Allosaurus is a
genusIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of large theropod
dinosaurDinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
that lived 155 to 150 million years ago during the
late JurassicThe Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 161.2 ± 4.0 to 145.5 ± 4.0 million years ago , which is preserved in Upper Jurassic strata. In European lithostratigraphy, the name "Malm" indicates rocks of Late Jurassic age...
period (
KimmeridgianIn the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
to early
TithonianIn the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
). The name
Allosaurus means "different lizard". It is derived from the
GreekAncient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
/
allos ("different, other") and /
sauros ("lizard"). The first remains that can definitely be ascribed to this genus were described in 1877 by paleontologist
Othniel Charles MarshOthniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of
paleontologicalPaleontology "old, ancient", ὄν, ὀντ- "being, creature", and λόγος "speech, thought") is the study of prehistoric life. It includes the study of fossils to determine organisms' evolution and interactions with each other and their environments...
circles. Indeed, it has been a top feature in several
filmA film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...
s and
documentariesDocumentary films constitute a broad category of nonfictional motion pictures intended to document some aspect of reality, primarily for the purposes of instruction or maintaining a historical record...
about prehistoric life.
Allosaurus was a large
bipedBipedalism is a form of terrestrial locomotion where an organism moves by means of its two rear limbs, or legs. An animal or machine that usually moves in a bipedal manner is known as a biped , meaning "two feet"...
al
predatorIn ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...
. Its
skullThe skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
was large and equipped with dozens of large, sharp teeth. It averaged 8.5 metres (27.9 ft) in length, though fragmentary remains suggest it could have reached over 12 metres (39.4 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
allosauridAllosauridae was a family of medium to large sized carnivorous theropod dinosaurs. Members included Saurophaganax, Allosaurus, and the poorly known Epanterias, which could well be a specimen of Allosaurus...
, a type of
carnosauriaCarnosauria is a group of large predatory dinosaurs that lived during the Jurassic and Cretaceous periods. While it originally contained a wide assortment of giant theropods that were not closely related, the group has since been defined to encompass only the allosaurs and their closest kin...
n theropod dinosaur. The genus has a complicated
taxonomyTaxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
, and includes an uncertain number of valid
speciesIn biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
, the best known of which is
A. fragilis. The bulk of
Allosaurus remains have come from
North AmericaNorth America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
's
Morrison FormationThe Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
, with material also known from
PortugalPortugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
and possibly
TanzaniaThe United Republic of Tanzania is a country in East Africa bordered by Kenya and Uganda to the north, Rwanda, Burundi, and the Democratic Republic of the Congo to the west, and Zambia, Malawi, and Mozambique to the south. The country's eastern borders lie on the Indian Ocean.Tanzania is a state...
. It was known for over half of the 20th century as
AntrodemusAntrodemus is a dubious genus of theropod dinosaur from the Kimmeridgian-Tithonian-age Upper Jurassic Morrison Formation of Middle Park, Colorado...
, but study of the copious remains from the
Cleveland Lloyd Dinosaur QuarryThe Cleveland Lloyd Dinosaur Quarry National Natural Landmark, located in The San Rafael Swell, near Cleveland, Utah contains the densest concentration of Jurassic dinosaur fossils ever found. Well over 15,000 bones have been excavated from this Jurassic 'predator trap' and there are many...
brought the name
Allosaurus back to prominence, and established it as one of the best-known dinosaurs.
As the most abundant large predator in the Morrison Formation,
Allosaurus was at the top of the
food chainA food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
, probably preying on contemporaneous large herbivorous dinosaurs and perhaps even other predators (e.g.
CeratosaurusCeratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
). Potential prey included
ornithopodOrnithopods or members of the clade Ornithopoda are a group of ornithischian dinosaurs that started out as small, bipedal running grazers, and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous world, and dominated the North American...
s, stegosaurids, and sauropods. Some paleontologists interpret
Allosaurus as having had cooperative
social behaviorIn physics, physiology and sociology, social behavior is behavior directed towards society, or taking place between, members of the same species. Behavior such as predation which involves members of different species is not social...
, 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 jaw like a
hatchetA hatchet is a single-handed striking tool with a sharp blade used to cut and split wood...
.
Description
Allosaurus was a typical large theropod, having a massive
skullThe skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
on a short
neckThe neck is the part of the body, on many terrestrial or secondarily aquatic vertebrates, that distinguishes the head from the torso or trunk. The adjective signifying "of the neck" is cervical .-Boner anatomy: The cervical spine:The cervical portion of the human spine comprises seven boney...
, a long
tailThe tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...
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 (
AMNHThe American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
680) estimated at 9.7 meters long (32 ft), and an estimated weight of 2.3 metric tons (2.5
short tonThe short ton is a unit of mass equal to . In the United States it is often called simply ton without distinguishing it from the metric ton or the long ton ; rather, the other two are specifically noted. There are, however, some U.S...
s). In his 1976
monographA monograph is a work of writing upon a single subject, usually by a single author.It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself...
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
modalIn statistics, the mode is the value that occurs most frequently in a data set or a probability distribution. In some fields, notably education, sample data are often called scores, and the sample mode is known as the modal score....
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 bonesThe femur , or thigh bone, is the most proximal bone of the leg in tetrapod vertebrates capable of walking or jumping, such as most land mammals, birds, many reptiles such as lizards, and amphibians such as frogs. In vertebrates with four legs such as dogs and horses, the femur is found only in...
he has measured. Using the subadult specimen nicknamed "Big Al", researchers using computer modelling arrived at a best estimate of 1500 kilograms (3,306.9 lb) for the individual, but by varying parameters they found a range from approximately 1400 kilograms (3,086.5 lb) to approximately 2000 kilograms (4,409.2 lb).
Several
gigantic specimensAllosaurus was not only one of the most abundant Late Jurassic dinosaurs, but also one of the best known. Its brain, anatomy and even behaviour were studied more accurate than those of any dinosaur on Earth. Many of its specimens were found: from Utah, Wyoming, Colorado and Montana to Portugal...
have been attributed to
Allosaurus, but may in fact belong to other genera. The closely related genus
SaurophaganaxSaurophaganax is a genus of allosaurid dinosaur from the Morrison Formation of Late Jurassic Oklahoma . Some paleontologists consider it to be a species of Allosaurus...
(
OMNHThe Sam Noble Oklahoma Museum of Natural History is a natural history museum in Norman, Oklahoma, operated by the University of Oklahoma. It is currently housed in a building on Chautauqua Avenue that opened on May 1, 2000. The museum's exhibits include a Native American gallery and collections of...
1708) 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 AllosaurusAllosaurus was not only one of the most abundant Late Jurassic dinosaurs, but also one of the best known. Its brain, anatomy and even behaviour were studied more accurate than those of any dinosaur on Earth. Many of its specimens were found: from Utah, Wyoming, Colorado and Montana to Portugal...
, once assigned to the genus
EpanteriasEpanterias is a dubious genus of theropod dinosaur from the Kimmeridgian-Tithonian-age Upper Jurassic upper Morrison Formation of Garden Park, Colorado. It was described by Edward Drinker Cope in 1878. The type species is Epanterias amplexus. This genus is based on what is now AMNH 5767, parts of...
(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 MexicoNew Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
; this large allosaurid may be another individual of
Saurophaganax.
Skull
The skull and teeth of
Allosaurus were modestly proportioned for a theropod of its size. Paleontologist
Gregory S. PaulGregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
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
premaxillaThe incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
(the bones that formed the tip of the snout), held five teeth with D-shaped cross-sections, and each
maxillaThe maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
(the main tooth-bearing bones in the upper jaw) had between 14 and 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, 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
hornsA horn is a pointed projection of the skin on the head of various animals, consisting of a covering of horn surrounding a core of living bone. True horns are found mainly among the ruminant artiodactyls, in the families Antilocapridae and Bovidae...
above and in front of the eyes. These horns were composed of extensions of the
lacrimal boneThe lacrimal bone, the smallest and most fragile bone of the face, is situated at the front part of the medial wall of the orbit. It has two surfaces and four borders.-Lateral or orbital surface:...
s, and varied in shape and size. There were also lower paired ridges running along the top edges of the
nasal boneThe nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, and form, by their junction, "the bridge" of the nose.Each has two surfaces and four borders....
s that led into the horns. The horns were probably covered in a
keratinKeratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
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
tyrannosauridsTyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
.
Inside the lacrimal bones were depressions that may have held
glandA gland is an organ in an animal's body that synthesizes a substance for release of substances such as hormones or breast milk, often into the bloodstream or into cavities inside the body or its outer surface .- Types :...
s, such as
salt glandThe salt gland is an organ for excreting excess salts. It is found in elasmobranchs, seabirds, and some reptiles. In sharks, salt glands are found in the rectum, but in birds and reptiles, they are found in or on the skull, in the area of the eyes, nostrils or mouth. In crocodiles, the salt is...
s. Within the maxillae were
sinusesThe pyramid shaped maxillary sinus is the largest of the paranasal sinuses, and drains into the nose. It is present at birth as rudimentary air cells, and develops throughout childhood.-General characteristics:...
that were better developed than those of more
basalIn phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
theropods such as
CeratosaurusCeratosaurus meaning "horned lizard", in reference to the horn on its nose , was a large predatory theropod dinosaur from the Late Jurassic Period , found in the Morrison Formation of North America, in Tanzania and Portugal...
and
MarshosaurusMarshosaurus was a genus of medium sized theropod, with a size up to 5 or 6 meters in length and a skull about 60 cm long. It is known from parts of at least three individuals from the Morrison Formation of Utah and Colorado.The holotype is a left ilium, or upper pelvis bone found at the...
; they may have been related to the sense of smell, perhaps holding something like
Jacobson's organThe vomeronasal organ , or Jacobson's organ, is an auxiliary olfactory sense organ that is found in many animals. It was discovered by Frederik Ruysch and later by Ludwig Jacobson in 1813....
. The roof of the braincase was thin, perhaps to improve
thermoregulationThermoregulation is the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different...
for the
brainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
. 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. The braincase and
frontalsThe frontal bone is a bone in the human skull that resembles a cockleshell in form, and consists of two portions:* a vertical portion, the squama frontalis, corresponding with the region of the forehead....
may also have had a joint.
Postcranial skeleton
Allosaurus had nine vertebrae in the neck, 14 in the back, and five in the
sacrumIn vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
supporting the hips. The number of tail vertebrae is unknown and varied with individual size; James Madsen estimated about 50, while Gregory S. Paul considered that to be too many and suggested 45 or less. There were hollow spaces in the neck and
anteriorStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
back vertebrae. Such spaces, which are also found in modern theropods (that is, the birds), are interpreted as having held air sacs used in
respirationThe respiratory system is the anatomical system of an organism that introduces respiratory gases to the interior and performs gas exchange. In humans and other mammals, the anatomical features of the respiratory system include airways, lungs, and the respiratory muscles...
. The rib cage was broad, giving it a barrel chest, especially in comparison to less
derivedIn phylogenetics, a derived trait is a trait that is present in an organism, but was absent in the last common ancestor of the group being considered. This may also refer to structures that are not present in an organism, but were present in its ancestors, i.e. traits that have undergone secondary...
theropods like
Ceratosaurus.
Allosaurus had
gastraliaGastralia are dermal bones found in the ventral body wall of crocodilian and Sphenodon species. They are found between the sternum and pelvis, and do not articulate with the vertebrae...
(belly ribs), but these are not common findings, and they may have
ossifiedOssification is the process of laying down new bone material by cells called osteoblasts. It is synonymous with bone tissue formation...
poorly. In one published case, the gastralia show evidence of injury during life. A
furculaThe ' is a forked bone found in birds, formed by the fusion of the two clavicles. In birds, its function is the strengthening of the thoracic skeleton to withstand the rigors of flight....
(wishbone) was also present, but has only been recognized since 1996; in some cases furculae were confused with gastralia. The
iliumThe ilium is the uppermost and largest bone of the pelvis, and appears in most vertebrates including mammals and birds, but not bony fish. All reptiles have an ilium except snakes, although some snake species have a tiny bone which is considered to be an ilium.The name comes from the Latin ,...
, the main hip bone, was massive, and the
pubic boneIn vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
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 characteristicSexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
, with females lacking fused bones to make egg-laying easier. This proposal has not attracted further attention, however.
The forelimbs of
Allosaurus were short in comparison to the hindlimbs (only about 35% the length of the hindlimbs in adults) and had three fingers per hand, tipped with large, strongly curved and pointed
clawA claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end...
s. The arms were powerful, and the forearm was somewhat shorter than the upper arm (1:1.2
humerusThe humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
/
ulnaThe ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...
ratio). The wrist had a version of the semilunate
carpalIn tetrapods, the carpus is the sole cluster of bones in the wrist between the radius and ulna and the metacarpus. The bones of the carpus do not belong to individual fingers , whereas those of the metacarpus do. The corresponding part of the foot is the tarsus...
also found in more derived theropods like
maniraptoraManiraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
ns. Of the three fingers, the innermost (or
thumbThe thumb is the first digit of the hand. When a person is standing in the medical anatomical position , the thumb is the lateral-most digit...
) was the largest, and diverged from the others. 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
hoofA hoof , plural hooves or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole...
-like than those of earlier theropods. Each foot had three weight-bearing toes and an inner
dewclawA dewclaw is a vestigial digit on the foot of many mammals, birds, and reptiles . It commonly grows high on the leg so that in digitigrade species, when the animal is standing, it does not make contact with the ground...
, which Madsen suggested could have been used for grasping in juveniles. There was also what is interpreted as the splint-like remnant of a fifth (outermost)
metatarsalThe metatarsus or metatarsal bones are a group of five long bones in the foot located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the medial side : the first, second, third, fourth, and fifth...
, perhaps used as a lever between the
Achilles tendonThe Achilles tendon , also known as the calcaneal tendon or the tendo calcaneus, is a tendon of the posterior leg. It serves to attach the plantaris, gastrocnemius and soleus muscles to the calcaneus bone.- Anatomy :The Achilles is the tendonous extension of 3 muscles in the lower leg:...
and foot.
Classification
Allosaurus was an allosaurid, a member of a
familyIn biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of large theropods within the larger group
CarnosauriaCarnosauria is a group of large predatory dinosaurs that lived during the Jurassic and Cretaceous periods. While it originally contained a wide assortment of giant theropods that were not closely related, the group has since been defined to encompass only the allosaurs and their closest kin...
. The family name Allosauridae was created for this genus in 1878 by
Othniel Charles MarshOthniel Charles Marsh was an American paleontologist. Marsh was one of the preeminent scientists in the field; the discovery or description of dozens of news species and theories on the origins of birds are among his legacies.Born into a modest family, Marsh was able to afford higher education...
, 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,
von HueneFriedrich von Huene was a German paleontologist who named more dinosaurs in the early 20th century than anyone else in Europe.-Biography:...
, 1926, Romer, 1956 and 1966, Steel, 1970, and
WalkerAlick Donald Walker was a British palaeontologist, after whom the Alwalkeria genus of dinosaur is named....
, 1964.
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
IndosaurusIndosaurus is a genus of theropod dinosaur once living in what is now India. It lived approximately 69 million years ago, in the Maastrichtian division of the Late Cretaceous...
,
PiatnitzkysaurusPiatnitzkysaurus is a genus of theropod dinosaur. It is known from the Canadon Asfalto Formation, Middle Jurassic of what is now Argentina. Once thought to be a basal carnosaur, it may instead be a megalosauroid...
,
PiveteausaurusPiveteausaurus is a genus of theropod dinosaur known from a partial skull discovered in the Middle Jurassic Marnes de Dives formation of Calvados, in northern France.-History and description:...
,
YangchuanosaurusYangchuanosaurus was a theropod dinosaur that lived in China during the late Oxfordian stage of the Late Jurassic, and was similar in size and appearance to its North American contemporary, Allosaurus...
,
AcrocanthosaurusAcrocanthosaurus is a genus of theropod dinosaur that existed in what is now North America during the Aptian and early Albian stages of the Early Cretaceous. Like most dinosaur genera, Acrocanthosaurus contains only a single species, A. atokensis. Its fossil remains are found mainly in the U.S...
,
ChilantaisaurusChilantaisaurus is a genus of neovenatorid theropod dinosaur from the late Cretaceous Ulansuhai Formation of China . The type species, C. tashuikouensis, was described by Hu in 1964. Chilantaisaurus was a large theropod, estimated as weighing between and...
,
CompsosuchusCompsosuchus is an extinct genus of abelisaurian dinosaur. It lived during the Late Cretaceous. It lived in India. Compsosuchus was described in 1933 by von Huene and Matley. The type species is C. solus. The genus is often considered a nomen dubium.-References:* at Dino Russ's Lair...
,
StokesosaurusStokesosaurus is a genus of small , early tyrannosaur from the Late Jurassic period of Utah and England. It was named after Utah geologist William Lee Stokes...
, and
SzechuanosaurusSzechuanosaurus is a dubious genus of theropod dinosaur from the Late Jurassic. This dinosaur lived in the Asia in the Oxfordian and early Kimmeridgian . It is based on four undiagnostic teeth from the Shangshaximiao Formation.-Discovery and species:Three species have been assigned to this genus...
. Given modern knowledge of theropod diversity and the advent of cladistic study of
evolutionEvolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
ary relationships, none of these theropods is now recognized as an allosaurid, although several, like
Acrocanthosaurus and
Yangchuanosaurus, are members of closely related families.
Allosauridae is one of four families in Carnosauria; the other three are
NeovenatoridaeNeovenatoridae is a family of large carnivorous dinosaurs. The group is a branch of the allosauroids, a large group of carnosaurs that also includes the sinraptorids, carcharodontosaurids, and allosaurids...
,
CarcharodontosauridaeCarcharodontosaurids were a group of carnivorous theropod dinosaurs. In 1931 Ernst Stromer named Carcharodontosauridae as a family, in modern paleontology this name indicates a clade within Carnosauria...
and
SinraptoridaeSinraptorids were a family of carnivorous theropod dinosaurs. They tended to be large predators, some growing to sizes of . Sinraptorids are carnosaurs, and many were initially classified within Megalosauridae or Allosauridae prior to recent analysis...
. Allosauridae has at times been proposed as ancestral to the
TyrannosauridaeTyrannosauridae is a family of coelurosaurian theropod dinosaurs which comprises two subfamilies containing up to six genera, including the eponymous Tyrannosaurus. The exact number of genera is controversial, with some experts recognizing as few as three...
(which would make it
paraphyleticA group of taxa is said to be paraphyletic if the group consists of all the descendants of a hypothetical closest common ancestor minus one or more monophyletic groups of descendants...
), one recent example being Gregory S. Paul's
Predatory Dinosaurs of the World, but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the
CoelurosauriaCoelurosauria is the clade containing all theropod dinosaurs more closely related to birds than to carnosaurs. In the past, it was used to refer to all small theropods, although this classification has been abolished...
. Allosauridae is the smallest of the carnosaur families, with only
Saurophaganax and a currently unnamed
FrenchThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
allosauroidAllosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Sinraptoridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae...
accepted as possible valid
generaIn biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
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.
Early discoveries and research
The discovery and early study of
Allosaurus is complicated by the multiplicity of names coined during the
Bone WarsThe Bone Wars, also known as the "Great Dinosaur Rush", refers to a period of intense fossil speculation and discovery during the Gilded Age of American history, marked by a heated rivalry between Edward Drinker Cope and Othniel Charles Marsh...
of the late 19th century. The first described
fossilFossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
in this history was a bone obtained secondhand by Ferdinand Vandiveer Hayden in 1869. It came from
Middle ParkMiddle Park is a high basin in the Rocky Mountains of north-central Colorado in the United States. It is located in Grand County, on the southwest slope of Rocky Mountain National Park, approximately 50 miles west of Boulder.-Description:The basin surrounds the headwaters of the Colorado River...
, near
Granby, ColoradoThe Town of Granby is a Statutory Town that is the most populous town in Grand County, Colorado, United States. Granby is situated along U.S. Highway 40 in Middle Park about west of Denver, Colorado, southwest of Rocky Mountain National Park...
, probably from
Morrison FormationThe Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
rocks. The locals had identified such bones as "petrified
horseThe horse is one of two extant subspecies of Equus ferus, or the wild horse. It is a single-hooved mammal belonging to the taxonomic family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
hoofs". Hayden sent his specimen to
Joseph LeidyJoseph Leidy was an American paleontologist.Leidy was professor of anatomy at the University of Pennsylvania, and later was a professor of natural history at Swarthmore College. His book Extinct Fauna of Dakota and Nebraska contained many species not previously described and many previously...
, who identified it as half of a tail vertebra, and tentatively assigned it to the European dinosaur genus
PoekilopleuronPoekilopleuron is an extinct genus of large basal tetanuran theropod dinosaur, perhaps belonging to the clade Allosauroidea. It measured 9 metres long and 1 ton in mass...
as
Poicilopleuron [sic]
valens. He later decided it deserved its own genus,
Antrodemus.
Allosaurus itself is
based onA holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
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
GreekAncient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
allos/αλλος, meaning "strange" or "different" and
sauros/σαυρος, meaning "lizard" or "reptile". It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery. The species epithet
fragilis is
LatinLatin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
for "fragile", referring to lightening features in the vertebrae. The bones were collected from the Morrison Formation of
Garden ParkGarden Park, in southcentral Colorado, is known for its Jurassic dinosaurs and the role the specimens played in the infamous bone wars of the late 19th century. Located north of Cañon City, Colorado, the name originates from the area providing vegetables to the miners at nearby Cripple Creek in...
, north of
Cañon CityThe City of Cañon City is a Home Rule Municipality that is the county seat and the most populous city of Fremont County, State of Colorado. The United States Census Bureau estimated that the city population was 16,000 in 2005. Cañon City is noted for being the location of nine state and four ...
. Marsh and
Edward Drinker CopeEdward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...
, 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 and
Labrosaurus, and Cope's
Epanterias.
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 MudgeBenjamin Franklin Mudge was an American lawyer, geologist and teacher. Briefly the mayor of Lynn, Massachusetts, he later moved to Kansas where he was appointed the first State Geologist. He led the first geological survey of the state in 1864, and published the first book on the geology of Kansas...
of the type specimen of
Allosaurus in Colorado, Marsh elected to concentrate work in
WyomingWyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...
; when work resumed at Garden Park in 1883, M. P. Felch found an almost complete
Allosaurus and several partial skeletons. In addition, one of Cope's collectors, H. F. Hubbell, found a specimen in the
Como BluffComo Bluff is a long ridge extending east-west, located between the towns of Rock River and Medicine Bow, Wyoming. The ridge is an anticline, formed as a result of compressional geological folding. Three geological formations, the Sundance, the Morrison, and the Cloverly Formations, containing...
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. This is the well-known mount poised over a partial
ApatosaurusApatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
skeleton as if
scavengingScavenging is both a carnivorous and herbivorous feeding behavior in which individual scavengers search out dead animal and dead plant biomass on which to feed. The eating of carrion from the same species is referred to as cannibalism. Scavengers play an important role in the ecosystem by...
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.
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 WillistonSamuel Wendell Williston was an American educator and paleontologist who was the first to propose that birds developed flight cursorially , rather than arboreally . He was also an entomologist, specialising in Diptera.-Early life:Williston was born in Boston, Massachusetts to Samuel Williston and...
suggested that too many names had been coined. For example, Williston pointed out in 1901 that Marsh had never been able to adequately distinguish
Allosaurus from
Creosaurus. The most influential early attempt to sort out the convoluted situation was produced by
Charles W. GilmoreCharles Whitney Gilmore was an American paleontologist, who named dinosaurs in North America and Mongolia, including the Cretaceous sauropod Alamosaurus, Alectrosaurus, Archaeornithomimus, Bactrosaurus, Brachyceratops, Chirostenotes, Mongolosaurus, Parrosaurus, Pinacosaurus, Styracosaurus and...
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.
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). "
Antrodemus" has been used informally for convenience when distinguishing between the skull Gilmore restored and the composite skull restored by Madsen.
Cleveland-Lloyd discoveries
Although sporadic work at what became known as the
Cleveland Lloyd Dinosaur QuarryThe Cleveland Lloyd Dinosaur Quarry National Natural Landmark, located in The San Rafael Swell, near Cleveland, Utah contains the densest concentration of Jurassic dinosaur fossils ever found. Well over 15,000 bones have been excavated from this Jurassic 'predator trap' and there are many...
in
Emery CountyEmery County is a county located in the U.S. state of Utah. As of 2000 the population was 10,860, and by 2009 had been estimated to decrease to 10,629. It was named for George W. Emery, governor of the Utah Territory in 1875...
,
UtahUtah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
had taken place as early as 1927, and the fossil site itself described by William J. Stokes in 1945, 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. 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
taphonomyTaphonomy is the study of decaying organisms over time and how they become fossilized . The term taphonomy was introduced to paleontology in 1940 by Russian scientist Ivan Efremov to describe the study of the transition of remains, parts, or products of organisms, from the biosphere, to the...
of the site, suggesting numerous mutually-exclusive explanations for how it may have formed. Suggestions have ranged from animals getting stuck in a bog, to becoming trapped in deep mud, to falling victim to
droughtA drought is an extended period of months or years when a region notes a deficiency in its water supply. Generally, this occurs when a region receives consistently below average precipitation. It can have a substantial impact on the ecosystem and agriculture of the affected region...
-induced mortality around a waterhole, to getting trapped in a spring-fed pond or seep. 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) to 12 meters (39 ft) long, and the disarticulation is an advantage for describing bones usually found fused.
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 (
paleobiologicalPaleobiology is a growing and comparatively new discipline which combines the methods and findings of the natural science biology with the methods and findings of the earth science paleontology...
and
paleoecologicalPaleoecology uses data from fossils and subfossils to reconstruct the ecosystems of the past. It involves the study of fossil organisms and their associated remains, including their life cycle, living interactions, natural environment, and manner of death and burial to reconstruct the...
topics). Such studies have covered topics including skeletal variation, growth, skull construction, hunting methods, the
brainThe brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
, and the possibility of gregarious living and parental care. Reanalysis of old material (particularly of large 'allosaur' specimens), new discoveries in Portugal, and several very complete new specimens have also contributed to the growing knowledge base. Fossil footprints attributed to
Allosaurus were discovered in Bałtów,
PolandPoland , officially the Republic of Poland , is a country in Central Europe bordered by Germany to the west; the Czech Republic and Slovakia to the south; Ukraine, Belarus and Lithuania to the east; and the Baltic Sea and Kaliningrad Oblast, a Russian exclave, to the north...
, by Polish paleontologist Gerard Gierliński in the early 21st century.
"Big Al"
One of the more significant
Allosaurus finds was the 1991 discovery of "Big Al" (
MORThe Museum of the Rockies, is located in Bozeman, Montana. The museum, originally affiliated with Montana State University in Bozeman, and now, also the Smithsonian Institution, is known for its paleontological collections, although these are not its sole focus...
693), a 95% complete, partially articulated specimen that measured about 8 meters (about 26 ft) in length. MOR 693 was excavated near
Shell, WyomingShell is an unincorporated community in Big Horn County, Wyoming, United States.The community is named for the abundance of fossil shells located in the area. Nearby exposed formations such as the Cloverly Formation and the Morrison Formation have yielded numerous fossils of dinosaurs and other...
, by a joint Museum of the Rockies and
University of WyomingThe University of Wyoming is a land-grant university located in Laramie, Wyoming, situated on Wyoming's high Laramie Plains, at an elevation of 7,200 feet , between the Laramie and Snowy Range mountains. It is known as UW to people close to the university...
Geological Museum team. This skeleton was discovered by a Swiss team, led by Kirby Siber. The same team later excavated 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, and was a subadult estimated at only 87% grown. The specimen was described by Breithaupt in 1996. 19 of its bones were broken or showed signs of
infectionAn infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
, which may have contributed to "Big Al's" death.
PathologicPathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
bones included five ribs, five vertebrae, and four bones of the feet; several damaged bones showed
osteomyelitisOsteomyelitis simply means an infection of the bone or bone marrow...
, 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.
Species and taxonomy
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 speciesIn biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the 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
tetanuranTetanurae, or "stiff tails", is a clade that includes most theropod dinosaurs, as well as birds. Tetanurans first appear during the early or middle Jurassic Period.-Definition:...
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
KimmeridgianIn the geologic timescale, the Kimmeridgian is an age or stage in the Late or Upper Jurassic epoch or series. It spans the time between 155.7 ± 4 Ma and 150.8 ± 4 Ma . The Kimmeridgian follows the Oxfordian and precedes the Tithonian....
–
TithonianIn the geologic timescale the Tithonian is the latest age of the Late Jurassic epoch or the uppermost stage of the Upper Jurassic series. It spans the time between 150.8 ± 4 Ma and 145.5 ± 4 Ma...
Upper Jurassic-age Morrison Formation of the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, spread across the states of
ColoradoColorado is a U.S. state that encompasses much of the Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains...
,
MontanaMontana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
,
New MexicoNew Mexico is a state located in the southwest and western regions of the United States. New Mexico is also usually considered one of the Mountain States. With a population density of 16 per square mile, New Mexico is the sixth-most sparsely inhabited U.S...
,
OklahomaOklahoma is a state located in the South Central region of the United States of America. With an estimated 3,751,351 residents as of the 2010 census and a land area of 68,667 square miles , Oklahoma is the 28th most populous and 20th-largest state...
,
South DakotaSouth Dakota is a state located in the Midwestern region of the United States. It is named after the Lakota and Dakota Sioux American Indian tribes. Once a part of Dakota Territory, South Dakota became a state on November 2, 1889. The state has an area of and an estimated population of just over...
, 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 study of skull elements from the Cleveland Lloyd site found wide variation between individuals, calling into question previous species-level distinctions based such features as the shape of the lacrimal horns, and the proposed differentiation of "A. jimmadseni" based on the shape of the
jugalThe jugal is a skull bone found in most reptiles, amphibians, and birds. In mammals, the jugal is often called the malar or Zygomatic. It is connected to the quadratojugal and maxilla, as well as other bones, which may vary by species....
.
A. europaeus was found in the Kimmeridgian-age Porto Novo Member of the
Lourinhã FormationThe Lourinhã Formation is a geological formation in West Portugal, named for the municipality of Lourinhã, from which a wide array of fossils comes...
, but may be the same as
A. fragilis.
A. tendagurensis was found in Kimmeridgian-age rocks of
TendaguruThe Tendaguru Beds are a fossil-rich formation in Tanzania. It has been considered the richest of Late Jurassic strata in Africa. Continental reconstructions show Tendaguru to have been in the southern hemisphere during the Late Jurassic. Tendaguru is similar to the Morrison Formation except in...
, in
MtwaraMtwara is a southern region of Tanzania which has been underdeveloped for a long time: development is constrained by the lack of highway and energy infrastructures. The Dar es Salaam-Kibiti-Lindi-Mtwara road has been improved by the completion of the Mkapa bridge over the Rufiji River...
, 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
dubiousIn zoological nomenclature, a nomen dubium is a scientific name that is of unknown or doubtful application...
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. Later researchers suggested that the bone was
pathologicPathology is the precise study and diagnosis of disease. The word pathology is from Ancient Greek , pathos, "feeling, suffering"; and , -logia, "the study of". Pathologization, to pathologize, refers to the process of defining a condition or behavior as pathological, e.g. pathological gambling....
, showing an injury to the living animal, and that part of the unusual form of the rear of the bone was due to plaster reconstruction. It is now regarded as an example of
A. fragilis. Other remains thought to pertain to
Allosaurus have come from across the world, including
AustraliaAustralia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
,
SiberiaSiberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
, and
SwitzerlandSwitzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, but these fossils have been reassessed as belonging to other dinosaurs.
The issue of synonyms is complicated by the type specimen of
Allosaurus fragilis (catalog number YPM 1930) being extremely fragmentary, consisting of a few incomplete vertebrae, limb bone fragments, rib fragments, and a tooth. Because of this, several scientists have interpreted the type specimen as potentially dubious, and thus the genus
Allosaurus itself or at least the species
A. fragilis would be a
nomen dubium ("dubious name", based on a specimen too incomplete to compare to other specimens or to classify). To address this situation,
Gregory S. PaulGregory Scott Paul is a freelance researcher, author and illustrator who works in paleontology, and more recently has examined sociology and theology. He is best known for his work and research on theropod dinosaurs and his detailed illustrations, both live and skeletal...
and
Kenneth CarpenterKenneth Carpenter is a paleontologist. He is the museum director of the USU Eastern Prehistoric Museum and author or co-author of a number of books on dinosaurs and Mesozoic life...
(2010) submitted a petition to the
ICZNThe International Commission on Zoological Nomenclature is an organization dedicated to "achieving stability and sense in the scientific naming of animals". Founded in 1895, it currently comprises 28 members from 20 countries, mainly practicing zoological taxonomists...
to have the name
A. fragilis officially transferred to a more complete specimen (as a neotype). This request is currently pending review.
Paleoecology
Allosaurus was the most common large theropod in the vast tract of Western American fossil-bearing rock known as the
Morrison FormationThe Morrison Formation is a distinctive sequence of Late Jurassic sedimentary rock that is found in the western United States, which has been the most fertile source of dinosaur fossils in North America. It is composed of mudstone, sandstone, siltstone and limestone and is light grey, greenish...
, accounting for 70 to 75% of theropod specimens, and as such was at the top
trophic levelThe trophic level of an organism is the position it occupies in a food chain. The word trophic derives from the Greek τροφή referring to food or feeding. A food chain represents a succession of organisms that eat another organism and are, in turn, eaten themselves. The number of steps an organism...
of the Morrison
food webA food web depicts feeding connections in an ecological community. Ecologists can broadly lump all life forms into one of two categories called trophic levels: 1) the autotrophs, and 2) the heterotrophs...
. The Morrison Formation is interpreted as a semiarid environment with distinct
wetThe the wet season, or rainy season, is the time of year, covering one or more months, when most of the average annual rainfall in a region occurs. The term green season is also sometimes used as a euphemism by tourist authorities. Areas with wet seasons are dispersed across portions of the...
and
dry seasonThe dry season is a term commonly used when describing the weather in the tropics. The weather in the tropics is dominated by the tropical rain belt, which oscillates from the northern to the southern tropics over the course of the year...
s, and flat
floodplainA floodplain, or flood plain, is a flat or nearly flat land adjacent a stream or river that stretches from the banks of its channel to the base of the enclosing valley walls and experiences flooding during periods of high discharge...
s. Vegetation varied from
riverA river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
-lining forests of conifers, tree ferns, and
fernA fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
s (
gallery forestGallery forests are evergreen forests that form as corridors along rivers or wetlands and project into landscapes that are otherwise only sparsely treed such as savannas, grasslands or deserts....
s), to fern
savannaA savanna, or savannah, is a grassland ecosystem characterized by the trees being sufficiently small or widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of C4 grasses.Some...
s with occasional trees such as the
AraucariaAraucaria is a genus of evergreen coniferous trees in the family Araucariaceae. There are 19 extant species in the genus, with a highly disjunct distribution in New Caledonia , Norfolk Island, eastern Australia, New Guinea, Argentina, Chile, and southern Brazil.-Description:Araucaria are mainly...
-like conifer
Brachyphyllum.
The Morrison Formation has been a rich fossil hunting ground. The flora of the period has been revealed by fossils of
green algaeChlorophyta is a division of green algae, informally called chlorophytes. The name is used in two very different senses so that care is needed to determine the use by a particular author...
, fungi,
mossMosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es, horsetails, ferns,
cycadCycads are seed plants typically characterized by a stout and woody trunk with a crown of large, hard and stiff, evergreen leaves. They usually have pinnate leaves. The individual plants are either all male or all female . Cycads vary in size from having a trunk that is only a few centimeters...
s,
ginkgoGinkgo , also spelled gingko and known as the Maidenhair Tree, is a unique species of tree with no close living relatives...
es, and several families of conifers. Animal fossils discovered include bivalves,
snailSnail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
s,
ray-finned fishesThe Actinopterygii or ray-finned fishes constitute a class or sub-class of the bony fishes.The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines , as opposed to the fleshy, lobed fins that characterize...
,
frogFrogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s,
salamanderSalamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s,
turtleTurtles are reptiles of the order Testudines , characterised by a special bony or cartilaginous shell developed from their ribs that acts as a shield...
s,
sphenodontsSphenodontia is an order of lizard-like reptiles that includes only one living genus, the tuatara , and only two living species...
,
lizardLizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
s, terrestrial and aquatic
crocodylomorphaThe Crocodylomorpha are an important group of archosaurs that include the crocodilians and their extinct relatives.During Mesozoic and early Tertiary times the Crocodylomorpha were far more diverse than they are now. Triassic forms were small, lightly built, active terrestrial animals. These were...
ns, several species of
pterosaurPterosaurs were flying reptiles of the clade or order Pterosauria. They existed from the late Triassic to the end of the Cretaceous Period . Pterosaurs are the earliest vertebrates known to have evolved powered flight...
, numerous dinosaur species, and early
mammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
s such as
docodontsDocodonta is an order of extinct proto-mammals that lived during the mid- to late-Mesozoic era. Their most distinguishing physical features were their relatively sophisticated set of molars, from which the order gets its name. In the fossil record, Docodonta is represented primarily by isolated...
,
multituberculatesThe Multituberculata were a group of rodent-like mammals that existed for approximately one hundred and twenty million years—the longest fossil history of any mammal lineage—but were eventually outcompeted by rodents, becoming extinct during the early Oligocene. At least 200 species are...
,
symmetrodontsSymmetrodonta is a basal group of Mesozoic mammals characterized by the triangular aspect of the molars when viewed from above and the absence of a well-developed talonid. The traditional group of symmetrodonts ranges in age from the latest Triassic to the Late Cretaceous. One species,...
, and
triconodontsTriconodonta is the generic name for a group of early mammals which were close relatives of the ancestors of all present-day mammals. Triconodonts lived between the Triassic and the Cretaceous. They are one of the groups that can be classified as mammals by any definition...
. Dinosaurs known from the Morrison include the theropods
Ceratosaurus,
OrnitholestesOrnitholestes was a small theropod dinosaur of the late Jurassic of Western Laurasia . To date, it is known only from a single partial skeleton, and badly crushed skull found at the Bone Cabin Quarry near Medicine Bow, Wyoming, in 1900...
, and
TorvosaurusTorvosaurus is a genus of large theropod dinosaur that lived during the Late Jurassic period...
, the sauropods
ApatosaurusApatosaurus , also known by the popular but scientifically deprecated synonym Brontosaurus, is a genus of sauropod dinosaur that lived from about 154 to 150 million years ago, during the Jurassic Period . It was one of the largest land animals that ever existed, with an average length of and a...
,
BrachiosaurusBrachiosaurus is a genus of sauropod dinosaur from the Jurassic Morrison Formation of North America. It was first described by Elmer S. Riggs in 1903 from fossils found in the Grand River Canyon of western Colorado, in the United States. Riggs named the dinosaur Brachiosaurus altithorax,...
,
CamarasaurusCamarasaurus meaning 'chambered lizard', referring to the hollow chambers in its vertebrae was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America...
, and
DiplodocusDiplodocus , or )is a genus of diplodocid sauropod dinosaur whose fossils were first discovered in 1877 by S. W. Williston. The generic name, coined by Othniel Charles Marsh in 1878, is a Neo-Latin term derived from Greek "double" and "beam", in reference to its double-beamed chevron bones...
, and the
ornithischiaOrnithischia or Predentata is an extinct order of beaked, herbivorous dinosaurs. The name ornithischia is derived from the Greek ornitheos meaning 'of a bird' and ischion meaning 'hip joint'...
ns
CamptosaurusCamptosaurus is a genus of plant-eating, beaked ornithischian dinosaurs of the Late Jurassic period of western North America. The name means 'flexible lizard', ....
,
DryosaurusDryosaurus is a genus of an ornithopod dinosaur that lived in the Late Jurassic period. It was an iguanodont . Fossils have been found in the western United States, and were first discovered in the late 19th century...
, and
StegosaurusStegosaurus is a genus of armored stegosaurid dinosaur. They lived during the Late Jurassic period , some 155 to 150 million years ago in what is now western North America. In 2006, a specimen of Stegosaurus was announced from Portugal, showing that they were present in Europe as well...
. It is commonly found at the same sites as
Apatosaurus,
Camarasaurus,
Diplodocus, and
Stegosaurus. The Late Jurassic formations of Portugal where
Allosaurus is present are interpreted as having been similar to the Morrison but with a stronger
marineAn ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...
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
LusotitanLusotitan is a genus of herbivorous brachiosaurid sauropod dinosaur from the Late Jurassic Period of Portugal.In 1947 by Manuel de Matos, collector of the Geological Survey of Portugal, fossils of a large sauropod were found in the Portuguese Lourinhã Formation dating to the Tithonian stage of the...
,
Camptosaurus and
DraconyxDraconyx is a genus of dinosaur from the Late Jurassic. It was an ornithopod which lived in what is now Portugal. It was found in Lourinhã, in 1991, and described by Octávio Mateus and Miguel Telles Antunes in 2001.-Etymology:...
).
Allosaurus coexisted with fellow large theropods
Ceratosaurus and
Torvosaurus in both the United States and Portugal. The three appear to have had different
ecological nicheIn ecology, a niche is a term describing the relational position of a species or population in its ecosystem to each other; e.g. a dolphin could potentially be in another ecological niche from one that travels in a different pod if the members of these pods utilize significantly different food...
s, 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.
Ceratosaurus, better known than
Torvosaurus, differed noticeably from
Allosaurus in functional anatomy by having a taller, narrower skull with large, broad teeth.
Allosaurus was itself a potential food item to other carnivores, as illustrated by an
Allosaurus pubic footIn vertebrates, the pubic bone is the ventral and anterior of the three principal bones composing either half of the pelvis.It is covered by a layer of fat, which is covered by the mons pubis....
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.
Life history
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
eggsAn egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
—crushed eggs from Colorado have been suggested as those of
Allosaurus. Based on
histologicalHistology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
analysis of limb bones, the upper age limit for
Allosaurus is estimated at 22 to 28 years, which is comparable to that of other large theropods like
TyrannosaurusTyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
. From the same analysis, its maximum growth appears to have been at age 15, with an estimated growth rate of about 150 kilograms (330
lbThe pound or pound-mass is a unit of mass used in the Imperial, United States customary and other systems of measurement...
) per year.
Medullary bone tissue, also found in dinosaurs as diverse as
TyrannosaurusTyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
and
TenontosaurusTenontosaurus is a genus of medium- to large-sized ornithopod dinosaur. The genus is known from the late Aptian to Albian ages of the middle Cretaceous period sediments of western North America, dating between 115 to 108 million years ago...
, has been found in at least one
Allosaurus specimen, a
shin boneThe tibia , shinbone, or shankbone is the larger and stronger of the two bones in the leg below the knee in vertebrates , and connects the knee with the ankle bones....
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
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
to shells. Its presence in the
Allosaurus individual establishes sex and shows she had reached reproductive age. 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.
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
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 tail spikeThagomizer is an informal name for the distinctive arrangement of four to ten spikes on the tails of stegosaurid dinosaurs. These spikes are believed to have been a defensive measure against predators.-Paleobiology:...
, and a
Stegosaurus neck plate with a U-shaped wound that correlates well with an
Allosaurus snout. 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. 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 first decade of the 21st century may have found other solutions to this question.
Robert T. BakkerRobert T. Bakker is an American paleontologist who helped reshape modern theories about dinosaurs, particularly by adding support to the theory that some dinosaurs were endothermic...
, comparing
Allosaurus to
CenozoicThe Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
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
sawA saw is a tool that uses a hard blade or wire with an abrasive edge to cut through softer materials. The cutting edge of a saw is either a serrated blade or an abrasive...
-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.
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
alligatorAn alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....
s (13,000 N),
lionThe lion is one of the four big cats in the genus Panthera, and a member of the family Felidae. With some males exceeding 250 kg in weight, it is the second-largest living cat after the tiger...
s (4,167 N), and
leopardThe leopard , Panthera pardus, is a member of the Felidae family and the smallest of the four "big cats" in the genus Panthera, the other three being the tiger, lion, and jaguar. The leopard was once distributed across eastern and southern Asia and Africa, from Siberia to South Africa, but its...
s (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
palateThe palate is the roof of the mouth in humans and other mammals. It separates the oral cavity from the nasal cavity. A similar structure is found in crocodilians, but, in most other tetrapods, the oral and nasal cavities are not truly separate. The palate is divided into two parts, the anterior...
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 visionBinocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a...
to 20° of width, slightly less than that of modern
crocodiliaCrocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
ns. As with crocodilians, this may have been enough to judge prey distance and time attacks. 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).
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
lairLair may refer to:*An animal's lair or home; see :Category:Shelters built or used by animals*Lair , a 2007 video game*In Scots language, lair refers to a burial-plot in a graveyard...
s 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
packA pack hunter is a predator belonging to the animal kingdom, which has evolved to hunt its prey by working together with other members of its species. Normally, such animals are closely related. The most commonly known pack hunter is the Gray Wolf, the ancestor of all breeds of domesticated dogs...
or to settle
territorialIn ethology the term territory refers to any sociographical area that an animal of a particular species consistently defends against conspecifics...
disputes.
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
vertebrateVertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
s in general, and modern
diapsidDiapsids are a group of reptiles that developed two holes in each side of their skulls, about 300 million years ago during the late Carboniferous period. Living diapsids are extremely diverse, and include all crocodiles, lizards, snakes, and tuatara...
carnivores (including lizards, crocodiles, and birds) very rarely cooperate to hunt in such a way. Instead, they are typically territorial and will kill and
cannibalizeIn zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
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
crocodileA crocodile is any species belonging to the family Crocodylidae . The term can also be used more loosely to include all extant members of the order Crocodilia: i.e...
s and
Komodo dragonThe Komodo dragon , also known as the Komodo monitor, is a large species of lizard found in the Indonesian islands of Komodo, Rinca, Flores, Gili Motang and Gili Dasami. A member of the monitor lizard family , it is the largest living species of lizard, growing to a maximum length of in rare cases...
s. 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 bladeIn anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
, and cannibalized allosaur skeletons among the bones at Bakker's lair sites.
Brain and senses
The brain of
Allosaurus, as interpreted from spiral
CT scanningX-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
of an endocast, was more consistent with
crocodiliaCrocodilia is an order of large reptiles that appeared about 84 million years ago in the late Cretaceous Period . They are the closest living relatives of birds, as the two groups are the only known survivors of the Archosauria...
n brains than those of the other living
archosaurArchosaurs are a group of diapsid amniotes whose living representatives consist of modern birds and crocodilians. This group also includes all extinct non-avian dinosaurs, many extinct crocodilian relatives, and pterosaurs. Archosauria, the archosaur clade, is a crown group that includes the most...
s, birds. The structure of the
vestibular apparatusThe vestibular system, which contributes to balance in most mammals and to the sense of spatial orientation, is the sensory system that provides the leading contribution about movement and sense of balance. Together with the cochlea, a part of the auditory system, it constitutes the labyrinth of...
indicates that the skull was held nearly horizontal, as opposed to strongly tipped up or down. The structure of the
inner earThe inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...
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 bulbThe olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
s were large and seem to have been well suited for detecting odors, although the area for evaluating smells was relatively small.
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 runnning or
migrationAnimal migration is the relatively long-distance movement of individuals, usually on a seasonal basis. It is a ubiquitous phenomenon, found in all major animal groups, including birds, mammals, fish, reptiles, amphibians, insects, and crustaceans. The trigger for the migration may be local...
, 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
AlbertosaurusAlbertosaurus is a genus of tyrannosaurid theropod dinosaur that lived in western North America during the Late Cretaceous Period, more than 70 million years ago. The type species, A. sarcophagus, was apparently restricted in range to the modern-day Canadian province of Alberta, after which...
,
OrnithomimusOrnithomimus is a genus of ornithomimid dinosaur from the Late Cretaceous Period of what is now North America.In 1890 Ornithomimus velox was named by Othniel Charles Marsh on the basis of a foot and partial hand from the Maastrichtian Denver Formation. Another seventeen species have been named since...
or
ArchaeornithomimusArchaeornithomimus is a genus of ornithomimosaurian theropod dinosaur from the Late Cretaceous of China, 70 million years ago....
. 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 proximal phalanges" and occurred across all three weight-bearing toes in "statistically indistinguishable" numbers. Since the lower end of the third metatarsal would have contacted the ground first while an allosaur was running it would have borne the most stress. If the allosaurs' stress fractures were caused by damage accumulating while walking or running this bone should have experience more stress fractures than the others. The lack of such a bias in the examined
Allosaurus fossils indicates an origin for the stress fractures from a source other than running. The authors conclude that these fractures occurred during interaction with prey, like an allosaur trying to hold struggling prey with its feet. The abundance of stress fractures and avulsion injuries in
Allosaurus provide evidence for "very active" predation-based rather than scavenging diets.
The left
scapulaIn anatomy, the scapula , omo, or shoulder blade, is the bone that connects the humerus with the clavicle ....
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-Places:* Ilion or, Latinized, Ilium, another name for the legendary city of Troy, hence the title of Homer's Iliad*Ilium , an ancient city in Epirus...
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
involucrumInvolucrum is a layer of new bone growth outside existing bone seen in pyogenic osteomyelitis. It results from the stripping off of the periosteum by the accumulation of pus within the bone, and new bone growing from the periosteum....
.
Other pathologies reported in
Allosaurus include:
- Willow breaks in two ribs.
- Healed fractures in the humerus
The humerus is a long bone in the arm or forelimb that runs from the shoulder to the elbow....
and radiusIn classical geometry, a radius of a circle or sphere is any line segment from its center to its perimeter. By extension, the radius of a circle or sphere is the length of any such segment, which is half the diameter. If the object does not have an obvious center, the term may refer to its...
.
- Distortion of joint
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...
surfaces in the foot possibly due to osteoarthritisOsteoarthritis also known as degenerative arthritis or degenerative joint disease, is a group of mechanical abnormalities involving degradation of joints, including articular cartilage and subchondral bone. Symptoms may include joint pain, tenderness, stiffness, locking, and sometimes an effusion...
or developmental issues.
- Distortions of the joint surfaces of the tail vertebrae possibly due to osetoarthritis or developmental issues.
- "[E]xtensive 'neoplastic' ankylosis
Ankylosis or anchylosis is a stiffness of a joint due to abnormal adhesion and rigidity of the bones of the joint, which may be the result of injury or disease. The rigidity may be complete or partial and may be due to inflammation of the tendinous or muscular structures outside the joint or of...
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
Amputation is the removal of a body extremity by trauma, prolonged constriction, or surgery. As a surgical measure, it is used to control pain or a disease process in the affected limb, such as malignancy or gangrene. In some cases, it is carried out on individuals as a preventative surgery for...
of a chevron and foot bone, both possibly a result of bites.
- "[E]xtensive exostoses" in the first phalanx of the third toe.
- Lesions similar to those caused by osteomyelitis
Osteomyelitis simply means an infection of the bone or bone marrow...
in two scapulae.
- Bone spurs in a premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
, ungualAn ungual is a highly modified distal toe bone which ends in a hoof, claw, or nail. Elephants and other ungulates have ungual phalanges, as did the sauropods and horned dinosaurs. A claw is a highly modified ungual phalange.As an adjective, ungual means related to nail, as in periungual .-External...
, and two metacarpals.
- Exostosis in a pedal phalanx possibly attributable to an infectious disease.
- A metacarpal with a round depressed fracture.
In popular culture
Along with
TyrannosaurusTyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...
,
Allosaurus has come to represent the quintessential large, carnivorous dinosaur in popular culture. It is a common dinosaur in museums, due in particular to the excavations at the Cleveland Lloyd Dinosaur Quarry; by 1976, as a result of cooperative operations, 38 museums in eight countries on three continents had Cleveland-Lloyd allosaur material or casts.
Allosaurus is the official
state fossilMost American states have made a state fossil designation, in many cases during the 1980s. It is common to designate one species in which fossilization has occurred, rather than a single specimen, or a category of fossils not limited to a single species....
of
UtahUtah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
.
Allosaurus has been depicted in popular culture since the early years of the 20th century. It is top predator in both
Arthur Conan DoyleSir Arthur Ignatius Conan Doyle DL was a Scottish physician and writer, most noted for his stories about the detective Sherlock Holmes, generally considered a milestone in the field of crime fiction, and for the adventures of Professor Challenger...
's 1912 novel,
The Lost World, and its
1925 film adaptationThe Lost World is a 1925 silent film adaptation of Arthur Conan Doyle's 1912 novel of the same name. The movie was produced by First National Pictures, a large Hollywood studio at the time, and stars Wallace Beery as Professor Challenger. This version was directed by Harry O...
, the first full-length motion picture to feature dinosaurs.
Allosaurus was used as the starring dinosaur of the 1956 film
The Beast of Hollow MountainThe Beast of Hollow Mountain is a 1956 scifi/horror western about an American cowboy living in Mexico who discovers his missing cattle are being preyed upon by an Allosaurus...
, and the 1969 film
The Valley of GwangiThe Valley of Gwangi is a 1969 American western-fantasy film directed by Jim O'Connolly and written by William Bast. The film is also known as Gwangi, The Lost Valley, The Valley Time Forgot, and The Valley Where Time Stood Still...
, two
genreGenre , Greek: genos, γένος) is the term for any category of literature or other forms of art or culture, e.g. music, and in general, any type of discourse, whether written or spoken, audial or visual, based on some set of stylistic criteria. Genres are formed by conventions that change over time...
combinations of living dinosaurs with
WesternsThe Western is a genre of various visual arts, such as film, television, radio, literature, painting and others. Westerns are devoted to telling stories set primarily in the latter half of the 19th century in the American Old West, hence the name. Some Westerns are set as early as the Battle of...
. In
The Valley of Gwangi, Gwangi is billed as an
Allosaurus, although
Ray HarryhausenRay Harryhausen is an American film producer and special effects creator...
based his model for the creature on Charles R. Knight's depiction of a
Tyrannosaurus. Harryhausen sometimes confuses the two, stating in a DVD interview "They're both meat eaters, they're both tyrants... one was just a bit larger than the other."
Allosaurus appeared in the second episode of the 1999
BBCThe British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
television series
Walking with DinosaursWalking with Dinosaurs is a six-part documentary television miniseries that was produced by BBC, narrated by Kenneth Branagh, and first aired in the United Kingdom, in 1999. The series was subsequently aired in North America on the Discovery Channel in 2000, with Branagh's voice replaced with that...
and the follow-up special
The Ballad of Big AlThe Ballad of Big Al is a combination biography-sequel for Walking with Dinosaurs ...
, which speculated on the life of the "Big Al" specimen, based on scientific evidence from the numerous injuries and pathologies in its skeleton.
Allosaurus also made an appearance in the Discovery Channel series
Dinosaur RevolutionDinosaur Revolution is a four-part American nature documentary produced by Creative Differences, although it was believed to be a Pixar project when it was first revealed to the public due to a press release saying so. The first two episodes aired on Discovery Channel on September 4, 2011. The...
. Its depiction in this series was based upon a specimen with a smashed lower jaw that was uncovered by paleontologist Thomas Holtz.
External links