Allosaurus

Source: Wikipedia, the free encyclopedia.

Allosaurus
Temporal range:
Ma
A. jimmadseni specimen "Big Al II" (SMA 0005)
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: Saurischia
Clade: Theropoda
Family: †Allosauridae
Subfamily: †Allosaurinae
Marsh, 1878
Genus: †Allosaurus
Marsh, 1877
Type species
†Allosaurus fragilis
Marsh, 1877
Other species[1]
Synonyms
Genus synonymy

Allosaurus (

paleontologist Othniel Charles Marsh
. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles.

Allosaurus was a large

allosaurid
, a type of carnosaurian theropod dinosaur.

The genus has a very complicated

Cleveland-Lloyd Dinosaur Quarry
returned the name "Allosaurus" to prominence.

As the most abundant large predator of the Morrison Formation, Allosaurus was at the top of the food chain and probably preyed on contemporaneous large herbivorous dinosaurs, with the possibility of hunting other predators. Potential prey included

sauropods. Some paleontologists interpret Allosaurus as having had cooperative social behavior
and hunting in packs, while others believe individuals may have been aggressive toward each other and that congregations of this genus are the result of lone individuals feeding on the same carcasses.

Discovery and history

Early discoveries and research

Mounted A. fragilis specimen (AMNH 5753), posed as scavenging an Apatosaurus
AMNH 5753 in a Charles R. Knight life restoration (Outdated)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. It came from 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.[4] He later decided it deserved its own genus, Antrodemus.[5]

Allosaurus itself is based on YPM 1930, a small collection of fragmentary bones including parts of three vertebrae, a rib fragment, a tooth, a toe bone, and (most useful for later discussions) the shaft of the right humerus (upper arm). Othniel Charles Marsh gave these remains the formal name Allosaurus fragilis in 1877. Allosaurus comes from the Greek words allos/αλλος, meaning "strange" or "different", and sauros/σαυρος, meaning "lizard" or "reptile".[6] It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery.[7][8] 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, north of Cañon City.[7] 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[9] and Labrosaurus,[10] as well as Cope's Epanterias.[11]

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 Mudge of the type specimen of Allosaurus in Colorado, Marsh elected to concentrate work in Wyoming. When work resumed at Garden Park in 1883, M. P. Felch found an almost complete Allosaurus and several partial skeletons.[12] In addition, one of Cope's collectors, H. F. Hubbell, found a specimen in the Como Bluff area of Wyoming in 1879, but apparently did not mention its completeness and Cope never unpacked it. Upon unpacking it in 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.[13] This is the well-known mount poised over a partial Apatosaurus skeleton as if 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.[14]

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.[15] For example, Williston pointed out in 1901 that Marsh had never been able to adequately distinguish Allosaurus from Creosaurus.[16] The most influential early attempt to sort out the convoluted situation was produced by Charles W. Gilmore in 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.[17] 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.[18] "Antrodemus" has been used informally for convenience when distinguishing between the skull Gilmore restored and the composite skull restored by Madsen.[19]

Cleveland-Lloyd discoveries

A. fragilis at the Cleveland-Lloyd Dinosaur Quarry museum, Utah

Although sporadic work at what became known as the

state fossil of Utah in 1988.[23]

Recent work: 1980s–present

The period since Madsen's monograph has been marked by a great expansion in studies dealing with topics concerning Allosaurus in life (paleobiological and paleoecological topics). Such studies have covered topics including skeletal variation,[24] growth,[25][26] skull construction,[27] hunting methods,[28] the brain,[29] and the possibility of gregarious living and parental care.[30] Reanalysis of old material (particularly of large 'allosaur' specimens),[31][32] new discoveries in Portugal,[33] and several very complete new specimens[34][35][36] have also contributed to the growing knowledge base.

"Big Al" and "Big Al II"

"Big Al" at the Museum of the Rockies

In

University of Wyoming Geological Museum team.[37] This skeleton was discovered by a Swiss team, led by Kirby Siber. Chure and Loewen in 2020 identified the individual as a representative of the species Allosaurus jimmadseni. In 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 Allosaurus jimmadseni.[1]

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,[37] as it was a subadult estimated at only 87% grown.[38] The specimen was described by Breithaupt in 1996.[35] Nineteen of its bones were broken or showed signs of serious infection, which may have contributed to "Big Al's" death. 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.[38][39] "Big Al II" is also known to have multiple injuries.[40]

Species

Diagram comparing skulls of the three recognized species; A. fragilis (A), A. jimmadseni (B), A. europaeus (C)

Six species of Allosaurus have been named: A. amplus,[41] A. atrox,[42] A. europaeus,[43] the type species A. fragilis,[44] A. jimmadseni[1][42] and A. lucasi.[45] Among these, 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.[1] However, A. europaeus does not show any unique characters compared to the North American species, so a reevaluation of its validity is required.[46][47]

A. fragilis is the type species and was named by Marsh in 1877.

Upper Jurassic-age Morrison Formation of the United States, spread across Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming.[44] Details of the humerus (upper arm) of A. fragilis have been used as diagnostic among Morrison theropods,[18] but A. jimmadseni indicates that this is no longer the case at the species level.[42]

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.

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.[22]

A. fragilis, A. jimmadseni, A. amplus, and A. lucasi are all known from remains discovered in the

jugal.[53] A. europaeus was found in the Kimmeridgian-age Porto Novo Member of the Lourinhã Formation,[43] but it may be the same as A. fragilis.[46]

Allosaurus material from Portugal was first reported in

chevrons, part of the hips, and legs. This specimen was assigned to A. fragilis,[33] but the subsequent discovery of a partial skull and neck (ML 415) near Lourinhã, in the Kimmeridgian-age Porto Novo Member of the Lourinhã Formation, spurred the naming of the new species as A. europaeus by Octávio Mateus and colleagues. The species appeared earlier in the Jurassic than A. fragilis and differs from other species of Allosaurus in cranial details.[43] However, more material may show it to be A. fragilis, as originally described.[46]

The issue of species and potential synonyms is complicated by the

neotype),[54] a decision that was ratified by the ICZN on December 29, 2023.[55]

Synonyms

Holotype material of Creosaurus atrox

Creosaurus, Epanterias, and Labrosaurus are regarded as junior synonyms of Allosaurus.[44] 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 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.[56] Later researchers suggested that the bone was pathologic, showing an injury to the living animal,[17] and that part of the unusual form of the rear of the bone was due to plaster reconstruction.[57] It is now regarded as an example of A. fragilis.[44]

Cast of synonym "A. atrox" at the South Australian Museum.

In his 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 different sex due to rarity.[31] Allosaurus atrox was originally named by Marsh in 1878 as the type species of its own genus, Creosaurus, and is based on YPM 1890, an assortment of bones that includes a couple of pieces of the skull, portions of nine tail vertebrae, two hip vertebrae, an ilium, and ankle and foot bones.[9] Although the idea of two common Morrison allosaur species was followed in some semi-technical and popular works,[50] the 2000 thesis on Allosauridae noted that Charles Gilmore mistakenly reconstructed USNM 4734 as having a shorter skull than the specimens referred by Paul to atrox, refuting supposed differences between USNM 4734 and putative A. atrox specimens like DINO 2560, AMNH 600, and AMNH 666.[42]

"Allosaurus agilis", seen in Zittel, 1887, and Osborn, 1912, is a typographical error for A. fragilis.[42] "Allosaurus ferox" is a typographical error by Marsh for A. fragilis in a figure caption for the partial skull YPM 1893[58] and YPM 1893 has been treated as a specimen of A fragilis.[44] Likewise, "Labrosaurus fragilis" is a typographical error by Marsh (1896) for Labrosaurus ferox.[57] "A. whitei" is a nomen nudum coined by Pickering in 1996 for the complete Allosaurus specimens that Paul referred to A. atrox.[42]

"Madsenius" was coined by David Lambert in 1990,[59] 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 Bakker as "Madsenius trux".[60] However, "Madsenius" is now seen as yet another synonym of Allosaurus because Bakker's action was predicated upon the false assumption of USNM 4734 being distinct from long-snouted Allosaurus due to errors in Gilmore's 1920 reconstruction of USNM 4734.[61]

"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.[62][63][61]

Formerly assigned species and fossils

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

Richard Swann Lull to the new ornithopod species Dryosaurus grandis, except for a tooth.[65] It was transferred to Antrodemus by Oliver Hay in 1902, but Hay later clarified that this was an inexplicable error on his part.[66][67] Gilmore considered the tooth nondiagnostic but transferred it to Dryptosaurus, as D. medius.[17] 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.[44] It may be closely related to Acrocanthosaurus.[68]

Allosaurus valens is a new combination for Antrodemus valens used by Friedrich von Huene in 1932;[42] Antrodemus valens itself may also pertain to Allosaurus fragilis,[44] as Gilmore suggested in 1920.[17]

A. lucaris, another Marsh name, was given to a partial skeleton in 1878.[9] He later decided it warranted its own genus, Labrosaurus,[10] but this has not been accepted, and A. lucaris is also regarded as another specimen of A. fragilis.[44] Allosaurus lucaris, is known mostly from vertebrae, sharing characters with Allosaurus.[69] 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.[54]

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

Buryatia, Russia.[70] It was transferred to Chilantaisaurus in 1990,[71] but is now considered a nomen dubium indeterminate beyond Theropoda.[72]

Allosaurus meriani was a new combination by George Olshevsky for Megalosaurus meriani Greppin, 1870, based on a tooth from the Late Jurassic of Switzerland.[73][74] However, a recent overview of Ceratosaurus included it in Ceratosaurus sp.[57]

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.[75][76] However, it was considered indeterminate beyond Dinosauria by Chure,[42] 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.[77]

A. amplexus was named by Gregory S. Paul for giant Morrison allosaur remains, and included in his conception Saurophagus maximus (later Saurophaganax).[31] A. amplexus was originally coined by Cope in 1878 as the type species of his new genus Epanterias,[11] and is based on what is now AMNH 5767, parts of three vertebrae, a coracoid, and a metatarsal.[78] Following Paul's work, this species has been accepted as a synonym of A. fragilis.[44] A 2010 study by Paul and Kenneth Carpenter, however, indicates that Epanterias is temporally younger than the A. fragilis type specimen, so it is a separate species at minimum.[54]

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.[32] 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.[24] This reassignment was rejected in a review of basal tetanurans.[44]

There are also several species left over from the synonymizations of Creosaurus and Labrosaurus with Allosaurus.

Creosaurus potens was named by Lull in 1911 for a vertebra from the Early Cretaceous of Maryland.[65] It is now regarded as a dubious theropod.[44] Labrosaurus stechowi, described in 1920 by Janensch based on isolated Ceratosaurus-like teeth from the Tendaguru beds of Tanzania,[79] was listed by Donald F. Glut as a species of Allosaurus,[76] is now considered a dubious ceratosaurian related to Ceratosaurus.[57][80] L. sulcatus, named by Marsh in 1896 for a Morrison theropod tooth,[58] which like L. stechowi is now regarded as a dubious Ceratosaurus-like ceratosaur.[57][80]

A. tendagurensis tibia, Naturkunde Museum Berlin

A. tendagurensis was named in 1925 by Werner Janensch for a partial shin (MB.R.3620) found in the Kimmeridgian-age Tendaguru Formation in Mtwara, Tanzania.[81] Although tabulated as a tentatively valid species of Allosaurus in the second edition of the Dinosauria,[44] subsequent studies place it as indeterminate beyond Tetanurae, either a carcharodontosaurian or megalosaurid.[82][83] Although obscure, it was a large theropod, possibly around 10 metres (33 ft) long and 2.5 tonnes (2.5 long tons; 2.8 short tons) in weight.[84]

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).[85] They were reclassified as an indeterminate theropod.[72] Also, reports of Allosaurus in Shanxi, China go back to at least 1982.[86] These were interpreted as Torvosaurus remains in 2012.[72]

An

abelisaur.[93]

Description

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 8.5 m (28 ft) and mass of 1.7 metric tons (1.9 short tons),[76][94] with the largest definitive Allosaurus specimen (AMNH 680) estimated at 9.7 metres (32 feet) long,[84] with an estimated weight of 2.3–2.7 metric tons (2.5–3.0 short tons).[84][95] In his 1976 monograph on Allosaurus, James H. Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of 12 to 13 m (39 to 43 ft).[18] As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between 1.5 metric tons (1.7 short tons), 1 to 4 metric tons (1.1 to 4.4 short tons), and approximately 1 metric ton (1.1 short tons) for modal adult weight (not maximum).[96] John Foster, a specialist on the Morrison Formation, suggests that 1 metric ton (1.1 short tons) is reasonable for large adults of A. fragilis, but that 700 kg (1,500 lb) is a closer estimate for individuals represented by the average-sized thigh bones he has measured.[97] Using the subadult specimen nicknamed "Big Al", since assigned to the species Allosaurus jimmadseni,[1] researchers using computer modeling arrived at a best estimate of 1.5 metric tons (1.7 short tons) for the individual, but by varying parameters they found a range from approximately 1.4 metric tons (1.5 short tons) to approximately 2 metric tons (2.2 short tons).[98] A separate computational project estimated the adaptive optimum body mass in Allosaurus to be ~2,345 kg.[99] A. europaeus has been measured up to 7 m (23 ft) in length and 1 metric ton (1.1 short tons) in body mass.[94]

A. jimmadseni skeletal reconstruction

Several gigantic specimens have been attributed to Allosaurus, but may in fact belong to other genera. The closely related genus Saurophaganax (OMNH 1708) reached perhaps 10.5 m (34 ft) in length,[94] and its single species has sometimes been included in the genus Allosaurus as Allosaurus maximus, though recent studies support it as a separate genus.[42] Another potential specimen of Allosaurus, once assigned to the genus Epanterias (AMNH 5767), may have measured 12.1 metres (40 feet) in length.[84] A more recent discovery is a partial skeleton from the Peterson Quarry in Morrison rocks of New Mexico; this large allosaurid may be another individual of Saurophaganax.[100]

David K. Smith, examining Allosaurus fossils by quarry, found that the

jugal.[53] 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.[101]

Skull

A. jimmadseni skull with diagram highlighting individual bones

The skull and teeth of Allosaurus were modestly proportioned for a theropod of its size. Paleontologist

serrated
teeth.

The skull had a pair of horns above and in front of the eyes. These horns were composed of extensions of the lacrimal bones,[18] and varied in shape and size. There were also lower paired ridges running along the top edges of the nasal bones that led into the horns.[18] The horns were probably covered in a keratin sheath and may have had a variety of functions, including acting as sunshades for the eyes,[18] being used for display, and being used in combat against other members of the same species[31][102] (although they were fragile).[18] There was a ridge along the back of the skull roof for muscle attachment, as is also seen in tyrannosaurids.[31]

Inside the lacrimal bones were depressions that may have held

braincase and frontals may also have had a joint.[18]

Postcranial skeleton

Life restoration of A. fragilis

Allosaurus had nine

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 characteristic, with females lacking fused bones to make egg-laying easier.[18]
This proposal has not attracted further attention, however.

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)

metatarsal, perhaps used as a lever between the Achilles tendon and foot.[110]

Skin

Skin impressions from Allosaurus have been described. One impression, from a juvenile specimen, measures 30 cm² and is associated with the anterior dorsal ribs/pectoral region. The impression shows small

scales measuring 1–3 mm in diameter. A skin impression from the "Big Al Two" specimen, associated with the base of the tail, measures 20 cm x 20 cm and shows large scales measuring up to 2 cm in diameter. However, it has been noted that these scales are more similar to those of 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.[111]

Another Allosaurus fossil features a skin impression from the mandible, showing scales measuring 1–2 mm in diameter. The same fossil also preserves skin impressions from the ventral side of the neck, showing broad scutes. A small skin impression from an Allosaurus skull has been reported but never described.[111]

Classification

Allosaurus was an allosaurid, a member of a

Romer, 1956 and 1966,[113][114] Steel, 1970,[115] and Walker, 1964.[116]

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,[117] Acrocanthosaurus, Chilantaisaurus, Compsosuchus, Stokesosaurus, and Szechuanosaurus.[118] Given modern knowledge of theropod diversity and the advent of cladistic study of evolutionary relationships, none of these theropods is now recognized as an allosaurid, although several, like Acrocanthosaurus and Yangchuanosaurus, are members of closely related families.[44]

Restored skeleton of Saurophaganax or A. maximus
Illustrations showing the skull of A. jimmadseni from the side (A), top (B), and back (C)

Below is a cladogram based on the analysis of Benson et al. in 2010.[119]

Allosauroidea

Allosauridae is one of four families in Allosauroidea; the other three are

Sinraptoridae.[44] Allosauridae has at times been proposed as ancestral to the Tyrannosauridae (which would make it paraphyletic), one example being Gregory S. Paul's Predatory Dinosaurs of the World,[120] but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the Coelurosauria.[121] Allosauridae is the smallest of the carnosaur families, with only Saurophaganax and a currently unnamed French allosauroid accepted as possible valid genera besides Allosaurus in the most recent review.[44] Another genus, Epanterias, is a potential valid member, but it and Saurophaganax may turn out to be large examples of Allosaurus.[31] Recent reviews have kept the genus Saurophaganax and included Epanterias with Allosaurus.[96][44]

Paleobiology

Life history

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 eggs—crushed eggs from Colorado have been suggested as those of Allosaurus.[76] Based on 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 lb) per year.[25]

Medullary bone tissue (endosteally derived, ephemeral, mineralization located inside the

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.[122] 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.[123] 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.[124]

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.

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.[125] Conversely, the skull bones appear to have generally grown isometrically, increasing in size without changing in proportion.[53]

Feeding

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

Sauropods seem to be likely candidates as both live prey and as objects of scavenging, based on the presence of scrapings on sauropod bones fitting allosaur teeth well and the presence of shed allosaur teeth with sauropod bones.[127] 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.[31] Another possibility is that it preferred to hunt juveniles instead of fully grown adults.[97][50] 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.[28]

A. fragilis showing its maximum possible gape, based on Bakker (1998) and 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 N,[27][128] but the skull could withstand nearly 55,500 N of vertical force against the tooth row.[27] 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.[27] 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.[129] 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.[130] 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.[44] 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.[97] This is compatible with other evidence that the forelimbs were strong and capable of restraining prey.[108] 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.[131][132]

A biomechanical study published in 2013 by Eric Snively and colleagues found that Allosaurus had an unusually low attachment point on the skull for the longissimus capitis superficialis neck muscle compared to other theropods such as Tyrannosaurus. 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 falcons, such as kestrels: 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.[133] In addition, Allosaurus was able to "move its head and neck around relatively rapidly and with considerable control", at the cost of power.[134]

Allosaurus and Stegosaurus skeletons, the Denver Museum of Nature and Science

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 crocodilians. As with crocodilians, this may have been enough to judge prey distance and time attacks.[135][136][137] The arms, compared with those of other theropods, were suited for both grasping prey at a distance or clutching it close,[108] and the articulation of the claws suggests that they could have been used to hook things.[17] Finally, the top speed of Allosaurus has been estimated at 30–55 kilometres (19–34 mi) per hour.[138]

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.[139]

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.[140][141] 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.[142][99] A single dead adult Barosaurus or Brachiosaurus would have had enough calories to sustain multiple large theropods for weeks or months,[143] though the vast majority of the Morrison’s sauropod fossil record consisted of much smaller-bodied taxa such as Camarasaurus lentus or Diplodocus.[144]

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,[145] 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.[146] 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. Allosaurs typically lived in harsh environments dominated by large sauropods, many of whom would have died annually during their migrations and dry season conditions,[147] making it possible for them to meet their energy budgets by scavenging sauropod-falls even if they had broken limb bones. Tyrannosaurs may have been less resilient to appendicular fractures, because they didn't have access to sauropod-falls and therefore relied on predation to a greater degree than allosaurs. Loss of locomotor ability was probably much more dangerous for them.

Social behavior

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.[148] Such a depiction is common in semitechnical and popular dinosaur literature.[12][117][50] 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.[30] However, there is actually little evidence of gregarious behavior in theropods,[44] and social interactions with members of the same species would have included antagonistic encounters, as shown by injuries to gastralia[34] 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.[149]

Although Allosaurus may have hunted in packs,

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 dragons. The same interpretation applies to Bakker's lair sites.[151] There is some evidence for cannibalism in Allosaurus, including Allosaurus shed teeth found among rib fragments, possible tooth marks on a shoulder blade,[152] and cannibalized allosaur skeletons among the bones at Bakker's lair sites.[153]

Brain and senses

Endocast (cast of the brain cavity) of Allosaurus

The brain of Allosaurus, as interpreted from spiral

endocast, was more consistent with crocodilian brains than those of the other living archosaurs, birds. The structure of the 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.[154] The olfactory bulbs were large and well suited for detecting odors,[29] but were typical for an animal of its size.[155]

Paleopathology

Mounted A. fragilis skeleton (USNM4734), which has several healed injuries

In 2001, Bruce Rothschild and others published a study examining evidence for

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.[156]

The left

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 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.[157]

Skeletal restoration of "Big Al II" showing bones with pathologies

Other pathologies reported in Allosaurus include:[123][157]

Paleoecology

Restoration of Barosaurus rearing to defend itself against a pair of A. fragilis

Allosaurus was the most common large theropod in the vast tract of

semiarid environment with distinct wet and dry seasons, and flat floodplains.[159] Vegetation varied from river-lining forests of conifers, tree ferns, and ferns (gallery forests), to fern savannas with occasional trees such as the Araucaria-like conifer Brachyphyllum.[160]

Locations in the Morrison Formation (yellow) where Allosaurus remains have been found

The Morrison Formation has been a rich fossil hunting ground. The flora of the period has been revealed by fossils of

Cathetosaurus, Brachiosaurus, Suuwassea, Apatosaurus, Brontosaurus, Barosaurus, Diplodocus, Supersaurus, Amphicoelias, and Maraapunisaurus, and the ornithischians Camptosaurus, Dryosaurus, and Stegosaurus.[161] Allosaurus is commonly found at the same sites as Apatosaurus, Camarasaurus, Diplodocus, and Stegosaurus.[162] The Late Jurassic formations of Portugal where Allosaurus is present are interpreted as having been similar to the Morrison, but with a stronger marine influence. 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).[163]

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.[163] The three appear to have had different ecological niches, 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.[153] Ceratosaurus, better known than Torvosaurus, differed noticeably from Allosaurus in functional anatomy by having a taller, narrower skull with large, broad teeth.[19] Allosaurus was itself a potential food item to other carnivores, as illustrated by an Allosaurus pubic foot marked by the teeth of another theropod, probably Ceratosaurus or Torvosaurus. 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.[164] 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 Saurophaganax or 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.[165]

References

  1. ^
    PMID 32002317
    .
  2. ^ "Allosaurus". Merriam-Webster.com Dictionary.
  3. ^ "Allosaurus". Dictionary.com Unabridged (Online). n.d.
  4. ^ Leidy, Joseph (1870). "Remarks on Poicilopleuron valens, Clidastes intermedius, Leiodon proriger, Baptemys wyomingensis, and Emys stevensonianus". Proceedings of the Academy of Natural Sciences of Philadelphia. 22: 3–4.
  5. ^ Leidy, Joseph (1873). "Contribution to the extinct vertebrate fauna of the western territories". Report of the U.S. Geological Survey of the Territories I: 14–358.
  6. OCLC 17396377
    .
  7. ^
    S2CID 130488291
    .
  8. ^ Creisler, Ben (July 7, 2003). "Dinosauria Translation and Pronunciation Guide A". Dinosauria On-Line. Archived from the original on January 5, 2010. Retrieved September 11, 2007.
  9. ^
    S2CID 131371457
    .
  10. ^
    S2CID 219247096
    .
  11. ^
    doi:10.1086/272127
    .
  12. ^
    ISBN 978-0-517-46890-6
    .
  13. ISBN 978-0-679-43386-6
    .
  14. doi:10.1080/02724634.1999.10011202
    .
  15. JSTOR 3623553
    .
  16. doi:10.2475/ajs.s4-11.62.111
    .
  17. ^
    hdl:2027/uiug.30112032536010. Archived
    (PDF) from the original on October 9, 2022.
  18. ^ a b c d e f g h i j k l m n o p q r Madsen, James H. Jr. (1993) [1976]. Allosaurus fragilis: A Revised Osteology. Utah Geological Survey Bulletin 109 (2nd ed.). Salt Lake City: Utah Geological Survey.
  19. ^ a b Henderson, Donald M. (1998). "Skull and tooth morphology as indicators of niche partitioning in sympatric Morrison Formation theropods". Gaia. 15: 219–266.
  20. S2CID 13589884
    .
  21. Cleveland-Lloyd Dinosaur Quarry
    , Upper Jurassic Morrison Formation, Utah: a re-evaluation". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 57–65.
  22. ^
    S2CID 220410105
    .
  23. ^ "Utah Symbols – State Fossil". Pioneer: Utah's Online Library, State of Utah. Archived from the original on January 8, 2010. Retrieved June 16, 2010.
  24. ^
    doi:10.1080/02724634.1998.10011039
    .
  25. ^
    S2CID 35111050
    .
  26. ^ a b Foster, John R.; Chure, Daniel J. (2006). "Hindlimb allometry in the Late Jurassic theropod dinosaur Allosaurus, with comments on its abundance and distribution". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 119–122.
  27. ^
    S2CID 4396729
    .
  28. ^
    ISSN 0871-5424
    .
  29. ^
    PMID 10597341
    .
  30. ^
    ISBN 978-0-935868-94-4
    .
  31. ^
    ISBN 978-0-671-61946-6
    .
  32. ^
    ISBN 978-7-5027-3898-3
    .
  33. ^
    S2CID 130952546. Archived from the original
    (PDF) on October 25, 2007.
  34. ^
    ISSN 1290-4805
    .
  35. ^
    OCLC 36004754
    .
  36. ^ "Howe Dinosaur Quarry – Wyoming's Jurassic Treasure". GeoScience Adventures. July 24, 2007. Archived from the original on December 3, 2007. Retrieved September 27, 2007.
  37. ^ a b Breithaupt, Brent H. "The case of "Big Al" the Allosaurus: a study in paleodetective partnerships". Archived from the original on January 7, 2010. Retrieved October 3, 2007.
  38. ^
    S2CID 85654858
    .
  39. S2CID 242466868
    .
  40. PMID 26020001
    .
  41. doi:10.1127/njgpa/2015/0467
    .
  42. ^ a b c d e f g h i j Chure, Daniel J. (2000). A new species of Allosaurus from the Morrison Formation of Dinosaur National Monument (Utah–Colorado) and a revision of the theropod family Allosauridae. PhD dissertation. Columbia University.
  43. ^ a b c Mateus, Octávio; Walen, Aart; Antunes, Miguel Telles (2006). "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". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 123–129.
  44. ^
    ISBN 978-0-520-24209-8
    .
  45. ^ Dalman, Sebastian G. (2014). "Osteology of a large allosauroid theropod from the Upper Jurassic (Tithonian) Morrison Formation of Colorado, USA". Volumina Jurassica. 12 (2): 159–180.
  46. ^ a b c Malafaia, Elisabete; Dantas, Pedro; Ortega, Francisco; Escaso, Fernando (2007). "Nuevos restos de Allosaurus fragilis (Theropoda: Carnosauria) del yacimiento de Andrés (Jurásico Superior; centro-oeste de Portugal)" [New remains of Allosaurus fragilis (Theropoda: Carnosauria) of the Andrés deposit (Upper Jurassic; central-west Portugal)] (PDF). Cantera Paleontológica (in Spanish and English): 255–271. Archived (PDF) from the original on October 9, 2022.
  47. PMID 32076581
    .
  48. ^
    ISBN 978-0-7864-1166-5
    .
  49. ^ "New species of Allosaurus discovered in Utah". phys.org.
  50. ^
    OCLC 30361459
    .
  51. ^ a b Smith, David K. (1996). "A discriminant analysis of Allosaurus population using quarries as the operational units". Museum of Northern Arizona Bulletin. 60: 69–72.
  52. ^
    doi:10.1080/02724634.1999.10011153
    .
  53. ^
    S2CID 84635714
    .
  54. ^
    S2CID 81735811
    .
  55. ISSN 0007-5167
    .
  56. S2CID 131076004
    .
  57. ^ a b c d e Madsen, James H.; Welles, Samuel P. (2000). Ceratosaurus (Dinosauria, Theropoda), a Revised Osteology. Miscellaneous Publication, 00-2. Utah Geological Survey.
  58. ^ a b Marsh, Othniel Charles (1896). "The dinosaurs of North America". United States Geological Survey, 16th Annual Report, 1894–95. 55: 133–244.
  59. ^ "MADSENIUS". dinoruss.com. March 27, 2006. Archived from the original on June 27, 2008. Retrieved December 18, 2020.
  60. ^ Lambert, D. (1990) The Dinosaur Data Book, Facts on File, Oxford, England: 320 pp.
  61. ^ a b "Carnosauria". www.theropoddatabase.com. Retrieved December 18, 2020.
  62. ^ 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.
  63. ^ "Re: Raptor question". dml.cmnh.org. Archived from the original on June 24, 2021. Retrieved January 1, 2019.
  64. S2CID 130879860
    .
  65. ^ a b Lull, Richard Swann (1911). "The Reptilia of the Arundel Formation". Maryland Geological Survey: Lower Cretaceous: 173–178.
  66. hdl:2346/65015
    .
  67. hdl:10088/14046
    .
  68. ^ "Neotheropoda". The Theropod Database. Retrieved September 28, 2018.
  69. S2CID 131371457. Archived
    (PDF) from the original on October 9, 2022.
  70. ^ Riabinin, Anatoly Nikolaenvich (1914). "Zamtka o dinozavry ise Zabaykalya". Trudy Geologichyeskago Muszeyah Imeni Petra Velikago Imperatorskoy Academiy Nauk (in Russian). 8 (5): 133–140.
  71. ISBN 978-0-520-06727-1
    .
  72. ^
    S2CID 85354215
    .
  73. ^ Greppin, J.B. (1870). "Description geologique du Jura bernois et de quelques districts adjacents". Beiträge zur Geologischen Karte der Schweiz (in French). 8: 1–357.
  74. ^ Olshevsky, 1978. The archosaurian taxa (excluding the Crocodylia). Mesozoic Meanderings. 1, 1–50.
  75. ^ Olshevsky, G., 1991, A revision of the parainfraclass Archosauria Cope, 1869, excluding the advanced Crocodylia. Mesozoic Meanderings 2, 196 pp
  76. ^
    ISBN 978-0-89950-917-4
    .
  77. ^ "Apatodonmirus". The Theropod Database. Retrieved September 28, 2018.
  78. hdl:2027/mdp.39015042532476
    .
  79. ^ Janensch, Werner (1920). "Uber Elaphrosaurus bambergi und die Megalosaurier aus den Tendaguru-Schichten Deutsch-Ostafricas". Sitzungsberichte Gesellschaft Naturforschender Freunde Berlin. 8: 225–235.
  80. ^ a b Tykoski, Ronald S.; and Rowe, Timothy. (2004). "Ceratosauria", in The Dinosauria (2nd). 47–70.
  81. ^ Janensch, Werner (1925). "Die Coelurosaurier und Theropoden der Tendaguru-Schichten Deutsch-Ostafrikas". Palaeontographica (in German). 1 (Suppl. 7): 1–99.
  82. S2CID 131517482
    .
  83. ^ Rauhut, Oliver W. M. "Theropod dinosaurs from the Late Jurassic of Tendaguru (Tanzania)". Special Papers in Palaeontology. 86: 195–239.
  84. ^ a b c d Mortimer, Mickey (July 21, 2003). "And the largest Theropod is..." The Dinosaur Mailing List. Archived from the original on March 25, 2010. Retrieved September 8, 2007.
  85. ^ Kurzanov, Sergei S.; Efimov, Mikhail B.; Gubin, Yuri M. (2003). "New archosaurs from the Jurassic of Siberia and Mongolia". Paleontological Journal. 37 (1): 53–57.
  86. ISBN 978-0-8065-0782-8
    .
  87. doi:10.1080/03115518108565427
    .
  88. ^ Welles, Samuel P. (1983). "Allosaurus (Saurischia, Theropoda) not yet in Australia". Journal of Paleontology. 57 (2): 196.
  89. ^ Molnar, Ralph E.; Flannery, Timothy F.; Rich, Thomas H.V. (1985). "Aussie Allosaurus after all". Journal of Paleontology. 59 (6): 1511–1535.
  90. doi:10.1080/02724634.1998.10011116
    .
  91. doi:10.1139/e00-064
    .
  92. PMID 19584929
    .
  93. S2CID 130568551. Archived
    (PDF) from the original on October 9, 2022.
  94. ^ a b c Paul, Gregory S. (2010). The Princeton Field Guide to Dinosaurs. Princeton University Press. pp. 94–96.
  95. hdl:10088/25281
    .
  96. ^ a b Foster, John R. (2003). Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. New Mexico Museum of Natural History and Science Bulletin 23. Albuquerque: New Mexico Museum of Natural History and Science. p. 37.
  97. ^
    OCLC 77830875
    .
  98. ^ Bates, Karl T.; Falkingham, Peter L.; Breithaupt, Brent H.; Hodgetts, David; Sellers, William I.; Manning, Phillip L. (2009). "How big was 'Big Al'? Quantifying the effect of soft tissue and osteological unknowns on mass predictions for Allosaurus (Dinosauria:Theropoda)". Palaeontologia Electronica. 12 (3): unpaginated. Archived from the original on December 25, 2009. Retrieved December 13, 2009.
  99. ^
    PMID 37910492
    .
  100. ^ Foster, John. 2007. Jurassic West: the Dinosaurs of the Morrison Formation and Their World. Bloomington, Indiana:Indiana University Press. p. 117.
  101. doi:10.1093/zoolinnean/zlaa181
    .
  102. ^ Molnar, Ralph E. (1977). "Analogies in the evolution of combat and display structures in ornithopods and ungulates". Evolutionary Theory. 3: 165–190.
  103. ^ Paul, Gregory S. (1988). Predatory Dinosaurs of the World. 91 and Figure 4–5 (93).
  104. ^ 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.
  105. ^ Paul, Gregory S. (1988). Predatory Dinosaurs of the World. 277.
  106. doi:10.1080/02724634.1996.10011341
    .
  107. doi:10.1006/zjls.1998.0193. Archived from the original
    (PDF) on October 25, 2007. Retrieved October 25, 2007.
  108. ^
    S2CID 84702973
    .
  109. ISBN 1-4051-3413-5
    .
  110. ^ 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.
  111. ^
    S2CID 245820672
    .
  112. ^ von Huene, Friedrich (1926). "The carnivorous Saurischia in the Jura and Cretaceous formations, principally in Europe". Revista del Museo de La Plata. 29: 35–167.
  113. ISBN 978-0-89464-985-1
    .
  114. ISBN 978-0-7167-1822-2
    .
  115. ^ Steel, R. (1970). "Part 14. Saurischia. Handbuch der Paläoherpetologie/Encyclopedia of Paleoherpetology". Gustav Fischer Verlag, Stuttgart: 1–87.
  116. S2CID 86378219
    .
  117. ^
    ISBN 978-0-380-83519-5
    .
  118. ISBN 978-0-380-75896-8
    .
  119. ^
    S2CID 22646156
    .
  120. ^ Paul, Gregory S. (1988). "The allosaur-tyrannosaur group", Predatory Dinosaurs of the World. 301–347.
  121. S2CID 129684676
    .
  122. PMID 18195356
    .
  123. ^
    S2CID 41596233
    .
  124. ^ "Pregnant T. rex could aid in dino sex-typing". Science Daily. March 15, 2016. Archived from the original on April 14, 2016.
  125. ^ Loewen, Mark A. (2002). "Ontogenetic changes in hindlimb musculature and function in the Late Jurassic theropod Allosaurus". Journal of Vertebrate Paleontology. 22 (3, Suppl): 80A.
  126. ISBN 978-0-253-34539-4
    .
  127. ^ Fastovsky, David E.; and Smith, Joshua B. (2004). "Dinosaur Paleoecology", in The Dinosauria (2nd ed.). 614–626.
  128. PMID 22378742
    .
  129. S2CID 4388901
    .
  130. S2CID 4392259
    .
  131. PMID 26716007
    .
  132. ^ "Better to eat you with? How dinosaurs' jaws influenced diet". Science Daily. November 3, 2015. Archived from the original on March 7, 2016.
  133. doi:10.26879/338
    .
  134. ^ Ohio University (May 22, 2013). "Allosaurus fed more like a falcon than a crocodile: Engineering, anatomy work reveals differences in dinosaur feeding styles". ScienceDaily. Retrieved May 22, 2013.
  135. PMID 15759265
    .
  136. PMID 10597341
    .
  137. S2CID 85694979
    .
  138. ISSN 0871-5424
    .
  139. doi:10.3989/egeol.03595-6106. Archived
    (PDF) from the original on October 9, 2022.
  140. doi:10.2110/palo.2008.p08-058r
    . Retrieved January 17, 2024.
  141. ISSN 1755-6910
    .
  142. PMID 38025762
    .
  143. ISSN 0304-3800
    .
  144. ISBN 9780253051578
    .
  145. ISSN 0304-3800
    .
  146. PMID 38291378
    .
  147. ISSN 0024-1164
    .
  148. JSTOR 2424244
    .
  149. ^ Tanke, Darren H. (1998). "Head-biting behavior in theropod dinosaurs: Paleopathological evidence". Gaia (15): 167–184.
  150. ISBN 978-0-253-21313-6
    .
  151. S2CID 84175628
    .
  152. S2CID 220415208
    .
  153. ^
    ISBN 978-0-253-34373-4
    .
  154. ISSN 1552-4825
    .
  155. PMID 18957367
    .
  156. ^ 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 Carpenter, K., Indiana University Press, p. 331–336.
  157. ^ a b Molnar, R.E. (2001). "Theropod paleopathology: a literature survey". In Tanke, D.H.; Carpenter, K. (eds.). Mesozoic Vertebrate Life. Indiana University Press. pp. 337–363.
  158. ^ Foster, John R. (2003). Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A. New Mexico Museum of Natural History and Science Bulletin, 23. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. p. 29.
  159. ISBN 978-1-55971-038-1
    .
  160. ^ Carpenter, Kenneth (2006). "Biggest of the big: a critical re-evaluation of the mega-sauropod Amphicoelias fragillimus". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 131–138.
  161. ^ Chure, Daniel J.; Litwin, Ron; Hasiotis, Stephen T.; Evanoff, Emmett; Carpenter, Kenneth (2006). "The fauna and flora of the Morrison Formation: 2006". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 233–248.
  162. doi:10.1017/S0094837300025768
    .
  163. ^ a b Mateus, Octávio (2006). "Jurassic dinosaurs from the Morrison Formation (USA), the Lourinhã and Alcobaça Formations (Portugal), and the Tendaguru Beds (Tanzania): A comparison". In Foster, John R.; Lucas, Spencer G. (eds.). Paleontology and Geology of the Upper Jurassic Morrison Formation. New Mexico Museum of Natural History and Science Bulletin, 36. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. pp. 223–231.
  164. ISSN 0871-5424
    .
  165. PMID 32459808
    .

External links
Retrieved from "https://en.wikipedia.org/w/index.php?title=Allosaurus&oldid=1220485161"