treasure |access-date=September 27, 2007 |date=July 24, 2007 |publisher=GeoScience Adventures}}</ref> have also contributed to the growing knowledge base.

==="Big Al" and "Big Al II"===
[[File:Big Al Allosaurus.jpg|left|thumb|"Big Al" ''A. jimmadseni'' skeleton at the [[Museum of the Rockies]]]]
In [[1991 in paleontology|1991]], "Big Al" ([[Museum of the Rockies|MOR]] 693), a 95%&nbsp;complete, partially articulated specimen of ''Allosaurus'' was discovered, measuring about {{convert|8|m}} long. MOR 693 was excavated near [[Shell, Wyoming]], by a joint [[Museum of the Rockies]] and [[University of Wyoming Geological Museum]] team.<ref name=BBbigal>{{cite web|last=Breithaupt |first=Brent H. |url=http://www2.nature.nps.gov/geology/paleontology/pub/fossil_conference_6/breithaupt.htm |title=The case of "Big Al" the ''Allosaurus'': a study in paleodetective partnerships |access-date=October 3, 2007 |archive-url=https://web.archive.org/web/20100107103137/http://nature.nps.gov/geology/paleontology/pub/fossil_conference_6/breithaupt.htm |archive-date=January 7, 2010 |url-status=dead}}</ref> This skeleton was discovered by a Swiss team, led by Kirby Siber. Chure and Loewen in [[2020 in paleontology|2020]] identified the individual as a representative of the species ''A. jimmadseni''. In [[1996 in paleontology|1996]], the same team discovered a second ''Allosaurus'', "Big Al II". This specimen, the best preserved skeleton of its kind to date, is also referred to ''A. jimmadseni''.<ref name=DJC20/>

The completeness, preservation, and scientific importance of this skeleton gave "Big Al" its name. The individual itself was below the average size for ''Allosaurus fragilis'',<ref name=BBbigal/> as it was a subadult estimated at only 87%&nbsp;grown.<ref name=RRH02>{{cite journal |last=Hanna |first=Rebecca R. |year=2002 |title=Multiple injury and infection in a sub-adult theropod dinosaur (''Allosaurus fragilis'') with comparisons to allosaur pathology in the Cleveland-Lloyd Dinosaur Quarry Collection |journal=Journal of Vertebrate Paleontology |volume=22 |issue=1 |pages=76–90 |doi=10.1671/0272-4634(2002)022[0076:MIAIIA]2.0.CO;2 |issn=0272-4634|title-link=Cleveland-Lloyd Dinosaur Quarry |s2cid=85654858 }}</ref> The specimen was described by Breithaupt in 1996.<ref name=BB96/> Nineteen of its bones were broken or showed signs of serious infection, which may have contributed to "Big Al's" death. [[Paleopathology|Pathologic]] bones included five ribs, five vertebrae, and four bones of the feet. Several of its damaged bones showed signs of [[osteomyelitis]], a severe bone infection. A particular problem for the living animal was infection and trauma to the right foot that probably affected movement and may have also predisposed the other foot to injury because of a change in gait. "Big Al" had an infection on the first phalanx on the third toe that was afflicted by an [[involucrum]]. The infection was long-lived, perhaps up to six months.<ref name=RRH02/><ref>{{Cite journal |journal=PaleorXiv |last=Wilkin |first=Jack |date=November 24, 2019 |title=Review of Pathologies on MOR 693: An Allosaurus from the Late Jurassic of Wyoming and Implications for Understanding Allosaur Immune Systems |url=https://osf.io/f3rh6 |doi=10.31233/osf.io/f3rh6|s2cid=242466868 }}</ref> "Big Al II" is also known to have multiple injuries.<ref>{{cite journal | last1 = Foth | first1 = C. | last2 = Evers | first2 = S. | last3 = Pabst | first3 = B. | last4 = Mateus | first4 = O. | last5 = Flisch | first5 = A. | last6 = Patthey | first6 = M. | last7 = Rauhut | first7 = O. W. M. | year = 2015 | title = New insights into the lifestyle of ''Allosaurus'' (Dinosauria: Theropoda) based on another specimen with multiple pathologies | journal = PeerJ | volume = 3 | page = e824v1 | doi=10.7717/peerj.940| pmid = 26020001 | pmc = 4435507 | doi-access = free }}</ref>

===Portuguese discoveries===

[[File:Cliffs of Lourinhã Formation outcrops.png|thumb|right|Cliffs of [[Lourinhã Formation]] outcrops, Portugal]] 
In 1988, during construction works of a warehouse, a skeleton of a large theropod was discovered near the village of Andrés, [[Leiria District]], [[Portugal]].<ref name="PMetal99"/><ref name=":3">{{Cite journal |last1=Malafaia |first1=E. |last2=Ortega |first2=F. |last3=Escaso |first3=F. |last4=Dantas |first4=P. |last5=Pimentel |first5=N. |last6=Gasulla |first6=J. M. |last7=Ribeiro |first7=B. |last8=Barriga |first8=F. |last9=Sanz |first9=J. L. |date=December 10, 2010 |title=Vertebrate fauna at the Allosaurus fossil-site of Andrés (Upper Jurassic), Pombal, Portugal |url=https://revistas.ucm.es/index.php/JIGE/article/view/JIGE1010220193A |journal=Journal of Iberian Geology |language=es |volume=36 |issue=2 |pages=193–204 |doi=10.5209/rev_JIGE.2010.v36.n2.7 |issn=1886-7995|doi-access=free |bibcode=2010JIbG...36..193M }}</ref> The Andrés quarry is included in the Bombarral Formation ("Grés Superiores"). The lower part of this formation is diachronic with the [[Alcobaça Formation]] in the northen [[Lusitanian Basin]], and is dated to the Early [[Tithonian]]. This specimen was reported in 1999 as the first occurrence of ''Allosaurus fragilis'' outside North America.<ref name="PMetal99"/> The specimen, labeled MNHNUL/AND.001, is deposited in the [[National Museum of Natural History and Science, Lisbon]]. It consists of a partial skeleton, composed of an incomplete right quadrate, several vertebrae and chevrons, several dorsal ribs and gastralia, a partial pelvis, most of the hind limbs and several indeterminate fragments.<ref name="PMetal99"/> In 2003, Miguel Telles Antunes and Octávio Mateus published a review of the dinosaurs from Portugal, where they assigned the Andrés specimen to ''Allosaurus'' sp.<ref name=":4">{{Cite journal |last1=Antunes |first1=Miguel Telles |last2=Mateus |first2=Octávio |date=2003 |title=Dinosaurs of Portugal |journal=Palevol |volume=2 |issue=1 |pages=77–95|doi=10.1016/S1631-0683(03)00003-4 |bibcode=2003CRPal...2...77A }}</ref>

The [[Guimarota]] coal mine in [[Leiria District|Leiria]], [[Portugal]], produced plenty of remains of micro-vertebrates while it was being explored.<ref>Martin, T. & Krebs, B. 2000 ''Guimarota. A Jurassic ecosystem.'' Munich: Dr Friedrich Pfeil.</ref> The Guimarota beds belong to the [[Alcobaça Formation]], and are dated of the Late [[Kimmeridgian]]. In 2005, Oliver Rauhut and Regina Fechner describe the right maxilla of a juvenile theropod (IPFUB Gui Th 4) from the [[Guimarota]] mine, that was stored in the collections of the Institute of Geological Sciences of the [[Free University of Berlin]]. They attribute the maxilla to ''Allosaurus'' sp. based on the large maxillary fenestra and coeval presence of the other ''Allosaurus'' specimens.<ref name=":5">{{Cite journal |last1=Rauhut |first1=Oliver W. M |last2=Fechner |first2=Regina |date=June 7, 2005 |title=Early development of the facial region in a non-avian theropod dinosaur |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=272 |issue=1568 |pages=1179–1183 |doi=10.1098/rspb.2005.3071 |issn=0962-8452 |pmc=1559819 |pmid=16024380}}</ref> This specimen allowed the authors to conclude that the development of paranasal pneumacity in theropods is [[Heterochrony|heterochronic]], with juveniles having more pronouced pneumaticity than adults.<ref name=":5"/>

{{multiple image
|direction = horizontal
|align = right
|total_width = 300
|image1 = Allosaurus europaeus ML415 skull.png
|alt1 = 
|image2 = A. europaeus material.png
|alt2 =
|footer = ''A. europaeus'' holotype skull with diagram showing preserved elements
}}

In 2006, a new species of ''Allosaurus'', ''A. europaeus'', was reported based a specimen found in a beach near Vale Frades, [[Lourinhã]], [[Portugal]].<ref name="OMetal06">{{cite book |last1=Mateus |first1=Octávio |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |last2=Walen, Aart |last3=Antunes, Miguel Telles |publisher=New Mexico Museum of Natural History and Science |year=2006 |editor=Foster, John R. |series=New Mexico Museum of Natural History and Science Bulletin, '''36''' |location=Albuquerque, New Mexico |pages=123–129 |chapter=The large theropod fauna of the Lourinha Formation (Portugal) and its similarity to that of the Morrison Formation, with a description of a new species of ''Allosaurus'' |editor2=Lucas, Spencer G.}}</ref> The specimen, labeled ML415, is deposited in the [https://museulourinha.org/ Lourinhã Museum], and consists of a partial skull, three cervical vertebrae and cervical ribs. It was found in rocks of the Praia Azul Member of the [[Lourinhã Formation]], which in that sector is dated to the Early [[Tithonian]].<ref>{{Cite journal |last1=Mateus |first1=O. |last2=Dinis |first2=J. |last3=Cunha |first3=P. P. |date=September 30, 2017 |title=The Lourinhã Formation: the Upper Jurassic to lower most Cretaceous of the Lusitanian Basin, Portugal – landscapes where dinosaurs walked |url=http://cienciasdaterra.novaidfct.pt/index.php/ct-esj/article/view/355 |journal=Ciências da Terra - Earth Sciences Journal |volume=19 |issue=1 |pages=75–97 |doi=10.21695/cterra/esj.v19i1.355|hdl=10316/79879 |hdl-access=free }}</ref>

In 2005, the Andrés quarry was reactivated for further prospection, which yielded remains of a diverse vertebrate fauna and new ''Allosaurus'' remains.<ref name="MDOE07">{{cite journal |last1=Malafaia |first1=Elisabete |last2=Dantas, Pedro |last3=Ortega, Francisco |last4=Escaso, Fernando |year=2007 |title=Nuevos restos de ''Allosaurus fragilis'' (Theropoda: Carnosauria) del yacimiento de Andrés (Jurásico Superior; centro-oeste de Portugal) |trans-title=New remains of ''Allosaurus fragilis'' (Theropoda: Carnosauria) of the Andrés deposit (Upper Jurassic; central-west Portugal) |url=http://www.dfmf.uned.es/~fortega/uned_fo_pdf/2007_Malafaia_etal_EJIP07.pdf |url-status=live |journal=Cantera Paleontológica |language=es, en |pages=255–271 |archive-url=https://ghostarchive.org/archive/20221009/http://www.dfmf.uned.es/~fortega/uned_fo_pdf/2007_Malafaia_etal_EJIP07.pdf |archive-date=October 9, 2022}}</ref><ref name=":3"/> These new remains (such as a partial right frontal, MNHNUL/AND.001/062), along with further preparation of the original Andrés specimen, allowed for a more detailed comparison with other ''Allosaurus'' species.<ref name="MDOE07"/> The authors concluded that the Andrés specimen is compatible with the diagnosis of ''A. fragilis'', and also disputed the attribution of the Vale Frades specimen to a new species, claiming that the autapomorphies proposed in the diagnosis of ''A. europaeus'' can be explained by individual variation.<ref name="MDOE07"/> In 2010, new ''Allosaurus'' elements from the Andrés quarry are reported, including new cranial remains such as a right quadrate-quadratojudal, two lacrimals, a right dentary, a right frontal, the posterior end of the right mandible and a complete braincase. A second complete left ilium suggests the presence of a second ''Allosaurus'' individual in the quarry, larger than the first.<ref name=":3"/> The authors once again claim that ''A. europaeus'' should be considered a ''[[nomen dubium]]'' until a more detailed description of the Vale Frades specimen is published.<ref name=":3"/>

A detailed description of the remains of the Andrés specimen was published on the doctoral thesis of Elisabete Malafaia.<ref name=":6">Malafaia, E. (2017). ''Phylogenetic analysis, paleoenvironmental and paleobiogeographic interpretation of theropod dinosaurs from the Upper Jurassic of the Lusitanian Basin'' [Doctoral Thesis, Universidade de Lisboa]. <nowiki>https://repositorio.ulisboa.pt/handle/10451/35031</nowiki></ref> The remains, catalogued as MNHN/UL.AND.#, were collected between 1988 and 2010, and include cranial elements (such as the maxilla, nasal, lacrimals, prefrontal, postorbitals, frontals, palatines, quadrate, quadratojugal, squamosal, vomer, braincase, articular, surangulars, prearticular, angulars, supradentary and coronoid, isolated mesial and lateral teeth) and postcranial elements (intercentrum of the atlas, dorsal, sacral and caudal vertebrae, cervical and dorsal ribs, chevrons, coracoid, ilium, pubes, femora, tibiae, fibulae, astragalus and calcaneum, distal tarsal III, second, third, and fourth metatarsals, and several phalanges).<ref name=":6"/> Duplicate elements reported in the thesis include the previously mentioned left ilium, a fragmentary pubic peduncle in articulation with the pubes, and a right frontal, caudal vertebra, and pedal phalanges of a third much smaller individual. The author claims that the Andrés specimens present noticeable differences with both ''A. fragilis'' and the type specimen of ''A. europaeus'', but tentatively assigns it to ''Allosaurus'' cf. ''europaeus'', pending the discovery of more specimens that allow the comparison between the two.<ref name=":6"/>

In 2024, Burigo and Mateus publish a redescription and revised diagnosis of the Vale Frades specimen.<ref name=":2"/> The authors report new elements, such as the atlas-axis, coronoid, new teeth and rib fragments, and confirm the validity of the species. A specimen-level phylogenetic analysis using scored cranial characters was performed. The authors claim that the Andrés specimen is attributable to ''A. europaeus'', and that ''A. europaeus'' is more closely related to ''A. jimmadsenni'' than to ''A. fragilis''.<ref name=":2"/>

In 2025, Malafaia and colleagues publish a detailed description of the cranial elements of the Andrés specimen in a scientific journal and suggest that ''A. europaeus'' is synonymous with ''A. fragilis''.<ref name=Malafaia2025>{{Cite journal |last=Malafaia |first=Elisabete |last2=Dantas |first2=Pedro |last3=Escaso |first3=Fernando |last4=Mocho |first4=Pedro |last5=Ortega |first5=Francisco |date=2025-05-01 |title=Cranial osteology of a new specimen of Allosaurus Marsh, 1877 (Theropoda: Allosauridae) from the Upper Jurassic of Portugal and a specimen-level phylogenetic analysis of Allosaurus |url=https://doi.org/10.1093/zoolinnean/zlaf029 |journal=Zoological Journal of the Linnean Society |volume=204 |issue=1 |pages=zlaf029 |doi=10.1093/zoolinnean/zlaf029 |issn=0024-4082}}</ref> 

===Species===
[[File:Skulls of Allosaurus species.png|thumb|upright|Diagram comparing skulls of three recognized species; ''A. fragilis'' (A), ''A. jimmadseni'' (B), ''A. europaeus'' (C)]]
Seven species of ''Allosaurus'' have been named: ''A. anax'',<ref name="DEA24"/> ''A. amplus'',<ref>{{cite journal | last1 = Galton | first1 = Peter M. | last2 = Carpenter | first2 = Kenneth | last3 = Dalman | first3 = Sebastian G. | year = 2015 | title = The holotype pes of the Morrison dinosaur ''Camptonotus amplus'' Marsh, 1879 (Upper Jurassic, western USA) – is it ''Camptosaurus'', Sauropoda or ''Allosaurus''? | journal = Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen | volume = 275 | issue = 3| pages = 317–335 | doi = 10.1127/njgpa/2015/0467 |doi-access=free| bibcode = 2015NJGPA.275..317G }}</ref> ''A. atrox'',<ref name=DJC00/> ''A. europaeus'',<ref name=OMetal06/> the [[type species]] ''A. fragilis'',<ref name=HMC04/> ''A. jimmadseni''<ref name=DJC20>{{cite journal |last1=Chure |first1=D.J. |last2=Loewen |first2=M.A. |year=2020 |title=Cranial anatomy of ''Allosaurus jimmadseni'', a new species from the lower part of the Morrison Formation (Upper Jurassic) of Western North America |journal=PeerJ |volume=8 |page=e7803 |doi=10.7717/peerj.7803|pmid=32002317 |pmc=6984342 |doi-access=free }}</ref><ref name=DJC00/> and ''A. lucasi''.<ref>{{cite journal | last1 = Dalman | first1 = Sebastian G. | year = 2014 | title = Osteology of a large allosauroid theropod from the Upper Jurassic (Tithonian) Morrison Formation of Colorado, USA | url = https://vjs.pgi.gov.pl/article/view/26617 | journal = Volumina Jurassica | volume = 12 | issue = 2 | pages = 159–180 | doi = <!-- none --> | archive-date = November 9, 2021 | access-date = September 30, 2020 | archive-url = https://web.archive.org/web/20211109005352/https://vjs.pgi.gov.pl/article/view/26617 | url-status = live }}</ref> Among these (excluding ''A. anax'', which was named in 2024), Daniel Chure and Mark Loewen in 2020 only recognized the species ''A. fragilis'', ''A. europaeus'', and the newly-named ''A. jimmadseni'' as being valid species.<ref name=DJC20/> Some studies have suggested that ''A. europaeus'' does not show any unique characters compared to the North American species,<ref name="MDOE07"/><ref>{{Cite journal |last1=Evers |first1=Serjoscha W. |last2=Foth |first2=Christian |last3=Rauhut |first3=Oliver W.M. |date=February 7, 2020 |title=Notes on the cheek region of the Late Jurassic theropod dinosaur ''Allosaurus'' |journal=PeerJ |volume=8 |pages=e8493 |doi=10.7717/peerj.8493 |issn=2167-8359 |pmc=7008823 |pmid=32076581 |doi-access=free }}</ref><ref name=Malafaia2025/> though other authors have suggested that the species is valid and has a number of distinguishing characters.<ref name=":2">{{Cite journal |last1=Burigo |first1=André |last2=Mateus |first2=Octávio |date=January 2025 |title=''Allosaurus europaeus'' (Theropoda: Allosauroidea) Revisited and Taxonomy of the Genus |journal=Diversity |language=en |volume=17 |issue=1 |pages=29 |doi=10.3390/d17010029 |doi-access=free |issn=1424-2818}}</ref>

''A. fragilis'' is the type species and was named by Marsh in 1877.<ref name=OCM77/> It is known from the remains of at least 60 individuals, all found in the [[Kimmeridgian]]–[[Tithonian]] [[Upper Jurassic]]-age Morrison Formation of the United States, spread across [[Colorado]], [[Montana]], [[New Mexico]], [[Oklahoma]], [[South Dakota]], Utah, and Wyoming.<ref name=HMC04/> Details of the [[humerus]] (upper arm) of ''A. fragilis'' have been used as diagnostic among Morrison theropods,<ref name=JM76/> but ''A. jimmadseni'' indicates that this is no longer the case at the species level.<ref name=DJC00/>

''A. jimmadseni'' has been scientifically described based on two nearly complete skeletons. The first specimen to wear the identification was unearthed in Dinosaur National Monument in northeastern Utah, with the original "Big Al" individual subsequently recognized as belonging to the same species.<ref name=DJC20/><ref name=DJC00/><ref name=DFG03>{{cite book |last=Glut |first=Donald F. |title=Dinosaurs: The Encyclopedia. 3rd Supplement |year=2003 |publisher=McFarland & Co. |location=Jefferson, North Carolina |isbn=978-0-7864-1166-5 |pages=[https://archive.org/details/dinosaursencyclo00glut_2/page/221 221–233] |chapter=Allosaurus |chapter-url=https://archive.org/details/dinosaursencyclo00glut_2 |url=https://archive.org/details/dinosaursencyclo00glut_2/page/221 }}</ref><ref>{{Cite web|url=https://phys.org/news/2020-01-species-allosaurus-utah.html|title=New species of Allosaurus discovered in Utah|website=phys.org|access-date=January 24, 2020|archive-date=November 9, 2021|archive-url=https://web.archive.org/web/20211109005406/https://phys.org/news/2020-01-species-allosaurus-utah.html|url-status=live}}</ref> This species differs from ''A. fragilis'' in several anatomical details, including a [[jugal]] (cheekbone) with a straight lower margin. Fossils are confined to the Salt Wash Member of the Morrison Formation, with ''A. fragilis'' only found in the higher Brushy Basin Member.<ref name=LSCC03>{{cite journal |last1=Loewen |first1=Mark A. |last2=Sampson, Scott D. |last3=Carrano, Matthew T. |last4= Chure, Daniel J. |year=2003 |title=Morphology, taxonomy, and stratigraphy of ''Allosaurus'' from the Upper Jurassic Morrison Formation |journal=Journal of Vertebrate Paleontology |volume=23 |issue=3|page=72A | doi = 10.1080/02724634.2003.10010538 |s2cid=220410105 }}</ref> However, stratigraphic work done by Suzannah Maidment found that both species were actually coeval and were instead segregated by geography, with ''A. fragilis'' mostly found in the southern parts of the Morrison Formation, while ''A. jimmadseni'' is largely found in the northern parts.<ref>{{cite journal |title=Diversity through time and space in the Upper Jurassic Morrison Formation, western U.S.A. |journal=Journal of Vertebrate Paleontology |date=2023 |doi=10.1080/02724634.2024.2326027 |url=https://www.tandfonline.com/doi/full/10.1080/02724634.2024.2326027 |last1=Maidment |first1=Susannah C. R. |volume=43 |issue=5 |url-access=subscription }}</ref> The specific name ''jimmadseni'' is named in honor of Madsen, for his contributions to the taxonomy of the genus, notably for his 1976 work.<ref name="DJC20" />

[[File:Allosaurus anax (holotype, OMNH 1771).png|thumb|left|upright=0.9|Holotype postorbital of ''A. anax'']]
''A. fragilis'', ''A. jimmadseni'', ''A. anax'', ''A. amplus'', and ''A. lucasi'' are all known from remains discovered in the [[Kimmeridgian]]–[[Tithonian]] [[Upper Jurassic]]-age Morrison Formation of the United States, spread across [[Colorado]], [[Montana]], [[New Mexico]], [[Oklahoma]], [[South Dakota]], [[Utah]] and [[Wyoming]]. ''A. fragilis'' is regarded as the most common, known from the remains of at least 60 individuals.<ref name=HMC04/> For a while in the late 1980s and early 1990s, it was common to recognize ''A. fragilis'' as the short-snouted species, with the long-snouted taxon being ''A. atrox.''<ref name=GSP88/><ref name=LG93>{{cite book |last1=Lessem |first1=Don |last2=Glut, Donald F. |year=1993 |title=The Dinosaur Society's Dinosaur Encyclopedia |chapter=Allosaurus |pages=[https://archive.org/details/dinosaursocietys00less/page/19 19–20] |publisher=Random House |isbn=978-0-679-41770-5 |oclc=30361459 |chapter-url=https://archive.org/details/dinosaursocietys00less/page/19 }}</ref> However, subsequent analysis of specimens from the Cleveland-Lloyd Dinosaur Quarry, Como Bluff, and Dry Mesa Quarry showed that the differences seen in the Morrison Formation material could be attributed to individual variation.<ref name=DKS96/><ref name=DKS99/> A study of skull elements from the Cleveland-Lloyd site found wide variation between individuals, calling into question previous species-level distinctions based on such features as the shape of the lacrimal horns and the proposed differentiation of ''A. jimmadseni'' based on the shape of the [[jugal]].<ref name=KC2010/> ''A. anax'' was described and named in 2024 from several fossils representing various skeleton parts, the holotype being a [[postorbital]] numbered as OMNH 1771. This species is characterized by the lack of rugose ornamentation on the postorbital, the dorsal vertebrae with hourglass-shaped centra and [[Skeletal pneumaticity|pneumatic]] foramina, and other features of the postorbital, cervical vertebrae, and [[fibula]]. The specific name comes from the Ancient Greek ἄναξ (''anax'', "king", "lord" or "tribal chief"), and is intended to be an updated reference to the now [[Nomen dubium|dubious]] saurischian genus ''[[Saurophaganax]]'', to which the fossils were previously attributed.<ref name="DEA24">{{Cite journal |last1=Danison |first1=Andrew |last2=Wedel |first2=Mathew |last3=Barta |first3=Daniel |last4=Woodward |first4=Holly |last5=Flora |first5=Holley |last6=Lee |first6=Andrew |last7=Snively |first7=Eric |year=2024 |title=Chimerism in specimens referred to ''Saurophaganax maximus'' reveals a new species of ''Allosaurus'' (Dinosauria, Theropoda) |journal=Vertebrate Anatomy Morphology Palaeontology |language=en |volume=12 |doi=10.18435/vamp29404 |issn=2292-1389 |doi-access=free}}</ref>

The ''Allosaurus'' material from Portugal has a controversial taxonomic research history. The Andrés ''Allosaurus'' specimens, consisting of very complete cranial and post-cranial remains, have been attributed to ''A. fragilis'',<ref name="PMetal99"/><ref>Dantas, P., Pérez-Moreno, B., Chure, D., Silva, C. M. da, Santos, V. F., Póvoas, L., Cachão, M., Sanz, J., Pires, C., Bruno, G., Ramalheiro, G., & Galopim De Carvalho, A. M. (1999). O dinossáurio carnívoro ''Allosaurus fragilis'' no Jurássico superior português. ''Al-Madan'', ''8'', 23–28. <nowiki>https://doi.org/10.13140/RG.2.1.3224.1762</nowiki></ref><ref name="MDOE07"/> ''A.'' sp<ref name=":4"/>'', A. europaeus''<ref name="OMetal06"/> and ''A.'' cf. ''europaeus''.<ref name=":6"/> The Vale Frades ''Allosaurus'', consisting of a partial skull and cervical vertebrae and ribs, is the type specimen of ''A. europaeus'',<ref name="OMetal06"/> although the validity of that species has been previously questioned.<ref name="MDOE07"/><ref name=":3"/> In 2024, a revised diagnosis of ''A. europaeus'' was published, confirming the validity of the species.<ref name=":2"/> The specific affinities of the Andrés specimens are still unclear.

The issue of species and potential synonyms was historically complicated by the [[Type (biology)|type specimen]] of ''Allosaurus fragilis'' ([[Peabody Museum of Natural History|YPM]] 1930) being extremely fragmentary, consisting of a few incomplete vertebrae, limb fragments, rib fragments, and a single tooth. Because of this, several scientists have interpreted the type specimen as potentially dubious, meaning the genus ''Allosaurus'' itself or at least the species ''A. fragilis'' would be a ''nomen dubium'' ("dubious name", based on a specimen too incomplete to compare to other specimens or to classify). To address this situation, [[Gregory S. Paul]] and [[Kenneth Carpenter]] ([[2010 in paleontology|2010]]) submitted a petition to the [[International Commission on Zoological Nomenclature|ICZN]] to have the name ''A. fragilis'' officially transferred to the more complete specimen USNM 4734 (as a [[neotype]]),<ref name="GPKC2010">{{cite journal |last1=Paul |first1=Gregory S. |author-link1=Gregory S. Paul |last2=Carpenter |first2=Kenneth |author-link2=Kenneth Carpenter |year=2010 |title=''Allosaurus'' Marsh, 1877 (Dinosauria, Theropoda): proposed conservation of usage by designation of a neotype for its type species ''Allosaurus fragilis'' Marsh, 1877 |url=http://gspauldino.com/images/BZN67(1)Case3506.pdf |journal=Bulletin of Zoological Nomenclature |volume=67 |issue=1 |pages=53–56 |doi=10.21805/bzn.v67i1.a7 |s2cid=81735811 |archive-date=August 9, 2017 |access-date=September 28, 2018 |archive-url=https://web.archive.org/web/20170809142848/http://gspauldino.com/images/BZN67(1)Case3506.pdf |url-status=live }}</ref> a decision that was ratified by the ICZN on December 29, 2023.<ref>{{cite journal |title=Opinion 2486 (Case 3506) – Allosaurus Marsh, 1877 (Dinosauria, Theropoda): usage conserved by designation of a neotype for its type species Allosaurus fragilis Marsh, 1877 |journal=The Bulletin of Zoological Nomenclature |date=December 2023 |volume=80 |issue=1 |pages=65–68 |doi=10.21805/bzn.v80.a015 |url=https://bioone.org/journals/the-bulletin-of-zoological-nomenclature/volume-80/issue-1/bzn.v80.a015/Opinion-2486-Case-3506--Allosaurus-Marsh-1877-Dinosauria-Theropoda/10.21805/bzn.v80.a015.short |issn=0007-5167|url-access=subscription }}</ref>

Teeth of indeterminate species of ''Allosaurus'' have been reported from Tönniesberg and Kahlberg in [[Saxony]], Germany, dating to the upper Kimmeridigian.<ref name=":2"/>

===Synonyms===
[[File:Creosaurus.jpg|thumb|Holotype material of ''Creosaurus atrox'']]
''Creosaurus'', ''Epanterias'', and ''Labrosaurus'' are provisionally regarded as junior synonyms of ''Allosaurus'',<ref name=HMC04/> though the latter two require new analyses to clarify their specific status.<ref name=":2"/> Most of the species that are regarded as synonyms of ''A. fragilis'', or that were misassigned to the genus, are obscure and based on very scrappy remains. One exception is ''Labrosaurus ferox'', named in [[1884 in paleontology|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.<ref name=OCM84>{{cite journal |last=Marsh |first=Othniel Charles |year=1884 |title=Principal characters of American Jurassic dinosaurs. Part VIII |journal=American Journal of Science |series=Series 3 |volume=27 |issue=160 |pages=329–340 |doi=10.2475/ajs.s3-27.160.329 |url=https://zenodo.org/record/1450066 |bibcode=1884AmJS...27..329M |s2cid=131076004 |archive-date=December 16, 2021 |access-date=June 28, 2019 |archive-url=https://web.archive.org/web/20211216182115/https://zenodo.org/record/1450066 |url-status=live }}</ref> Later researchers suggested that the bone was [[Pathology|pathologic]], showing an injury to the living animal,<ref name=CWG20/> and that part of the unusual form of the rear of the bone was due to plaster reconstruction.<ref name=MW00>{{cite book |last1=Madsen |first1=James H. |last2=Welles, Samuel P. |title=Ceratosaurus (Dinosauria, Theropoda), a Revised Osteology |year=2000 |series=Miscellaneous Publication, '''00-2''' |publisher=Utah Geological Survey }}</ref> It is now regarded as an example of ''A. fragilis''.<ref name=HMC04/>

In his [[1988 in paleontology|1988]] book, ''Predatory Dinosaurs of the World'', the freelance artist & author Gregory S. Paul proposed that ''A. fragilis'' had tall pointed horns and a slender build compared to a postulated second species ''A. atrox'', as well as not being a [[Sexual dimorphism|different sex]] due to rarity.<ref name=GSP88/> ''Allosaurus atrox'' was originally named by Marsh in [[1878 in paleontology|1878]] as the type species of its own genus, ''Creosaurus'', and is based on YPM 1890, an assortment of bones that includes a couple of pieces of the skull, portions of nine tail vertebrae, two hip vertebrae, an [[Ilium (bone)|ilium]], and ankle and foot bones.<ref name=OCM78/> Although the idea of two common Morrison allosaur species was followed in some semi-technical and popular works,<ref name=LG93/> the [[2000 in paleontology|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.<ref name=DJC00/>

"Allosaurus agilis", seen in Zittel, [[1887 in paleontology|1887]], and Osborn, [[1912 in paleontology|1912]], is a typographical error for ''A. fragilis.''<ref name=DJC00/> "Allosaurus ferox" is a typographical error by Marsh for ''A. fragilis'' in a figure caption for the partial skull YPM 1893<ref name=OCM96>{{cite journal |last=Marsh |first=Othniel Charles|year=1896 |title=The dinosaurs of North America |journal=United States Geological Survey, 16th Annual Report, 1894–95 |volume=55 |pages=133–244}}</ref> and YPM 1893 has been treated as a specimen of ''A fragilis''.<ref name=HMC04/> Likewise, "Labrosaurus fragilis" is a typographical error by Marsh ([[1896 in paleontology|1896]]) for ''Labrosaurus ferox''.<ref name=MW00/> "A. whitei" is a ''[[nomen nudum]]'' coined by Pickering in 1996 for the complete ''Allosaurus'' specimens that Paul referred to ''A. atrox''.<ref name=DJC00/>

"Madsenius" was coined by [[David Lambert (author)|David Lambert]] in [[1990 in paleontology|1990]],<ref>{{cite web |title=MADSENIUS |url=http://www.dinoruss.com:80/de_4/5a8d03b.htm |website=dinoruss.com |access-date=December 18, 2020 |archive-url=https://web.archive.org/web/20080627012337/http://www.dinoruss.com/de_4/5a8d03b.htm |archive-date=June 27, 2008 |date=March 27, 2006 |url-status=live }}</ref> being based on remains from Dinosaur National Monument assigned to ''Allosaurus'' or ''Creosaurus'' (a synonym of ''Allosaurus''), and was to be described by paleontologist [[Robert T. Bakker|Robert Bakker]] as "Madsenius trux".<ref>Lambert, D. (1990) ''The Dinosaur Data Book'', Facts on File, Oxford, England: 320 pp.</ref> 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 in paleontology|1920]] reconstruction of USNM 4734.<ref name="database">{{cite web |title=Carnosauria |url=https://www.theropoddatabase.com/Carnosauria.htm#Allosaurusfragilis |access-date=December 18, 2020 |website=theropoddatabase.com |archive-date=May 13, 2021 |archive-url=https://web.archive.org/web/20210513103854/https://theropoddatabase.com/Carnosauria.htm#Allosaurusfragilis |url-status=live }}</ref>

"Wyomingraptor" was informally coined by 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 as a ''nomen nudum'', with the remains referable to ''Allosaurus''.<ref name=database/><ref>Bakker, 1997. Raptor family values: Allosaur parents brought great carcasses into their lair to feed their young. In Wolberg, Sump and Rosenberg (eds). Dinofest International, Proceedings of a Symposium, Academy of Natural Sciences. 51–63.</ref><ref>{{cite web|url=http://dml.cmnh.org/1997Apr/msg00586.html|title=Re: Raptor question|website=dml.cmnh.org|access-date=January 1, 2019|archive-date=June 24, 2021|archive-url=https://web.archive.org/web/20210624195650/http://dml.cmnh.org/1997Apr/msg00586.html|url-status=dead}}</ref>

===Formerly assigned species and fossils===
[[File:Antrodemus.jpg|thumb|left|''[[Antrodemus]] valens'' holotype tail vertebra (above) compared to the same of ''Allosaurus'' (below)]]
Several species initially classified within or referred to ''Allosaurus'' do not belong within the genus. ''A. medius'' was named by Marsh in 1888 for various specimens from the [[Early Cretaceous]] [[Arundel Formation]] of [[Maryland]],<ref name=OCM88>{{cite journal |last=Marsh |first=Othniel Charles |year=1888 |title=Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation |journal=American Journal of Science |series=Series 3 |volume=35 |issue=205 |pages=89–94 |doi=10.2475/ajs.s3-35.205.89 |url=https://zenodo.org/record/1450082 |bibcode=1888AmJS...35...89M |s2cid=130879860 |archive-date=January 17, 2021 |access-date=June 28, 2019 |archive-url=https://web.archive.org/web/20210117164000/https://zenodo.org/record/1450082 |url-status=live }}</ref> although most of the remains were removed by [[R. S. Lull|Richard Swann Lull]] to the new ornithopod species ''[[Dryosaurus|Dryosaurus grandis]]'', except for a tooth.<ref name=RSL11>{{cite journal |last=Lull |first=Richard Swann | year=1911 |title=The Reptilia of the Arundel Formation |journal=Maryland Geological Survey: Lower Cretaceous |pages=173–178}}</ref> It was transferred to ''Antrodemus'' by Oliver Hay in 1902, but Hay later clarified that this was an inexplicable error on his part.<ref>{{Cite journal |last=Hay |first=Oliver Perry |date=1902 |title=Bibliography and catalogue of the fossil vertebrata of North America |url=https://pubs.er.usgs.gov/publication/b179 |journal=Bulletin |page=23 |doi=10.3133/b179 |bibcode=1902usgs.rept....1H |hdl=2346/65015 |hdl-access=free |archive-date=March 21, 2023 |access-date=March 21, 2023 |archive-url=https://web.archive.org/web/20230321191229/https://pubs.er.usgs.gov/publication/b179 |url-status=live }}</ref><ref>{{Cite journal |last=Hay |first=Oliver Perry |date=1908 |title=On certain genera and species of carnivorous dinosaurs, with special reference to Ceratosaurus nasicornis Marsh |url=http://repository.si.edu/xmlui/handle/10088/14046 |doi=10.5479/si.00963801.35-1648.351 |journal=Proceedings of the United States National Museum|volume=35 |issue=1648|pages=351–366|hdl=10088/14046 }}</ref> Gilmore considered the tooth nondiagnostic but transferred it to ''[[Dryptosaurus]]'', as ''D. medius''.<ref name=CWG20/> 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.<ref name=HMC04/> It may be closely related to ''[[Acrocanthosaurus]]''.<ref>{{cite web|url=http://theropoddatabase.com/Neotheropoda.htm#Allosaurusmedius|title=Neotheropoda|publisher=The Theropod Database|access-date=September 28, 2018|archive-date=May 24, 2021|archive-url=https://web.archive.org/web/20210524172840/https://theropoddatabase.com/Neotheropoda.htm#Allosaurusmedius|url-status=live}}</ref>

''Allosaurus valens'' is a new combination for ''Antrodemus valens'' used by Friedrich von Huene in 1932;<ref name=DJC00/> ''Antrodemus valens'' itself may also pertain to ''Allosaurus fragilis'',<ref name=HMC04/> as [[Charles W. Gilmore|Gilmore]] suggested in 1920.<ref name=CWG20/>

''A. lucaris'', another Marsh name, was given to a partial skeleton in 1878.<ref name=OCM78/> He later decided it warranted its own genus, ''Labrosaurus'',<ref name=OCM79/> but this has not been accepted, and ''A. lucaris'' is also regarded as another specimen of ''A. fragilis''.<ref name=HMC04/> ''Allosaurus lucaris'', is known mostly from vertebrae, sharing characters with ''Allosaurus''.<ref name="marsh1878">{{cite journal|last=Marsh|first=O.C.|year=1878|title=Notice of new dinosaurian reptiles |url=http://marsh.dinodb.com/marsh/Marsh%201878%20-%20Notice%20of%20new%20dinosaurian%20reptiles.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://marsh.dinodb.com/marsh/Marsh%201878%20-%20Notice%20of%20new%20dinosaurian%20reptiles.pdf |archive-date=October 9, 2022 |url-status=live|journal=American Journal of Science|volume=15 |issue=87 |pages=241–244|doi=10.2475/ajs.s3-15.87.241|bibcode=1878AmJS...15..241M|s2cid=131371457}}</ref> Paul and Carpenter stated that the type specimen of this species, YPM 1931, was from a younger age than ''Allosaurus'', and might represent a different genus. However, they found that the specimen was undiagnostic, and thus ''A. lucaris'' was a ''nomen dubium''.<ref name=GPKC2010/>

''Allosaurus sibiricus'' was described in 1914 by A. N. Riabinin on the basis of a bone, later identified as a partial fourth metatarsal, from the Early Cretaceous of [[Republic of Buryatia|Buryatia]], Russia.<ref name=ANNR14>{{cite journal |last=Riabinin |first=Anatoly Nikolaenvich |year=1914 |title=Zamtka o dinozavry ise Zabaykalya |journal=Trudy Geologichyeskago Muszeyah imeni Petra Velikago Imperatorskoy Academiy Nauk |volume=8 |issue=5 |pages=133–140 |language=ru}}</ref> It was transferred to ''Chilantaisaurus'' in 1990,<ref name=MKD90>{{cite book |last1=Molnar |first1=Ralph E. |last2=Kurzanov, Sergei M. |last3= Dong Zhiming |year=1990 |chapter=Carnosauria |editor=Weishampel, David B. |editor2=Dodson, Peter |editor3=Osmólska, Halszka |title=The Dinosauria |edition=1st |publisher=University of California Press |location=Berkeley |pages=169–209 |isbn=978-0-520-06727-1}}</ref> but is now considered a ''nomen dubium'' indeterminate beyond Theropoda.<ref name=":0">{{cite journal | last1 = Carrano | first1 = Benson | last2 = Sampson | year = 2012 | title = The phylogeny of Tetanurae (Dinosauria: Theropoda) | journal = Journal of Systematic Palaeontology | volume = 10 | issue = 2| pages = 211–300 | doi=10.1080/14772019.2011.630927| bibcode = 2012JSPal..10..211C | s2cid = 85354215 }}</ref>

''Allosaurus meriani'' was a new combination by George Olshevsky for ''[[Megalosaurus]] meriani'' Greppin, 1870, based on a tooth from the Late Jurassic of Switzerland.<ref name=JG70>{{cite journal |last=Greppin |first=J.B. |year=1870 |title=Description geologique du Jura bernois et de quelques districts adjacents |journal=Beiträge zur Geologischen Karte der Schweiz |volume=8 |pages=1–357 |language=fr}}</ref><ref>Olshevsky, 1978. The archosaurian taxa (excluding the Crocodylia). Mesozoic Meanderings. 1, 1–50.</ref> However, a recent overview of ''Ceratosaurus'' included it in ''Ceratosaurus'' sp.<ref name=MW00/>

''[[Apatodon|Apatodon mirus]]'', based on a scrap of vertebra Marsh first thought to be a mammalian jaw, has been listed as a synonym of ''Allosaurus fragilis''.<ref>Olshevsky, G., 1991, A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings 2, 196 pp</ref><ref name=DFG97/> However, it was considered indeterminate beyond Dinosauria by Chure,<ref name=DJC00/> 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.<ref>{{cite web|url=http://theropoddatabase.com/Non-theropods.htm#Apatodonmirus|title=Apatodonmirus|publisher=The Theropod Database|access-date=September 28, 2018|archive-date=May 18, 2021|archive-url=https://web.archive.org/web/20210518161057/https://theropoddatabase.com/Non-theropods.htm#Apatodonmirus|url-status=live}}</ref>

[[File:Clash of Titans Saurophaganax and Apatosaurus.jpg|thumb|upright|Mounted skeletons showing ''[[Saurophaganax]]'' as an ''Allosaurus''-like taxon attacking ''[[Apatosaurus]]'' sp., in [[Oklahoma Museum of Natural History]]. The latter dinosaur may be closer to the actual identity of ''Saurophaganax'', and the former instead represents ''A. anax'']]
''A. amplexus'' was named by [[Gregory S. Paul]] for giant Morrison allosaur remains, and included in his conception ''Saurophagus maximus'' (later ''Saurophaganax'').<ref name=GSP88/> ''A. amplexus'' was originally coined by Cope in 1878 as the type species of his new genus ''[[Epanterias]]'',<ref name=EDC78>{{cite journal |last=Cope |first=Edward Drinker |year=1878 |title=A new opisthocoelous dinosaur |journal=American Naturalist |volume=12 |issue=6 |pages=406–408 |doi=10.1086/272127|doi-access=free }}</ref> and is based on what is now AMNH 5767, parts of three vertebrae, a [[coracoid]], and a metatarsal.<ref name=OM21>{{cite journal |last1=Osborn |first1=Henry Fairfield |author-link1=Henry Fairfield Osborn |last2=Mook, Charles C. |year=1921 |title=''Camarasaurus'', ''Amphicoelias'', and other sauropods of Cope |journal=Memoirs of the American Museum of Natural History |series=New Series |volume=3 |issue=1 |pages=247–387 |bibcode=1919GSAB...30..379O |doi=10.1130/GSAB-30-379 |hdl=2027/mdp.39015042532476 |hdl-access=free }}</ref> Following Paul's work, this species has been accepted as a synonym of ''A. fragilis''.<ref name=HMC04/> A 2010 neotype designation by Greogry S. Paul and Kenneth Carpenter, however, suggested that ''Epanterias'' holotype is temporally younger than the ''A. fragilis'' type specimen, and that it is not the same taxon as the ''Allosaurus'' holotype.<ref name=GPKC2010/>

''A. maximus'' was a new combination by David K. Smith for Chure's ''Saurophaganax maximus'', a taxon created by Chure in 1995 for giant allosaurid remains from the Morrison of Oklahoma. These remains had been known as ''Saurophagus'', but that name was already in use, leading Chure to propose a substitute.<ref name=DJC95/> 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''.<ref name=DKS98/> This reassignment was rejected in a review of basal tetanurans.<ref name=HMC04/> A 2024 reassessment of fossil material assigned to ''Saurophaganax'' suggested that the holotype neural arch of this taxon could not confidently be assigned to a theropod, but that it exhibited some similarities to sauropods. Other ''Saurophaganax'' bones could be referred to diplodocid sauropods. As such, the researchers assigned the remaining theropod bones to a new species of ''Allosaurus'', ''A. anax''.<ref name="DEA24"/>

There are also several species left over from the synonymizations of ''Creosaurus'' and ''Labrosaurus'' with ''Allosaurus''. ''[[Capitalsaurus|Creosaurus potens]]'' was named by Lull in 1911 for a vertebra from the Early Cretaceous of Maryland.<ref name=RSL11/> It is now regarded as a dubious theropod.<ref name=HMC04/> ''Labrosaurus stechowi'', described in 1920 by Janensch based on isolated ''Ceratosaurus''-like teeth from the Tendaguru beds of Tanzania,<ref name=WJ20>{{cite journal |last=Janensch |first=Werner |year=1920 |title=Uber ''Elaphrosaurus bambergi'' und die Megalosaurier aus den Tendaguru-Schichten Deutsch-Ostafricas |journal=Sitzungsberichte Gesellschaft Naturforschender Freunde Berlin |volume=8 |pages=225–235}}</ref> was listed by [[Donald F. Glut]] as a species of ''Allosaurus'',<ref name=DFG97/> is now considered a dubious ceratosaurian related to ''[[Ceratosaurus]]''.<ref name=MW00/><ref name=TR04>Tykoski, Ronald S.; and Rowe, Timothy. (2004). "Ceratosauria", in ''The Dinosauria'' (2nd). 47–70.</ref> ''L. sulcatus'', named by Marsh in 1896 for a Morrison theropod tooth,<ref name=OCM96/> which like ''L. stechowi'' is now regarded as a dubious ''Ceratosaurus''-like ceratosaur.<ref name=MW00/><ref name=TR04/>

[[File:Allosaurus tendagurensis.jpg|thumb|left|''A. tendagurensis'' tibia, Naturkunde Museum Berlin]]
''A. tendagurensis'' was named in 1925 by [[Werner Janensch]] for a partial [[Tibia|shin]] (MB.R.3620) found in the Kimmeridgian-age [[Tendaguru Formation]] in [[Mtwara Region|Mtwara]], Tanzania.<ref name=WJ25>{{cite journal |last=Janensch |first=Werner |year=1925 |title=Die Coelurosaurier und Theropoden der Tendaguru-Schichten Deutsch-Ostafrikas |journal=Palaeontographica |issue=Suppl. 7 |volume=1 |pages=1–99 |language=de }}</ref> Although tabulated as a tentatively valid species of ''Allosaurus'' in the second edition of the Dinosauria,<ref name=HMC04/> subsequent studies place it as indeterminate beyond Tetanurae, either a carcharodontosaurian or megalosaurid.<ref name=OWMR05>{{cite journal |last=Rauhut |first=Oliver W.M. |year=2005 |title=Post-cranial remains of 'coelurosaurs' (Dinosauria, Theropoda) from the Late Jurassic of Tanzania |journal=Geological Magazine |volume=142 |issue=1 |pages=97–107 |doi=10.1017/S0016756804000330 |bibcode=2005GeoM..142...97R |s2cid=131517482 |url=http://edoc.hu-berlin.de/18452/22460 }}</ref><ref name=OR2011>{{cite journal |last=Rauhut |first=Oliver W. M. |title=Theropod dinosaurs from the Late Jurassic of Tendaguru (Tanzania) |journal=Special Papers in Palaeontology |volume=86 |pages=195–239 }}</ref> Although obscure, it was a large theropod, possibly around {{convert|10|m}} long and {{convert|2.5|t|}} in weight.<ref name=MMDML03/>

Kurzanov and colleagues in 2003 designated six teeth from Siberia as ''Allosaurus'' sp. (meaning the authors found the specimens to be most like those of ''Allosaurus'', but did not or could not assign a species to them).<ref name=KEG03>{{cite journal |last1=Kurzanov |first1=Sergei S. |last2=Efimov, Mikhail B. |last3= Gubin, Yuri M. |year=2003 |title=New archosaurs from the Jurassic of Siberia and Mongolia |journal=Paleontological Journal |volume=37 |issue=1 |pages=53–57}}</ref> They were reclassified as an indeterminate theropod.<ref name=":0"/> Also, reports of ''Allosaurus'' in [[Shanxi]], China go back to at least 1982.<ref name=DFG82>{{cite book |last=Glut |first=Donald F. |title=The New Dinosaur Dictionary |year=1982 |publisher=Citadel Press |location=Secaucus, NJ |isbn=978-0-8065-0782-8 |page=[https://archive.org/details/newdinosaurdicti00glut/page/44 44] |url=https://archive.org/details/newdinosaurdicti00glut/page/44 }}</ref> These were interpreted as ''[[Torvosaurus]]'' remains in 2012.<ref name=":0"/>

An [[Talus bone|astragalus]] (ankle bone) thought to belong to a species of ''Allosaurus'' was found at [[Cape Paterson, Victoria]] in Early Cretaceous beds in southeastern Australia. It was thought to provide evidence that Australia was a [[Refugium (population biology)|refugium]] for animals that had gone extinct elsewhere.<ref name=MFR81>{{cite journal |last1=Molnar |first1=Ralph E. |last2=Flannery, Timothy F. |last3= Rich, Thomas H.V. |year=1981 |title=An allosaurid theropod dinosaur from the Early Cretaceous of Victoria, Australia |journal=Alcheringa |volume=5 |pages=141–146 |doi=10.1080/03115518108565427 |issue=2 |bibcode=1981Alch....5..141M }}</ref> This identification was challenged by [[Samuel Paul Welles|Samuel Welles]], who thought it more resembled that of an [[Ornithomimidae|ornithomimid]],<ref name=SPW83>{{cite journal |last=Welles |first=Samuel P. |year=1983 |title=''Allosaurus'' (Saurischia, Theropoda) not yet in Australia |journal=Journal of Paleontology |volume=57 |issue=2 |page=196 }}</ref> but the original authors defended their identification.<ref name=MFR85>{{cite journal |last1=Molnar |first1=Ralph E. |last2=Flannery, Timothy F. |last3= Rich, Thomas H.V. |year=1985 |title=Aussie ''Allosaurus'' after all |journal=Journal of Paleontology |volume=59 |issue=6 |pages=1511–1535  }}</ref> With fifteen years of new specimens and research to look at, Daniel Chure reexamined the bone and found that it was not ''Allosaurus'', but could represent an allosauroid.<ref name=DJC98>{{cite journal |last=Chure |first=Daniel J. |year=1998 |title=A reassessment of the Australian ''Allosaurus'' and its implications for the Australian refugium concept |journal=Journal of Vertebrate Paleontology |volume=18 |issue=3, Suppl |pages=1–94 | doi = 10.1080/02724634.1998.10011116}}</ref> Similarly, Yoichi Azuma and [[Phil Currie]], in their description of ''[[Fukuiraptor]]'', noted that the bone closely resembled that of their new genus.<ref name=AC00>{{cite journal |last1=Azuma |first1=Yoichi |last2=Currie, Philip J. |year=2000 |title=A new carnosaur (Dinosauria: Theropoda) from the Lower Cretaceous of Japan |journal=Journal of Vertebrate Paleontology |volume=37 |issue=12 |pages=1735–1753 |doi=10.1139/e00-064 |bibcode=2000CaJES..37.1735A |url=http://doc.rero.ch/record/14299/files/PAL_E1450.pdf |archive-date=April 29, 2023 |access-date=January 3, 2023 |archive-url=https://web.archive.org/web/20230429154614/https://doc.rero.ch/record/14299/files/PAL_E1450.pdf |url-status=live }}</ref> This specimen is sometimes referred to as "[[List of informally named dinosaurs#Allosaurus robustus|Allosaurus robustus]]", an informal museum name.<ref name=DFG03/> It likely belonged to something similar to ''[[Australovenator]]'',<ref name=SHetal09>{{cite journal |last1=Hocknull |first1=Scott A. |last2=White, Matt A. |last3=Tischler, Travis R. |last4=Cook, Alex G. |last5=Calleja, Naomi D. |author6=Sloan, Trish |author7= Elliott, David A. |year=2009 |title=New Mid-Cretaceous (Latest Albian) Dinosaurs from Winton, Queensland, Australia |journal=PLOS ONE |volume=4 |issue=7 |doi=10.1371/journal.pone.0006190 |pages=e6190 |pmid=19584929 |pmc=2703565 |editor1-last=Sereno |editor1-first=Paul|bibcode=2009PLoSO...4.6190H |doi-access=free }}</ref> although one study considered it to belong to an [[abelisaur]].<ref name=agnolinetal2010>{{cite journal |last1=Agnolin |first1=F. L. |last2=Ezcurra, M. D. |last3=Pais, D. F. |last4= Salisbury, S. W. |year=2010 |title=A reappraisal of the Cretaceous non-avian dinosaur faunas from Australia and New Zealand: Evidence for their Gondwanan affinities |journal=Journal of Systematic Palaeontology |volume=8 |issue=2 |pages=257–300 |doi=10.1080/14772011003594870|bibcode=2010JSPal...8..257A |s2cid=130568551 |url=https://espace.library.uq.edu.au/view/UQ:206067/UQ206067.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://espace.library.uq.edu.au/view/UQ:206067/UQ206067.pdf |archive-date=October 9, 2022 |url-status=live }}</ref>

==Description==
[[File:Allosaurus size comparison.svg|thumb|left|The size range of ''Allosaurus'' compared with a human]]
''Allosaurus'' was a typical large [[theropod]], having a massive skull on a short neck, a long, slightly sloping tail, and reduced forelimbs. ''Allosaurus fragilis'', the best-known species, had an average length of {{cvt|8.5|m}} and mass of {{cvt|1.7|MT|ST}},<ref name=DFG97>{{cite book|chapter=Allosaurus|last=Glut|first=Donald F.|title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=105–117 |isbn=978-0-89950-917-4}}</ref><ref name=G.S.Paul2010>{{cite book |last=Paul |first=Gregory S. |year=2010 |title=The Princeton Field Guide to Dinosaurs |publisher=Princeton University Press |pages=94–96}}</ref> with the largest definitive ''Allosaurus'' specimen ([[American Museum of Natural History|AMNH]] 680) estimated at {{cvt|9.7|m}} long,<ref name=MMDML03>{{cite web|publisher=The Dinosaur Mailing List |url=http://dml.cmnh.org/2003Jul/msg00355.html |title=And the largest Theropod is... |last=Mortimer |first=Mickey |date=July 21, 2003 |access-date=September 8, 2007 |archive-url=https://web.archive.org/web/20100325195202/http://dml.cmnh.org/2003Jul/msg00355.html |archive-date=March 25, 2010 |url-status=live}}</ref> with an estimated weight of {{cvt|2.3|-|2.7|MT|ST}}.<ref name=MMDML03/><ref>{{cite journal|last1=Campione|first1=N. E.|last2=Evans|first2=D. C.|last3=Brown|first3=C. M.|last4=Carrano|first4=M. T.|date=2014|title=Body mass estimation in non-avian bipeds using a theoretical conversion to quadruped stylopodial proportions|journal=Methods in Ecology and Evolution|volume=5|issue=9|pages=913–923|doi=10.1111/2041-210X.12226|bibcode=2014MEcEv...5..913C |doi-access=free|hdl=10088/25281}}</ref> In his 1976 [[monograph]] on ''Allosaurus'', James H. Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of {{cvt|12|to|13|m}}.<ref name="JM76">{{cite book|last=Madsen|first=James H. Jr.|orig-year=1976 |year=1993 |title=Allosaurus fragilis: A Revised Osteology |series=Utah Geological Survey Bulletin '''109''' |publisher=Utah Geological Survey |location=Salt Lake City |edition=2nd}}</ref> As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between {{cvt|1.5|MT|ST}}, {{cvt|1|to|4|MT|ST}}, and approximately {{convert|1|MT|ST}} for [[mode (statistics)|modal]] adult weight (not maximum).<ref name=JRF03>{{cite book|last=Foster|first=John R.|year=2003 |title=Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque |series= New Mexico Museum of Natural History and Science Bulletin '''23''' |page=37}}</ref> [[John Foster (paleontologist)|John Foster]], a specialist on the Morrison Formation, suggests that {{cvt|1|MT|ST}} is reasonable for large adults of ''A. fragilis'', but that {{cvt|700|kg}} is a closer estimate for individuals represented by the average-sized [[femur|thigh bones]] he has measured.<ref name=JF07>{{cite book|last=Foster| first=John|title=Jurassic West: The Dinosaurs of the Morrison Formation and Their World |chapter=Allosaurus fragilis |pages=170–176 |publisher=Indiana University Press |location=Bloomington, Indiana |isbn=978-0-253-34870-8 |year=2007 |oclc=77830875}}</ref> Using the subadult specimen nicknamed "Big Al", since assigned to the species ''Allosaurus jimmadseni'',<ref name=DJC20/> researchers using computer modeling arrived at a best estimate of {{cvt|1.5|MT|ST}} for the individual, but by varying parameters they found a range from approximately {{cvt|1.4|MT|ST}} to approximately {{cvt|2|MT|ST}}.<ref name=KTBetal09>{{cite journal|last1=Bates|first1=Karl T.|last2=Falkingham, Peter L.|last3= Breithaupt, Brent H.|last4= Hodgetts, David|last5= Sellers, William I.|author6= Manning, Phillip L. |year=2009 |title=How big was 'Big Al'? Quantifying the effect of soft tissue and osteological unknowns on mass predictions for ''Allosaurus'' (Dinosauria:Theropoda)|journal=Palaeontologia Electronica |volume=12 |issue=3 |pages=unpaginated |url=http://palaeo-electronica.org/2009_3/186/index.html |access-date=December 13, 2009| archive-url= https://web.archive.org/web/20091225141532/http://palaeo-electronica.org/2009_3/186/index.html| archive-date= December 25, 2009 | url-status= live}}</ref> A separate computational project estimated the adaptive optimum body mass in ''Allosaurus'' to be ~2,345&nbsp;kg.<ref name="ReferenceA">{{Cite journal |last1=Pahl |first1=Cameron C. |last2=Ruedas |first2=Luis A. |date=November 1, 2023 |title=Big boned: How fat storage and other adaptations influenced large theropod foraging ecology |journal=PLOS ONE |language=en |volume=18 |issue=11 |pages=e0290459 |doi=10.1371/journal.pone.0290459 |doi-access=free |issn=1932-6203 |pmc=10619836 |pmid=37910492|bibcode=2023PLoSO..1890459P }}</ref> ''A. europaeus'' has been measured up to {{cvt|7|m}} in length and {{cvt|1|MT|ST}} in body mass.<ref name=G.S.Paul2010/>
[[File:Allosaurus jimmadseni skeletal.png|thumb|''A. jimmadseni'' skeletal reconstruction]]
Several gigantic specimens have been attributed to ''Allosaurus'', but may in fact belong to other genera. The dubious genus ''[[Saurophaganax]]'' ([[Sam Noble Oklahoma Museum of Natural History|OMNH]] 1708) was estimated to reach around {{cvt|10.5|m}} in length,<ref name=G.S.Paul2010/> and its single species was sometimes included in the genus ''Allosaurus'' as ''Allosaurus maximus''.<ref name=DJC00>{{cite book|last=Chure|first=Daniel J.|year=2000 |title=A new species of ''Allosaurus'' from the Morrison Formation of Dinosaur National Monument (Utah–Colorado) and a revision of the theropod family Allosauridae |series=PhD dissertation |publisher=Columbia University}}</ref> However, a 2024 study concluded that some material assigned to ''Saurophaganax'' actually belonged to a [[diplodocid]] [[sauropod]] with the material confidently assigned to [[Allosauridae]] belonging to a new species of ''Allosaurus'', ''A. anax'', and the body mass of this species was tentatively estimated around {{convert|3.8|-|4.6|MT|ST}} based on fragmentary material.<ref name="DEA24"/> Another potential specimen of ''Allosaurus'', once assigned to the genus ''[[Epanterias]]'' (AMNH 5767), may have measured {{cvt|12.1|m}} in length.<ref name=MMDML03/> A more recent discovery is a partial skeleton from the Peterson Quarry in Morrison rocks of [[New Mexico]]; this large allosaurid was suggested to be a potential specimen of ''Saurophaganax'' prior to this taxon's 2024 reassessment.<ref name=JF07b>Foster, John. 2007. ''Jurassic West: the Dinosaurs of the Morrison Formation and Their World''. Bloomington, Indiana:Indiana University Press. p. 117.</ref>

David K. Smith, examining ''Allosaurus'' fossils by quarry, found that the [[Cleveland-Lloyd Dinosaur Quarry]] (Utah) specimens are generally smaller than those from [[Como Bluff]] (Wyoming) or [[Brigham Young University]]'s [[Dry Mesa Quarry]] (Colorado), but the shapes of the bones themselves did not vary between the sites.<ref name=DKS96>{{cite journal |last=Smith |first=David K. |year=1996 |title=A discriminant analysis of ''Allosaurus'' population using quarries as the operational units |journal=Museum of Northern Arizona Bulletin |volume=60 |pages=69–72}}</ref> A later study by Smith incorporating Garden Park (Colorado) and [[Dinosaur National Monument]] (Utah) specimens found no justification for multiple species based on skeletal variation; skull variation was most common and was gradational, suggesting individual variation was responsible.<ref name=DKS98/> Further work on size-related variation again found no consistent differences, although the Dry Mesa material tended to clump together on the basis of the [[Talus bone|astragalus]], an ankle bone.<ref name=DKS99>{{cite journal |doi=10.1080/02724634.1999.10011153 |last=Smith |first=David K. |year=1999 |title=Patterns of size-related variation within ''Allosaurus'' |journal=Journal of Vertebrate Paleontology |volume=19 |issue=2 |pages=402–403|bibcode=1999JVPal..19..402S }}</ref> [[Kenneth Carpenter]], using skull elements from the Cleveland-Lloyd site, found wide variation between individuals, calling into question previous species-level distinctions based on such features as the shape of the horns, and the proposed differentiation of ''A. jimmadseni'' based on the shape of the [[jugal]].<ref name=KC2010>{{cite journal |last=Carpenter |first=Kenneth |year=2010 |title=Variation in a population of Theropoda (Dinosauria): ''Allosaurus'' from the Cleveland-Lloyd Quarry (Upper Jurassic), Utah, USA |journal=Paleontological Research |volume=14 |issue=4 |pages=250–259 |doi=10.2517/1342-8144-14.4.250 |bibcode=2010PalRe..14..250C |s2cid=84635714 }}</ref> A study published by Motani et al., in 2020 suggests that ''Allosaurus'' was also sexually dimorphic in the width of the femur's head against its length.<ref>{{Cite journal|title=Sex estimation from morphology in living animals and dinosaurs|first=Ryosuke|last=Motani|journal=Zoological Journal of the Linnean Society|year=2021|volume=192|issue=4|pages=1029–1044|doi=10.1093/zoolinnean/zlaa181|doi-access=free}}</ref>

===Skull===
[[File:Allosaurus jimmadseni skull and diagram.png|thumb|''A. jimmadseni'' skull with diagram highlighting individual bones]]
The skull and teeth of ''Allosaurus'' were modestly proportioned for a theropod of its size. Paleontologist [[Gregory S. Paul]] gives a length of {{cvt|845|mm}} for a skull belonging to an individual he estimates at {{cvt|7.9|m}} long.<ref name=GSP88>{{cite book |last=Paul |first=Gregory S. |title=Predatory Dinosaurs of the World |year=1988 |publisher=Simon & Schuster |location=New York |isbn=978-0-671-61946-6 |chapter=Genus ''Allosaurus'' |pages=[https://archive.org/details/predatorydinosau00paul/page/307 307–313] |chapter-url=https://archive.org/details/predatorydinosau00paul/page/307 }}</ref> Each [[premaxilla]] (the bones that formed the tip of the snout) held five teeth with D-shaped cross-sections, and each [[maxilla]] (the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each [[dentary]] (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, narrower, and more curved toward the back of the skull. All of the teeth had saw-like edges. They were shed easily, and were replaced continually, making them common fossils.<ref name=JM76/> Its skull was light, robust and equipped with dozens of sharp, [[serrated]] teeth.

The skull had a pair of [[Horn (anatomy)|horn]]s above and in front of the eyes. These horns were composed of extensions of the [[lacrimal bone]]s,<ref name=JM76/> and varied in shape and size. There were also lower paired ridges running along the top edges of the [[nasal bone]]s that led into the horns.<ref name=JM76/> The horns were probably covered in a [[keratin]] sheath and may have had a variety of functions, including acting as sunshades for the eyes,<ref name=JM76/> being used for display, and being used in combat against other members of the same species<ref name=GSP88/><ref name=REM77>{{cite journal |last=Molnar |first=Ralph E. |author-link=Ralph Molnar |year=1977 |title=Analogies in the evolution of combat and display structures in ornithopods and ungulates |journal=Evolutionary Theory |volume=3 |pages=165–190}}</ref> (although they were fragile).<ref name=JM76/> There was a ridge along the back of the skull roof for muscle attachment, as is also seen in [[Tyrannosauridae|tyrannosaurid]]s.<ref name=GSP88/>

Inside the lacrimal bones were depressions that may have held [[gland]]s, such as [[salt gland]]s.<ref name=DBN85>{{cite book |last=Norman |first=David B. |author-link=David B. Norman |title=The Illustrated Encyclopedia of Dinosaurs: An Original and Compelling Insight into Life in the Dinosaur Kingdom |chapter=Carnosaurs |year=1985 |publisher=Crescent Books |location=New York |pages=62–67 |isbn=978-0-517-46890-6 }}</ref> Within the maxillae were [[Maxillary sinus|sinus]]es that were better developed than those of more [[Basal (phylogenetics)|basal]] theropods such as ''[[Ceratosaurus]]'' and ''[[Marshosaurus]]''; they may have been related to the [[sense of smell]], perhaps holding something like [[Vomeronasal organ|Jacobson's organ]]s. The roof of the braincase was thin, perhaps to improve [[thermoregulation]] for the brain.<ref name=JM76/> The skull and lower jaws had joints that permitted motion within these units. In the lower jaws, the bones of the front and back halves loosely articulated, permitting the jaws to bow outward and increasing the animal's gape.<ref name="GSP88e">[[Gregory S. Paul|Paul, Gregory S.]] (1988). ''Predatory Dinosaurs of the World''. 91 and Figure 4–5 (93).</ref> The [[braincase]] and [[Frontal bone|frontal]]s may also have had a joint.<ref name=JM76/>

===Postcranial skeleton===
[[File:Allosaurus Revised.jpg|thumb|left|Life restoration of ''A. fragilis'']]
''Allosaurus'' had nine [[vertebra]]e in the neck, 14 in the back, and five in the [[sacrum]] supporting the hips.<ref>Madsen, 1976; note that not everyone agrees on where the neck ends and the back begins, and some authors such as Gregory S. Paul interpret the count as 10 neck and 13 back vertebrae.</ref> The number of tail vertebrae is unknown and varied with individual size; [[James Henry Madsen Jr.|James Madsen]] estimated about 50,<ref name=JM76/> while [[Gregory S. Paul]] considered that to be too many and suggested 45 or less.<ref name=GSP88/> There were hollow spaces in the neck and [[Anatomical terms of location|anterior]] back vertebrae.<ref name=JM76/> Such spaces, which are also found in modern theropods (that is, the birds), are interpreted as having held [[Parabronchi|air sacs]] used in [[Respiratory system|respiration]].<ref name="HMC04">{{cite book |last1=Holtz |first1=Thomas R. Jr. |author-link1=Thomas R. Holtz Jr. |title=The Dinosauria |last2=Molnar |first2=Ralph E. |author-link2=Ralph Molnar |last3=Currie |first3=Philip J. |author-link3=Philip J. Currie |publisher=University of California Press |year=2004 |isbn=978-0-520-24209-8 |editor=Weishampel |editor-first=David B. |editor-link=David B. Weishampel |edition=2nd |location=Berkeley |pages=71–110 |chapter=Basal Tetanurae |editor2=Dodson |editor-first2=Peter |editor-link2=Peter Dodson |editor3=Osmólska |editor-first3=Halszka |editor-link3=Halszka Osmólska}}</ref> The rib cage was broad, giving it a barrel chest, especially in comparison to less [[Synapomorphy|derived]] theropods like ''Ceratosaurus''.<ref name="GSP88b">[[Gregory S. Paul|Paul, Gregory S.]] (1988). ''Predatory Dinosaurs of the World''. 277.</ref> ''Allosaurus'' had [[Gastralium|gastralia]] (belly ribs), but these are not common findings,<ref name=JM76/> and they may have [[Ossification|ossified]] poorly.<ref name=GSP88/> In one published case, the gastralia show evidence of injury during life.<ref name=DJC00b>{{cite journal |last=Chure |first=Daniel J. |year=2000 |title=Observations on the morphology and pathology of the gastral basket of ''Allosaurus'', based on a new specimen from Dinosaur National Monument |journal=Oryctos |volume=3 |pages=29–37|issn=1290-4805}}</ref> A [[furcula]] (wishbone) was also present, but has only been recognized since 1996; in some cases furculae were confused with gastralia.<ref name=DJC00b/><ref name=CM96>{{cite journal |doi=10.1080/02724634.1996.10011341 |last1=Chure |first1=Daniel J. |year=1996 |last2=Madsen |first2=James |title=On the presence of furculae in some non-maniraptoran theropods |journal=Journal of Vertebrate Paleontology |volume=16| issue=3 |pages=573–577|bibcode=1996JVPal..16..573C }}</ref> The [[Ilium (bone)|ilium]], the main hip bone, was massive, and the [[Pubis (bone)|pubic bone]] had a prominent foot that may have been used for both muscle attachment and as a prop for resting the body on the ground. Madsen noted that in about half of the individuals from the [[Cleveland-Lloyd Dinosaur Quarry]], independent of size, the pubes had not fused to each other at their foot ends. He suggested that this was a [[Sexual dimorphism|sexual characteristic]], with females lacking fused bones to make egg-laying easier.<ref name=JM76/> This proposal has not attracted further attention, however.
[[File:Allosaurus-fragilis-Klauen.JPG|thumb|Hand and claws of ''A. fragilis'']]
The forelimbs of ''Allosaurus'' were short in comparison to the hindlimbs (only about 35% the length of the hindlimbs in adults)<ref name=MG98>{{cite journal|last=Middleton |first=Kevin M. |year=2000 |title=Theropod forelimb design and evolution |journal=Zoological Journal of the Linnean Society |volume=128 |pages=149–187 |doi=10.1006/zjls.1998.0193 |url=http://www.brown.edu/Departments/EEB/EML/files/kevin_zjls00.pdf |access-date=October 25, 2007 |issue=2 |archive-url=https://web.archive.org/web/20071025123319/http://www.brown.edu/Departments/EEB/EML/files/kevin_zjls00.pdf |archive-date=October 25, 2007 |url-status=dead }}</ref> and had three fingers per hand, tipped with large, strongly curved and pointed [[claw]]s.<ref name=JM76/> The arms were powerful,<ref name=GSP88/> and the forearm was somewhat shorter than the upper arm (1:1.2 [[ulna]]/[[humerus]] ratio).<ref name=CWG20>{{cite journal |last=Gilmore |first=Charles W. |author-link=Charles W. Gilmore |year=1920 |title=Osteology of the carnivorous dinosauria in the United States National Museum, with special reference to the genera ''Antrodemus'' (''Allosaurus'') and ''Ceratosaurus'' |journal=Bulletin of the United States National Museum |issue=110 |pages=1–159 |doi=10.5479/si.03629236.110.i|url=http://repository.si.edu/bitstream/handle/10088/10107/1/USNMB_1101920_unitfo.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://repository.si.edu/bitstream/handle/10088/10107/1/USNMB_1101920_unitfo.pdf |archive-date=October 9, 2022 |url-status=live |hdl=2027/uiug.30112032536010 }}</ref> The wrist had a version of the semilunate [[Carpal bones|carpal]]<ref name=KC02>{{cite journal |last=Carpenter |first=Kenneth |year=2002 |title=Forelimb biomechanics of nonavian theropod dinosaurs in predation |journal=[[Senckenbergiana Lethaea]] |volume=82 |issue=1 |pages=59–76 |doi=10.1007/BF03043773|s2cid=84702973 }}</ref> also found in more derived theropods like [[maniraptora]]ns. Of the three fingers, the innermost (or thumb) was the largest,<ref name=GSP88/> and diverged from the others.<ref name=CWG20/> The phalangeal formula is 2-3-4-0-0, meaning that the innermost finger (phalange) has two bones, the next has three, and the third finger has four.<ref>Martin, A.J.  (2006). Introduction to the Study of Dinosaurs. Second Edition. Oxford, Blackwell Publishing. 560 pp. {{ISBN|1-4051-3413-5}}.</ref> The legs were not as long or suited for speed as those of [[tyrannosaurid]]s, and the claws of the toes were less developed and more [[hoof]]-like than those of earlier theropods.<ref name=GSP88/> Each foot had three weight-bearing toes and an inner [[dewclaw]], which Madsen suggested could have been used for grasping in juveniles.<ref name=JM76/> There was also what is interpreted as the splint-like remnant of a fifth (outermost) [[Metatarsus|metatarsal]], perhaps used as a lever between the [[Achilles tendon]] and foot.<ref name=GSP88d>Paul, Gregory S. (1988). ''Predatory Dinosaurs of the World''. 113; note illustrations of ''Allosaurus'' on 310 and 311 as well; Madsen (1976) interpreted these bones as possible upper portions of the inner metatarsal.</ref>

=== Skin ===
Skin impressions from ''Allosaurus'' have been described. One impression, from a juvenile specimen, measures 30&nbsp;cm² and is associated with the anterior dorsal ribs/pectoral region. The impression shows small [[Scale (anatomy)|scales]] measuring 1–3&nbsp;mm in diameter. A skin impression from the "Big Al Two" specimen, associated with the base of the tail, measures 20&nbsp;cm × 20&nbsp;cm and shows large scales measuring up to 2&nbsp;cm in diameter. However, it has been noted that these scales are more similar to those of [[Sauropoda|sauropods]], and due to the presence of non-theropod remains associated with the tail of "Big Al Two" there is a possibility that this skin impression is not from ''Allosaurus''.<ref name=":1">{{Cite journal |last1=Hendrickx |first1=Christophe |last2=Bell |first2=Phil R. |last3=Pittman |first3=Michael |last4=Milner |first4=Andrew R. C. |last5=Cuesta |first5=Elena |last6=O'Connor |first6=Jingmai |last7=Loewen |first7=Mark |last8=Currie |first8=Philip J. |author-link8=Philip J. Currie |last9=Mateus |first9=Octávio |last10=Kaye |first10=Thomas G. |last11=Delcourt |first11=Rafael |date=June 2022 |title=Morphology and distribution of scales, dermal ossifications, and other non-feather integumentary structures in non-avialan theropod dinosaurs |url=https://onlinelibrary.wiley.com/doi/10.1111/brv.12829 |journal=Biological Reviews |language=en |volume=97 |issue=3 |pages=960–1004 |doi=10.1111/brv.12829 |issn=1464-7931 |pmid=34991180 |s2cid=245820672 |archive-date=September 28, 2022 |access-date=November 7, 2022 |archive-url=https://web.archive.org/web/20220928224916/https://onlinelibrary.wiley.com/doi/10.1111/brv.12829 |url-status=live |url-access=subscription }}</ref>

Another ''Allosaurus'' fossil features a skin impression from the [[mandible]], showing scales measuring 1–2&nbsp;mm in diameter. The same fossil also preserves skin measuring 20 × 20&nbsp;cm from the ventral side of the neck, showing scutate scales measuring 0.5&nbsp;cm wide and 11&nbsp;cm long. A small skin impression from an ''Allosaurus'' skull has been reported but never described.<ref name=":1"/>

==Classification==
[[File:Allosaurus anax.png|thumb|right|upright=0.9|Life restoration of ''A. anax'']]
''Allosaurus'' was an allosaurid, a member of a [[Family (biology)|family]] of large theropods within the larger group [[Carnosauria]]. The family name [[Allosauridae]] was created for this genus in 1878 by [[Othniel Charles Marsh]],<ref name="OCM78">{{cite journal |last=Marsh |first=Othniel Charles |author-link=Othniel Charles Marsh |year=1878 |title=Notice of new dinosaurian reptiles |url=https://zenodo.org/record/1450042 |journal=American Journal of Science and Arts |volume=15 |issue=87 |pages=241–244 |bibcode=1878AmJS...15..241M |doi=10.2475/ajs.s3-15.87.241 |s2cid=131371457 |archive-date=August 18, 2020 |access-date=June 28, 2019 |archive-url=https://web.archive.org/web/20200818111419/https://zenodo.org/record/1450042 |url-status=live }}</ref> but the term was largely unused until the 1970s in favor of [[Megalosauridae]], another family of large theropods that eventually became a [[wastebasket taxon]]. 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. Major publications using the name "Megalosauridae" instead of "Allosauridae" include [[Charles W. Gilmore|Gilmore]], 1920,<ref name=CWG20/> [[Friedrich von Huene|von Huene]], 1926,<ref name=FvH26>{{cite journal |last=von Huene |first=Friedrich |year=1926 |title=The carnivorous Saurischia in the Jura and Cretaceous formations, principally in Europe |journal=Revista del Museo de La Plata |volume=29 |pages=35–167}}</ref> [[Alfred Sherwood Romer|Romer]], 1956 and 1966,<ref name=ASR56>{{cite book |last=Romer |first=Alfred S. |year=1956 |title=Osteology of the Reptiles |publisher=University of Chicago Press |location=Chicago |isbn=978-0-89464-985-1}}</ref><ref name=ASR66>{{cite book |last=Romer |first=Alfred S. |title= Vertebrate Paleontology |url=https://archive.org/details/vertebratepaleon0000rome_q8n3 |url-access=registration |edition=Third |year=1966 |publisher= University of Chicago Press |location= Chicago |isbn=978-0-7167-1822-2}}</ref> Steel, 1970,<ref name=Steel70>{{cite journal|last=Steel|first=R.|year= 1970|title=Part 14. Saurischia. Handbuch der Paläoherpetologie/Encyclopedia of Paleoherpetology|journal= Gustav Fischer Verlag, Stuttgart|pages=1–87}}</ref> and [[Alick Walker|Walker]], 1964.<ref name=ADW64>{{cite journal |last=Walker |first=Alick D. |year=1964 |title=Triassic reptiles from the Elgin area: ''Ornithosuchus'' and the origin of carnosaurs |journal=Philosophical Transactions of the Royal Society B |volume=248 |pages=53–134 |issue=744 |doi=10.1098/rstb.1964.0009 |bibcode=1964RSPTB.248...53W |jstor=2416617|s2cid=86378219 }}</ref>

Following the publication of Madsen's influential monograph, Allosauridae became the preferred family assignment, but it too was not strongly defined. Semi-technical works used Allosauridae for a variety of large theropods, usually those that were larger and better-known than megalosaurids. Typical theropods that were thought to be related to ''Allosaurus'' included ''[[Indosaurus]]'', ''[[Piatnitzkysaurus]]'', ''[[Piveteausaurus]]'', ''[[Yangchuanosaurus]]'',<ref name=DL83>{{cite book |last1=Lambert |first1=David |last2=the Diagram Group |title=A Field Guide to Dinosaurs |year=1983 |publisher=Avon Books |location=New York |isbn=978-0-380-83519-5 |chapter=Allosaurids |pages=[https://archive.org/details/fieldguidetodino00lamb/page/80 80–81] |chapter-url=https://archive.org/details/fieldguidetodino00lamb/page/80 }}</ref> ''[[Acrocanthosaurus]]'', ''[[Chilantaisaurus]]'', ''[[Compsosuchus]]'', ''[[Stokesosaurus]]'', and ''[[Szechuanosaurus]]''.<ref name=DL90>{{cite book |last1=Lambert |first1=David |last2=the Diagram Group |title=The Dinosaur Data Book |year=1990 |publisher=Avon Books |location=New York |isbn=978-0-380-75896-8 |chapter=Allosaurids |page=[https://archive.org/details/dinosaurdatabook00lamb/page/130 130] |chapter-url=https://archive.org/details/dinosaurdatabook00lamb/page/130 }}</ref> Given modern knowledge of theropod diversity and the advent of cladistic study of [[evolution]]ary relationships, none of these theropods is now recognized as an allosaurid, although several, like ''Acrocanthosaurus'' and ''Yangchuanosaurus'', are members of closely related families.<ref name=HMC04/>
[[File:Allosaurus jimmadseni skull illustration.png|thumb|Illustrations showing the skull of ''A. jimmadseni'' from the side (A), top (B), and back (C)]]
[[File:WLA hmns Allosaurus.jpg|thumb|''A. jimmadseni'' specimen "Big Al II" (SMA 0005)]]
Below is a cladogram based on the analysis of Benson et al. in 2010.<ref name="bensonetal2010">{{cite journal |last1=Benson |first1=R.B.J. |last2=Carrano |first2=M.T. |last3=Brusatte |first3=S.L. |author-link3=Stephen L. Brusatte |year=2010 |title=A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic |url=https://repository.si.edu/bitstream/handle/10088/8609/paleo_Benson_10.pdf |journal=Naturwissenschaften |volume=97 |issue=1 |pages=71–78 |bibcode=2010NW.....97...71B |doi=10.1007/s00114-009-0614-x |pmid=19826771 |s2cid=22646156 |archive-date=August 31, 2021 |access-date=August 6, 2018 |archive-url=https://web.archive.org/web/20210831103656/https://repository.si.edu/bitstream/handle/10088/8609/paleo_Benson_10.pdf |url-status=live }}</ref>

{{clade| style=font-size:100%; line-height:100%
|label1=[[Allosauroidea]]
|1={{clade
 |1=[[Sinraptoridae]] [[File:Alpkarakush UDL.png|80px]]
 |2={{clade
   |1='''''Allosaurus''''' <span style="{{MirrorH}}">[[File:Allosaurus anax.png|80px]]</span>
   |2={{clade
      |1={{clade
         |1=''[[Neovenator]]'' <span style="{{MirrorH}}">[[File:Neovenator.png|80px]]</span>
         |2={{clade
            |1=''[[Fukuiraptor]]'' 
            |2=''[[Megaraptor]]'' <span style="{{MirrorH}}">[[File:MegaraptorNV.jpg|80px]]</span> }} }}
      |2={{clade
         |1=''[[Eocarcharia]]''
         |2={{clade
            |1=''[[Acrocanthosaurus]]'' <span style="{{MirrorH}}">[[File:Acrocanthosaurus restoration.jpg|80px]]</span>
            |2={{clade
               |1=''[[Shaochilong]]'' <span style="{{MirrorH}}">[[File:Shaochilong.jpg|80px]]</span>
               |2={{clade
                  |1=''[[Tyrannotitan]]''
                  |2={{clade
                     |1=''[[Carcharodontosaurus]]'' [[File:Carcharodontosaurus UDL.png|80px]]
                     |2=''[[Giganotosaurus]]'' [[File:Giganotosaurus BW.jpg|80px]]
                     |3=''[[Mapusaurus]]'' [[File:Mapusaurus BW.jpg|80px]] }} }} }} }} }} }} }} }} }}

Allosauridae is one of four families in Allosauroidea; the other three are [[Neovenatoridae]],<ref name="bensonetal2010"/> [[Carcharodontosauridae]] and [[Sinraptoridae]].<ref name="HMC04"/> Allosauridae has at times been proposed as ancestral to the [[Tyrannosauridae]] (which would make it [[Paraphyly|paraphyletic]]), one example being Gregory S. Paul's ''Predatory Dinosaurs of the World'',<ref name="GSP88c">Paul, Gregory S. (1988). "The allosaur-tyrannosaur group", ''Predatory Dinosaurs of the World''. 301–347.</ref> but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the [[Coelurosauria]].<ref name="TRHJ94">{{cite journal|last=Holtz |first=Thomas R. Jr. |year= 1994 |title=The phylogenetic position of the Tyrannosauridae: Implications for theropod systematics |journal=Journal of Paleontology |volume=68 |issue=5 |pages=1100–1117 |jstor=1306180|doi=10.1017/S0022336000026706 |bibcode=1994JPal...68.1100H |s2cid=129684676 }}</ref> Allosauridae is the smallest of the carnosaur families, with only ''Saurophaganax'' and a currently unnamed French [[Allosauroidea|allosauroid]] accepted as possible valid [[Genus|genera]] besides ''Allosaurus'' in the most recent review.<ref name="HMC04"/> Another genus, ''Epanterias'', is a potential valid member, but it and ''Saurophaganax'' may turn out to be large examples of ''Allosaurus''.<ref name="GSP88"/> Some reviews have kept the genus ''[[Saurophaganax]]'' and included ''Epanterias'' with ''Allosaurus''.<ref name="HMC04"/><ref name="JRF03"/>

The controversial ''Saurophaganax'', initially recognized as a large ''Allosaurus''-like theropod, has had a controversial taxonomic history. In 2019, Rauhut and Pol noted that its taxonomic placement within [[Allosauroidea]] is unstable, being recovered as a sister taxon of [[Metriacanthosauridae]] or Allosauria, or even as the basalmost carcharodontosaurian.<ref name="Rauhut2019">{{Cite journal|last1=Rauhut|first1=Oliver W. M.|last2=Pol|first2=Diego|date=December 11, 2019|title=Probable basal allosauroid from the early Middle Jurassic Cañadón Asfalto Formation of Argentina highlights phylogenetic uncertainty in tetanuran theropod dinosaurs|journal=Scientific Reports|language=en|volume=9|issue=1|pages=18826|doi=10.1038/s41598-019-53672-7|pmid=31827108|pmc=6906444|bibcode=2019NatSR...918826R |issn=2045-2322}} [https://www.nature.com/articles/s41598-019-53672-7#MOESM1 Supplementary information] {{Webarchive|url=https://web.archive.org/web/20241007165345/https://www.nature.com/articles/s41598-019-53672-7#MOESM1 |date=October 7, 2024 }}</ref> In 2024, ''Saurophaganax'' was reassessed as a [[nomen dubium|dubious]], [[chimera (paleontology)|chimeric]] taxon with the holotype being so fragmentary that it could only be confidently referred to the [[Saurischia]], and some specimens more likely belonging to a [[diplodocid]] [[sauropod]].<ref name="DEA24"/>

==Paleobiology==
===Life history===
[[File:Fossil displays - Natural History Museum of Utah - DSC07215.JPG|thumb|left|Skeletons at different growth stages on display, the [[Natural History Museum of Utah]]]]
The wealth of ''Allosaurus'' fossils, from nearly all ages of individuals, allows scientists to study how the animal grew and how long its lifespan may have been. Remains may reach as far back in the lifespan as [[egg]]s—crushed eggs from Colorado have been suggested as those of ''Allosaurus''.<ref name=DFG97/> Based on [[Histology|histological]] analysis of limb bones, bone deposition appears to stop at around 22 to 28 years, which is comparable to that of other large theropods like ''[[Tyrannosaurus]]''. From the same analysis, its maximum growth appears to have been at age 15, with an estimated growth rate of about 150 kilograms (330 [[pound (mass)|lb]]) per year.<ref name=PBetal06/>

Medullary bone tissue (endosteally derived, ephemeral, mineralization located inside the [[Bone marrow|medulla]] of the long bones in gravid female birds) has been reported in at least one ''Allosaurus'' specimen, a [[Tibia|shin bone]] from the [[Cleveland-Lloyd Dinosaur Quarry|Cleveland-Lloyd Quarry]]. Today, this bone tissue is only formed in female birds that are laying eggs, as it is used to supply [[calcium]] to shells. Its presence in the ''Allosaurus'' individual has been used to establish sex and show it had reached reproductive age.<ref name=LW08>{{cite journal |last1=Lee |first1=Andrew H. |year=2008 |title=Sexual maturity in growing dinosaurs does not fit reptilian growth models |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=105 |issue=2 |pages=582–587 |doi=10.1073/pnas.0708903105 |pmid=18195356 |last2=Werning |first2=S |pmc=2206579|bibcode = 2008PNAS..105..582L |doi-access=free }}</ref> However, other studies have called into question some cases of medullary bone in dinosaurs, including this ''Allosaurus'' individual. Data from extant birds suggested that the medullary bone in this ''Allosaurus'' individual may have been the result of a bone pathology instead.<ref name=Chin09>{{cite journal | last1 = Chinsamy | first1 = A. | last2 = Tumarkin-Deratzian | first2 = A. | year = 2009 | title = Pathological Bone Tissues in a Turkey Vulture and a Nonavian Dinosaur: Implications for Interpreting Endosteal Bone and Radial Fibrolamellar Bone in Fossil Dinosaurs | journal = Anat. Rec. | volume = 292 | issue = 9| pages = 1478–1484 | doi=10.1002/ar.20991| pmid = 19711479 | s2cid = 41596233 | doi-access = free }}</ref> However, with the confirmation of medullary tissue indicating sex in a specimen of ''Tyrannosaurus'', it may be possible to ascertain whether or not the ''Allosaurus'' in question was indeed female.<ref>{{cite web |url=https://www.sciencedaily.com/releases/2016/03/160315085637.htm |title= Pregnant T. rex could aid in dino sex-typing | date=March 15, 2016 |work=Science Daily |archive-url=https://web.archive.org/web/20160414064736/https://www.sciencedaily.com/releases/2016/03/160315085637.htm |archive-date=April 14, 2016}}</ref>
[[File:Allosaurus Juvenile Reconstruction.jpg|thumb|Restoration of a juvenile ''Allosaurus'']] 
The discovery of a juvenile specimen with a nearly complete hindlimb shows that the legs were relatively longer in juveniles, and the lower segments of the leg (shin and foot) were relatively longer than the thigh. These differences suggest that younger ''Allosaurus'' were faster and had different hunting strategies than adults, perhaps chasing small prey as juveniles, then becoming ambush hunters of large prey upon adulthood.<ref name=FC06/> The [[thigh bone]] became thicker and wider during growth, and the cross-section less circular, as muscle attachments shifted, muscles became shorter, and the growth of the leg slowed. These changes imply that juvenile legs has less predictable stresses compared with adults, which would have moved with more regular forward progression.<ref name=LCS02>{{cite journal |last=Loewen |first=Mark A. |year=2002 |title=Ontogenetic changes in hindlimb musculature and function in the Late Jurassic theropod ''Allosaurus'' |journal=Journal of Vertebrate Paleontology |volume=22 |issue=3, Suppl |page=80A }}</ref> Conversely, the skull bones appear to have generally grown [[allometry|isometrically]], increasing in size without changing in proportion.<ref name=KC2010/>

===Feeding===
[[File:Steg Bitten Plate.jpg|thumb|left|Bitten ''Stegosaurus'' plate close-up, showing how well the damage matches the front of an ''Allosaurus'' "mouth"]]
Most paleontologists accept ''Allosaurus'' as an active predator of large animals. There is dramatic evidence for allosaur attacks on ''Stegosaurus'', including an ''Allosaurus'' tail vertebra with a partially healed puncture wound that fits a ''Stegosaurus'' [[Thagomizer|tail spike]], and a ''Stegosaurus'' neck plate with a U-shaped wound that correlates well with an ''Allosaurus'' snout.<ref name=KSMW05>{{cite book |first1=Kenneth |last1=Carpenter |last2=Sanders, Frank|last3= McWhinney, Lorrie A.|last4= Wood, Lowell |title=The Carnivorous Dinosaurs|year=2005 |chapter=Evidence for predator-prey relationships: Examples for ''Allosaurus'' and ''Stegosaurus'' |editor=Carpenter, Kenneth |pages=325–350 |publisher=Indiana University Press |location=Bloomington and Indianapolis |isbn= 978-0-253-34539-4 }}</ref> [[Sauropod]]s seem to be likely candidates as both live prey and as objects of [[Scavenger|scavenging]], based on the presence of scrapings on sauropod bones fitting allosaur teeth well and the presence of shed allosaur teeth with sauropod bones.<ref name=FS04>Fastovsky, David E.; and Smith, Joshua B. (2004). "Dinosaur Paleoecology", in ''The Dinosauria'' (2nd ed.). 614–626.</ref> 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.<ref name=GSP88/> Another possibility is that it preferred to hunt juveniles instead of fully grown adults.<ref name=LG93/><ref name=JF07/> Research in the 1990s and the first decade of the 21st century may have found other solutions to this question. [[Robert T. Bakker]], comparing ''Allosaurus'' to [[Cenozoic]] saber-toothed carnivorous mammals, found similar adaptations, such as a reduction of jaw muscles and increase in neck muscles, and the ability to open the jaws extremely wide. Although ''Allosaurus'' did not have saber teeth, Bakker suggested another mode of attack that would have used such neck and jaw adaptations: the short teeth in effect became small serrations on a [[saw]]-like cutting edge running the length of the upper jaw, which would have been driven into prey. This type of jaw would permit slashing attacks against much larger prey, with the goal of weakening the victim.<ref name=BB98/>
[[File:Allosaurus Jaws Steveoc86.jpg|thumb|''A. fragilis'' showing its maximum possible gape, based on [[Robert T. Bakker|Bakker]] (1998) and [[Emily Rayfield|Rayfield]] et al. (2001)]]
Similar conclusions were drawn by another study using [[finite element analysis]] on an ''Allosaurus'' skull. According to their biomechanical analysis, the skull was very strong but had a relatively small bite force. By using jaw muscles only, it could produce a bite force of 805 to 8,724 [[Newton (unit)|N]],<ref name=ERetal01/><ref name="BatesFalkingham2012">{{Cite journal|last1=Bates|first1=K. T.|last2=Falkingham|first2=P.L.|date=February 29, 2012|title=Estimating maximum bite performance in ''Tyrannosaurus rex'' using multi-body dynamics|journal=Biology Letters|volume=8|issue=4|pages=660–664|doi=10.1098/rsbl.2012.0056|pmid=22378742|pmc=3391458}}</ref> but the skull could withstand nearly 55,500 N of vertical force against the tooth row.<ref name=ERetal01/> 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. They also suggested that the architecture of the skull could have permitted the use of different strategies against different prey; the skull was light enough to allow attacks on smaller and more agile ornithopods, but strong enough for high-impact ambush attacks against larger prey like stegosaurids and sauropods.<ref name=ERetal01/> Their interpretations were challenged by other researchers, who found no modern analogs to a hatchet attack and considered it more likely that the skull was strong to compensate for its open construction when absorbing the stresses from struggling prey.<ref name=FK02>{{cite journal |last1=Frazzetta |first1=T. H. |year=2002 |title=Prey attack by a large theropod dinosaur |journal=Nature |volume=416 |pages=387–388 |doi=10.1038/416387a |pmid=11919619 |last2=Kardong |first2=K. V. |issue=6879|bibcode = 2002Natur.416..387F |s2cid=4388901 }}</ref> 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.<ref name=ERetal02>{{cite journal |last1=Rayfield |first1=Emily J. |year=2002 |title=Prey attack by a large theropod dinosaur: Response to Frazzetta and Kardong, 2002 |journal=Nature |volume=416 |page=388 |doi=10.1038/416388a |last2=Norman |first2=D. B. |last3=Upchurch |first3=P. |issue=6879|bibcode = 2002Natur.416..388R |s2cid=4392259 |doi-access=free }}</ref> Another possibility for handling large prey is that theropods like ''Allosaurus'' were "flesh grazers" which could take bites of flesh out of living sauropods that were sufficient to sustain the predator so it would not have needed to expend the effort to kill the prey outright. This strategy would also potentially have allowed the prey to recover and be fed upon in a similar way later.<ref name=HMC04/> An additional suggestion notes that ornithopods were the most common available dinosaurian prey, and that ''Allosaurus'' may have subdued them by using an attack similar to that of modern big cats: grasping the prey with their forelimbs, and then making multiple bites on the throat to crush the trachea.<ref name=JF07/> This is compatible with other evidence that the forelimbs were strong and capable of restraining prey.<ref name=KC02/> Studies done by Stephen Lautenschager et al. from the University of Bristol also indicate ''Allosaurus'' could open its jaws quite wide and sustain considerable muscle force. 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. The findings also indicate that large carnivorous dinosaurs, like modern carnivores, had wider jaw gapes than herbivores.<ref>{{cite journal |last=Lautenschlager |first= Stephan |title= Estimating cranial musculoskeletal constraints in theropod dinosaurs |volume= 2 |issue= 11 |pages= 150495 |journal= Royal Society Open Science|date=November 4, 2015 |doi= 10.1098/rsos.150495 |pmid= 26716007 |pmc= 4680622 |bibcode= 2015RSOS....250495L }}</ref><ref>{{cite web |url=https://www.sciencedaily.com/releases/2015/11/151103213705.htm |title= Better to eat you with? How dinosaurs' jaws influenced diet |date=November 3, 2015 |work=Science Daily |url-status=live |archive-url=https://web.archive.org/web/20160307232743/https://www.sciencedaily.com/releases/2015/11/151103213705.htm |archive-date=March 7, 2016}}</ref>

[[File:Denver Museum new Allosaurus skull vs Stegosaurus.jpg|left|thumb|''Allosaurus'' and ''Stegosaurus'' skeletons, the [[Denver Museum of Nature and Science]]]]
A [[Biomechanics|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#Longissimus capitis|longissimus capitis superficialis]] neck muscle compared to other theropods such as ''[[Tyrannosaurus]]''. This would have allowed the animal to make rapid and forceful vertical movements with the skull. The authors found that vertical strikes as proposed by Bakker and Rayfield are consistent with the animal's capabilities. They also found that the animal probably processed carcasses by vertical movements in a similar manner to [[falcon]]s, such as [[kestrel]]s: The animal could have gripped prey with the skull and feet, then pulled back and up to remove flesh. This differs from the prey-handling envisioned for tyrannosaurids, which probably tore flesh with lateral shakes of the skull, similar to crocodilians.<ref name=ESetal2013>{{cite journal |last1=Snively |first1=Eric. |last2=Cotton, John R.|last3= Ridgely, Ryan|last4= Witmer, Lawrence M. |year=2013 |title=Multibody dynamics model of head and neck function in ''Allosaurus'' (Dinosauria, Theropoda) |journal=Palaeontologia Electronica |volume=16 |issue=2 |page=338 |doi=10.26879/338 |doi-access=free |bibcode=2013PalEl..16..338S }}</ref> In addition, ''Allosaurus'' was able to "move its head and neck around relatively rapidly and with considerable control", at the cost of power.<ref name=Scidaily2013>{{cite web|last=Ohio University|title=Allosaurus fed more like a falcon than a crocodile: Engineering, anatomy work reveals differences in dinosaur feeding styles|url=https://www.sciencedaily.com/releases/2013/05/130521152638.htm|website=ScienceDaily|access-date=May 22, 2013|date=May 22, 2013|archive-date=November 9, 2021|archive-url=https://web.archive.org/web/20211109005339/https://www.sciencedaily.com/releases/2013/05/130521152638.htm|url-status=live}}</ref>

Other aspects of feeding include the eyes, arms, and legs. The shape of the skull of ''Allosaurus'' limited potential [[binocular vision]] to 20° of width, slightly less than that of modern [[crocodilia]]ns. As with crocodilians, this may have been enough to judge prey distance and time attacks.<ref>{{cite journal |last1=Rogers |first1=Scott W. |title=Reconstructing the behaviors of extinct species: An excursion into comparative paleoneurology |journal=American Journal of Medical Genetics Part A |date=March 9, 2005 |volume=134A |issue=4 |pages=349–356 |doi=10.1002/ajmg.a.30538 |pmid=15759265 |url=https://onlinelibrary.wiley.com/doi/10.1002/ajmg.a.30538 |language=en |issn=1552-4825|url-access=subscription }}</ref><ref>{{Cite journal |last=Rogers |first=Scott W. |date=October 15, 1999 |title=Allosaurus, crocodiles, and birds: Evolutionary clues from spiral computed tomography of an endocast |url=https://onlinelibrary.wiley.com/doi/10.1002/(SICI)1097-0185(19991015)257:53.0.CO;2-W |journal=The Anatomical Record |language=en |volume=257 |issue=5 |pages=162–173 |doi=10.1002/(SICI)1097-0185(19991015)257:5<162::AID-AR5>3.0.CO;2-W |pmid=10597341 |issn=0003-276X|url-access=subscription }}</ref><ref name=KAS06>{{cite journal |last=Stevens |first=Kent A. |year=2006 |title=Binocular vision in theropod dinosaurs |journal=Journal of Vertebrate Paleontology |volume=26 |issue=2 |pages=321–330 |doi=10.1671/0272-4634(2006)26[321:BVITD]2.0.CO;2 |s2cid=85694979 |issn=0272-4634 }}</ref> The arms, compared with those of other theropods, were suited for both grasping prey at a distance or clutching it close,<ref name=KC02/> and the articulation of the claws suggests that they could have been used to hook things.<ref name=CWG20/> Finally, the top speed of ''Allosaurus'' has been estimated at {{cvt|30|-|55|km}} per hour.<ref name=PC98>{{cite journal |last=Christiansen |first=Per |year=1998 |title=Strength indicator values of theropod long bones, with comments on limb proportions and cursorial potential |journal=Gaia |volume=15 |pages=241–255 |issn=0871-5424}}</ref>

A paper on the cranio-dental morphology of ''Allosaurus'' and how it worked has deemed the hatchet jaw attack unlikely, reinterpreting the unusually wide gape as an adaptation to allow ''Allosaurus'' to deliver a muscle-driven bite to large prey, with the weaker jaw muscles being a trade-off to allow for the widened gape.<ref>{{cite journal|url=http://digital.csic.es/bitstream/10261/22490/1/102.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://digital.csic.es/bitstream/10261/22490/1/102.pdf |archive-date=October 9, 2022 |url-status=live|last1=Anton|first1=M.|last2=Sánchez|first2=I.|last3=Salesa|first3=Manuel|last4=Turner|first4=A|year=2003|title=The muscle-powered bite of ''Allosaurus'' (Dinosauria; Theropoda): An interpretation of cranio-dental morphology.|journal=Estudios Geológicos|volume=59|issue=5|pages=313–323|doi=10.3989/egeol.03595-6106}}</ref>

[[File:Barosaurus lentus1.jpg|thumb|right|Restoration of ''[[Barosaurus]]'' rearing to defend itself against a pair of ''A. fragilis'']]
Sauropod carrion may also have been important to large theropods in the Morrison Formation. Forensic techniques indicate that sauropod carcasses were targeted by ''Allosaurus'' at all stages of decomposition, indicating that late-stage decay pathogens were not a significant deterrent.<ref>{{Cite journal |last1=Bader |first1=Kenneth |last2=Hasiotis |first2=Stephen |year=2009 |title=Application of forensic science techniques to trace fossils on dinosaur bones from a quarry in the Upper Jurassic Morrison Formation, Northeastern Wyoming |url=https://doi.org/10.2110/palo.2008.p08-058r |access-date=January 17, 2024 |journal=PALAIOS |volume=24 |issue=3 |pages=140–158 |language=en |publication-place=PALAIOS |doi=10.2110/palo.2008.p08-058r|bibcode=2009Palai..24..140B |url-access=subscription }}</ref><ref>{{cite journal |last1=Storrs |first1=Glenn W. |last2=Oser |first2=Sara E. |last3=Aull |first3=Mark |title=Further analysis of a Late Jurassic dinosaur bone-bed from the Morrison Formation of Montana, USA, with a computed three-dimensional reconstruction |journal=Earth and Environmental Science Transactions of the Royal Society of Edinburgh |date=September 23, 2013 |volume=103 |issue=3–4 |pages=443–458 |doi=10.1017/S1755691013000248 |url=https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/abs/further-analysis-of-a-late-jurassic-dinosaur-bonebed-from-the-morrison-formation-of-montana-usa-with-a-computed-threedimensional-reconstruction/7539F3414CA4B031A33C115C94A2C954 |issn=1755-6910 |archive-date=January 17, 2024 |access-date=January 17, 2024 |archive-url=https://web.archive.org/web/20240117201743/https://www.cambridge.org/core/journals/earth-and-environmental-science-transactions-of-royal-society-of-edinburgh/article/abs/further-analysis-of-a-late-jurassic-dinosaur-bonebed-from-the-morrison-formation-of-montana-usa-with-a-computed-threedimensional-reconstruction/7539F3414CA4B031A33C115C94A2C954 |url-status=live |url-access=subscription }}</ref> A survey of sauropod bones from the Morrison Formation also reported widespread bite marks on sauropod bones in low-economy regions, which suggests that large theropods scavenged large sauropods when available, with the scarcity of such bite marks on the remains of smaller bones being potentially attributable to much more complete consumption of smaller or adolescent sauropods and on ornithischians, which would have been more commonly taken as live prey.<ref name="ReferenceA"/><ref>{{Cite journal |last1=Lei |first1=Roberto |last2=Tschopp |first2=Emanuel |last3=Hendrickx |first3=Christophe |last4=Wedel |first4=Mathew J. |last5=Norell |first5=Mark |last6=Hone |first6=David W. E. |date=November 14, 2023 |title=Bite and tooth marks on sauropod dinosaurs from the Morrison Formation |journal=PeerJ |language=en |volume=11 |pages=e16327 |doi=10.7717/peerj.16327 |doi-access=free |pmid=38025762 |pmc=10655710 |issn=2167-8359}}</ref> A single dead adult ''Barosaurus'' or ''Brachiosaurus'' would have had enough calories to sustain multiple large theropods for weeks or months,<ref>{{Cite journal |last1=Pahl |first1=Cameron C. |last2=Ruedas |first2=Luis A. |date=October 15, 2021 |title=Carnosaurs as Apex Scavengers: Agent-based simulations reveal possible vulture analogues in late Jurassic Dinosaurs |url=https://www.sciencedirect.com/science/article/pii/S0304380021002611 |journal=Ecological Modelling |volume=458 |pages=109706 |doi=10.1016/j.ecolmodel.2021.109706 |bibcode=2021EcMod.45809706P |issn=0304-3800|url-access=subscription }}</ref> though the vast majority of the Morrison's sauropod fossil record consisted of much smaller-bodied taxa such as ''Camarasaurus lentus'' or ''Diplodocus''.<ref name="Foster">{{cite book |last=Foster |first=John |author-link= |date=October 20, 2020 |title=Jurassic West, Second Addition: The Dinosaurs of the Morrison Formation and Their World  |url= https://iupress.org/9780253051578/jurassic-west-second-edition/ |location= |publisher=Indiana University Press |page= |isbn= 9780253051578}}</ref>

It has also been argued that disabled individuals such as Big Al and Big Al II were physically incapable of hunting due to their numerous injuries but were able to survive nonetheless as scavengers of giant sauropod-falls,<ref>{{Cite journal |last1=Pahl |first1=Cameron C. |last2=Ruedas |first2=Luis A. |date=March 1, 2023 |title=''Allosaurus'' was predominantly a scavenger |url=https://www.sciencedirect.com/science/article/pii/S0304380022003593 |journal=Ecological Modelling |volume=477 |pages=110261 |doi=10.1016/j.ecolmodel.2022.110261 |bibcode=2023EcMod.47710261P |issn=0304-3800|url-access=subscription }}</ref> Interestingly, a recent review of paleopathologies in theropods may support this conclusion. The researchers found a positive association between allosaurids and fractures to the appendicular skeleton, while tyrannosaurs had a statistically negative association with these types of injuries.<ref>{{Cite journal |last1=Baiano |first1=Mattia A. |last2=Cerda |first2=Ignacio A. |last3=Bertozzo |first3=Filippo |last4=Pol |first4=Diego |date=January 31, 2024 |title=New information on paleopathologies in non-avian theropod dinosaurs: a case study on South American abelisaurids |journal=BMC Ecology and Evolution |volume=24 |issue=1 |pages=6 |doi=10.1186/s12862-023-02187-x |doi-access=free |issn=2730-7182 |pmc=10829224 |pmid=38291378|bibcode=2024BMCEE..24....6B }}</ref> The fact that allosaurs were more likely to survive and heal even when severe fractures limited their locomotion abilities can be explained, in part, by different resource accessibility paradigms for the two groups, as allosauroids generally lived in sauropod-inhabited ecosystems, some of which, including the Morrison, have been interpreted as arid and highly water-stressed environments; however, the water-stressed nature of the Morrison has been heavily criticized in several more recent works on the basis of fossil evidence for the presence of extensive forest cover and aquatic ecosystems.<ref name="Foster"/>

===Social behavior===
[[File:Labrosaurus.jpg|thumb|left|The holotype dentary of ''Labrosaurus ferox'', which may have been injured by the bite of another ''A. fragilis'']]
It has been speculated since the 1970s that ''Allosaurus'' preyed on sauropods and other large dinosaurs by hunting in groups.<ref name=JF76>{{cite journal |last=Farlow |first=James O. |year=1976 |title=Speculations about the diet and foraging behavior of large carnivorous dinosaurs |journal=American Midland Naturalist |volume=95 |issue=1 |pages=186–191 |doi=10.2307/2424244|jstor=2424244 }}</ref>
Such a depiction is common in semitechnical and popular dinosaur literature.<ref name=DBN85/><ref name=LG93/><ref name=DL83/> [[Robert T. Bakker]] has extended social behavior to parental care, and has interpreted shed allosaur teeth and chewed bones of large prey animals as evidence that adult allosaurs brought food to lairs for their young to eat until they were grown, and prevented other carnivores from scavenging on the food.<ref name=RTB97/> However, there is actually little evidence of gregarious behavior in theropods,<ref name=HMC04/> and social interactions with members of the same species would have included antagonistic encounters, as shown by injuries to gastralia<ref name=DJC00b/> and bite wounds to skulls (the pathologic lower jaw named ''Labrosaurus ferox'' is one such possible example). Such head-biting may have been a way to establish dominance in a pack or to settle territorial disputes.<ref name=TC98>{{cite journal |last=Tanke |first=Darren H. |author-link=Darren Tanke |year=1998 |title=Head-biting behavior in theropod dinosaurs: Paleopathological evidence |journal=Gaia |issue=15 |pages=167–184 |url=https://www.academia.edu/2132861 |archive-date=November 9, 2021 |access-date=December 4, 2017 |archive-url=https://web.archive.org/web/20211109012815/https://www.academia.edu/2132861 |url-status=live }}</ref>

Although ''Allosaurus'' may have hunted in packs,<ref name=completedino>{{cite book |title=The Complete Dinosaur |chapter-url=https://books.google.com/books?id=FOViD-lDPy0C&q=Allosaurus+behavior&pg=PA228 |last=Currie |first=Philip J. |chapter=Theropods |editor=Farlow, James |editor2=Brett-Surman, M.K. |year=1999 |publisher=Indiana University Press |location=Indiana |isbn=978-0-253-21313-6 |page=228 }}</ref> it has been argued that ''Allosaurus'' and other theropods had largely aggressive interactions instead of cooperative interactions with other members of their own species. The study in question noted that cooperative hunting of prey much larger than an individual predator, as is commonly inferred for theropod dinosaurs, is rare among vertebrates in general, and modern [[diapsid]] carnivores (including lizards, crocodiles, and birds) rarely cooperate to hunt in such a way. Instead, they are typically territorial and will kill and cannibalize intruders of the same species, and will also do the same to smaller individuals that attempt to eat before they do when aggregated at feeding sites. According to this interpretation, the accumulation of remains of multiple ''Allosaurus'' individuals at the same site; e.g., in the [[Cleveland-Lloyd Dinosaur Quarry|Cleveland–Lloyd Quarry]], are not due to pack hunting, but to the fact that ''Allosaurus'' individuals were drawn together to feed on other disabled or dead allosaurs, and were sometimes killed in the process. This could explain the high proportion of juvenile and subadult allosaurs present, as juveniles and subadults are disproportionally killed at modern group feeding sites of animals like crocodiles and [[Komodo dragon]]s. The same interpretation applies to Bakker's lair sites.<ref name=RB07>{{cite journal|last1=Roach|first1=Brian T. |year=2007 |title=A reevaluation of cooperative pack hunting and gregariousness in ''Deinonychus antirrhopus'' and other nonavian theropod dinosaurs|journal=Bulletin of the Peabody Museum of Natural History |volume=48 |issue=1 |pages=103–138 |doi=10.3374/0079-032X(2007)48[103:AROCPH]2.0.CO;2|last2=Brinkman|first2=Daniel L.|s2cid=84175628 }}</ref> There is some evidence for cannibalism in ''Allosaurus'', including ''Allosaurus'' shed teeth found among rib fragments, possible tooth marks on a shoulder blade,<ref name=BGD04>{{cite journal |last=Goodchild Drake |first=Brandon |year=2004 |title=A new specimen of ''Allosaurus'' from north-central Wyoming |journal=Journal of Vertebrate Paleontology |volume=24 |issue=3, Suppl |page=65A | doi = 10.1080/02724634.2004.10010643 |s2cid=220415208 }}</ref> and cannibalized allosaur skeletons among the bones at Bakker's lair sites.<ref name=BB04/> On the other hand, pathological analysis done by Foth ''et al.'' argued evidence of surviving serious injuries may support gregariousness in ''Allosaurus''.<ref name=":02">{{cite journal |last1=Foth |first1=Christian |last2=Evers |first2=Serjoscha W. |last3=Pabst |first3=Ben |last4=Mateus |first4=Octávio |last5=Flisch |first5=Alexander |last6=Patthey |first6=Mike |last7=Rauhut |first7=Oliver W.M. |date=12 May 2015 |title=New insights into the lifestyle of Allosaurus (Dinosauria: Theropoda) based on another specimen with multiple pathologies |journal=PeerJ |volume=3 |pages=e940 |doi=10.7717/peerj.940 |pmc=4435507 |pmid=26020001 |doi-access=free}}</ref>

===Brain and senses===
[[File:Allo-endo.tif|thumb|right|[[Endocast]] (cast of the brain cavity) of ''Allosaurus'']]
The brain of ''Allosaurus'', as interpreted from spiral [[CT scan]]ning of an [[Endocranial cast|endocast]], was more consistent with [[crocodilia]]n brains than those of the other living [[archosaur]]s, birds. The structure of the [[Vestibular system|vestibular apparatus]] indicates that the skull was held nearly horizontal, as opposed to strongly tipped up or down. The structure of the [[inner ear]] was like that of a crocodilian, indicating that ''Allosaurus'' was more adapted to hear lower frequencies and would have had difficulty hearing subtle sounds.<ref>{{Cite journal |last=Rogers |first=Scott W. |date=May 2005 |title=Reconstructing the behaviors of extinct species: An excursion into comparative paleoneurology |url=https://onlinelibrary.wiley.com/doi/10.1002/ajmg.a.30538 |journal=American Journal of Medical Genetics Part A |language=en |volume=134A |issue=4 |pages=349–356 |doi=10.1002/ajmg.a.30538 |pmid=15759265 |issn=1552-4825 |archive-date=January 17, 2024 |access-date=January 17, 2024 |archive-url=https://web.archive.org/web/20240117170649/https://onlinelibrary.wiley.com/doi/10.1002/ajmg.a.30538 |url-status=live |url-access=subscription }}</ref> The [[olfactory bulb]]s were large and well suited for detecting odors,<ref name=SWR99/> but were typical for an animal of its size.<ref>{{cite journal | pmc=2660930 | date=2008 | last1=Zelenitsky | first1=D. K. | last2=Therrien | first2=F. | last3=Kobayashi | first3=Y. | title=Olfactory acuity in theropods: Palaeobiological and evolutionary implications | journal=Proceedings of the Royal Society B: Biological Sciences | volume=276 | issue=1657 | pages=667–673 | doi=10.1098/rspb.2008.1075 | pmid=18957367 }}</ref>

===Paleopathology===
[[File:Allosaurus fragilis USNM4734.jpg|thumb|Mounted ''A. fragilis'' skeleton (USNM 4734), which has several healed injuries]]
In 2001, Bruce Rothschild and others published a study examining evidence for [[stress fracture]]s and [[tendon avulsion]]s in [[theropod]] dinosaurs and the implications for their behavior. Since stress fractures are caused by repeated trauma rather than singular events they are more likely to be caused by the behavior of the animal than other kinds of injury. Stress fractures and tendon avulsions occurring in the forelimb have special behavioral significance since while injuries to the feet could be caused by running or [[animal migration|migration]], resistant prey items are the most probable source of injuries to the hand. ''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. When the researchers looked for stress fractures, they found that ''Allosaurus'' had a significantly greater number of stress fractures than ''[[Albertosaurus]]'', ''[[Ornithomimus]]'' or ''[[Archaeornithomimus]]''. Of the 47 hand bones the researchers studied, three were found to contain stress fractures. Of the feet, 281 bones were studied and 17 were found to have stress fractures. The stress fractures in the foot bones "were distributed to the [[proximal]] [[phalanges]]" and occurred across all three weight-bearing toes in "statistically indistinguishable" numbers. Since the lower end of the third metatarsal would have contacted the ground first while an allosaur was running, it would have borne the most stress. If the allosaurs' stress fractures were caused by damage accumulating while walking or running this bone should have experience more stress fractures than the others. The lack of such a bias in the examined ''Allosaurus'' fossils indicates an origin for the stress fractures from a source other than running. The authors conclude that these fractures occurred during interaction with prey, like an allosaur trying to hold struggling prey with its feet. The abundance of stress fractures and avulsion injuries in ''Allosaurus'' provide evidence for "very active" predation-based rather than scavenging diets.<ref name="rothschild-dino">Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and [[Kenneth Carpenter|Carpenter, K.]], Indiana University Press, p. 331–336.</ref>

The left [[scapula]] and [[fibula]] of an ''Allosaurus fragilis'' specimen cataloged as USNM 4734 are both pathological, both probably due to healed fractures. The specimen USNM 8367 preserved several pathological gastralia which preserve evidence of healed fractures near their middle. Some of the fractures were poorly healed and "formed pseudoarthroses". A specimen with a fractured rib was recovered from the [[Cleveland-Lloyd Dinosaur Quarry|Cleveland-Lloyd Quarry]]. Another specimen had fractured ribs and fused vertebrae near the end of the tail. An apparent subadult male ''Allosaurus fragilis'' was reported to have extensive pathologies, with a total of fourteen separate injuries. The specimen MOR 693 had pathologies on five ribs, the sixth neck vertebra, the third, eighth, and thirteenth back vertebrae, the second tail vertebra and its chevron, the [[gastralia]] right scapula, manual phalanx I left [[Ilium (bone)|ilium]] metatarsals III and V, the first phalanx of the third toe and the third phalanx of the second. The ilium had "a large hole...caused by a blow from above". The near end of the first phalanx of the third toe was afflicted by an [[involucrum]].<ref name="molnar-pathology"/>

Additionally, a subadult ''Allosaurus'' individual that suffered from [[spondyloarthropathy]] has been discovered in Dana Quarry in Wyoming. This finding represents the first known fossil evidence of spondyloarthropathy occurring in a theropod.<ref>{{Cite journal |last1=Xing |first1=Lida |last2=Rothschild |first2=Bruce M. |last3=Du |first3=Chunlei |last4=Wang |first4=Donghao |last5=Wen |first5=Kexiang |last6=Su |first6=Jiayin |date=January 2, 2024 |title=New palaeopathology cases of Allosaurus fragilis (Dinosauria: Theropoda) |url=https://www.tandfonline.com/doi/full/10.1080/08912963.2022.2155817 |journal=[[Historical Biology]] |language=en |volume=36 |issue=1 |pages=203–208 |doi=10.1080/08912963.2022.2155817 |bibcode=2024HBio...36..203X |issn=0891-2963 |access-date=June 29, 2024 |via=Taylor and Francis Online|url-access=subscription }}</ref>
[[File:Allosaurus "Big Al II".jpg|thumb|Skeletal restoration of "Big Al II" showing bones with pathologies]]
Other pathologies reported in ''Allosaurus'' include:<ref name=Chin09/><ref name="molnar-pathology">{{cite book|last=Molnar |first=R.E. |year=2001 |chapter=Theropod paleopathology: a literature survey |title=Mesozoic Vertebrate Life |editor1-last=Tanke |editor1-first=D.H. |editor2-last=Carpenter |editor2-first=K. |publisher=Indiana University Press |pages=337–363}}</ref><!--<ref>{{Cite web|url=https://paleorxiv.org/f3rh6/|access-date=February 11, 2023|website=paleorxiv.org|doi=10.31233/osf.io/f3rh6}}</ref>-->
* [[Willow breaks]] in two ribs
* Healed fractures in the [[humerus]] and [[Radius (bone)|radius]]
* Distortion of [[joint]] surfaces in the foot, possibly due to [[osteoarthritis]] or developmental issues
* [[Osteopetrosis]] along the endosteal surface of a [[tibia]].
* Distortions of the joint surfaces of the tail vertebrae, possibly due to [[osteoarthritis]] or developmental issues
* "[E]xtensive '[[neoplastic]]' [[ankylosis]] of caudals", possibly due to physical trauma, as well as the fusion of chevrons to centra
* Coossification of vertebral centra near the end of the tail
* [[Amputation]] of a chevron and foot bone, both possibly a result of bites
* "[E]xtensive [[exostoses]]" in the first phalanx of the third toe
* Lesions similar to those caused by [[osteomyelitis]] in two [[scapulae]]
* [[Bone spurs]] in a [[premaxilla]], [[ungual]], and two [[metacarpals]]
* Exostosis in a pedal phalanx possibly attributable to an infectious disease
* A metacarpal with a round depressed fracture

==Paleoecology==

[[File:Alloquarrynolang.png|thumb|left|Locations in the [[Morrison Formation]] (yellow) where ''Allosaurus'' remains have been found]]
''Allosaurus'' was the most common large theropod in the vast tract of [[American West|Western American]] fossil-bearing rock known as the [[Morrison Formation]], accounting for 70 to 75% of theropod specimens,<ref name=JF07/> and as such was at the top [[trophic level]] of the Morrison food chain.<ref name=JRF03a>{{cite book |last=Foster |first=John R. |title=Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. |year=2003 |series=New Mexico Museum of Natural History and Science Bulletin, '''23''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |page=29}}</ref> The Morrison Formation is interpreted as a [[semiarid]] environment with distinct [[wet season|wet]] and [[dry season]]s, and flat [[floodplain]]s.<ref name=DAR89>{{cite book |last=Russell |first=Dale A. |author-link=Dale Russell |title=An Odyssey in Time: Dinosaurs of North America |year=1989 |publisher=NorthWord Press |location=Minocqua, Wisconsin |isbn=978-1-55971-038-1 |pages=64–70 }}</ref> Vegetation varied from river-lining forests of [[conifer]]s, [[tree fern]]s, and [[fern]]s ([[gallery forest]]s), to fern [[savanna]]s with occasional trees such as the ''[[Araucaria]]''-like conifer ''[[Brachyphyllum]]''.<ref name=KC06>{{cite book |last=Carpenter |first=Kenneth |author-link=Kenneth Carpenter |year=2006 |chapter=Biggest of the big: a critical re-evaluation of the mega-sauropod ''Amphicoelias fragillimus'' |editor=Foster, John R. |editor2=Lucas, Spencer G. |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin, '''36''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |pages=131–138 }}</ref>

The Morrison Formation has been a rich fossil hunting ground. The flora of the period has been revealed by fossils of [[Chlorophyta|green algae]], fungi, [[moss]]es, [[Equisetum|horsetails]], ferns, [[cycad]]s, [[ginkgo]]es, and several families of [[conifer]]s. Animal fossils discovered include [[bivalve]]s, [[snail]]s, [[Actinopterygii|ray-finned fishes]], frogs, [[salamander]]s, turtles, [[Sphenodontia|sphenodont]]s, lizards, terrestrial and aquatic [[crocodylomorpha|crocodylomorphs]], several species of [[pterosaur]], numerous dinosaur species, and early [[mammal]]s such as [[Docodonta|docodont]]s, [[Multituberculata|multituberculate]]s, [[Symmetrodonta|symmetrodont]]s, and [[Triconodonta|triconodont]]s. Dinosaurs known from the Morrison include the theropods ''[[Ceratosaurus]]'', ''[[Ornitholestes]]'', ''[[Tanycolagreus]]'', and ''[[Torvosaurus]]'', the [[sauropod]]s ''[[Haplocanthosaurus]]'', ''[[Camarasaurus]]'', ''[[Cathetosaurus]]'', ''[[Brachiosaurus]]'', ''[[Suuwassea]]'', ''[[Apatosaurus]]'', ''[[Brontosaurus]]'', ''[[Barosaurus]]'', ''[[Diplodocus]]'', ''[[Supersaurus]]'', ''[[Amphicoelias]]'', and ''[[Maraapunisaurus]]'', and the [[ornithischia]]ns ''[[Camptosaurus]]'', ''[[Dryosaurus]]'', and ''[[Stegosaurus]]''.<ref name=DJCetal06>{{cite book |last1=Chure |first1=Daniel J. |last2=Litwin, Ron|last3= Hasiotis, Stephen T.|last4= Evanoff, Emmett|last5= Carpenter, Kenneth |year=2006 |chapter=The fauna and flora of the Morrison Formation: 2006 |editor=Foster, John R. |editor2=Lucas, Spencer G. |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin '''36''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |pages=233–248}}</ref> ''Allosaurus'' is commonly found at the same sites as ''Apatosaurus'', ''Camarasaurus'', ''Diplodocus'', and ''Stegosaurus''.<ref name="DBBM80">{{cite journal |last1=Dodson |first1=Peter |author-link1=Peter Dodson |last2=Behrensmeyer |first2=A.K. |last3=Bakker |first3=Robert T. |author-link3=Robert T. Bakker |last4=McIntosh |first4=John S. |year=1980 |title=Taphonomy and paleoecology of the dinosaur beds of the Jurassic Morrison Formation |journal=Paleobiology |volume=6 |issue=2 |pages=208–232 |doi=10.1017/S0094837300025768}}</ref> The Late Jurassic formations of Portugal where ''Allosaurus'' is present are interpreted as having been similar to the Morrison, but with a stronger [[Ocean|marine]] influence. Many of the dinosaurs of the Morrison Formation are the same genera as those seen in Portuguese rocks (mainly ''Allosaurus'', ''Ceratosaurus'', ''Torvosaurus'', and ''Stegosaurus''), or have a close counterpart (''Brachiosaurus'' and ''[[Lusotitan]]'', ''Camptosaurus'' and ''[[Draconyx]]'').<ref name=OM06>{{cite book |last=Mateus |first=Octávio |year=2006 |chapter=Jurassic dinosaurs from the Morrison Formation (USA), the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): A comparison |editor=Foster, John R. |editor2=Lucas, Spencer G. |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin, '''36''' |publisher=New Mexico Museum of Natural History and Science |location=Albuquerque, New Mexico |pages=223–231}}</ref>

[[File:Dry season at the Mygatt-Moore Quarry.PNG|thumb|alt=Allosaurus and Ceratosaurus fighting|Dry season at the Mygatt-Moore Quarry showing ''Ceratosaurus'' (center) and ''Allosaurus'' fighting over the desiccated carcass of another theropod]]
''Allosaurus'' coexisted with fellow large theropods ''[[Ceratosaurus]]'' and ''[[Torvosaurus]]'' in both the United States and Portugal.<ref name=OM06/> The three appear to have had different [[ecological niche]]s, based on anatomy and the location of fossils. ''Ceratosaurus'' and ''Torvosaurus'' may have preferred to be active around waterways, and had lower, thinner bodies that would have given them an advantage in forest and underbrush terrains, whereas ''Allosaurus'' was more compact, with longer legs, faster but less maneuverable, and seems to have preferred dry floodplains.<ref name=BB04>{{cite book |last1=Bakker |first1=Robert T. |last2=Bir, Gary |year=2004 |chapter=Dinosaur crime scene investigations: theropod behavior at Como Bluff, Wyoming, and the evolution of birdness |editor=Currie, Philip J. |editor2=Koppelhus, Eva B. |editor3=Shugar, Martin A. |editor4=Wright, Joanna L. |title=Feathered Dragons: Studies on the Transition from Dinosaurs to Birds |publisher=Indiana University Press |location=Bloomington and Indianapolis |pages=301–342 |isbn=978-0-253-34373-4}}</ref> ''Ceratosaurus'', better known than ''Torvosaurus'', differed noticeably from ''Allosaurus'' in functional anatomy by having a taller, narrower skull with large, broad teeth.<ref name=DH98/><!--if anyone finds the ref where ''Allosaurus'' was suggested as a female ''Ceratosaurus'', here's a good place to put it for irony--> ''Allosaurus'' was itself a potential food item to other carnivores, as illustrated by an ''Allosaurus'' [[Pubis (bone)|pubic foot]] marked by the teeth of another theropod, probably ''[[Ceratosaurus]]'' or ''[[Torvosaurus]]''. The location of the bone in the body (along the bottom margin of the torso and partially shielded by the legs), and the fact that it was among the most massive in the skeleton, indicates that the ''Allosaurus'' was being scavenged.<ref name=CFJ98>{{cite journal |last=Chure |first=Daniel J. |year=2000 |title=Prey bone utilization by predatory dinosaurs in the Late Jurassic of North America, with comments on prey bone use by dinosaurs throughout the Mesozoic |journal=Gaia |volume=15 |pages=227–232 |issn=0871-5424 |url=https://www.academia.edu/18277086 |archive-date=November 9, 2021 |access-date=December 4, 2017 |archive-url=https://web.archive.org/web/20211109012826/https://www.academia.edu/18277086 |url-status=live }}</ref>

A bone assemblage in the Upper Jurassic Mygatt-Moore Quarry preserves an unusually high occurrence of theropod bite marks, most of which can be attributed to ''Allosaurus'' and ''Ceratosaurus'', while others could have been made by ''Torvosaurus'' given the size of the striations. While the position of the bite marks on the herbivorous dinosaurs is consistent with predation or early access to remains, bite marks found on ''Allosaurus'' material suggest scavenging, either from the other theropods or from another ''Allosaurus''. The unusually high concentration of theropod bite marks compared to other assemblages could be explained either by a more complete utilization of resources during a dry season by theropods, or by a collecting bias in other localities.<ref>{{Cite journal|last1=Drumheller|first1=Stephanie K.|last2=McHugh|first2=Julia B.|last3=Kane|first3=Miriam|last4=Riedel|first4=Anja|last5=D’Amore|first5=Domenic C.|date=May 27, 2020|title=High frequencies of theropod bite marks provide evidence for feeding, scavenging, and possible cannibalism in a stressed Late Jurassic ecosystem|journal=PLOS ONE|language=en|volume=15|issue=5|pages=e0233115|doi=10.1371/journal.pone.0233115|issn=1932-6203|pmc=7252595|pmid=32459808|bibcode=2020PLoSO..1533115D|doi-access=free}}</ref>

==References==
{{Reflist|30em}}

==External links==
{{Sister project links |wikt=Allosaurus |commons=Allosaurus|commonscat=yes |n=no |q=no |s=no |b=wikijunior:Dinosaurs/Allosaurus |species=Allosaurus}}
* [https://web.archive.org/web/20130929080234/http://archosaur.us/theropoddatabase/Carnosauria.htm#Allosaurusfragilis Specimens, discussion, and references pertaining to ''Allosaurus fragilis''] at The Theropod Database
* [http://pioneer.utah.gov/research/utah_symbols/fossil.html Utah State Fossil, ''Allosaurus''] ({{Webarchive|url=https://web.archive.org/web/20100617044418/http://pioneer.utah.gov/research/utah_symbols/fossil.html |date=June 17, 2010 }}), from Pioneer: Utah's Online Library
* [https://web.archive.org/web/20070926062344/http://skeletaldrawing.com/psgallery/images/allosaurus.jpg Restoration of MOR 693 ("Big Al")] and [https://web.archive.org/web/20071007120836/http://www.skeletaldrawing.com/psgallery/pages/allosaurdeepmuscle.html muscle and organ restoration] at Scott Hartman's Skeletal Drawing website
* [http://dml.cmnh.org/1995Nov/msg00278.html List of the many possible ''Allosaurus'' species...] ({{Webarchive|url=https://web.archive.org/web/20050324010259/http://dml.cmnh.org/1995Nov/msg00278.html |date=March 24, 2005 }})

{{Theropoda|A.}}
{{Taxonbar|from=Q14400}}
{{Authority control}}

[[Category:Allosauridae]]
[[Category:Dinosaur genera]]
[[Category:Kimmeridgian dinosaurs]]
[[Category:Tithonian dinosaurs]]
[[Category:Lourinhã Formation]]
[[Category:Morrison Formation]]
[[Category:Dinosaurs of the United States]]
[[Category:Fossil taxa described in 1877]]
[[Category:Taxa named by Othniel Charles Marsh]]