Allosauridae is a family of medium to large bipedal,
carnivorous
A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other ...
allosauroid
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 ...
theropod
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...
dinosaurs
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is the ...
from the Late
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
. Allosauridae is a fairly old taxonomic group, having been first named by the American paleontologist
Othniel Charles Marsh
Othniel Charles Marsh (October 29, 1831 – March 18, 1899) was an American professor of Paleontology in Yale College and President of the National Academy of Sciences. He was one of the preeminent scientists in the field of paleontology. Among ...
in 1878. Allosaurids are characterized by an
astragalus
''Astragalus'' is a large genus of over 3,000 species of herbs and small shrubs, belonging to the legume family Fabaceae and the subfamily Faboideae. It is the largest genus of plants in terms of described species. The genus is native to tempe ...
with a restriction of the ascending process to the lateral part of the
bone
A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, ...
neotheropod
Neotheropoda (meaning "new theropods") is a clade that includes coelophysoids and more advanced theropod dinosaurs, and is the only group of theropods that survived the Triassic–Jurassic extinction event. All neotheropods became extinct by the e ...
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
The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammal has ...
has five teeth and the
maxilla
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. T ...
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.Madsen, James H., Jr. (1993) 976 ''Allosaurus fragilis: A Revised Osteology''. Utah Geological Survey Bulletin 109 (2nd ed.). Salt Lake City: Utah Geological Survey. 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.Paul, Gregory S. (1988). Predatory Dinosaurs of the World. This
cranial kinesis Cranial kinesis is the term for significant movement of skull bones relative to each other in addition to movement at the joint between the upper and lower jaw. It is usually taken to mean relative movement between the upper jaw and the braincase.
...
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
The spinal column, a defining synapomorphy shared by nearly all vertebrates, Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristi ...
(9 cervical, 14 dorsal, 5 sacral) and an estimated 45–50 caudal vertebrae. Gastralia and furculae are rarely preserved as fossils but are presumed to occur in all allosaurids.Chure, Daniel J.; Madsen, James (1996). "On the presence of furculae in some non-maniraptoran theropods". ''Journal of Vertebrate Paleontology''. 16 (3): 573–577. doibr>10.1080/02724634.1996.10011341 /ref> 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
Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally ca ...
, 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.Gilmore, Charles W. (1920). Osteology of the Carnivorous Dinosauria in the United States National Museum: With Special Reference to the Genera Antrodemus (Allosaurus) and Ceratosaurus. United States National Museum Bulletin Volume 110. 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.
Classification
In 2019, Rauhut and Pol described ''
Asfaltovenator vialidadi
''Asfaltovenator'' (meaning "Cañadón Asfalto Formation hunter" after the fossil formation in which its fossils were found) is a genus of possibly allosauroid dinosaur from the Lower Jurassic Cañadón Asfalto Formation from Chubut Province, Ar ...
'', a basal allosauroid displaying a mosaic of primitive and derived features seen within
Tetanurae
Tetanurae (/ˌtɛtəˈnjuːriː/ or "stiff tails") is a clade that includes most theropod dinosaurs, including megalosauroids, allosauroids, tyrannosauroids, ornithomimosaurs, compsognathids and maniraptorans (including birds). Tetanurans ar ...
. Their phylogenetic analysis found traditional
Megalosauroidea
Megalosauroidea (meaning 'great/big lizard forms') is a superfamily (or clade) of tetanuran theropod dinosaurs that lived from the Middle Jurassic to the Late Cretaceous period. The group is defined as '' Megalosaurus bucklandii'' and all taxa s ...
to represent a basal
grade
Grade most commonly refers to:
* Grade (education), a measurement of a student's performance
* Grade, the number of the year a student has reached in a given educational stage
* Grade (slope), the steepness of a slope
Grade or grading may also ref ...
of
carnosaurs
Carnosauria is an extinct large group of predatory dinosaurs that lived during the Jurassic and Cretaceous periods. Starting from the 1990s, scientists have discovered some very large carnosaurs in the carcharodontosaurid family, such as ''Gi ...
,
paraphyletic
In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...
with respect to
Allosauroidea
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 amo ...