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Allosaurus

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Moonfire
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« Reply #15 on: December 02, 2009, 12:15:28 am »



Hand and claws of A. fragilis
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« Reply #16 on: December 02, 2009, 12:16:35 am »

Classification

Allosaurus was an allosaurid, a member of a family of large theropods within the larger group Carnosauria. The family name Allosauridae was created for this genus in 1878 by Othniel Charles Marsh,[21] but the term was largely unused until the 1970s in favor of Megalosauridae, another family of large theropods that eventually became a wastebasket taxon. This, along with the use of Antrodemus for Allosaurus during the same period, is a point that needs to be remembered when searching for information on Allosaurus in publications that predate James Madsen's 1976 monograph. Major publications using the name Megalosauridae instead of Allosauridae include Gilmore, 1920,[18] von Huene, 1926,[22] Romer, 1956 and 1966,[23][24] Steel, 1970,[25] and Walker, 1964.[26]
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Moonfire
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« Reply #17 on: December 02, 2009, 12:17:25 am »

Following the publication of Madsen's influential monograph, Allosauridae became the preferred family assignment, but it too was not strongly defined. Semi-technical works used Allosauridae for a variety of large theropods, usually those that were larger and better-known than megalosaurids. Typical theropods that were thought to be related to Allosaurus included Indosaurus, Piatnitzkysaurus, Piveteausaurus, Yangchuanosaurus,[27] Acrocanthosaurus, Chilantaisaurus, Compsosuchus, Stokesosaurus, and Szechuanosaurus.[28] Given modern knowledge of theropod diversity and the advent of cladistic study of evolutionary relationships, none of these theropods is now recognized as an allosaurid, although several, like Acrocanthosaurus and Yangchuanosaurus, are members of closely related families.[13]
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Moonfire
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« Reply #18 on: December 02, 2009, 12:17:36 am »

Allosauridae is one of three families in Carnosauria; the other two are Carcharodontosauridae and Sinraptoridae.[13] Allosauridae has at times been proposed as ancestral to the Tyrannosauridae (which would make it paraphyletic), one recent example in Gregory S. Paul's Predatory Dinosaurs of the World,[29] but this has been rejected, with tyrannosaurids identified as members of a separate branch of theropods, the Coelurosauria.[30] Allosauridae is the smallest of the carnosaur families, with only Saurophaganax and a currently unnamed French allosauroid accepted as possible valid genera besides Allosaurus in the most recent review.[13] Another genus, Epanterias, is a potential valid member, but it and Saurophaganax may turn out to be large examples of Allosaurus.[8] Recent reviews have kept the genus Saurophaganax and included Epanterias with Allosaurus.[4][13]
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« Reply #19 on: December 02, 2009, 12:21:30 am »



Allosaurus fragilis, an allosaurid theropod from the Late Jurassic pf North America, pencil drawing

http://en.wikipedia.org/wiki/Allosaurus

http://commons.wikimedia.org/wiki/Allosaurus
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« Reply #20 on: December 07, 2009, 11:26:04 pm »

Discovery and history
Early discoveries and research


The discovery and early study of Allosaurus is complicated by the multiplicity of names coined during the Bone Wars of the late 1800s. The first described fossil in this history was a bone obtained secondhand by Ferdinand Vandiveer Hayden in 1869. It came from Middle Park, near Granby, Colorado, probably from Morrison Formation rocks. The locals had identified such bones as "petrified horse hoofs". Hayden sent his specimen to Joseph Leidy, who identified it as half of a tail vertebra, and tentatively assigned it to the European dinosaur genus Poekilopleuron as Poicilopleuron [sic] valens.[31] He later decided it deserved its own genus, Antrodemus.[32]
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« Reply #21 on: December 07, 2009, 11:26:49 pm »

Allosaurus itself is based on YPM 1930, a small collection of fragmentary bones including parts of three vertebrae, a rib fragment, a tooth, a toe bone, and, most useful for later discussions, the shaft of the right humerus (upper arm). Othniel Charles Marsh gave these remains the formal name Allosaurus fragilis in 1877. Allosaurus comes from the Greek allos/αλλος, meaning "strange" or "different" and saurus/σαυρος, meaning "lizard" or "reptile".[33] It was named 'different lizard' because its vertebrae were different from those of other dinosaurs known at the time of its discovery.[34][35] The species epithet fragilis is Latin for "fragile", referring to lightening features in the vertebrae. The bones were collected from the Morrison Formation of Garden Park, north of Caņon City.[34] Marsh and Edward Drinker Cope, who were in scientific competition, went on to coin several other genera based on similarly sparse material that would later figure in the taxonomy of Allosaurus. These include Marsh's Creosaurus[21] and Labrosaurus,[36] and Cope's Epanterias.[37]
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« Reply #22 on: December 07, 2009, 11:27:34 pm »

In their haste, Cope and Marsh did not always follow up on their discoveries (or, more commonly, those made by their subordinates). For example, after the discovery by Benjamin Mudge of the type specimen of Allosaurus in Colorado, Marsh elected to concentrate work in Wyoming; when work resumed at Garden Park in 1883, M. P. Felch found an almost complete Allosaurus and several partial skeletons.[10] In addition, one of Cope's collectors, H. F. Hubbell, found a specimen in the Como Bluff area of Wyoming in 1879, but apparently did not mention its completeness, and Cope never unpacked it. Upon unpacking in 1903 (several years after Cope had died), it was found to be one of the most complete theropod specimens then known, and in 1908 the skeleton, now cataloged as AMNH 5753, was put on public view.[38] This is the well-known mount poised over a partial Apatosaurus skeleton as if scavenging it, illustrated as such by Charles R. Knight. Although notable as the first free-standing mount of a theropod dinosaur, and often illustrated and photographed, it has never been scientifically described.[39]
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« Reply #23 on: December 07, 2009, 11:27:54 pm »

The multiplicity of early names complicated later research, with the situation compounded by the terse descriptions provided by Marsh and Cope. Even at the time, authors such as Samuel Wendell Williston suggested that too many names had been coined.[40] For example, Williston pointed out in 1901 that Marsh had never been able to adequately distinguish Allosaurus from Creosaurus.[41] The most influential early attempt to sort out the convoluted situation was produced by Charles W. Gilmore in 1920. He came to the conclusion that the tail vertebra dubbed Antrodemus by Leidy was indistinguishable from those of Allosaurus, and Antrodemus thus should be the preferred name because as the older name it had priority.[18] Antrodemus became the accepted name for this familiar genus for over fifty years, until James Madsen published on the Cleveland-Lloyd specimens and concluded that Allosaurus should be used because Antrodemus was based on material with poor, if any, diagnostic features and locality information (for example, the geological formation that the single bone of Antrodemus came from is unknown).[3] "Antrodemus" has been used informally for convenience when distinguishing between the skull Gilmore restored and the composite skull restored by Madsen.[42]
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« Reply #24 on: December 07, 2009, 11:29:03 pm »



The skeletal mount of AMNH 5753, posed as scavenging an Apatosaurus.
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« Reply #25 on: December 07, 2009, 11:29:41 pm »



AMNH 5753 in a Charles R. Knight life restoration.
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« Reply #26 on: December 07, 2009, 11:31:52 pm »



Mounted A. fragilis skeleton (USNM4734) found by Gilmore, at the National Museum of Natural History

http://en.wikipedia.org/wiki/Allosaurus

http://commons.wikimedia.org/wiki/Allosaurus
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« Reply #27 on: December 13, 2009, 01:57:29 am »

Cleveland-Lloyd discoveries

Although sporadic work at what became known as the Cleveland-Lloyd Dinosaur Quarry in Emery County, Utah had taken place as early as 1927, and the fossil site itself described by William J. Stokes in 1945,[43] major operations did not begin there until 1960. Under a cooperative effort involving nearly 40 institutions, thousands of bones were recovered between 1960 and 1965.[3] The quarry is notable for the predominance of Allosaurus remains, the condition of the specimens, and the lack of scientific resolution on how it came to be. The majority of bones belong to the large theropod Allosaurus fragilis (it is estimated that the remains of at least 46 A. fragilis have been found there, out of at minimum 73 dinosaurs), and the fossils found there are disarticulated and well-mixed. Nearly a dozen scientific papers have been written on the taphonomy of the site, coming up with numerous contradictory explanations for how it formed. Suggestions have ranged from animals getting stuck in a bog, to becoming trapped in deep mud, to falling victim to drought-induced mortality around a waterhole, to getting trapped in a spring-fed pond or seep.[44] Regardless of the actual cause, the great quantity of well-preserved Allosaurus remains has allowed this genus to be known in detail, making it among the best-known theropods. Skeletal remains from the quarry pertain to individuals of almost all ages and sizes, from less than 1 meter (3.3 ft)[45] to 12 meters (39 ft) long, and the disarticulation is an advantage for describing bones usually found fused.[3]
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« Reply #28 on: December 13, 2009, 01:58:33 am »

Recent work: 1980s–present

The period since Madsen's monograph has been marked by a great expansion in studies dealing with topics concerning Allosaurus in life (paleobiological and paleoecological topics). Such studies have covered topics including skeletal variation,[46] growth,[47][48] skull construction,[49] hunting methods,[50] the brain,[51] and the possibility of gregarious living and parental care.[52] Reanalysis of old material (particularly of large 'allosaur' specimens),[8][53] new discoveries in Portugal,[54] and several very complete new specimens[15][55][56] have also contributed to the growing knowledge base. Fossil footprints attributed to Allosaurus were discovered in Bałtów, Poland, by Polish paleontologist Gerard Gierliński in the early 2000s.[57]
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« Reply #29 on: December 13, 2009, 01:59:30 am »

"Big Al"

One of the more significant Allosaurus finds was the 1991 discovery of "Big Al" (MOR 693), a 95% complete, partially articulated specimen that measured about 8 meters (about 26 ft) in length. MOR 693 was excavated near Shell, Wyoming, by a joint Museum of the Rockies and University of Wyoming Geological Museum team.[58] This skeleton was 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.[56]

The completeness, preservation, and scientific importance of this skeleton gave "Big Al" its name; the individual itself was below the average size for Allosaurus fragilis,[58] and was a subadult estimated at only 87% grown.[59] The specimen was described by Breithaupt in 1996.[55] Nineteen of its bones were broken or showed signs of infection, which may have contributed to "Big Al's" death. Pathologic bones included five ribs, five vertebrae, and four bones of the feet; several damaged bones showed osteomyelitis, a bone infection. A particular problem for the living animal was infection and trauma to the right foot that probably affected movement and may have also predisposed the other foot to injury because of a change in gait.[59]
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