Allosauridae is a family of medium to large bipedal, carnivorous allosauroid neotheropod dinosaurs from the Late Jurassic. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles Marsh in 1878. Allosaurids are characterized by an astragalus with a restriction of the ascending process to the lateral part of the bone, a larger medial than lateral condyle, and a horizontal groove across the face of the condyles.
|An A. fragilis skeletal mount, at the San Diego Natural History Museum|
Allosaurids have a general anatomy typical of other neotheropod dinosaurs, contributing to the difficulty in defining the family's membership. A typical 8m specimen of Allosaurus fragilis had a skull of about 0.85m. The premaxilla has five teeth and the maxilla usually around 16. The dentary also typically has 16 teeth. All teeth are serrated and continuously replaced throughout the life of the animal. Allosaurid skulls are characterized by two sets of crests formed by the nasal and lacrimal bones respectively. These crests would have been covered by keratin sheathes. The skull also exhibits features consistent with significant cranial kinesis: a synovial joint between the braincase and the frontals and a loose articulation between the dentary and the angular/surangular. This cranial kinesis would have dampened forces on the bones of the skull and allowed allosaurids to open their mouths to very large angles.
Allosaurids have 28 precaudal vertebrae (9 cervical, 14 dorsal, 5 sacral) and an estimated 45-50 caudal vertebrae. Gastralia and ferculae are rarely preserved as fossils but are presumed to occur in all allosaurids The pubis is highly elongated and extends ventrally to form a pubic foot which like in other large dinosaurs is thought to have been used to support the weight of the body in a resting crouch position.
Like most other theropods, allosaurids have very short forelimbs relative to their hindlimbs with three digits on the hand and four on the foot. The first digit of the hand forms a semi-opposable thumb and digits 4 and 5 are absent. Digits 2-4 of the foot are robust but digit 1 is reduced and does not touch the ground and digit 5 is absent. All distal phalanges were capped with large claws, those on the hand were especially long and were curved to facilitate raking and grasping of prey items  Phalangeal formulae of the hand and foot are 4-3-4 and 2-3-4-5 respectively.
Allosauroidea is a superfamily or clade of theropod dinosaurs which contains four families — the Metriacanthosauridae, Allosauridae, Carcharodontosauridae, and Neovenatoridae. Allosauroids, alongside the family Megalosauroidea, were among the apex predators that were active during the Middle Jurassic to Late Cretaceous periods. Of the fourteen allosauroid taxa, five are known for specimens with relatively complete skulls; the taxa are Allosaurus, Sinraptor, Yangchuanosaurus, Carchardontosaurus, and Acrocanthosaurus. The most famous and best understood allosauroid is the North American genus Allosaurus.
The oldest-known allosauroid, Shidaisaurus jinae, appeared in the early Middle Jurassic (probably Bajocian stage) of China. The last known definitive surviving members of the group died out around 93 million years ago in Asia (Shaochilong) and South America (Mapusaurus), though the megaraptorans may belong to the group as well. Additional, but highly fragmentary, remains probably belonging to carcharodontosaurids have been found from the Late Maastrichtian (70-66 Ma ago) in Brazil. An alternative interpretation is to attribute the remains to abelisaurids, which share the distinct pattern of curved wrinkled enamel found in the Brazilian remains with the carcharodontosaurids. This similarity between abelisaurids and carcharodontosaurids means that a definitive match between the Brazilian fossil and carcharodontosaurids cannot be made.Allosauroids had long, narrow skulls, large orbits, three-fingered hands, and usually had "horns" or ornamental crests on their heads. Although allosauroids vary in size, the group maintains a similar center of mass and hip position on their bodies. Allosauroids also exhibit reptilian-style immune systems, secreting fibrin at injured sites to prevent infections from spreading through the bloodstream. This characteristic has been observed by examining injuries and infections on allosauroid bones. It is possible that allosauroids were social animals, as many remains of allosauroids have been found in close proximity to each other. Allosauroids were likely active predators, and from studying endocasts, probably best responded to odors and loud low-frequency noises.Allosaurus
Allosaurus () is a genus of carnivorous theropod dinosaur that lived 155 to 145 million years ago during the late Jurassic period (Kimmeridgian to late Tithonian). The name "Allosaurus" means "different lizard" alluding to its unique concave vertebrae (at the time of its discovery). It is derived from the Greek ἄλλος/allos ("different, other") and σαῦρος/sauros ("lizard / generic reptile"). The first fossil remains that could definitively be ascribed to this genus were described in 1877 by paleontologist Othniel Charles Marsh. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles. Indeed, it has been a top feature in several films and documentaries about prehistoric life.
Allosaurus was a large bipedal predator. Its skull was large and equipped with dozens of sharp, serrated teeth. It averaged 9.5 metres (31 ft) in length, though fragmentary remains suggest it could have reached over 12 m (39 ft). Relative to the large and powerful hindlimbs, its three-fingered forelimbs were small, and the body was balanced by a long and heavily muscled tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. The genus has a complicated taxonomy, and includes an uncertain number of valid species, the best known of which is A. fragilis. The bulk of Allosaurus remains have come from North America's Morrison Formation, with material also known from Portugal and possibly Tanzania. It was known for over half of the 20th century as Antrodemus, but a study of the copious remains from the Cleveland-Lloyd Dinosaur Quarry brought the name "Allosaurus" back to prominence and established it as one of the best-known dinosaurs.
As the most abundant large predator in the Morrison Formation, Allosaurus was at the top of the food chain, probably preying on contemporaneous large herbivorous dinosaurs, and perhaps even other predators. Potential prey included ornithopods, stegosaurids, and sauropods. Some paleontologists interpret Allosaurus as having had cooperative social behavior, and hunting in packs, while others believe individuals may have been aggressive toward each other, and that congregations of this genus are the result of lone individuals feeding on the same carcasses.Antrodemus
Antrodemus ("chamber bodied") is a dubious genus of theropod dinosaur from the Kimmeridgian-Tithonian-age Upper Jurassic Morrison Formation of Middle Park, Colorado. It contains one species, Antrodemus valens, first described and named as a species of Poekilopleuron by Joseph Leidy in 1870.
The first described fossil specimen was a bone obtained secondhand by Ferdinand Vandiveer Hayden in 1869. It came from Middle Park, near Granby, Colorado, probably from Morrison Formation rocks. The locals had identified such bones as petrified horse hooves. Hayden sent his specimen to Joseph Leidy, who identified it as half of a tail vertebra, and tentatively assigned it to the European dinosaur genus Poekilopleuron as Poicilopleuron [sic] valens. He later decided it deserved its own genus, Antrodemus.In 1920, Charles W. Gilmore came to the conclusion that the tail vertebra named Antrodemus by Leidy was indistinguishable from those of Allosaurus, and that Antrodemus should be the preferred name because, as the older name, it had priority. Antrodemus became the accepted name for this familiar genus for over fifty years, until James Madsen published on the Cleveland-Lloyd specimens of Allosaurus and concluded that name 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). Subsequent authors have agreed with this assessment and have considered Antrodemus a nomen dubium.Carcharodontosauridae
Carcharodontosaurids (from the Greek καρχαροδοντόσαυρος, carcharodontósauros: "shark-toothed lizards") were a group of carnivorous theropod dinosaurs. In 1931 Ernst Stromer named Carcharodontosauridae as a family, which, in modern paleontology, indicates a clade within Carnosauria. Carcharodontosaurids included some of the largest land predators ever known: Giganotosaurus, Mapusaurus, Carcharodontosaurus, and Tyrannotitan all rivaled or slightly exceeded Tyrannosaurus in length. A 2015 paper by Christophe Hendrickx and colleagues gives a maximum length estimate of 14 meters (46 feet) for the largest carcharodontosaurids, while the smallest carcharodontosaurids were estimated to have been at least 6 meters (20 feet) long.Dinosaur classification
Dinosaur classification began in 1842 when Sir Richard Owen placed Iguanodon, Megalosaurus, and Hylaeosaurus in "a distinct tribe or suborder of Saurian Reptiles, for which I would propose the name of Dinosauria." In 1887 and 1888 Harry Seeley divided dinosaurs into the two orders Saurischia and Ornithischia, based on their hip structure. These divisions have proved remarkably enduring, even through several seismic changes in the taxonomy of dinosaurs.
The largest change was prompted by entomologist Willi Hennig's work in the 1950s, which evolved into modern cladistics. For specimens known only from fossils, the rigorous analysis of characters to determine evolutionary relationships between different groups of animals (clades) proved incredibly useful. When computer-based analysis using cladistics came into its own in the 1990s, paleontologists became among the first zoologists to almost wholeheartedly adopt the system. Progressive scrutiny and work upon dinosaurian interrelationships, with the aid of new discoveries that have shed light on previously uncertain relationships between taxa, have begun to yield a stabilizing classification since the mid-2000s. While cladistics is the predominant classificatory system among paleontology professionals, the Linnean system is still in use, especially in works intended for popular distribution.Epanterias
Epanterias 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 three vertebrae, a coracoid, and a metatarsal. Although Cope thought it was a sauropod, it was later shown to be a theropod. Gregory S. Paul reassessed the material as pertaining to a large species of Allosaurus in 1988 (which he classified as Allosaurus amplexus). Other authors have gone further and considered E. amplexus as simply a large individual of Allosaurus fragilis. In 2010, Gregory S. Paul and Kenneth Carpenter noted that the E. amplexus specimen comes from higher in the Morrison Formation than the type specimen of Allosaurus fragilis, and is therefore "probably a different taxon". They also considered its holotype specimen not diagnostic and classified it as a nomen dubium.Gualicho
Gualicho (named in reference to the gualichu) is a genus of theropod dinosaur. The type species is Gualicho shinyae. Gualicho lived in what is now northern Patagonia, on what was then a South American island continent split off from the supercontinent Gondwana. The fossils were found in the Huincul Formation, dating to the late Cenomanian-early Turonian age of the upper Cretaceous Period, around 93 million years ago.Indosaurus
Indosaurus (meaning "Indian lizard") is a genus of theropod dinosaur once living in what is now India. It lived about 69 to 66 million years ago, in the Maastrichtian division of the Late Cretaceous. It weighed roughly 700 kg (1540 lb).
The fossil evidence from Jabalpur, India, includes the now-lost holotype GSI K27/565, a partial skull of unusual thickness found by Charles Alfred Matley in the Lameta Formation; other parts of the skeleton have later been referred to it. The cranium suggests that Indosaurus may have had horns above its eyes, although all the fossil evidence has since been lost. Indosaurus may have been related to the unusual South American dinosaur, Carnotaurus. If this is the case, then India had not been a separate continent for the previous 100 million years, as many paleontologists had thought. Instead, the two land masses possibly were connected intermittently by land bridges, allowing dinosaurs from both areas to migrate.
The type species, Indosaurus matleyi, was named by Huene and Matley in 1933. The generic name refers to India. The specific name honours Matley. This species now also includes Megalosaurus matleyi; confusingly, the dubious tooth taxon Orthogoniosaurus shares the same specific name (but is based on different material). Some paleontologists have speculated that Indosuchus and Compsosuchus should also be included within Indosaurus.
Originally assigned by Huene to the Allosauridae, Indosaurus is today considered a member of the Abelisauridae.Indosuchus
Indosuchus is a genus of abelisaurid dinosaur from the Late Cretaceous Period (70 to 66 million years ago – the Maastrichtian), a theropod related to Abelisaurus. Like most theropods, Indosuchus was a bipedal carnivore. It was about 7 metres long, weighed about 1.2 tonnes, and had a crested skull, flattened on the top.List of pathological conditions reported in Mesozoic dinosaurs
This list of pathological conditions reported in Mesozoic dinosaurs enumerates the various types of injury, disease, deformity or parasite infection identified among Mesozoic dinosaur fossils.Metriacanthosauridae
Metriacanthosauridae is an extinct family of theropod dinosaurs that lived from the Middle Jurassic to the Early Cretaceous. When broken down into its Greek roots, it means "moderately-spined lizards". The family is split into two subgroups: Metriacanthosaurinae, which includes dinosaurs closely related to Metriacanthosaurus, and another group composed of the close relatives of Yangchuanosaurus. Metriacanthosaurids are considered carnosaurs, belonging to the Allosauroidea superfamily. The group includes species of large range in body size. Of their physical traits, most notable are their neural spines. Their fossils can be found mostly in the Northern hemisphere. Metriacanthosauridae is used as a senior synonym of Sinraptoridae.Neovenatoridae
Neovenatoridae is a family of large carnivorous dinosaurs representing a branch of the allosauroids, a large group of carnosaurs that also includes the sinraptorids, carcharodontosaurids, and allosaurids. Compared to other allosauroids, neovenatorids had short, wide shoulder blades, and their ilia (upper hip bones) had many cavities.. They lived in Africa, Asia, Europe, South America and North America.Orionides
Orionides is a clade of tetanuran theropod dinosaurs from the Middle Jurassic to the Present. The clade includes most theropod dinosaurs, including birds.Piatnitzkysauridae
Piatnitzkysauridae is an extinct family of megalosauroid dinosaurs. It consists of three known dinosaur genera: Condorraptor, Marshosaurus, and Piatnitzkysaurus. The most complete and well known member of this family is Piatnitzkysaurus, which also gives the family its name.Saurophaganax
Saurophaganax ("lord of lizard-eaters") is a genus of allosaurid dinosaur from the Morrison Formation of Late Jurassic (latest Kimmeridgian age, about 151 million years ago) Oklahoma, United States. Some paleontologists consider it to be a species of Allosaurus (A. maximus). Saurophaganax represents a very large Morrison allosaurid characterized by horizontal laminae at the bases of the dorsal neural spines above the transverse processes, and "meat-chopper" chevrons. The maximum size of S. maximus has been estimated at anywhere from 10.5 meters (34 ft) to 13 meters (43 ft) in length, and about 3 metric tons (3.3 short tons) to 4.5 metric tons (5.0 short tons) in weight.Siats
Siats is an extinct genus of large neovenatorid theropod dinosaur known from the Late Cretaceous Cedar Mountain Formation of Utah, US. It contains a single species, Siats meekerorum. S. meekerorum could be the first neovenatorid discovered in North America and the geologically youngest allosauroid yet discovered from the continent. It was initially classified as a megaraptoran, a clade of large theropods with very controversial relationships. This group may be examples of tyrannosauroids, neovenatorid allosauroids, or basal coelurosaurs.Theropod paleopathology
Theropod paleopathology is the study of injury and disease in theropod dinosaurs. In 2001, Ralph E. Molnar published a survey of pathologies in theropod dinosaur bone that uncovered pathological features in 21 genera from 10 theropod families. Pathologies have been seen on most theropod body parts, with the most common sites of preserved injury and disease being the ribs and tail vertebrae. The least common sites of preserved pathology are the weight-bearing bones like the tibia, femur and sacrum. Most pathologies preserved in theropod fossils are the remains of injuries, but infections and congenital deformities have also been documented. Pathologies are less frequently documented in small theropods, although this may simply be because the larger bones of correspondingly larger animals would be more likely to fossilize in the first place.Valdoraptor
Valdoraptor (meaning "Wealden plunderer") is a genus of theropod dinosaur from the Early Cretaceous. Its fossils were found in England. It is known only from bones of the feet. The holotype, BMNH R2559 (incorrectly given by Owen as BMNH R2556), was found near Cuckfield in layers of the Tunbridge Wells Sand Formation dating from the late Valanginian. The specimen is damaged lacking parts of the upper and lower ends. It has a conserved length of 215 millimetres (8.5 in) and an estimated length of 240 millimetres (9.4 in). This genus is paleontologically significant for being the first ornithomimosaur specimen known from England and represents the earliest record of ornithomimosaurs.Yangchuanosaurus
Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China during the Bathonian and Callovian stages of the Middle Jurassic, and was similar in size and appearance to its North American and European relative, Allosaurus. It hails from the Upper Shaximiao Formation and was the largest predator in a landscape that included the sauropods Mamenchisaurus and Omeisaurus and the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. It was named after the area in which was discovered, Yongchuan, in China.