Allosaurus

Allosaurus Temporal range: Late Jurassic (Kimmeridgian to Tithonian), 155–145 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Mounted A. fragilis skeleton cast, San Diego Natural History Museum
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Family:	†Allosauridae
Subfamily:	†Allosaurinae Marsh, 1878
Genus:	†Allosaurus Marsh, 1877
Type species
†Allosaurus fragilis Marsh, 1877
Other species
†A. europaeus Mateus et al., 2006 †A. jimmadseni Chure & Loewen, 2020 †A. anax Danison et al., 2024
Synonyms
Genus synonymy Antrodemus? Leidy, 1870 Apatodon? Marsh, 1878 Creosaurus Marsh, 1878 Epanterias? Cope, 1878 Labrosaurus Marsh, 1879 "Madsenius" Bakker, 1990 "Wyomingraptor" Bakker, 1997

Allosaurus (/ˌæləˈsɔːrəs/)^[1][2] is an extinct genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic period (Kimmeridgian to late Tithonian ages). The name "Allosaurus" means "different lizard", alluding to its unique (at the time of its discovery) concave vertebrae. It is derived from the Greek words ἄλλος (allos) ("different", "strange", or "other") and σαῦρος (sauros) ("lizard" or "reptile"). The first fossil remains that could definitively be ascribed to this genus were described in 1877 by famed paleontologist Othniel Charles Marsh. The genus has a very complicated taxonomy and includes at least three 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 the Lourinhã Formation in Portugal. It was known for over half of the 20th century as Antrodemus, but a study of the abundant remains from the Cleveland-Lloyd Dinosaur Quarry returned the name "Allosaurus" to prominence. As one of the first well-known theropod dinosaurs, it has long attracted attention outside of paleontological circles.

Allosaurus was a large bipedal predator for its time. Its skull was light, robust, and equipped with dozens of sharp, serrated teeth. It averaged 8.5 metres (28 ft) in length for A. fragilis, with the largest specimens estimated as being 9.7 metres (32 ft) long. Relative to the large and powerful legs, its three-fingered hands were small and the body was balanced by a long, muscular tail. It is classified as an allosaurid, a type of carnosaurian theropod dinosaur. As the most abundant large predator of the Morrison Formation, Allosaurus was at the top of the food chain and probably preyed on contemporaneous large herbivorous dinosaurs, with the possibility of hunting other predators. Potential prey included 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.