'''Allosaurus''' (
IPA pronunciation: ) is a
genus of large
theropod dinosaur that lived 155 to 145
million years ago, in the
late Jurassic period. The name ''Allosaurus'' comes from the
Greek '''allos/αλλος''', meaning 'strange' or 'different' and '''saurus/σαυρος''', meaning 'lizard' or 'reptile'.
[1] It was named 'different lizard' because its
vertebrae were different from those of other dinosaurs known at the time of its discovery. The genus contains three described species, the best known of which is ''A. fragilis''. Several other dinosaurs originally classified as ''Allosaurus'' are now in separate genera. The bulk of ''Allosaurus'' remains have come from
North America's
Morrison Formation, with material also from
Portugal.
''Allosaurus'' was a multi-ton
bipedal
predator with a large skull, equipped with dozens of large, sharp
teeth. Its average height was 8.5
meters (30
ft) and it was up to 12-13 meters (39-43 ft) long. Relative to the large and powerful hindlimbs, its three fingered forelimbs were small, and the body was balanced by a long, heavy tail. As an
apex predator and the most common large predator in the
Morrison Formation, ''Allosaurus'' was at the top of the
food chain, probably preying on dinosaurs such as ''
Stegosaurus'' and ''
Camptosaurus''. It also shared the landscape with several giant
sauropods such as ''
Apatosaurus'', ''
Diplodocus'' and ''
Camarasaurus'', though it is unknown whether it would have attacked an adult.
Description
''Allosaurus'' was a typical large
theropod, having a massive
skull on a short
neck, a long
tail and reduced forelimbs. ''Allosaurus fragilis'', the best-known species, had an average length of 8.5 meters (30 ft),
[ Dinosaurs: The Encyclopedia, , Donald F., Glut, McFarland & Co, 1997, ] with the largest definitive ''Allosaurus'' specimen (
AMNH 680) estimated at 9.7 meters long (32 ft)
[ And the Largest Theropod Is.... Mortimer, Mickey ][ Carnosauria ] and 2.3
metric tons in weight (2.5
tons).
[ James Madsen in his 1976 monograph on ''Allosaurus'' mentioned a range of bone sizes which he interpreted to show a maximum length of 12 to 13 meters (40 to 43 ft).][ ''Allosaurus fragilis'': A Revised Osteology, , James H., Jr., Madsen, Utah Geological Survey, 1993, ] As with dinosaurs in general, its weight is debatable, with estimates made since 1980 of 1500 kilograms (3300 lb), 1000 to 4000 kilograms (2200 to 8800 lb), and 1010 kilograms (2230 lb) for modal adult weight (not maximum).[ Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A., , John R., Foster, New Mexico Museum of Natural History and Science, 2003, ] Several gigantic specimens have been attributed to ''Allosaurus'', but may in fact belong to other genera. The closely related genus ''Saurophaganax'' (OMNH 1708) reached perhaps 10.9 meters (36 ft) in length,[ and has sometimes been included in the genus ''Allosaurus'' as ''Allosaurus maximus'', though recent studies lend support to the idea that it does belong in a separate genus.][ A new species of ''Allosaurus'' from the Morrison Formation of Dinosaur National Monument (Utah-Colorado) and a revision of the theropod family Allosauridae, , Daniel J., Chure, Columbia University, 2000, ] Another potential specimen of ''Allosaurus'', once assigned to the genus ''Epanterias'' (AMNH 5767), may have measured 12.1 meters in length (39.7 ft).[ ]
Its skull and teeth were modestly-proportioned for a theropod of its size.[ Predatory Dinosaurs of the World, , Gregory S., Paul, Simon & Schuster, 1988, ] Each premaxilla (the bones that formed the tip of the snout), held five teeth, with D-shaped cross-sections, and each maxilla (the main tooth-bearing bones in the upper jaw) had between 14 and at least 17 teeth; the number of teeth does not exactly correspond to the size of the bone. Each dentary (the tooth-bearing bone of the lower jaw) had between 14 and 17 teeth, with an average count of 16. The teeth became shorter, more narrow, and more curved toward the back of the skull. All of the teeth were serrated. They were shed easily, as they were replaced continually, thus they are common fossils.
The skull was ornamented by a pair of horns above and in front of the eyes. These horns were composed of extensions of the lacrimal bones.[ The shape and size of the horns varied. There were also lower paired ridges running along the top edges of the nasal bones.][ The horns were probably covered in a keratin sheath and may have had a variety of functions, including acting as sunshades for the eye,][ being used for display, and being used in combat against other members of the same species][ Analogies in the evolution of combat and display structures in ornithopods and ungulates, , Ralph E., Molnar, Evolutionary Theory, 1977 ][ (although they were fragile).][ Inside the lacrimals were depressions that may have held salt glands.]
The skull showed evidence of being composed of separate modules, which could be moved in relation to one another, allowing large pieces of meat to be swallowed. The skeleton of ''Allosaurus'', like other theropods, displayed bird-like features, such as a furcula (wishbone) and neck vertebrae hollowed by air sacs. Although short in comparison to the hindlimbs, the forelimbs were massive, with three-fingered hands and large, eagle-like claws.
Classification
''Allosaurus'' was an allosaurid, a member of a clade of large theropods. In 1988 Gregory S. Paul proposed that the family Allosauridae led to the Tyrannosauridae (and thus would be paraphyletic),[ Predatory Dinosaurs of the World, , Gregory S., Paul, Simon & Schuster, 1988, ] but this has been rejected.[ The Dinosauria (second edition), Holtz, Jr., T.R., Molnar, R.E, and Currie, P.J., , , University of California Press, 2004, ISBN 0-520-24209-2 ] The allosaurids ''Saurophaganax'' and ''Epanterias'' are sometimes considered to be large examples of ''Allosaurus'';[ recent reviews have kept the genus ''Saurophaganax'' and included ''Epanterias'' with ''Allosaurus''.]
An astragalus (ankle bone) thought to belong to a species of ''Allosaurus'' was found at Cape Patterson, Victoria in Early Cretaceous beds in southeastern Australia. It was thought to provide evidence that Australia was a refugium for animals that had gone extinct elsewhere.[ An allosaurid theropod dinosaur from the Early Cretaceous of Victoria, Australia, , Ralph E., Molnar, Alcheringa, 1981 ] This identification was challenged by Samuel Welles, who thought it more resembled that of an ornithomimid,[ ''Allosaurus'' (Saurischia, Theropoda) not yet in Australia, , Samuel P., Welles, Journal of Paleontology, 1983 ] but the original authors defended their identification.[ Aussie ''Allosaurus'' after all, , Ralph E., Molnar, Journal of Paleontology, 1985 ] With fifteen years of new specimens and research to look at, Daniel J. Chure reexamined the bone and found that it was not ''Allosaurus'', but could represent an allosauroid.[ A reassessment of the Australian ''Allosaurus'' and its implications for the Australian refugium concept, , Daniel J., Chure, Journal of Vertebrate Paleontology, 1998 ] Similarly, Yoichi Azuma and Phil Currie, in their description of the basal allosauroid ''Fukuiraptor'', noted that the bone closely resembled that of their new genus.[ A new carnosaur (Dinosauria: Theropoda) from the Lower Cretaceous of Japan, , Yoichi, Azuma, Journal of Vertebrate Paleontology, 2000 ]
Discovery and history
Life restoration of ''Allosaurus fragilis''.
The first ''Allosaurus'' fossil to be described was a 'petrified horse hoof' given to Ferdinand Vandiveer Hayden in 1869, by the natives of Middle Park, near Granby, Colorado. It was actually a caudal vertebra (a tail bone), which Joseph Leidy tentatively assigned first to the ''Poekilopleuron'' genus and later to a new genus, ''Antrodemus''.[2] However, it was Othniel Charles Marsh who gave the formal name ''Allosaurus fragilis'' to the genus and type species in 1877,[3] based on much better material, including a partial skeleton, from Garden Park, north of Cañon City, Colorado. The species epithet ''fragilis'' is Latin for 'fragile', referring to lightening features in the vertebrae.
It is unclear how many species of ''Allosaurus'' there were. The material from the Cleveland Lloyd Dinosaur Quarry specimen is much smaller and more lightly-built than the huge and robust ''Allosaurus'' from Brigham Young University's Dry Mesa Quarry. One species of ''Allosaurus'' has been described from Portugal, ''A. europaeus''.[4]
"Big Al"
One of the more significant finds was the 1991 discovery of "Big Al" (MOR 593), a 95% complete, partially articulated, specimen that measured 7.5-8 meters (24-26 ft) in length. Nineteen bones were broken or showed signs of infection, which probably contributed to Big Al's death.[Hanna, R.R. (2002). "Multiple injury and infection in a sub-adult theropod dinosaur (''Allosaurus fragilis'') with comparisons to allosaur pathology in the Cleveland-Lloyd dinosaur quarry collection." ''Journal of Vertebrate Paleontology'', '22'(1): 76-90.] It was featured in "The Ballad of Big Al", a special programme in the BBC's ''Walking with Dinosaurs'' series. The fossils were excavated near Shell, Wyoming by the Museum of the Rockies and the University of Wyoming Geological Museum. The completeness of this skeleton gave Big Al its name — the individual itself was below the average size for ''Allosaurus fragilis'', and may have been a subadult or a new, smaller species. The specimen was described by Breithaupt in 1996.[Breithaupt (1996). "The discovery of a nearly complete ''Allosaurus'' from the Jurassic Morrison Formation, eastern Bighorn Basin, Wyoming." In Brown, C.E., Kirkwood, S.C., and Miller, T.S. eds. ''Forty-Seventh Annual Field Conference Guidebook'', 309-313. Wyoming Geological Association, Casper.]
This skeleton was initially discovered by a Swiss team, led by Kirby Siber. The same team later excavated a second ''Allosaurus'', "Big Al Two", which is the best preserved skeleton of its kind to date.
Paleoecology
''Allosaurus'' is the most common theropod in the vast tract of dinosaur-bearing rock in the American west and southwest known as the Morrison Formation.[ Paleoecological Analysis of the Vertebrate Fauna of the Morrison Formation (Upper Jurassic), Rocky Mountain Region, U.S.A., , John R., Foster, New Mexico Museum of Natural History and Science, 2003, ] The Morrison Formation is interpreted as a semiarid environment with distinct wet and dry seasons, with flat floodplains.[ An Odyssey in Time: Dinosaurs of North America, , Dale A., Russell, NorthWord Press, Inc., 1989, ] Vegetation varied from gallery forests of conifers, tree ferns, and ferns, to fern savannas with rare trees.[ Paleontology and Geology of the Upper Jurassic Morrison Formation, , Kenneth, Carpenter, New Mexico Museum of Natural History and Science, 2006, ] ''Allosaurus'' shared the Jurassic landscape with several other theropods, including ''Ceratosaurus'' and the massive ''Torvosaurus''.
A famous fossil bed can be found in the Cleveland Lloyd Dinosaur Quarry in Utah. This fossil bed contains over 10,000 bones, mostly of ''Allosaurus'', intermixed with the remains of other dinosaurs, such as ''Stegosaurus'' and ''Ceratosaurus''. It is still a mystery how the remnants of so many animals can be found in one place. The ratio of fossils of carnivorous animals over fossils of plant eaters is normally very small. Findings like these can be explained by pack hunting, although this is difficult to prove. Another possibility is that the Cleveland Lloyd site formed a 'predator trap', similar to the La Brea Tar Pits, that caused large numbers of predators to become mired in an inescapable sediment.[5]
In popular culture
''Allosaurus'' is the official state dinosaur of Utah, in the United States. Along with ''Tyrannosaurus'', ''Allosaurus'' has come to represent the quintessential large, carnivorous dinosaur in popular culture.
''Allosaurus'' is top predator in both Arthur Conan Doyle's novel, ''The Lost World'', and the 1925 film adaptation (not to be confused with ''Tyrannosaurus'', which also appears in the film). In the 1969 film ''The Valley of Gwangi'', Gwangi is billed as an ''Allosaurus'' (however, Ray Harryhausen based his model for the creature on ''Tyrannosaurus''. Harryhausen often confuses the two, stating in a DVD interview "They're both meat eaters, they're both Tyrants... one was just a bit larger than the other.")
''Allosaurus'' appears in the second and fifth episodes of the BBC television series ''Walking with Dinosaurs''. The ''Walking with Dinosaurs'' special '' chronicles the life of a specimen of ''Allosaurus'' nicknamed "Big Al".
References
1. Greek-English Lexicon, Abridged Edition, Liddell & Scott, , , Oxford University Press, Oxford, UK, 1980, ISBN 0-19-910207-4
2. Leidy J (1870). Remarks on ''Poicilopleuron valens'', ''Clidastes intermedius'', ''Leiodon proriger'', ''Baptemys wyomingensis'', and ''Emys stevensonianus''. Proc. Acad. Nat. Sci. Philadelphia 1870: 3-5
3. Marsh OC. (1877). Notice of new dinosaurian reptiles from the Jurassic formation. ''American Journal of Science and Arts'' 14:514-516
4. Mateus, O., Walen, A., and Antunes, M.T. (2006). "The large theropod fauna of the Lourinha Formation (Portugal) and its similarity to that of the Morrison Formation, with a description of a new species of ''Allosaurus''." ''New Mexico Museum of Natural History and Science Bulletin'', '36'.
5. Cleveland-Lloyd Dinosaur Quarry, Utah. The "Predator Trap". Retrieved on August 27, 2007.
External links
★ ''Allosaurus'', the story of "Big Al", from the University of Wyoming Geological Museum in Laramie.
★ ''Allosaurus'' at DinoData.
★ Public Pioneer, Utah State Fossil, ''Allosaurus'', from Utah.gov.
★ ''Allosaurus fragilis'', Smithsonian National Museum of Natural History, Department of Paleobiology.
★ List of the many possible ''Allosaurus'' species...
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