Editing Allosaurus (section)

==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"/>