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a carnivorous allosaurid theropod dinosaur from the Late Jurassic of North America.
Pronunciation: AL-oh-SOR-us
Meaning: Strange Lizard
Author/s: Marsh (1877)
Synonyms: See below
First Discovery: Colorado, USA
Chart Position: 35

Allosaurus fragilis

Along with Tyrannosaurus, Allosaurus has come to represent the quintessential large, carnivorous dinosaur of its period in popular culture. Along with Tyrannosaurus, Allosaurus has led a rather charmed life-after-death too. Both have laid claim to remains of other dinosaurs that were named long before them and both have survived some legitimate hostile takeovers when, by strict letter of zoological law, they should actually be languishing in the taxonomic waste bucket right now.

The first remnants of what we now know as Allosaurus were discovered in 1869 and named Poicilopleuron valens (a misspelled second species of the European Poekilopleuron) the following year by Joseph Leidy, who cheekily attached a backup name — Antrodemus — that would be triggered if it turned out to be a different critter entirely. In 1920 not only did Charles W. Gilmore prove this to be the case but he also showed that it was identical to Allosaurus which was named later, and thus should've been chalked off. However, Antrodemus was robbed of a place in the roll call of dinosaurs on the grounds of poor remains, the irony being; Allosaurus itself is based on extremely fragmentary fossils that are technically dubious and in no position to be anchoring a name, never mind several taxa. In an attempt to remedy this situation Paul and Carpenter submitted a petition to the ICZN in 2010 to have "Allosaurus fragilis" officially transferred to a more complete specimen, and though the case is still pending scientists have put too much time and effort into Allosaurus to accept anything other than a resounding "aye".

Allosaurus is as common as muck in the vast Morrison Formation with almost all growth stages represented, and it's been subjected to more scientific scrutiny than any other predatory dinosaur, the results of which are well-publicised. Allosaurus had strong legs, powerful arms, three fingers per hand, each tipped with a curved and pointed claw, and a broad rib cage complete with furcula (wishbone) that gave it a barrelled-chest. Its neck consisted of nine vertebrae, its back fourteen, its sacrum - supporting a hip with a massive boot-ended pubis - five, and its tail between 45 and 50, depending on the age of the specimen. Paired ridges that ran up its snout and became a pair of blunt horns in front and above its eyes were too flimsy for weapons but made it look mean. However, the manner in which Allosaurus killed things always seems to rustle up the most focus, which is often the case with extinct hunters.

Its skull was somewhat small for a predator of its size and sported fairly modest teeth. Although lightweight, it was super-strengthened too, and housed some loosely articulated parts that would allow its jaws to bow for a wider gape. While that may sound like a good thing, it's a design that would struggle to generate bite power, which has led paleontologists to jump to two equally plausible conclusions. Some experts suspect that Allosaurus would only tackle small prey, perhaps infant dinosaurs that they could devour with minimum effort. Others have suggested that Allosaurus adopted "hatchet attacks" — literally swinging their reinforced skull, jaws agape, downwards into prey until they died of shock and blood loss. Sure it's brutal, but it's also effective, and hunters needed to be both during the Late Jurassic.

Far from being indestructible killing machines, Allosaurus were just as mortal as any other creature, and equally prone to accident, incident, and outrageous clumsiness. One specimen — MOR 693, a 95% complete teenage specimen discovered near Shell, Wyoming and affectionately known as "Big Al" — has no less than 19 bones which show signs of fracture and various infections and disease, including a severe case of foot rot which probably led to his death. Another specimen was found with a conical puncture wound right in its pubis that matched the tail-spike of a dextrous stegosaur. And that proved to be fatal too.
Allosaurus is derived from the Greek "allos" (strange) and "sauros" (lizard) referring to its peculiar vertebrae that Marsh noted were "modified to ensure lightness". As it happens, most theropod's were.
The species epithet (or specific name), fragilis, means "fragile" in Latin because Marsh supposed that cavities in said vertebrae made them light at the expense of strength.
The first fossils of Allosaurus were discovered at Felch Quarry in the Brushy Basin Member of the Morrison Formation, Garden Park, near Canyon City, Colorado, U.S.A, by Benjamin Mudge. The Holotype (YPM 1930, housed at the Yale Peabody Museum) includes three vertebrae, a rib fragment, a tooth, a toe, and the right humerus (upper arm).
Era: Mesozoic
Epoch: Late Jurassic
Stage: Kimmeridgian-Tithonian
Age range: 156-145 mya
Est. max. length: 12 meters
Est. max. hip height: 3 meters
Est. max. weight: 2.5 tons
Diet: Carnivore
Creosaurus (CREE-o-SOR-us) named by O.C. Marsh in 1878.
Labrosaurus (LAB-ro-SOR-us) named by O.C. Marsh in 1879.
Possible synonyms:
Antrodemus (AN-tro-DEE-mus) named by J.M. Leidy in 1870.
Apatodon (uh-PAT-uh-don) named by O.C. Marsh in 1877.
Epanterias (e-pan-TEE-ree-as) named by E.D. Cope in 1878.
Okay, Allosaurus bite marks and shed teeth found mingled with same-species skeletal remains at Wyoming's Como Bluff is far from conclusive evidence that they went out of their way to murder each other. But we're willing to bet that they wouldn't shun cannibalism if one of their kind turned up dead, because no self-respecting carnivore would reject protein that couldn't fight back.
• Othniel C. Marsh (1877) "Notice of new dinosaurian reptiles from the Jurassic formation". American Journal of Science and Arts 14: 514-516.
• James H. Madsen, Jr. (1993) "Allosaurus fragilis: A revised osteology".
• B.P. Pérez-Moreno, D. J. Chure, C. Pires, C. Marques Da Silva, V. Dos Santos, P. Dantas, et al. (1999) "On the presence of Allosaurus fragilis (Theropoda: Carnosauria) in the Upper Jurassic of Portugal: First evidence of an intercontinental dinosaur species".
• B. Rothschild, D.H. Tanke and T.L. Ford (2001) "Theropod stress fractures and tendon avulsions as a clue to activity" in Tanke and Carpenter "Mesozoic Vertebrate Life".
• T.R. Holtz, Jr., R.E. Molnar and P.J. Currie (2004) "Basal Tetanurae" in Weishampel, Dodson and Osmólska (eds.) "The Dinosauria: Second Edition".
• Robert T. Bakker (1998) "Brontosaur killers: Late Jurassic allosaurids as sabre-tooth cat analogues". Gaia 15: 145-158.
• Samuel Wendell Williston (1901) "The dinosaurian genus Creosaurus, Marsh".
• G.S. Paul and K. Carpenter (March 2010) "Case 3506: Allosaurus Marsh, 1877 (Dinosauria, Theropoda): proposed conservation of usage by designation of a neotype for its type species Allosaurus fragilis Marsh, 1877".
• Christian Foth​, S.W. Evers, B. Pabst, O. Mateus, A. Flisch, M. Patthey and O.W.M. Rauhut (12th May 2015) "New insights into the lifestyle of Allosaurus (Dinosauria: Theropoda) based on another specimen with multiple pathologies".
• Bakker R.T. and Bir G. (2004) "Dinosaur crime scene investigations: theropod behavior at Como Bluff, Wyoming, and the evolution of birdness" in Currie, Koppelhus, Shugar and Wright (eds.) "Feathered Dragons: Studies on the Transition from Dinosaurs to Birds" (Page 301–342).
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To cite this page:
Atkinson, L. "ALLOSAURUS :: from DinoChecker's dinosaur archive".
›. Web access: 28th Feb 2017.