Species of Allosaurus

There have been a number of potential species assigned to the carnosaurian dinosaur genus "Allosaurus" since its description in 1877 by Othniel Charles Marsh, but only a handful are still regarded as valid. "Allosaurus" was originally described from material from the Upper Jurassic Morrison Formation of the western United States of America; the type species "A. fragilis" became one of the best-known species of dinosaur.

The genus "Allosaurus" was part of the Marsh/Edward Drinker Cope "Bone Wars" of the late 1800s, and its taxonomy became increasingly confused due to the competition, with several genera and species named by Cope and Marsh now regarded as synonyms of "Allosaurus" or "A. fragilis". Since the description of "Allosaurus", scientists have proposed additional species from such far-flung locales as Portugal, Siberia, Switzerland, and Tanzania, and unnamed remains from Australia and China have also been assigned to the genus at one time or another.

Potentially valid species

It is unclear how many species of "Allosaurus" there were. Seven species have been considered potentially valid since 1988 ("A. amplexus",cite book |last=Paul |first=Gregory S. |title=Predatory Dinosaurs of the World |year=1988 |publisher=Simon & Schuster |location=New York |isbn=0-671-61946-2 |chapter=Genus "Allosaurus" |pages=pp. 307–313 ] "A. atrox", "A. europaeus", the type species "A. fragilis",cite book|last=Holtz |first=Thomas R., Jr. |authorlink=Thomas R. Holtz, Jr. |coauthors=Molnar, Ralph E.; and Currie, Philip J. |year=2004 |editor=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.)|title=The Dinosauria |edition=2nd ed. |publisher=University of California Press |location=Berkeley |isbn=0-520-24209-2 |pages=71–110 ] the as-yet not formally described "A. jimmadseni",cite book |last=Chure |first=Daniel J. |year=2000 |title=A new species of "Allosaurus" from the Morrison Formation of Dinosaur National Monument (Utah–Colorado) and a revision of the theropod family Allosauridae |series=Ph.D. dissertation |publisher=Columbia University] "A. maximus",cite journal |last=Smith |first=David K. |year=1998 |title=A morphometric analysis of "Allosaurus" |journal=Journal of Vertebrate Paleontology |volume=18 |issue=1 |pages=126–142] and "A. tendagurensis"), although only a fraction are usually considered valid at any given time. There are also at least ten dubious or undescribed species that have been assigned to "Allosaurus" over the years, along with the species belonging to genera now sunk into "Allosaurus". In the most recent review of basal tetanuran theropods, only "A. fragilis" (including "A. amplexus" and "A. atrox"), "A. jimmadseni" (as an unnamed species), and "A. tendagurensis" were accepted as potentially valid species, with "A. europaeus" not yet proposed and "A. maximus" assigned to "Saurophaganax"."A. fragilis" is the type species and was named by Marsh in 1877.cite journal |last=Marsh |first=Othniel Charles |year=1877 |title=Notice of new dinosaurian reptiles from the Jurassic formation |journal=American Journal of Science and Arts |volume=14 |pages=514–516] It is known from the remains of at least sixty individuals, all found in the Kimmeridgian–Tithonian Upper Jurassic-age Morrison Formation of the United States, spread across the states of Colorado, Montana, New Mexico, Oklahoma, South Dakota, Utah, and Wyoming. Details of the humerus (upper arm) of "A. fragilis" have been used as diagnostic among Morrison theropods,cite book |last=Madsen |first=James H., Jr. |origyear=1976 |year=1993 |title="Allosaurus fragilis": A Revised Osteology |series=Utah Geological Survey Bulletin 109 |publisher=Utah Geological Survey |location=Salt Lake City |edition=2nd ed.] but the discovery of "A. jimmadseni" indicates that this will no longer be the case at the species level. "A. fragilis" has always been difficult to define on the basis of its fragmentary and limited holotype, and so authors have advanced different proposals for redefining the species on better material.

"A. amplexus" was named by Gregory S. Paul for giant Morrison allosaur remains, and included in his conception "Saurophagus maximus" (later "Saurophaganax"). "A. amplexus" was originally coined by Cope in 1878 as the type species of his new genus "Epanterias",cite journal |last=Cope |first=Edward Drinker |year=1878 |title=A new opisthocoelous dinosaur |journal=American Naturalist |volume=12 |issue=6 |pages=406] and is based on what is now AMNH 5767, parts of three vertebrae, a coracoid, and a metatarsal.cite journal |last=Osborn |first=Henry Fairfield |authorlink=Henry Fairfield Osborn |coauthors=and Mook, Charles C. |year=1921 |title="Camarasaurus", "Amphicoelias", and other sauropods of Cope |journal=Memoirs of the American Museum of Natural History, New Series |volume=3 |issue=3 |pages=247–387 ] Following Paul's work, this species has been accepted as a synonym of "A. fragilis".

"Allosaurus" material from Portugal was first reported in 1999 on the basis of MHNUL/AND.001, a partial skeleton including a quadrate, vertebrae, ribs, gastralia, chevrons, part of the hips, and hindlimbs. This specimen was assigned to "A. fragilis",cite journal |last=Pérez-Moreno |first=B.P. |coauthors=Chure, D.J.; Pires, C.; Silva, C.M.; Santos, V.; Dantas, P.; Póvoas, L.; Cachão, M.; Sanz, J.L.; and Galopim De Carvalho, A.M. |year=1999 |title=On the presence of "Allosaurus fragilis" (Theropoda: Carnosauria) in the Upper Jurassic of Portugal: First evidence of an intercontinental dinosaur species |journal=Journal of the Geological Society |volume=156 |issue=3 |pages=449–452 |doi=10.1144/gsjgs.156.3.0449 |url=http://correio.fc.ul.pt/~cmsilva/Artigos/CMS034.pdf |format=pdf] but the subsequent discovery of a partial skull and neck (ML 415) near Lourinhã, in the Kimmeridgian-age Porto Novo Member of the Lourinhã Formation, spurred the naming of the new species "A. europaeus". It differs from other species of "Allosaurus" in cranial details.cite book |last=Mateus |first=Octávio |coauthors=Walen, Aart; and Antunes, Miguel Telles |year=2006 |chapter=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" |editor=Foster, John R.; and Lucas, Spencer G. (eds.) |title=Paleontology and Geology of the Upper Jurassic Morrison Formation |series=New Mexico Museum of Natural History and Science Bulletin, 36 |publisher=New Mexico Museum of Natural History and Science |location=Albuqueque, New Mexico |pages=123–129] However, more material may show it to be "A. fragilis", as originally described.cite journal |last=Malafaia |first=Elisabete |coauthors=Dantas, Pedro; Ortega, Francisco; and Escaso, Fernando |year=2007 |title=Nuevos restos de Allosaurus fragilis (Theropoda: Carnosauria) del yacimiento de Andrés (Jurásico Superior; centro-oeste de Portugal) |journal=Cantera Paleontológica |pages=255–271 |language=Spanish with English abstract |url=http://www.dfmf.uned.es/~fortega/uned_fo_pdf/2007_Malafaia_etal_EJIP07.pdf |format=pdf]

Daniel Chure's work on Morrison allosaurid remains has been responsible, directly or indirectly, for "A. jimmadseni" and "A. maximus". "A. jimmadseni" is the proposed name for a new species of Morrison allosaur, based on a nearly complete skeleton and skull.cite book |last=Glut |first= Donald F. |title=Dinosaurs: The Encyclopedia. 3rd Supplement |year=2003 |publisher=McFarland & Co.|location=Jefferson, North Carolina |isbn=0-7864-1166-X |pages=221–233 |chapter=Allosaurus ] "A." sp. 2, as it is also known, differs from "A. fragilis" in several anatomical details including a jugal or cheekbone with a straight lower margin, and is also found only in the Salt Wash Member of the Morrison Formation, with "A. fragilis" only present in the higher Brushy Basin Member.cite journal |last=Loewen |first=Mark A. |coauthors=Sampson, Scott D.; Carrano, Matthew T.; and Chure, Daniel J. |year=2003 |title=Morphology, taxonomy, and stratigraphy of "Allosaurus" from the Upper Jurassic Morrison Formation |journal=Journal of Vertebrate Paleontology |volume=23 |issue=3, Suppl. |pages=72A ] "A. maximus" was coined by David K. Smith for Chure's "Saurophaganax maximus", a taxon created by Chure in 1995 for giant allosaurid remains from the Morrison of Oklahoma. These remains had been known as "Saurophagus", but that name was already in use, leading Chure to propose a substitute.cite book |last=Chure |first=Daniel J. |year=1995 |chapter=A reassessment of the gigantic theropod "Saurophagus maximus" from the Morrison Formation (Upper Jurassic) of Oklahoma, USA |editors=Ailing Sun and Yuangqing Wang (eds.) |title=Sixth Symposium on Mesozoic Terrestrial Ecosystems and Biota, Short Papers |publisher=China Ocean Press |location=Beijing |pages=103–106| isbn=7-5027-3898-3] Smith, in his 1998 analysis of variation, concluded that "S. maximus" was not different enough from "Allosaurus" to be a separate genus, but did warrant its own species, "A. maximus". This reassignment was rejected in the most recent review of basal tetanurans. There is also an "A. maximus" in Paul (1988), but it is a typographical error for "A. amplexus".

"A. tendagurensis" was named in 1925 by Werner Janensch for a partial shin (HM 67) found in the Kimmeridgian-age rocks of Tendaguru, in Mtwara, Tanzania.cite journal |last=Janensch |first=Werner |year=1925 |title=Die Coelurosaurier und Theropoden der Tendaguru-Schichten Deutsch-Ostafrikas |journal=Palaeontographica, Supplement 7 |volume=1 |pages=1–99 |language=German ] This species has not had strong support in recent years, with opinions on its identity ranging from a tentatively valid species of "Allosaurus", to a basal tetanuran,cite journal |last=Rauhut |first=Oliver W.M. |year=2005 |title=Post-cranial remains of 'coelurosaurs' (Dinosauria, Theropoda) from the Late Jurassic of Tanzania |journal=Geological Magazine |volume=142 |issue=1 |pages=97–107 |doi=10.1017/S0016756804000330 ] to simply a dubious theropod.cite book|chapter=Allosaurus |last=Glut |first=Donald F. |title=Dinosaurs: The Encyclopedia |year=1997 |publisher=McFarland & Co |location=Jefferson, North Carolina |pages=105–117 |isbn=0-89950-917-7] Although obscure, it was a large theropod, possibly around 10 meters long (33 ft) and 2.5 metric tons (2.8 short tons) in weight.cite web |publisher=The Dinosaur Mailing List |url=http://dml.cmnh.org/2003Jul/msg00355.html |title=And the Largest Theropod Is.... |last=Mortimer |first=Mickey |date=2003-07-21 |accessdate=2007-09-08]

Biological variation, "A. atrox", and "A. fragilis"

The perception that there were two common "Allosaurus" species in the Morrison Formation was popularized in Gregory S. Paul's 1988 book "Predatory Dinosaurs of the World". Paul proposed that "A. fragilis" had tall pointed horns and a slender build compared to a postulated second species "A. atrox", and was not a different gender due to rarity. "Allosaurus atrox" was originally named by Marsh in 1878 as the type species of its own genus, "Creosaurus", and is based on YPM 1890, an assortment of bones including a couple of pieces of the skull, portions of nine tail vertebrae, two hip vertebrae, an illium, and ankle and foot bones.cite journal |last=Marsh |first=Othniel Charles |year=1878 |title=Notice of new dinosaurian reptiles |journal=American Journal of Science and Arts |volume=15 |pages=241–244] Although the idea of two common Morrison allosaur species has had support in semi-technical and popular works,cite book |last=Lessem |first=Don |coauthors=and Glut, Donald F. |year=1993 |title=The Dinosaur Society's Dinosaur Encyclopedia |chapter="Allosaurus" |pages=19–20|publisher=Random House|isbn=0-679-41770-2] it has generally been rejected in the technical literature.

David K. Smith, examining "Allosaurus" fossils by quarry, found that the Cleveland-Lloyd Dinosaur Quarry (Utah) specimens are generally smaller than those from Como Bluff (Wyoming) or Brigham Young University's Dry Mesa Quarry (Colorado), but the shapes of the bones themselves did not vary between the sites.cite journal |last=Smith |first=David K. |year=1996 |title=A discriminant analysis of "Allosaurus" population using quarries as the operational units |journal=Museum of Northern Arizona Bulletin |volume=60 |pages=69–72] A later study by Smith incorporating Garden Park (Colorado) and Dinosaur National Monument (Utah) specimens found no justification for multiple species based on skeletal variation; skull variation was most common and was gradational, suggesting individual variation was responsible. Further work on size-related variation again found no consistent differences, although the Dry Mesa material tended to clump together on the basis of the astragalus, an ankle bone.cite journal |last=Smith |first=David K. |year=1999 |title=Patterns of size-related variation within "Allosaurus" |journal=Journal of Vertebrate Paleontology |volume=19 |issue=2 |pages=402–403]

Invalid and synonymous species

A number of species assigned to "Allosaurus" are no longer recognized as valid, for one reason or another. Species "A. agilis", seen in Zittel, 1887, and Osborn, 1912, is a typographical error for "A. fragilis." Marsh's "A. ferox" (1896; not to be confused with his 1884 "Labrosaurus ferox", also part of "Allosaurus" taxonomy) was coined for a partial skull in a footnote,cite journal |last=Marsh |first=Othniel Charles|year=1896 |title=The dinosaurs of North America |journal=United States Geological Survey, 16th Annual Report, 1894–95 |volume=55 |pages=133–244] and has been recognized as a specimen of "A fragilis." "A. lucaris", another Marsh name, was given to a partial skeleton in 1878. He later decided it warranted its own genus, "Labrosaurus",cite journal |last=Marsh |first=Othniel Charles |year=1879 |title=Principal characters of American Jurassic dinosaurs. Part II |journal=American Journal of Science, Series 3 |volume=17 |pages=86–92] but this has not been accepted, and "A. lucaris" is also regarded as another specimen of "A. fragilis". "A. whitei", an informally-described species coined by Pickering in 1996, is a recasting of the "A. atrox" versus "A. fragilis" debate using a better specimen to represent the "A. atrox" form, and has not been recognized.

Several species coined in genera other than "Allosaurus" are also now thought to be synonymous with "A. fragilis". "Labrosaurus ferox" was named in 1884 by Marsh for an oddly formed partial lower jaw, with a prominent gap in the tooth row at the tip of the jaw, and a rear section greatly expanded and turned down.cite journal |last=Marsh |first=Othniel Charles |year=1884 |title=Principal characters of American Jurassic dinosaurs. Part VIII |journal=American Journal of Science, Series 3 |volume=27 |pages=329–340] Later researchers suggested that the bone was pathologic, showing an injury to the living animal,cite journal |last=Gilmore |first=Charles W. |authorlink=Charles W. Gilmore |year=1920 |title=Osteology of the carnivorous dinosauria in the United States National Museum, with special reference to the genera "Antrodemus" ("Allosaurus") and "Ceratosaurus" |journal=Bulletin of the United States National Museum |volume=110 |pages=1–159] and that part of the unusual form of the rear of the bone was due to plaster reconstruction.cite book |last=Madsen |first=James H. |coauthors=and Welles, Samuel P. |title="Ceratosaurus" (Dinosauria, Theropoda), a Revised Osteology |series=Miscellaneous Publication, 00-2 |publisher=Utah Geological Survey |isbn=1-55791-380-3] It is recognized as most likely a specimen of "A. fragilis". "Allosaurus trihedrodon" started as "Laelaps trihedrodon", the name given to five theropod teeth by Cope in 1877.cite journal |last=Cope |first=Edward Drinker |year=1877 |title=On a carnivorous dinosaurian from the Dakota Beds of Colorado |journal=Bulletin of the United States Geological Survey |volume=3 |issue=33 |pages=805–806] Long lost but recently relocated, these specimens also appear to pertain to "Allosaurus",cite book |last=Chure |first=Daniel J. |year=2001 |chapter=On the type and referred material of "Laelaps trihedrodon" Cope 1877 (Dinosauria: Theropoda) |editors=Tanke, Darren; and Carpenter, Kenneth (eds.) |title=Mesozoic Vertebrate Life |publisher=Indiana University Press |location=Bloomington and Indianapolis |pages=10–18 |isbn=0-253-33907-3 ] perhaps "A. fragilis." This species is also partly responsible for confusion surrounding "Hypsirophus discursus", a species of stegosaurid named by Cope. Cope, who was considering "Hypsirophus" a theropod at the time, suggested that it might turn out to be the same as "Laelaps trihedrodon". Along with a mysterious theropod femur that he associated with "Hypsirophus" and which may have later been associated with "Epanterias," this uncertainty has led to the misconception that "Hypsirophus" is a chimera, based in part on "Allosaurus fragilis" remains. "Allosaurus valens" is a typo for "Antrodemus valens" accidentally used by Friedrich von Huene in 1932; "Antrodemus valens" itself may also pertain to "Allosaurus fragilis", as Gilmore suggested in 1920. "Apatodon mirus", based on a scrap of vertebra Marsh first thought to be a mammalian jaw, may or may not be the same as "Allosaurus".

Misassigned species

Several species initially classified within or referred to "Allosaurus" do not belong within the genus. "A. medius" was named by Marsh in 1888 for "various specimens" from the Early Cretaceous of Maryland,cite journal|last=Marsh |first=Othniel Charles |year=1888 |title=Notice of a new genus of Sauropoda and other new dinosaurs from the Potomac Formation |journal=American Journal of Science, Series 3 |volume=35 |pages=89–94] although most of the remains were removed by Richard Swann Lull to the new ornithopod species "Dryosaurus grandis", except for a tooth.cite journal |last=Lull |first=Richard Swann | year=1911 |title=The Reptilia of the Arundel Formation |journal=Maryland Geological Survey: Lower Cretaceous |pages=173–178] Gilmore considered the tooth nondiagnostic but transferred it to a new species, "Dryptosaurus medius". The referral was not accepted in the most recent review, and "Allosaurus medius" was simply listed as a dubious species of theropod. "Allosaurus sibiricus" was described in 1914 by A. N. Riabinin on the basis of a bone, later identified as a partial fourth metatarsal, from the Early Cretaceous of Buryatia, Russia.cite journal |last=Riabinin |first=Anatoly Nikolaenvich |year=1914 |title=Zamtka o dinozavry ise Zabaykalya |journal=Trudy Geologichyeskago Muszeyah Imeni Petra Velikago Imperatorskoy Academiy Nauk |volume=8 |issue=5 |pages=133–140 |language=Russian] It was transferred to "Chilantaisaurus" in 1990.cite book |last=Molnar |first=Ralph E. |coauthors=Kurzanov, Sergei M.; and Dong Zhiming |year=1990 |chapter=Carnosauria |editors=Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.) |title=The Dinosauria |edition=1st |publisher=University of California Press |location=Berkeley |pages=169–209 |isbn=0-520-06727-4] This is not the only report of "Allosaurus" from Siberia, or Asia in general. Kurzanov and colleagues in 2003 designated six teeth from Siberia as "Allosaurus" sp. (meaning the authors found the specimens to be most like those of "Allosaurus", but did not or could not assign a species).cite journal |last=Kurzanov |first=Sergei S. |coauthors=Efimov, Mikhail B.; and Gubin, Yuri M. |year=2003 |title=New archosaurs from the Jurassic of Siberia and Mongolia |journal=Paleontological Journal |volume=37 |issue=1 |pages=53–57] Also, reports of "Allosaurus" in Shanxi, China go back to at least 1982,cite book |last=Glut |first=Donald F. |title=The New Dinosaur Dictionary |year=1982 |publisher=Citadel Press |location=Secaucus, NJ |isbn=0-8065-0782-9 |pages=44 ] and tail vertebrae from Datong in Shanxi have been assigned to "A". sp..cite journal |last=Lü |first=Junchang |coauthors=and Hu, P. |year=1998 |title=Dinosaur remains from Datong suburb, Shanxi Province |journal=Vertebrata PalAsiatica |volume=36 |issue=3 |pages=252–256]

"Allosaurus meriani" was described in 1870 by Greppin as a species of "Megalosaurus", based on a tooth from the Late Jurassic of Switzerland.cite journal |last=Greppin |first=J.B. |year=1870 |title=Description geologique du Jura bernois et de quelques districts adjacents |journal=Beiträge zur geologischen Karte der Schweiz |volume=8 |pages=1–357 |language=French] It has occasionally been referred to "Allosaurus", but recent reviews have listed it as dubious theropod species "Megalosaurus meriani", or included it in "Ceratosaurus" sp. "Allosaurus stechowi" was described in 1920 by Janensch as "Labrosaurus stechowi" for isolated "Ceratosaurus"-like teeth from the Tendaguru beds of Tanzania.cite journal |last=Janensch |first=Werner |year=1920 |title=Uber "Elaphrosaurus bambergi" und die Megalosaurier aus den Tendaguru-Schichten Deutsch-Ostafricas |journal=Sitzungsberichte Gesellschaft Naturforschender Freunde Berlin |volume=8 |pages=225–235] With the synonymization of "Labrosaurus" and "Allosaurus", Donald F. Glut listed it as a species of "Allosaurus", but it is now either assigned to "Ceratosaurus" sp. or considered a dubious ceratosaurian.Tykoski, Ronald S.; and Rowe, Timothy. (2004). "Ceratosauria", in "The Dinosauria" (2nd). 47–70.]

There are also several species left over from the synonymizations of "Creosaurus" and "Labrosaurus" with "Allosaurus". "Creosaurus potens" was named by Lull in 1911 for a vertebra from the Early Cretaceous of Maryland. It is now regarded as a dubious theropod. "Labrosaurus huene" is an informal name used by von Huene (1956, 1958) for a tooth from the Late Jurassic of Szechuan, China, and "L. fragilis" is a typographical error by Marsh (1896) for "Labrosaurus ferox". "L. sulcatus", named by Marsh in 1896 for a Morrison theropod tooth, which like "L. stechowi" is now regarded as either "Ceratosaurus" sp. or a dubious ceratosaurian.

Possible Australian "Allosaurus"

An astragalus (ankle bone) thought to belong to a species of "Allosaurus" was found at Cape Paterson, 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.cite journal |last=Molnar |first=Ralph E. |coauthors=Flannery, Timothy F.; and Rich, Thomas H.V. |year=1981 |title=An allosaurid theropod dinosaur from the Early Cretaceous of Victoria, Australia |journal=Alcheringa |volume=5 |pages=141–146 ] This identification was challenged by Samuel Welles, who thought it more resembled that of an ornithomimid,cite journal |last=Welles |first=Samuel P. |year=1983 |title="Allosaurus" (Saurischia, Theropoda) not yet in Australia |journal=Journal of Paleontology |volume=57 |issue=2 |pages=196 ] but the original authors defended their identification.cite journal |last=Molnar |first=Ralph E. |coauthors=Flannery, Timothy F.; and Rich, Thomas H.V. |year=1985 |title=Aussie "Allosaurus" after all |journal=Journal of Paleontology |volume=59 |issue=6 |pages=1511–1535 ] With fifteen years of new specimens and research to look at, Daniel Chure reexamined the bone and found that it was not "Allosaurus", but could represent an allosauroid.cite journal |last=Chure |first=Daniel J. |year=1998 |title=A reassessment of the Australian "Allosaurus" and its implications for the Australian refugium concept |journal=Journal of Vertebrate Paleontology |volume=18 |issue=3, Suppl. |pages=34A ] 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.cite journal |last=Azuma |first=Yoichi |coauthors=and Currie, Philip J. |year=2000 |title=A new carnosaur (Dinosauria: Theropoda) from the Lower Cretaceous of Japan |journal=Journal of Vertebrate Paleontology |volume=37 |issue=12 |pages=1735–1753] This specimen is sometimes referred to as "Allosaurus robustus", an informal museum name. A speculative "polar" or "dwarf allosaur" was used for the "Spirits of the Ice Forest" episode of "Walking with Dinosaurs".

References