Temporal range: Late Jurassic, 155–146.8 Ma
|An Allosaurus model|
Antrodemidae Marsh, 1878
Allosauridae is a family of medium to large bipedal, carnivorous allosauriod neotheropod dinosaurs from the Late Jurassic and Early Cretaceous. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist Othniel Charles March in 1878. Constituent groups include Allosaurus, Erectopus, and Saurophaganax. Many taxa, including Antrodemus and Epanterias, have been at some point included as members of Allosauridae. Originally described in 1870, Antrodemus has since been identified as a nomen dubium, and generally collapsible with Allosaurus. Epanterias has also been subject to some controversy shifting from a separate genus, to an especially large Allosaurus fragilis Allosarids 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. Allosauridae is an extremely widely dispersed family, with members discovered on every continent except Antarctica and India.
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.
Allosaurids were the dominant predator of the Late Jurassic and Early Cretaceous, until being supplanted by the more advanced tyrannosaurids. Allosaurids have been discovered on every continent except Antarctica and the Indian subcontinent. A single species, Allosaurus fragilis has been discovered in both Colorado and Portugal  A distribution this wide is unmatched by any other family of dinosaurs.
Allosaurus fragilis, the most well-known member of the family, measured between 6 and 8 meters in length and weighed between 800 and 1000 kg as an adult. Allosaurus fragilis is neither the largest nor the smallest member of the family and is generally representative of the family as a whole. Gross growth rate peaked at around 15 years of age. Sexual maturity occurred at around 10 years of age. The age of sexual maturity is far earlier than would be predicted by reptilian growth models but more in line with that of birds. The oldest specimens of Allosaurus are estimated to have lived between 22 and 28 years.
Morphometric studies of individual variations within Allosaurus suggest the presence of sexual dimorphism, primarily in body size, but there is not consensus on the reliability of its identification in the fossil record. A 2016 study by John Mallon failed to identify significant sexual dimorphism in any dinosaur group but suggested that this failure was not due to a lack of dimorphism but rather to small sample size and non-sexual variation between individuals.
Many allosaurid specimens have pathologic features in various states of healing, suggesting an active lifestyle and predisposition to injury. The osteological evidence of healing of injuries suggest that traumatic injuries were often survived.
|Wikispecies has information related to: Allosauridae|
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