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''Torosaurus'' ("perforated lizard", in reference to the large openings in its frill) is a genus of herbivorous ceratopsid dinosaur that lived during the late Maastrichtian stage of the Cretaceous period, between 68 and 66 million years ago. Fossils have been discovered across the Western Interior of North America, from Saskatchewan to southern Texas. ''Torosaurus'' possessed one of the largest skulls of any known land animal. The frilled skull reached up to in length. From head to tail, ''Torosaurus'' is thought to have measured about long〔Holtz, Thomas R. Jr. (2008) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages'' (Supplementary Information )〕〔Holtz, Thomas R. Jr. (2011) ''Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages,'' (Winter 2010 Appendix. )〕 and weighed four to six tonnes. ''Torosaurus'' is distinguished from the contemporary ''Triceratops'' by an elongate frill with large openings (fenestrae), long squamosal bones of the frill with a trough on their upper surface, and the presence of five or more pairs of hornlets (epoccipitals) on the back of the frill. ''Torosaurus'' also lacked the long nose horn seen in ''Triceratops prorsus'', and instead resembled the earlier and more basal ''Triceratops horridus'' in having a short nose horn.〔 Three species have been named, ''Torosaurus latus'', ''T. gladius'' and ''T. utahensis''. ''T. gladius'' is no longer considered a valid species, however. Recently the validity of ''Torosaurus'' has been disputed. A 2010 study of fossil bone histology combined with an investigation of frill shape concluded that ''Torosaurus'' probably represented the mature form of ''Triceratops'', with the bones of typical ''Triceratops'' specimens still immature and showing signs of a first development of distinct ''Torosaurus'' frill holes. During maturation, the skull frill would have been greatly lengthened and holes would have appeared in it.〔〔Horner, Jack. TEDX Talks: "(Shape-shifting Dinosaurs )". Nov 2011. Accessed 20 Nov 2012.〕 In 2011, 2012 and 2013 however, studies of external features of known specimens have claimed that morphological differences between the two genera preclude their synonymy. The main problems are a lack of good transitional forms, the apparent existence of authentic ''Torosaurus'' subadults, different skull proportions independent of maturation and the assertion that hole formation at an adult stage is not part of a normal ceratopsian maturation sequence.〔〔〔 ==Discovery and species== In 1891, two years after the naming of ''Triceratops'', a pair of ceratopsian skulls with elongated frills bearing holes were found in southeastern Wyoming, Niobrara County, by John Bell Hatcher. Hatcher's employer, paleontologist Professor Othniel Charles Marsh, coined the genus ''Torosaurus'' for them.〔O.C. Marsh, 1891, "Notice of new vertebrate fossils", ''The American Journal of Science, series 3'' 42: 265-269〕 The name ''Torosaurus'' is frequently translated as "bull lizard" from the Latin noun ''taurus'' or Spanish ''toro'' but much more likely is derived from the Greek verb (''toreo'', "to pierce, perforate").〔Dodson, P. ''The Horned Dinosaurs''. Princeton Univ. Press (Princeton), 1996.〕 The allusion is to the ''fenestrae'' or ("window-like") holes in the elongated frill, which have traditionally served to distinguish it from the solid frill of ''Triceratops''. Much of the confusion over etymology of the name results from the fact that Marsh never explicitly explained it in his papers. Two ''Torosaurus'' species have been identified: *''T. latus'' (type species). ''Latus'' means "the wide one" in Latin, in reference to the frill. *''T. utahensis'' () Lawson, 1976 Another species was subsequently regarded as identical to ''T. latus'': *''T. gladius'' . ''Gladius'' is "sword" in Latin, in reference to the elongated shape of the squamosal. ''T. latus'' was based on holotype YPM 1830, a partial skull. The holotype of ''T. gladius'' was specimen YPM 1831, a larger skull. Both fossils were found in the Lance Formation, dating from the Maastrichtian. Similar specimens found in Wyoming, Montana, South Dakota, North Dakota, Colorado, Utah and Saskatchewan have since been referred to ''Torosaurus''. Those that can be identified with some certainty include: ANSP 15192, a smaller individual in South Dakota uncovered by Edwin Harris Colbert in 1944;〔Colbert, E.H. and J.D. Bump, 1947, "A skull of ''Torosaurus'' from South Dakota and a revision of the genus:, ''Proceedings of the Academy of Natural Sciences of Philadelphia'', 99: 93–106〕 MPM VP6841, a partial skeleton with skull, now mounted at Milwaukee; SMM P97.6.1, a skull lacking the snout; and two partial skulls from the Hell Creek Formation reported in 2002: MOR 981, discovered in 1998, and MOR 1122, from 2001.〔Farke, A., 2002, "A review of ''Torosaurus'' (Dinosauria: Ceratopsidae) specimens from Texas and New Mexico", ''Journal of Vertebrate Paleontology'', 22: 52A〕 Fragmentary remains that could possibly be identified with the genus have been found in the Big Bend Region of Texas and in the San Juan Basin of New Mexico.〔Lucas, S.G., Mack, G.H., Estep, G.W., 1998, "The Ceratopsian dinosaur ''Torosaurus'' from the Upper Cretaceous McRae Formation, Sierra County, New Mexico", ''New Mexico Geological Society Guidebook, 49th Field Conference, Las Cruces County II〕 Paleontologists have observed that ''Torosaurus'' specimens are uncommon in the fossil record; specimens of ''Triceratops'' are much more abundant. ''Torosaurus utahensis'' was originally described as ''Arrhinoceratops utahensis'' by Charles Whitney Gilmore in 1946, based on specimen USNM 15583, a frill fragment from Emery County, Utah.〔C.W. Gilmore, 1946, "Reptilian fauna of the North Horn Formation of central Utah", ''United States Department of the Interior Geological Survey Professional Paper'' 210-C: 29-53〕 In 1976 it was renamed ''Torosaurus utahensis'' by Douglas Lawson.〔D.A. Lawson, 1976, "''Tyrannosaurus'' and ''Torosaurus'', Maestrichtian dinosaurs from Trans-Pecos, Texas", ''Journal of Paleontology'' 50(1): 158-164〕 Review by Robert Sullivan ''et al.'' in 2005〔Sullivan, R. M., A. C. Boere, and S. G. Lucas. 2005. Redescription of the ceratopsid dinosaur ''Torosaurus utahensis'' (Gilmore, 1946) and a revision of the genus. ''Journal of Paleontology'' 79:564-582.〕 left it as ''Torosaurus utahensis'' and somewhat older than ''T. latus''. In 2008 Rebecca Hunt referred considerable additional material to this species.〔 However, subsequent studies suggested it may well be either ''Arrhinoceratops'' or a new genus, as dinosaurs from the northern Hell Creek formation and southern "''Alamosaurus'' fauna" rarely overlap and were probably separated by a geographic barrier. Research has not yet been published on whether ''T. utahensis'' should be regarded as a new genus or, as has been suggested for ''T. latus'', the mature growth stage of some species of ''Triceratops''.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Torosaurus」の詳細全文を読む スポンサード リンク
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