Allosaurus was a genus of large theropoddinosaur that lived 155 to 145 million years ago, during the late Jurassicperiod (Kimmeridgian to Tithonian). The name Allosaurus means "different lizard" and is derived from the Greek αλλος/allos ("different, strange") and σαυρος/sauros ("lizard"). The first remains that can definitely be ascribed to this genus were described in 1877 by Othniel Charles Marsh. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles, and has been a lead dinosaur in several films and documentaries.
Allosaurus was a large bipedalpredator with a large skull, equipped with dozens of large, sharp teeth. It averaged 8.5 meters (28 ft) in length, though fragmentary remains suggest it could have reached over 12 meters (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long, heavy tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as Antrodemus, but study of the copious remains from the Cleveland Lloyd Dinosaur Quarry brought the name Allosaurus back to prominence, and established it as one of the best-known dinosaurs.
As the prominent large predator in the Morrison Formation, Allosaurus was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs and perhaps even other predators (e.g Ceratosaurus). Potential prey included ornithopods, stegosaurids, and 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. It may have attacked large prey by ambush, using its upper jaws like a hatchet.
One particularly well-preserved specimen, nicknamed "Big Al", was found in Wyoming. While Allosaurus was a hunter, it was also a scavenger (like all predators). It would find dead animals or animals dying to feast on. "Big Al" had many different injuries from throughout its short, seven year life, yet surviving all but the last one, an infected toe wound. This would have left the animal unable to hunt, and it would have starved and/or died of thirst.
Allosaurus was first described in 1877 as Antrodemus, but it has since been renamed to Allosaurus after it was decided the original classification was based upon poor material.
The size range of Allosaurus compared with a human
Allosaurus stood about 8 feet (2.4 metres) tall and measured about 28 feet (8.5 metres) long, though some remains suggest it could reach up to 12 meters (40 feet) depending on the species. It's three-fingered forelimbs were smaller than its large hind legs, and the body was balanced by a long, heavy tail.[1] It weighed 2-3 tons. The skull was narrow and had a pair of horns above and in front of the eyes.[2]
A. jimmadseni skeletal reconstruction
Allosaurus was a typical large theropod, having a massive skull on a short neck, a long tail and reduced forelimbs. Allosaurus fragilis, the best-known species, had an average length of 8.5 meters (28 ft), with the largest definitive Allosaurus specimen (AMNH 680) estimated at 9.7 meters long (32 ft), and an estimated weight of 2.3 metric tons (2.5 short tons). In his 1976 monograph on Allosaurus, James Madsen mentioned a range of bone sizes which he interpreted to show a maximum length of 12 to 13 meters (40 to 43 ft). As with dinosaurs in general, weight estimates are debatable, and since 1980 have ranged between 1500 kilograms (3300 lb), 1000 to 4000 kilograms (2200 to 8800 lb), and 1010 kilograms (2230 lb) for modal adult weight (not maximum). John Foster, a specialist on the Morrison Formation, suggests that 1000 kg (2200 lb) is reasonable for large adults of A. fragilis, but that 700 kg (1500 lb) is a closer estimate for individuals represented by the average-sized thigh bones he has measured.
Several gigantic specimens have been attributed to Allosaurus, but may in fact belong to other genera. The closely related genus Saurophaganax (OMNH1708) reached perhaps 10.9 meters (36 ft) in length, and its single species has sometimes been included in the genus Allosaurus as Allosaurus maximus, though recent studies support it as a separate genus. Another potential specimen of Allosaurus, once assigned to the genus Epanterias (AMNH 5767), may have measured 12.1 meters in length (40 ft). 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 Saurophaganx. Foster, John. 2007. Jurassic West: the Dinosaurs of the Morrison Formation and Their World. Bloomington, Indiana:Indiana University Press. p. 117.
Skull[]
Skull of mounted Allosaurus skeleton (USNM4734) at the National Museum of Natural History
Skull of the Allosaurus fragilis skeleton mounted in the lobby of the San Diego Natural History Museum.
The skull and teeth of Allosaurus were modestly proportioned for a theropod of its size. Paleontologist Gregory S. Paul gives a length of 845 millimeters (33.3 in) for a skull belonging to an individual he estimates at 7.9 meters long (26 ft). 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 fourteen and seventeen 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 fourteen and seventeen teeth, with an average count of sixteen. The teeth became shorter, more narrow, 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.
The skull had a pair of horns above and in front of the eyes. These horns were composed of extensions of the lacrimal bones, 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. The horns were probably covered in a keratin sheath and may have had a variety of functions, including acting as sunshades for the eye, being used for display, and being used in combat against other members of the same species (although they were fragile). There was a ridge along the back of the skull roof for muscle attachment, as is also seen in tyrannosaurids.
Inside the lacrimal bones were depressions that may have held glands, such as salt glands. Within the maxillae were sinuses that were better developed than those of more basal theropods such as Ceratosaurus and Marshosaurus; they may have been related to the sense of smell, perhaps holding something like Jacobson's organ. The roof of the braincase was thin, perhaps to improve thermoregulation for the brain. 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. Paul, Gregory S. (1988). Predatory Dinosaurs of the World. 91 and Figure 4–5 (93). The braincase and frontals may also have had a joint.
A. jimmadseni skull with diagram highlighting individual bones
Allosaurus skull was double hinged. This allowed it to open its mouth extremely wide, allowing it to have a huge bite radius, uncommon in other theropods of its age. One hinge was near the front of the jaw like a snake's, and the other was near the back of the jawbone. However, previously it was assumed, that Allosaurus had a relatively low bite force of only 350 pounds per square inch, much less than the value of sharks and crocodiles and even inferior to that of most big cats, despite being much bigger.
A motion on how Allosaurus opened and closed its jaws
However, more recent studies concluded that Allosaurus didn't have a weak bite, as previously assumed. A study from 2021 estimated a bite force of 8,322 Newtons ( ~830kg), which is not weak at all. A very recent study from 2022 gave Allosaurus even a bite force of 9,389 Newtons (~938kg).
Postcranial skeleton[]
Allosaurus fragilis skeleton mounted in the lobby of the San Diego Natural History Museum.
Hand of a Allosaurus fragilis.
Allosaurus had nine vertebrae in the neck, fourteen in the back, and five in the sacrum supporting the hips.[3] The number of tail vertebrae is unknown and varied with individual size; James Madsen estimated about 50,[4] while Gregory S. Paul considered that to be too many and suggested 45 or less.[5] There were hollow spaces in the neck and anterior back vertebrae.[4] Such spaces, which are also found in modern theropods (that is, the birds), are interpreted as having held air sacs used in respiration.[6] The rib cage was broad, giving it a barrel chest, especially in comparison to less derived theropods like Ceratosaurus.[7]Allosaurus had gastralia (belly ribs), but these are not common findings,[4] and they may have ossified poorly.[5] In one published case, the gastralia show evidence of injury during life.[8] A furcula (wishbone) was also present, but has only been recognized since 1996; in some cases furculae were confused with gastralia.[8][9] The ilium, the main hip bone, was massive, and the 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 characteristic, with females lacking fused bones to make egg-laying easier.[4] This proposal has not attracted further attention, however.
Claw of Allosaurus fragilis.
The forelimbs of Allosaurus were short in comparison to the hindlimbs (only about 35% the length of the hindlimbs in adults)[10] and had three fingers per hand, tipped with large, strongly curved and pointed claws.[4] The arms were powerful,[5] and the forearm was somewhat shorter than the upper arm (1:1.2 humerus/ulna ratio).[11] The wrist had a version of the semilunate carpal[12] also found in more derived theropods like maniraptorans. Of the three fingers, the innermost (or thumb) was the largest,[5] and diverged from the others.[11] 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. The legs were not as long or suited for speed as those of tyrannosaurids, and the claws of the toes were less developed and more hoof-like than those of earlier theropods.[5] Each foot had three weight-bearing toes and an inner dewclaw, which Madsen suggested could have been used for grasping in juveniles.[4] There was also what is interpreted as the splint-like remnant of a fifth (outermost) metatarsal, perhaps used as a lever between the Achilles tendon and foot.[13]
Species[]
Diagram comparing skulls of the three recognized species; A. fragilis (A), A. jimmadseni (B), A. europaeus (C)
Allosaurus sp. skull (DINO 11541) from Dinosaur National Monument, still partially encased in matrix.
It is unclear how many species of Allosaurus there were. Seven species have been considered potentially valid since 1988 (A. amplexus, A. atrox, A. europaeus, the type species A. fragilis, the as-yet not formally described "A. jimmadseni", A. maximus, and A. tendagurensis), although only a fraction are usually considered valid at any given time. Additionally, there are at least ten dubious or undescribed species that have been assigned to Allosaurus over the years, along with the species belonging to genera now sunk into Allosaurus. In the most recent review of basal tetanuran theropods, only A. fragilis (including A. amplexus and A. atrox as synonyms), "A. jimmadseni" (as an unnamed species), and A. tendagurensis were accepted as potentially valid species, with A. europaeus not yet proposed and A. maximus assigned to Saurophaganax.
A. amplexus, A. atrox, A. fragilis, "A. jimmadseni", and A. maximus are all known from remains discovered in the Kimmeridgian–TithonianUpper Jurassic-age Morrison Formation of the United States, spread across the states of Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming. A. fragilis is regarded as the most common, known from the remains of at least sixty individuals. Debate has gone on since the 1980s regarding the possibility that there are two common Morrison Formation species of Allosaurus, with the second known as A. atrox; recent work has followed a "one species" interpretation, with the differences seen in the Morrison Formation material attributed to individual variation. A. europaeus was found in the Kimmeridgian-age Porto Novo Member of the Lourinhã Formation, but may be the same as A. fragilis. A. tendagurensis was found in Kimmeridgian-age rocks of Tendaguru, in Mtwara, Tanzania. Although the most recent review tentatively accepted it as a valid species of Allosaurus, it may be a more basal tetanuran, or simply a dubious theropod. Although obscure, it was a large theropod, possibly around 10 meters long (33 ft) and 2.5 metric tons (2.8 short tons) in weight.
Allosaurus is regarded as a probable synonym of the genera Antrodemus, Creosaurus, Epanterias, and Labrosaurus. Most of the species that are regarded as synonyms of A. fragilis, or that were misassigned to the genus, are obscure and were based on 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.[14] Later researchers suggested that the bone was pathologic, showing an injury to the living animal,[11] and that part of the unusual form of the rear of the bone was due to plaster reconstruction.[15] It is now regarded as an example of A. fragilis.[6] Other remains thought to pertain to Allosaurus have come from across the world, including Australia,[16]Siberia,[17] and Switzerland,[18] but these fossils have been reassessed as belonging to other dinosaurs.
Three species have been considered valid since 1988.
A. fragilis:
A. fragilis is the type species and was named by Marsh in 1877. It is known from the remains of at least sixty individuals, all found in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States. It grew up to 9 meters.
A. europaeus:
Allosaurus europaeus was discovered in 2006 described by M.T.Antunas in the same year. It lived in the Lourinha formation of Portugal. It grew up to 7 meters. It would've had several similar feeding habits, preying upon the diplodocids and stegosaurids that lived in its same area.
A. jimmadensi:
A. jimmadseni is a species of Morrison allosaur, based on a nearly complete skeleton and skull. It grew over 9 meters.
Epanterias amplexus was named by Gregory S. Paul for giant Morrison allosaur remains, and included in his conception Saurophagus maximus (later Saurophaganax).
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. Which means it is Saurophaganax. If Saurophaganax is actually proven to be synonymous, it grew up to 11+ meters and over 6 tonnes.
A. atrox/Creosaurus atrox:
Allosaurus atrox was originally named by Marsh in 1878 as the type species of its own genus, Creosaurus, and is based on YPM 1890, an assortment of bones including a couple of pieces of the skull, portions of nine tail vertebrae, two hip vertebrae, an illium, and ankle and foot bones.
A. amplus/Camptonotus amplus:
A. amplus is the synonym for Camptonotus amplus. It is not so well known. It grows up to 7.6 meters.
A. lucasi:
Two partial skeletons of allosaurid theropods belonging to an adult and a juvenile from the Upper Jurassic (Tithonian) Morrison Formation of McElmo Canyon in Montezuma County, southwestern Colorado, were discovered in 1953 by the late Joseph T. Gregory and David Techter. It grew up to 9 meters.
Synonyms[]
Creosaurus atrox
Labrosaurus felox
Antrodemus valens
Apatodon mirus
Unnamed allosaur from Portugal
Possible species[]
A. tendagurensis:
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. Although tabulated as a tentatively valid species of Allosaurus in the second edition of the Dinosauria, subsequent studies place it as indeterminate beyond Tetanurae, either a carcharodontosaurid or megalosaurid (It could probably be a Torvosaurus). Although obscure, it was a large theropod, possibly around 10 meters long (33 ft) and 2.5 metric tons (2.8 short tons) in weight.
Discovery and History[]
Allosaurus was first discovered in 1869 by Ferdinand Hayden and then named in 1877 by its founder Othniel Charles Marsh.
Remains of many individuals have been found, including some which are almost complete. Over sixty individuals from one species have been found.[19]
Restoration of the pelvis, fore and hindlimbs based on specimens O. C. Marsh had assigned to A. fragilis by 1884
Early discoveries and research[]
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 Vandiveer 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 Poicilopleuronvalens. He later decided it deserved its own genus, Antrodemus.
Allosaurus itself is based onYPM 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 allos/αλλος, meaning "strange" or "different" and saurus/σαυρος, meaning "lizard" or "reptile".[20] It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery.[21][22] 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.[21] Marsh and Edward Drinker Cope, who were in scientific competition, 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[23] and Labrosaurus,[24] and Cope's Epanterias.[25]
Mounted A. fragilis specimen (AMNH 5753), posed as scavenging an Apatosaurus
AMNH 5753 in a Charles R. Knight life restoration
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.[26] 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 in 1903 (several years after Cope had died), it was found to be one of the most complete theropod specimens then known, and in 1908 the skeleton, now cataloged as AMNH 5753, was put on public view.[27] This is the well-known mount poised over a partial Apatosaurus skeleton as if scavenging it, illustrated as such 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.[28]
Recent picture of AMNH 5753
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.[29] For example, Williston pointed out in 1901 that Marsh had never been able to adequately distinguish Allosaurus from Creosaurus.[30] 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 dubbed Antrodemus by Leidy was indistinguishable from those of Allosaurus, and Antrodemus thus should be the preferred name because as the older name it had priority.[11]Antrodemus became the accepted name for this familiar genus for over fifty years, until James 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).[4] "Antrodemus" has been used informally for convenience when distinguishing between the skull Gilmore restored and the composite skull restored by Madsen.[31]
Cleveland-Lloyd discoveries[]
Specimen at the Cleveland-Lloyd Dinosaur Quarry museum, Utah
Although sporadic work at what became known as the Cleveland-Lloyd Dinosaur Quarry in Emery County, Utah had taken place as early as 1927, and the fossil site itself described by William J. Stokes in 1945,[32] major operations did not begin there until 1960. Under a cooperative effort involving nearly 40 institutions, thousands of bones were recovered between 1960 and 1965.[4] The quarry is notable for the predominance of Allosaurus remains, the condition of the specimens, and the lack of scientific resolution on how it came to be. The majority of bones belong to the large theropod Allosaurus fragilis (it is estimated that the remains of at least 46 A. fragilis have been found there, out of at minimum 73 dinosaurs), and the fossils found there are disarticulated and well-mixed. Nearly a dozen scientific papers have been written on the taphonomy of the site, coming up with numerous contradictory explanations for how it formed. Suggestions have ranged from animals getting stuck in a bog, to becoming trapped in deep mud, to falling victim to drought-induced mortality around a waterhole, to getting trapped in a spring-fed pond or seep.[33] Regardless of the actual cause, the great quantity of well-preserved Allosaurus remains has allowed this genus to be known in detail, making it among the best-known theropods. Skeletal remains from the quarry pertain to individuals of almost all ages and sizes, from less than 1 meter (3.3 ft)[34] to 12 meters (39 ft) long, and the disarticulation is an advantage for describing bones usually found fused.[4]
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,[35] growth,[36][37] skull construction,[38] hunting methods,[39] the brain,[40] and the possibility of gregarious living and parental care.[41] Reanalysis of old material (particularly of large 'allosaur' specimens),[5][42] new discoveries in Portugal,[43] and several very complete new specimens[8][44][45] have also contributed to the growing knowledge base. Fossil footprints attributed to Allosaurus were discovered in Bałtów, Poland, by Polish paleontologist Gerard Gierliński in the early 2000s.[46]
"Big Al" and "Big Al Two"[]
"Big Al" at Museum of the Rockies.
Cast of "Big Al Two" in Switzerland
In 1991 "Big Al" (MOR 693), a 95% complete, partially articulated specimen of Allosaurus was discovered. It measured about 7 meters in length. MOR 693 was excavated near Shell, Wyoming, by a joint Museum of the Rockies and University of Wyoming Geological Museum team. This skeleton was discovered by a Swiss team, led by Kirby Siber. In 1996 the same team discovered a second Allosaurus, "Big Al Two", which is the best preserved skeleton of its kind to date.
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,[47] and was a subadult estimated at only 87% grown.[48] The specimen was described by Breithaupt in 1996.[44] Nineteen of its bones were broken or showed signs of infection, which may have contributed to "Big Al's" death. Pathologic bones included five ribs, five vertebrae, and four bones of the feet; several damaged bones showed osteomyelitis, a 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.[48]
Classification[]
Replica of an Allosaurus fragilis skull, Oklahoma Museum of Natural History.
Life restoration of A. anax
Allosaurus was an allosaurid, a member of a family of large theropods within the larger group Carnosauria. The family name Allosauridae was created for this genus in 1878 by Othniel Charles Marsh,[23] but the term was largely unused until the 1970s in favor of Megalosauridae, another family of large theropods that eventually became a wastebasket taxon. This, along with the use of Antrodemus for Allosaurus during the same period, is a point that needs to be remembered when searching for information on Allosaurus in publications that predate James Madsen's 1976 monograph. Major publications using the name Megalosauridae instead of Allosauridae include Gilmore, 1920,[11]von Huene, 1926,[49]Romer, 1956 and 1966,[50][51] Steel, 1970,[52] and Walker, 1964.[53]
Illustrations showing the skull of A. jimmadseni from the side (A), top (B), and back (C)
A. jimmadseni specimen "Big Al II" (SMA 0005)
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, Acrocanthosaurus, Chilantaisaurus, Compsosuchus, Stokesosaurus, and Szechuanosaurus. 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 related families.
Allosauridae is one of three families in Carnosauria; the other two are Carcharodontosauridae and Sinraptoridae. Allosauridae has at times been proposed as ancestral to the Tyrannosauridae (which would make it paraphyletic), one recent example in Gregory S. Paul's Predatory Dinosaurs of the World, Paul, Gregory S. (1988). "The allosaur-tyrannosaur group", Predatory Dinosaurs of the World. 301–347. but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the Coelurosauria. Allosauridae is the smallest of the carnosaur families, with only Saurophaganax and a currently unnamed Frenchallosauroid accepted as possible valid genera besides Allosaurus in the most recent review. Another genus, Epanterias, is a potential valid member, but it and Saurophaganax may turn out to be large examples of Allosaurus. Recent reviews have kept the genus Saurophaganax and included Epanterias with Allosaurus.
Notable Specimens[]
MOR 693 "Big Al": The Big Al specimen, being the most famous Allosaurus specimens, was discovered in 1991. Upon discovery, it was found to be ~8 meters (26 feet) long, found near Shell, Wyoming and excavated by a Museum of the Rockies and University of Wyoming Geological Museum joint team. It was found by a Swiss team, however, lead by Kirby Siver. Chure and Loewen (2020) identified Big Al as A. jimmadseni. It gained its common name due to completion, preservation and importance, but was below the average size for A. fragilis and was a subadult (~87% grown at death). Breithaupt (1996) described Big Al. Of the skeleton, 19 bones showed paleopathology. 5 ribs, 5 vertebrae and 4 feet bones show evidence of this; damaged bones show osteomyelitis with an infection of the first phalanx of the third toe, inflicted by an involucrum that was long-lived (up to ~6 months?) and infection and trauma of the right foot which likely affected movement and may have predisposed other injury due to a gait change.
SMA 0005 "Big Al II" or "Big Al 2"[54]: Discovered by the same team, Al II (0r 2) was discovered by the same team as Al I. It is the best-preserved specimen, assigned to A. jimmadseni. Like it's counterpart, it is known to have sustained many injuries.
USNM 4734: A partial tail missing the very end, appearing to articulate with the sacrum in situ and being mostly or quite complete. Before it was realized the remains were so complete, they were put into a dump pile at the quarry and lost, save for some caudals being mutilated and others completely lost, creating indentations in the nearby sandstone. Thus, most of the specimens value was lost, but the 33 recovered vertebrae were helpful for comparisons with contemporaneous theropods like Ceratosaurus[55].
USNM 8367: 8 caudals from Quarry Number(s) 10, 9, 8, 7, 6, 5, 4 (for the first 7 in the series) and 15 (for a caudal from the middle of the tail). They are heavy and stout, with the first 4 with centra that are higher than long. As the move back, they form a cylindrical shape, they reduce in height and they reduce at slower intervals[55].
"Arkhane".
M200000 "Arkhane": A mounted Allosaurus skeleton that is advertised as a new species, according to paleontologists who briefly studied it. It is mounted at the Royal Belgium Institute of Natural Sciences in a gallery that lasted until Spring 2021. It is 8.7 meters long, "authentic" and 70% complete[56]. The braincase seems to be missing from the mount, with much histological information retrieved from the specimen. Diet was inferred from stable isotopic analysis of the teeth, with strontium isotopic structures suggesting that the teeth are not of the same individual. A cortical core sample from the femur finds clear growth marks, with femoral length and these marks suggesting that this individual was a subadult or adult. The specimen was discovered in 1992 by Museon, a popular museum in the Netherlands from fluvial sandstones of the Morrison. However, field notes were lost, making much of the discovery data unknown[57].
Paleobiology[]
Life history[]
Skeletons at different growth stages
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. 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 lbs) per year.
Medullary bone tissue (endosteally derived, ephemeral, mineralization located inside the medulla of the long bones in gravid female birds) has been reported in at least one Allosaurus specimen, a shin bone from 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. 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. However, with the confirmation of medullary tissue indicating gender in a specimen of Tyrannosaurus, it may be possible to ascertain whether or not the Allosaurus in question was indeed female. By counting growth lines, it was shown that she was 10 years old at death, so sexual maturity in Allosaurus was attained well before maximum growth and size.
Restoration of a juvenile by a well known Paleoartist; Fred Wierum
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. 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. Conversely, the skull bones appear to have generally grown isometrically, increasing in size without changing in proportion.
Feeding[]
Allosaurus Skeleton and 2 Stegosaurus skeletons, Denver Museum of Nature and Science
Bitten Stegosaurus plate close-up, showing how well the damage matches the front of an Allosaurus "mouth"
Paleontologists accept Allosaurus as an active predator of large animals. 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. Fastovsky, David E.; and Smith, Joshua B. (2004). "Dinosaur Paleoecology", in The Dinosauria (2nd). 614–626. There is dramatic evidence for allosaur attacks on Stegosaurus. An Allosaurus tail vertebra has been found with a partially healed puncture which fits a Stegosaurus tail spike. Also, there is a Stegosaurus neck plate with a U-shaped wound that correlates well with an Allosaurus snout.[58] 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. Another possibility is that it preferred to hunt juveniles instead of fully grown adults. Research in the 1990s and 2000s may have found other solutions to this question. Robert T. Bakker, comparing Allosaurus to Cenozoic sabre-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 sabre 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 runs the length of the upper jaw and could have been driven into prey. This type of jaw would permit slashing attacks against much larger prey, with the goal of weakening the victim.[39]
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 2,148 N, less than the values for alligators (13,000 N), lions (4,167 N), and leopards (2,268 N), but the skull could withstand nearly 55,500 N of vertical force against the tooth row. The authors suggested that Allosaurus used its skull like a hatchet 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. Their interpretations were challenged by other researchers, who found no modern analogues 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. 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. 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. An additional suggestion notes that ornithopods were the most common available dinosaurian prey, and that allosaurs 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. This is compatible with other evidence that the forelimbs were strong and capable of restraining prey.
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. The similar wide field of view suggests that allosaurs, like modern crocodilians, were ambush hunters. The arms, compared with those of other theropods, were suited for both grasping prey at a distance or clutching it close, and the articulation of the claws suggests that they could have been used to hook things. Finally, the top speed of Allosaurus has been estimated at 30 to 55 kilometers per hour (19 to 34 miles per hour).
As the top predator of its age and habitat, Allosaurus hunted and scavenged whatever smaller or larger prey was abundant. However, it had a modestly-sized skull filled with slightly small teeth and was greatly outweighed by sauropods and probably preferred to hunt young, weak, old, sick, injured, or trapped sauropods over healthy adults. As sauropods were the dominant species of the time, they would be preyed upon by Allosaurus more often than not, with a common speculation being that this was done through hunting in packs, which it did to bring down any large prey that could put up a fight.
Another study showed the skull was very strong but had a relatively small bite force. The authors suggested that Allosaurus used its skull like a hatchet against prey, lifting its head up, with its mouth open, and crashing down on its prey. This 'Axe-bite' weakened the prey severely.
They suggested that different strategies could be used 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 stegosaurs and sauropods.[38]
Their ideas were challenged by other researchers, who found no modern examples of a hatchet attack. They thought it more likely that the skull was strong to absorb stresses from struggling prey.[59]
The original authors noted that Allosaurus itself has no modern equivalent, so the absence of a modern 'hatchet attacker' was not significant. They thought the tooth row was well-suited to such an attack, and that articulations (joints) in the skull helped to lessen stress.[60]
Another possibility for handling large prey is that theropods like Allosaurus were 'flesh grazers' which could take bites of flesh out of living sauropods, sufficient to sustain the predator so it did not need to kill the prey outright. This strategy might have allowed the prey to recover and be fed upon again later.[61]
A. fragilis showing its maximum possible gape, based on Bakker (1998) and Rayfieldet al. (2001)
Another idea is that ornithopods, the most common available prey, could be subdued by Allosaurus grasping the prey with their forelimbs, and then making bites on the throat to crush the trachea.[62] The forelimbs were strong and capable of restraining prey,[12] and the articulation of the claws suggests that they could have been used to hook things.[63]
The shape of the Allosaurus skull limited binocular vision to 20° of width, slightly less than that of modern crocodilians. As with crocodiles, this may have been enough to judge prey distance and time attacks.[64] The similar width of their field of view suggests that allosaurs, like modern crocodiles, were ambush hunters.[65]
Finally, the top speed of Allosaurus has been estimated at 30 to 55 kilometers per hour (19 to 34 miles per hour).[66]
Social behavior[]
It has been speculated since the 1970s that Allosaurus preyed on sauropods and other large dinosaurs by hunting in groups. Such a depiction is common in semitechnical and popular dinosaur literature. 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.However, there is actually little evidence of gregarious behavior in theropods, and social interactions with members of the same species would have included antagonistic encounters, as shown by injuries to gastralia 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.
The holotype dentary of Labrosaurus ferox, which may have been injured by the bite of another A. fragilis
Although Allosaurus may have hunted in packs, 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 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. There is some evidence for cannibalism in Allosaurus, including Allosaurus shed teeth found among rib fragments, possible tooth marks on a shoulder blade, and cannibalized allosaur skeletons among the bones at Bakker's lair sites.
Further publishments have been aired about potential cannibalism of Allosaurus; however the cases are suspected to be scavenging the dead specimens instead of active cannibalism [67]
Brain and senses[]
The brain of Allosaurus, as interpreted from spiral CT scanning of an endocast, was more consistent with crocodilian brains than those of the other living archosaurs, birds. 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, and so Allosaurus probably could have heard lower frequencies best, and would have had trouble with subtle sounds. The olfactory bulbs were large and seem to have been well suited for detecting odors, although the area for evaluating smells was relatively small.
Mounted A. fragilis skeleton (USNM4734), which has several healed injuries
Paleopathology[]
In 2001, Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions 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 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, 3 were found to contain stress fractures. Of the feet, 281 bones were studied and 17 found to have stress fractures. The stress fractures in the foot bones "were distributed to the proximalphalanges" 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.
Skeletal restoration of "Big Al II" showing bones with pathologies
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.
The left scapula and fibula of an Allosaurus fragilis specimen catalogued 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 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 probably caused by a blow from above".The near end of the first phalanx of the third toe was afflicted by an involucrum.
Other pathologies reported in Allosaurus include: Willow breaks in two ribs. Healed fractures in the humerus and 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 osetoarthritis or developmental issues. "Extensive '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. "Extensive exostoses" in the first phalanx of the third toe. Lesions similar to those caused by osteomyelitis in two scapulae. Bone spurs in a premaxilla, ungual, and two metacarpals. Exostosis in a pedal phalanx possibly attributable to an infectious disease. A metacarpal with a round depressed fracture.
Paleoecology[]
Restoration of Barosaurus rearing to defend itself against a pair of Allosaurus
Allosaurus was the most common large theropod in the vast tract of Western American fossil-bearing rock known as the Morrison Formation, accounting for 70 to 75% of theropod specimens, and as such was at the top trophic level of the Morrison food web. The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, and flat floodplains. 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.
Locations in the Morrison Formation (yellow) where Allosaurus remains have been found
The Morrison Formation has been a rich fossil hunting ground, holding fossils of green algae, fungi, mosses, horsetails, ferns, cycads, ginkgoes, and several families of conifers. Other fossils discovered include bivalves, snails, ray-finned fishes, frogs, salamanders, turtles, sphenodonts, lizards, terrestrial and aquatic crocodylomorphans, several species of pterosaur, numerous dinosaur species, and early mammals such as docodonts, multituberculates, symmetrodonts, and triconodonts. Such dinosaurs as the theropods Ceratosaurus, Ornitholestes, and Torvosaurus, the sauropodsApatosaurus, Brachiosaurus, Camarasaurus, and Diplodocus, and the ornithischiansCamptosaurus, Dryosaurus, and Stegosaurus are known from the Morrison.[68] 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 Apatosaurus), or have a close counterpart (Brachiosaurus and Lusotitan, Camptosaurus, and Draconyx).[69]
Outcrop of the Brushy Basin Member of the Morrison Formation, west of Green River, Utah, on the Colorado Plateau.
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,[69] The three appear to have had different ecological niches, based on anatomy and the location of fossils. Ceratosaurs and torvosaurs 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 allosaurs were more compact, with longer legs, faster but less maneuverable, and seem to have preferred dry floodplains.[70]Ceratosaurus, better known than Torvosaurus, differed noticeably from Allosaurus in functional anatomy by having a taller, narrower skull with large, broad teeth.[31] Torvosaurus was much bigger than Allosaurus and most likely the apex predator (Saurophaganax appeared after Torvosaurus).
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.
One of the most popular and well known dinosaurs, Allosaurus was the most ferocious meat-eater of the Jurassic. It was the first of the really big meat-eaters which had huge heads filled with lots of sharp teeth. It could run very fast, close to 40 mph, and had very strong arms and long, sharp, curved claws on its hands. One of its hand claws was more than one foot long!
Allosaurus lived among some of the largest dinosaurs to ever walk the earth and it is likely that it hunted some of smaller members of these families. Even the smaller members would have been huge, and this required Allosaurus to have great strength.
Allosaurus is the namesake of the very successful allosaurid family of dinosaurs. This family includes what may be the very largest carnivore, the Giganotosaurus, and other creatures such as the Acrocanthosaurus and Carcharodontosaurus. Its more distant relatives are the raptors and tyrannosaurs of the late Cretaceous.
Allosaurus had relatively small teeth for such a large dinosaur, especially when compared to later big carnivores. It probably had a weak bite compared to its size, but its mouth could open very wide. Allosaurus most likely used its very heavily muscled arms with its huge claws as potent weapons in bringing down and holding its prey. It also was close to having true stereo vision - its big eyes had some forward vision that would have allowed for a degree of depth perception.
There is a great deal known about this dinosaur's life style. Footprint evidence indicates it hunted in groups and that it cared for its young in large nests. It inhabited floodplains, meadows and some forests.
Allosaurus ("other lizard") was the most common predator of the Late jurassic and probably one of the most dangerous. Like most meat-eating dinosaurs, its jaws were filled with serrated teeth shaped like blades. Computer studies suggest that Allosaurus attacked by using its upper jaw like a battle ax to hack at its victim, then it used its lower jaw to bite out a slice of meat. It might have been easy for an Allosaurus to kill a fairly defenseless dinosaur like Camptosaurus, but Stegosaurus could certainly put up a fight, and the sauropods (giant long-necks) were so huge that they could easily crush even an adult Allosaurus. We know that Allosaurus led a dangerous life. The Allosaurus on display at the Smithsonian Institution has a smashed shouldeb blade, many broken ribs, and a lower jaw so damaged that paleontologists didn't realize it was an Allosaurus jaw for over 100 years! But these were tough dinosaurs: Their bones show that they lived long enough for their wounds to heal.
Fun Facts[]
The first fossil of Allosaurus ever found- the broken half of a backbone--was called a petrified horse hoof by its discoverers!
Trivia[]
Allosaurus is the official state dinosaur of Utah.
Gallery[]
Appearance in other media[]
Jurassic Park[]
Allosaurus appears in the 2018 movie, Jurassic World: Fallen Kingdom. Like all of InGen's theropod clones, the Allosaurus clones has pronated wrists, unlike their real-life counterparts. Allosaurus also appears in 2022 Jurassic World: Dominion where it escapes the black market and attacks Malta, and the live action Jurassic World short film Battle at Big Rock, alongside the ceratopsian, Nasutoceratops.
Allosaurus can be created in the Jurassic Park section of Jurassic Park: Builder. John Hammond says it is his favorite dinosaur.
Allosaurus appears in the free Jurassic World: Fallen Kingdom DLC for Jurassic World: Evolution. It looks almost exactly as the one in Jurassic World: Fallen Kingdom, although the only difference is that the game version has spines going down its back, with a more pronounced crest.
Allosaurus is featured in Jurassic World: Alive, with the first GEN based on the Fallen Kingdom dinosaur and the second GEN being based on the Battle at Big Rock dinosaur variant.
Allosaurus can be created in the park in Jurassic World: The Game as a rare dinosaur. It was inaccurate when it has two fingers instead of three and lacked the horned eyebrows, and people have complained about it since.
↑Madsen, James H, Jr. 1993 [1976]. Allosaurus fragilis: a revised osteology. 2nd ed, Utah Geological Survey Bulletin109. Salt Lake City: Utah Geological Survey.
↑Madsen, James H., Jr. (1993) [1976]. Allosaurus fragilis: A Revised Osteology. Utah Geological Survey Bulletin 109 (2nd ed.). Salt Lake City: Utah Geological Survey.
↑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 ten neck and thirteen back vertebrae.
↑ 12.012.1Template:Cite journalCite error: Invalid <ref> tag; name "KC02" defined multiple times with different content
↑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.
↑Cite error: Invalid <ref> tag; no text was provided for refs named DFG97
↑Holtz, Thomas R., Jr.; Molnar, Ralph E.; and Currie, Philip J. 2004. Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds) The Dinosauria. 2nd ed, Berkeley: University of California Press. pp. 71–110. ISBN 0-520-24209-2
↑Holtz, Thomas R., Jr.; Molnar, Ralph E.; and Currie, Philip J. 2004. Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds) The Dinosauria. 2nd ed, Berkeley: University of California Press. pp. 71–110. ISBN 0-520-24209-2
↑Foster, John Wikipedia:2007. "Allosaurus fragilis". Jurassic West: the dinosaurs of the Morrison Formation and their world. Bloomington, Indiana: Indiana University Press. pp. 170–176. ISBN 978-0-253-34870-8 OCLC 77830875
↑Gilmore, Charles W. 1920. "Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus". Bulletin of the United States National Museum110: 1–159.
