Editing Allosaurus (section)

==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