name = "Alectrosaurus"
phylum = Chordata
genus = "Alectrosaurus"
species = "A. olseni"
binomial = "Alectrosaurus olseni"
binomial_authority = Gilmore, 1933
"Alectrosaurus" (pronEng|əˌlɛktrəˈsɔrəs; meaning "unmarried lizard") is a
genusof tyrannosauroid theropod dinosaurfrom the Late CretaceousPeriod of Inner Mongolia. It was a bipedal carnivorewith a body shape similar to its much larger relative, "Tyrannosaurus rex". "Alectrosaurus" was much smaller though, most likely less than five meters (17 ft) long.
The generic name "Alectrosaurus" can also be translated as "alone lizard," and is derived from the Greek words "alektros" ("unmarried") and "sauros" ("lizard"). At the time of its discovery, it was unlike any other Asian carnivore known. There is one named
species("A. olseni"), which is named in honor of George Olsen, who discovered the first specimens in 1923 on the third American Museum of Natural Historyexpedition to Mongolia. Both genus and species were named by American paleontologistCharles Gilmore in 1933.
History of discovery
holotype( AMNH6554), or original specimen, of "Alectrosaurus" was a hind limb discovered in the Iren Dabasu Formationof the Inner MongoliaAutonomous Region (Nei Mongol Zizhiqu) of the People's Republic of China.Gilmore, C.W. (1933). On the dinosaurian fauna of the Iren Dabasu Formation. "Bulletin of the American Museum of Natural History" 67:23-78.] The age of this geologic formationis not clear, but is commonly cited as the Campanianstage of the Late CretaceousPeriod, about 83 to 74 million years ago.
More material, including comparable hind limb material as well as
skulland shoulder elements, has been referred to "Alectrosaurus". These fossils were found in the Bayan Shireh Formationof Outer Mongolia, a formation which is also of uncertain age.Perle, A. (1977). [On the first finding of "Alectrosaurus" (Tyrannosauridae, Theropoda) in the Late Cretaceous of Mongolia.] "Problemy Geologii Mongolii" 3:104-113. [In Russian] ] It may possibly extend into the early Campanian, but recent estimates suggest it was deposited from Cenomanianthrough Santoniantimes.Hicks, J.F., Brinkman, D.L., Nichols, D.J., and Watabe, M. (1999). Paleomagnetic and palynological analyses of Albian to Santonian strata at Bayn Shireh, Burkhant, and Khuren Dukh, eastern Gobi Desert, Mongolia. "Cretaceous Research" 20(6): 829-850.] Iren Dabasu and Bayan Shireh dinosaur faunas are similar, but van Itterbeecka "et al" claimed that the Iren Dabasu is probably Campanian- Maastrichtianin age and possibly correlated with the Nemegt Formation, so it is not surprising that a species of "Alectrosaurus" would be found there.van Itterbeecka, J., Horne, D.J., Bultynck, P., and Vandenbergh, N. (2005). Stratigraphy and palaeoenvironment of the dinosaur-bearing Upper Cretaceous Iren Dabasu Formation, Inner Mongolia, People's Republic of China. "Cretaceous Research" 26:699-725.]
Furthermore, several more partial skeletons may have been found in both Inner and Outer Mongolia.Currie, P.J. (2001). Theropods from the Cretaceous of Mongolia. In: Benton, M.J., Shishkin, M.A., Unwin, D.M., and Kurochkin, E.N. (Eds.). "The Age of Dinosaurs in Russia and Mongolia". Cambridge University Press:Cambridge, 434-455. ISBN 052154582X.] These remain undescribed as of early 2007.
"Alectrosaurus" is undoubtedly a
tyrannosauroid, but due to its fragmentary nature, there is presently very little confidence in restoring its relationships with other tyrannosauroids and many recent cladisticanalyses have omitted it altogether. One study recovered "Alectrosaurus" at no less than eight equally parsimonious positions in a tyrannosauroid cladogram.Holtz, T.R. (2004). Tyrannosauroidea. In: Weishampel, D.A., Dodson, P., and Osmólska, H. (Eds.). "The Dinosauria" (2nd Edition). University of California Press:Berkeley, 111-136. ISBN 0-520-24209-2.] Some paleontologists have considered " Alectrosaurus olseni" to be a species of " Albertosaurus"."Albertosaurus." In: Dodson, Peter & Britt, Brooks & Carpenter, Kenneth & Forster, Catherine A. & Gillette, David D. & Norell, Mark A. & Olshevsky, George & Parrish, J. Michael & Weishampel, David B. "The Age of Dinosaurs". Publications International, LTD. p. 106-107. ISBN 0-7853-0443-6.]
"Alectrosaurus" was originally characterized as a long-armed theropod, but this was due to the mistaken association of segnosaur forelimb elements.Mader, B.J., and Bradley, R.L. (1989). A redescription and revised diagnosis of the syntypes of the Mongolian tyrannosaur "Alectrosaurus olseni". "Journal of Vertebrate Paleontology" 9(1):41-55.] The remaining material represents the hind limb of a true tyrannosauroid, although characterized by the low ratio between the length of its
tibiaand femur, meaning that both bones are about the same size, as opposed to most other tyrannosauroids, where the tibia is usually longer. The hind foot (and ankle) are also closer in size to the tibia than most tyrannosauroids, where the foot is usually longer.
Bayan Shirehmaterial may or may not belong to this genus, and needs further study. One cladistic analysis showed that the two sets of specimens group together exclusive of any other taxa, so they are probably at least closely related, if not the same species.Holtz, T.R. (2001). The phylogeny and taxonomy of the Tyrannosauridae. In: Tanke, D.H., and Carpenter, K. (Eds.). "Mesozoic Vertebrate Life". Indiana University Press:Bloomington, 64-83. ISBN 0-253-33907-3.]
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