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''Pentaceratops'' (five-horned face) is a genus of herbivorous ceratopsid dinosaur from the late Cretaceous Period of what is now North America. ''Pentaceratops'' fossils were first discovered in 1921. The genus was named in 1923 when its type species ''Pentaceratops sternbergii'' was described. ''Pentaceratops'' lived around 76-73 million years ago, its remains having been mostly found in the Kirtland Formation〔 in the San Juan Basin in New Mexico. Other dinosaurs which shared its habitat include ''Parasaurolophus cyrtocristatus'', the pachycephalosaur ''Sphaerotholus'', the armored dinosaur ''Nodocephalosaurus'' and the tyrannosauroid ''Bistahieversor''. About a dozen skulls and skeletons have been uncovered, so that most bones are known. One exceptionally large specimen later became its own genus, ''Titanoceratops'', due to its more derived morphology closer to ''Triceratops'' and lack of unique characters shared with ''Pentaceratops'' proper,〔 although the author that originally assigned it to ''Pentaceratops'' has decided to ignore this in subsequent publications. ''Pentaceratops'' was about six meters (twenty feet) long, and has been estimated to have weighed around five tonnes. It had a short nose horn, two long brow horns, and long horns on the jugal bones. Its skull had a very long frill with triangular hornlets on the edge. ==Discoveries and species== The first specimens were collected by Charles Hazelius Sternberg in the San Juan Basin in New Mexico. Sternberg worked in commission for the Swedish Uppsala University . In 1921 he recovered a skull and a rump, specimens PMU R.200 and PMU R.286, at the Meyers Creek near the Kimbetoh Wash, in a layer of the Kirtland Formation, he sent the fossils to paleontologist Carl Wiman. In 1922 Sternberg decided to work on his own account and north of Tsaya Trading Post, in the Fossil Forest of San Juan County, he discovered a complete skeleton , which he sold to the American Museum of Natural History. The museum then sent out a team headed by Charles Mook and Peter Kaisen to assist Sternberg in securing this specimen; subsequent digging by Sternberg in 1923 brought the total of AMNH specimens to four. The rump of the main specimen was discarded by the museum because it had insufficient value as a display. The species was named and described by Henry Fairfield Osborn in 1923, as ''Pentaceratops sternbergii''. The generic name means "five-horned face", derived from the Greek ''penta'' (πέντα, meaning five), ''keras'' (κέρας, horn) and ''-ops'' (ὤψ, face),〔 in reference to its two long epijugal bones, spikes which protrude out sidewards from under its eyes, in addition to the three more obvious horns as with ''Triceratops''. Osborn obligingly gave it the specific name ''sternbergii'' honoring its discoverer as a veteran fossil hunter.〔H.F. Osborn, 1923, "A new genus and species of Ceratopsia from New Mexico, ''Pentaceratops sternbergii'', ''American Museum Novitates'' 93: 1-3〕 The name had been suggested to Osborn by William Diller Matthew; the specific epithet served as a consolation to the almost bankrupt Sternberg whose 1923 fossils were initially not acquired by the museum that had to use its 1923/1924 budget to process the finds of the great Asian expeditions by Roy Chapman Andrews.〔Sullivan, R.M. and S.G. Lucas, 2011, "Charles Hazelius Sternberg and his San Juan Basin Cretaceous dinosaur collections: Correspondence and photographs (1920-1925)", ''New Mexico Museum of Natural History and Science Bulletin'' 53: 429-471〕 The holotype was the skull discovered by Sternberg in 1922, specimen AMNH 6325. It was found in a layer of the Fruitland Formation, dating from the Campanian, about seventy-five million years old. The other three AMNH specimens were AMNH 1624, a smaller skull; AMNH 1622, a pair of brow horns; and AMNH 1625, a piece of skull frill.〔 In 1930, Wiman named a second species of ''Pentaceratops'': ''Pentaceratops fenestratus''. It was based on Sternberg's 1921 specimens and the specific name referred to a hole in the left squamosal.〔C. Wiman, 1930, "Über Ceratopsia aus der Oberen Kreide in New Mexico", ''Nova Acta Regiae Societatis Scientiarum Upsaliensis, Series 4'' 7(2): 1-19〕 This was later considered to be the same species as ''Pentaceratops sternbergii'' and thus a junior synonym, the hole being the likely effect of an injury. In 1929 Steinberg's son, George Fryer Sternberg, discovered specimen USNM V12002, a right squamosal. ''Pentaceratops'' proved to be a quite common fossil in the Fruitland and Kirtland formations. It has even been used as a guide fossil: the appearance of ''Pentaceratops sternbergii'' in the fossil record marks the end of the Judithian land vertebrate age and the start of the Kirtlandian.〔 Subsequent finds include specimens MNA Pl. 1668, MNA Pl. 1747, NMMNH P-27468 and USNM 2416, partial skeletons with skull; YPM 1229, a skeleton lacking the skull; UALP 13342 and UKVP 16100, skulls; UNM B-1701, USNM 12741, USNM 12743, USNM 8604, SMP VP-1596, SMP VP-1488, SMP VP-1500 and SMP VP-1712, fragmentary skulls. Apart from the San Juan Basin finds, a juvenile specimen of ''Pentaceratops'', SDMNH 43470, has been reported from the Williams Fork Formation of Colorado in 2006.〔 Sometimes the identification of a specimen as ''Pentaceratops'' has proven to be highly contentious. In 1998 Thomas Lehman described OMNH 10165, a very large skull and its associated skeleton found in New Mexico in 1941, and presently on display at the Sam Noble Oklahoma Museum of Natural History, as being the largest ''Pentaceratops'' exemplar known, with the distinction of having produced the largest known skull of any land vertebrate.〔Lehman, T.M., 1998, "A gigantic skull and skeleton of the horned dinosaur ''Pentaceratops sternbergi'' from New Mexico: Journal of Paleontology, 72(5): 894-906〕〔 However, in 2011, the skeleton was renamed as a separate genus, ''Titanoceratops'', due to its more derived morphology closer to ''Triceratops'' and lack of unique characters shared with ''Pentaceratops'' proper.〔 In 2014 Nicholas Longrich named a new species ''Pentaceratops aquilonius'', "the northern one", based on fragmentary fossils discovered during the 1930s near Manyberries in Canada. The species has a first epiparietal pointing upwards instead of forwards.〔Longrich, N., 2014, "The horned dinosaurs ''Pentaceratops'' and ''Kosmoceratops'' from the upper Campanian of Alberta and implications for dinosaur biogeography", ''Cretaceous Research'', 51: 292-308〕 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「Pentaceratops」の詳細全文を読む スポンサード リンク
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