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''Ornitholestes'' (meaning "bird robber") is a small theropod dinosaur of the late Jurassic (Brushy Basin Member of the Morrison Formation, middle Kimmeridgian age, about 154 million years ago〔Turner, C.E. and Peterson, F., (1999). "Biostratigraphy of dinosaurs in the Upper Jurassic Morrison Formation of the Western Interior, U.S.A." Pp. 77–114 in Gillette, D.D. (ed.), ''Vertebrate Paleontology in Utah''. Utah Geological Survey Miscellaneous Publication 99-1.〕) of Western Laurasia (the area that was to become North America). To date, ''Ornitholestes'' is known only from a single partial skeleton with a badly crushed skull found at the Bone Cabin Quarry near Medicine Bow, Wyoming, in 1900. It was described by Henry Fairfield Osborn in 1903. An incomplete hand was later attributed to ''Ornitholestes'', although it now appears to belong to ''Tanycolagreus''. The type (and only known) species is ''O. hermanni''. The specific name honors the American Museum of Natural History preparator Adam Hermann. ==Description== ''Ornitholestes'' was a bipedal carnivore.〔Lambert (1993), p. 79〕 Its head was proportionally smaller than that of most other predatory dinosaurs, but the skull was heavily built, with a short snout and robust lower jaw.〔Paul (1988''a''), p. 306; Norman (1985), p. 42; Norman (1990), p. 293〕 The orbits (eye sockets) were quite large, measuring over 25 percent of the skull's length.〔Osborn (1903), p. 460; Chure (1998), p. 238〕 There is no indication of a bony eye ring.〔Paul (1988''b''), p. 6〕 The front teeth of ''Ornitholestes'' were somewhat conical, with reduced serrations; the back teeth were recurved and more sharply serrated, similar to those of other theropod dinosaurs.〔Paul (1988''b''), p. 3; Norman (1990), p. 293〕 Henry Fairfield Osborn (1903) counted four teeth in the premaxilla, of which the front tooth was the largest in the upper jaw.〔Osborn (1903), p. 460; Osborn (1917), p. 734〕 In contrast, Gregory S. Paul (1988) depicted the skull with only three premaxillary teeth remaining, much smaller than those illustrated by Osborn.〔Paul (1988''b''), p. 4; Norman (1990), p. 293〕 Each maxilla (main tooth-bearing bone in the upper jaw) contained ten teeth, and each dentary (tooth-bearing bone in the lower jaw) contained twelve teeth.〔Osborn (1903), p. 460〕 The tooth rows of ''Ornitholestes'' were short, with the dentary (lower) row being even shorter than the maxillary (upper) row,〔Paul (1988''b''), p. 3; Norman (1990), p. 292〕 even though the dentary bone itself was exceptionally long at the back, reaching a point below the middle of the eye socket.〔Cristiano dal Sasso & Simone Maganuco, 2011, '' ''Scipionyx samniticus'' (Theropoda: Compsognathidae) from the Lower Cretaceous of Italy — Osteology, ontogenetic assessment, phylogeny, soft tissue anatomy, taphonomy and palaeobiology'', Memorie della Società Italiana de Scienze Naturali e del Museo Civico di Storia Naturale di Milano XXXVII(I): 1-281〕 Teeth did not extend as far back as the orbits, and neither tooth row spanned much more than one-third of the skull.〔Osborn (1903), p. 460; Norman (1990), p. 293〕 An area of broken bone near the external naris (nostril) appears to bulge upward, which led Gregory S. Paul to suggest in ''Predatory Dinosaurs of the World'' (1988) that ''Ornitholestes'' had a nasal horn "rather like a chicken's comb in looks."〔Paul (1988''a''), p. 303〕 Both Oliver W.M. Rauhut (2003) and Kenneth Carpenter ''et al''. (2005''a'') rejected that interpretation, and indicated that the upward flare of bone was due to post-mortem crushing of the skull.〔Rauhut (2003), p. 27; Carpenter ''et al''. (2005''a''), p. 53〕 Paul's updated illustration of ''Ornitholestes'' in his 2010 ''Princeton Field Guide to Dinosaurs'' no longer contains the nasal horn.〔Paul (2010), p. 123〕 ''Ornitholestes'' had a relatively short neck with a slight sigmoidal (S-shaped) curve.〔Carpenter ''et al''. (2005''a''), pp. 49, 54〕 The tail was long and whiplike, comprising over half of the body's length.〔Osborn (1917), p. 734; Lambert (1993), p. 78〕 Not all of the vertebrae were preserved, but Osborn (1917) estimated that ''Ornitholestes'' had nine or ten cervical (neck) vertebrae, thirteen dorsal (back) vertebrae, four sacral (hip) vertebrae, and 39 to 44 caudal (tail) vertebrae.〔Osborn (1917), p. 735–736〕 Carpenter ''et al''. (2005''a'') recorded that the specimen contained five sacral vertebrae.〔Carpenter ''et al''. (2005''a''), p. 58〕 ''Ornitholestes'' was a short-bodied theropod, and this was reflected in the short front-to-back dimensions of the cervical and dorsal vertebrae.〔Carpenter ''et al''. (2005''a''), p. 49, 69〕 The forelimbs of ''Ornitholestes'' were relatively long, slightly under two-thirds the length of the hind legs.〔Ostrom (1969), p. 146; Paul (2002), p. 236〕 The humerus (upper arm bone) was heavily built, and somewhat longer than the radius and ulna (forearm bones).〔Osborn (1917), p. 738; Carpenter ''et al''. (2005''b''), p. 45〕 Both the humerus and radius were straight-shafted.〔Carpenter ''et al''. (2005''a''), p. 60, 62〕 The claws on digits I and II of the hand were about the same size.〔Senter (2006), p. 1030〕 Although the hand's third ungual (claw bone) was not preserved, extrapolation from the closest relatives of ''Ornitholestes'' indicates that it was probably shorter than the first two.〔 ''Ornitholestes'' is often portrayed as a fast, long-legged theropod, but its lower limb bones were fairly short.〔Paul (1988''a''), p. 306〕 Osborn (1917) calculated that the, missing, tibia (shin bone) was only about 70.6% as long as the femur (thigh bone).〔Osborn (1917), p. 737〕 The metatarsals (foot bones) were spaced closely, but not fused together.〔Carpenter ''et al''. (2005''a''), p. 67〕 As is typical of theropods, the feet were tridactyl (with three clawed weight-bearing toes).〔Osborn (1903), p. 463〕 John H. Ostrom (1969) noted that the claw of digit II (the innermost toe) was larger than those of digits III and IV, and suggested that this digit may have borne a modified sickle claw similar to that of ''Deinonychus''.〔Ostrom (1969), p. 161〕 However, as both Ostrom (1969) and Paul (1988) noted, the poor preservation of digit II makes this hypothesis difficult to confirm.〔Ostrom (1969), p. 161; Paul (1988''b''), p. 6〕 In his 1903 description, Osborn wrote that the length of ''Ornitholestes'' along "the skull and vertebral column as restored" was .〔Osborn (1903), p. 459〕 However, this reconstruction was inaccurate, being based in part on Othniel Charles Marsh's restoration of the basal sauropodomorph ''Anchisaurus'', and the neck and trunk were both too elongated.〔Osborn (1917), p. 735; Paul (1988''b''), p. 3〕 David Norman (1985) and John Foster (2007) both estimated that ''Ornitholestes'' was about long.〔Norman (1985), p. 39; Foster (2007), p. 178〕 Gregory S. Paul's 1988 ''Predatory Dinosaurs of the World'' listed the length of ''Ornitholestes'' as approximately .〔Paul (1988''a''), p. 305〕 Paul (1988) and Foster (2007) both estimated that ''Ornitholestes'' weighed .〔Paul (1988''a''), p. 305; Foster (2007), p. 178〕 John A. Long and Peter Schouten (2008) suggested a slightly higher figure, .〔Long and Schouten (2008), p. 73〕 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「Ornitholestes」の詳細全文を読む スポンサード リンク
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