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Description

[edit]
Life restoration of Ornitholestes

Ornitholestes was a bipedal carnivore.[1] 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.[2] The orbits (eye sockets) were quite large, measuring over 25 percent of the skull's length.[3] There is no indication of a bony eye ring.[4]

The front teeth of Ornitholestes were somewhat conical, with reduced serrations; back teeth were recurved and more sharply serrated, similar to those of other theropod dinosaurs.[5] Henry Fairfield Osborn (1903) counted four teeth in the premaxilla, of which the front tooth was the largest in the upper jaw.[6] In contrast, Gregory S. Paul (1988) reconstructed the skull with only three premaxillary teeth, much smaller than those illustrated by Osborn.[7] Each maxilla (main tooth-bearing bone in the upper jaw) contained 10 teeth, and each dentary (tooth-bearing bone in the lower jaw) contained 12 teeth.[8] The tooth rows of Ornitholestes were short, with the dentary (lower) row being even shorter than the maxillary (upper) row.[9] Teeth did not extend as far back as the orbits, and neither tooth row spanned much more than one-third of the skull.[10]

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."[11] Both Oliver W.M. Rauhut (2003) and Kenneth Carpenter et al. (2005a) rejected that interpretation, and indicated that the upward flare of bone was due to post-mortem crushing of the skull.[12]

Ornitholestes had a relatively short neck with a slight sigmoidal (S-shaped) curve.[13] The tail was long and whiplike, comprising over half of the body's length.[14] Not all of the vertebrae were preserved, but Osborn (1917) estimated that Ornitholestes had nine or ten cervical (neck) vertebrae, 13 dorsal (back) vertebrae, four sacral (hip) vertebrae, and 39 to 44 caudal (tail) vertebrae.[15] Carpenter et al. (2005a) recorded that the specimen contained five sacral vertebrae.[16] Ornitholestes was a short-bodied theropod, and this was reflected in the short front-to-back dimensions of the cervical and dorsal vertebrae.[17]

The forelimbs of Ornitholestes were relatively long, slightly under two-thirds the length of the hind legs.[18] The humerus (upper arm bone) was heavily built, and somewhat longer than the radius and ulna (forearm bones).[19] Both the humerus and radius were straight-shafted.[20] The claws on digits I and II of the hand were about the same size.[21] 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.[22]

Ornitholestes is often portrayed as a fast, long-legged theropod, but its lower limb bones were fairly short.[23] Osborn (1917) calculated that the tibia (shin bone) was only about 70.6% as long as the femur (thigh bone).[24] The metatarsals (foot bones) were spaced closely, but not fused together.[25] As is typical of theropods, the feet were tridactyl (three-clawed).[26] 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.[27] However, as both Ostrom (1969) and Paul (1988) noted, the poor preservation of digit II makes this hypothesis difficult to confirm.[28]

In his 1903 description, Osborn wrote that the length of Ornitholestes along "the skull and vertebral column as restored" was 2.22 m (7.28 ft).[29] 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.[30] David Norman (1985) and John Foster (2007) both estimated that Ornitholestes was about 2 m (6.6 ft) long.[31] Gregory S. Paul's 1988 Predatory Dinosaurs of the World listed the length of Ornitholestes as approximately 2.08 m (6.82 ft).[32]

Paul (1988) and Foster (2007) both estimated that Ornitholestes weighed 12.6 kg (27.8 lb).[33] John A. Long and Peter Schouten (2008) suggested a slightly higher figure, 15 kg (33 lb).[34]

Discovery and naming

[edit]
The early 20th century mount of the holotype skeleton at the AMNH, which stands much the same today

Ornitholestes was the first theropod to be discovered in the 20th century.[35] The holotype skeleton (AMNH 619) was excavated in 1900 at Bone Cabin Quarry in Wyoming by an American Museum of Natural History expedition.[36] Henry Fairfield Osborn named and scientifically described the specimen in 1903.[37] The genus name Ornitholestes, initially suggested by Theodore Gill, means "bird robber" and is derived from the Greek ὄρνις/ornithos ("bird") and λῃστήσ/lestes ("robber").[38] The species name (O. hermanni) honors Adam Hermann, the head preparator at the Museum, who directed the restoration and mounting of the skeleton.[39]

Sources

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  • Osborn, Henry Fairfield (1903). "Ornitholestes hermanni, a new compsognathoid dinosaur from the Upper Jurassic". Bulletin of the American Museum of Natural History. 19 (12): 459–464.
  • Osborn, Henry Fairfield (1917). "Skeletal adaptations of Ornitholestes, Struthiomimus, Tyrannosaurus". Bulletin of the American Museum of Natural History. 35 (43): 733–771.
  • Ostrom, John H. (1969). "Osteology of Deinonychus antirrhopus, an unusual theropod from the Lower Cretaceous of Montana". Peabody Museum of Natural History Bulletin. 30: 1–165.
  • Norman, David B. (1985). "Coelurosaurs". The Illustrated Encyclopedia of Dinosaurs. Salamander Books Ltd. pp. 38–43. ISBN 0517468905.
  • Paul, Gregory S. (1988a). "Ornitholestians and Allosaurs". Predatory Dinosaurs of the World. Simon & Schuster. pp. 302–318. ISBN 0671619462. {{cite book}}: Check date values in: |year= (help)CS1 maint: year (link)
  • Paul, Gregory S. (1988b). "The small predatory dinosaurs of the mid-Mesozoic: The horned theropods of the Morrison and Great Oolite—Ornitholestes and Proceratosaurus—and the sickle-claw theropods of the Cloverly, Djadokhta and Judith River—Deinonychus, Velociraptor and Saurornitholestes". Hunteria. 2 (4): 1–9. {{cite journal}}: Check date values in: |year= (help)CS1 maint: year (link)
  • Norman, David B. (1990). "Problematic Theropoda: Coelurosaurs". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka (ed.). The Dinosauria. University of California Press. pp. 280–305. ISBN 0520067266.{{cite book}}: CS1 maint: multiple names: editors list (link)
  • Lambert, David (1993). "Ornitholestes". The Ultimate Dinosaur Book. Dorling Kindersley. pp. 78–79. ISBN 156458304X.
  • Paul, Gregory S. (2002). "Were Some Dinosaurs Also Neoflightless Birds?". Dinosaurs of the Air: The Evolution and Loss of Flight in Dinosaurs and Birds. Johns Hopkins University Press. pp. 224–257. ISBN 0801867630.
  • Rauhut, Oliver W.M. (2003). "Operational Taxonomic Units". The Interrelationships and Evolution of Basal Theropod Dinosaurs. Palaeontological Association. pp. 12–43. ISBN 090170279X.
  • Carpenter, Kenneth; Miles, Clifford; Ostrom, John H.; Cloward, Karen (2005a). "Redescription of the Small Maniraptoran Theropods Ornitholestes and Coelurus". In Carpenter, Kenneth (ed.). The Carnivorous Dinosaurs. Life of the Past. Indiana University Press. pp. 49–71. ISBN 0253345391. {{cite book}}: Check date values in: |year= (help)CS1 maint: multiple names: authors list (link) CS1 maint: year (link)
  • Carpenter, Kenneth; Miles, Clifford; Cloward, Karen (2005b). "New Small Theropod from the Upper Jurassic Morrison Formation of Wyoming". In Carpenter, Kenneth (ed.). The Carnivorous Dinosaurs. Life of the Past. Indiana University Press. pp. 23–48. ISBN 0253345391. {{cite book}}: Check date values in: |year= (help)CS1 maint: multiple names: authors list (link) CS1 maint: year (link)
  • Senter, Phil (2006). "Forelimb function in Ornitholestes hermanni Osborn (Dinosauria, Theropoda)". Palaeontology. 49 (5): 1029–1034.
  • Foster, John (2007). "Gargantuan to Minuscule: The Morrison Menagerie, Part II". Jurassic West: The Dinosaurs of the Morrison Formation and Their World. Indiana University Press. pp. 162–242. ISBN 0253348706.
  • Long, John A.; Schouten, Peter (2008). "Ornitholestes and kin". Feathered Dinosaurs: The Origin of Birds. Oxford University Press. pp. 72–77. ISBN 0195372662.{{cite book}}: CS1 maint: multiple names: authors list (link)


References

[edit]
  1. ^ Lambert (1993), p. 79
  2. ^ Paul (1988a), p. 306; Norman (1985), p. 42; Norman (1990), p. 293
  3. ^ Osborn (1903), p. 460; Chure (1998), p. 238
  4. ^ Paul (1988b), p. 6
  5. ^ Paul (1988b), p. 3; Norman (1990), p. 293
  6. ^ Osborn (1903), p. 460; Osborn (1917), p. 734
  7. ^ Paul (1988b), p. 4; Norman (1990), p. 293
  8. ^ Osborn (1903), p. 460
  9. ^ Paul (1988b), p. 3; Norman (1990), p. 292
  10. ^ Osborn (1903), p. 460; Norman (1990), p. 293
  11. ^ Paul (1988a), p. 303
  12. ^ Rauhut (2003), p. 27; Carpenter et al. (2005a), p. 53
  13. ^ Carpenter et al. (2005a), pp. 49, 54
  14. ^ Osborn (1917), p. 734; Lambert (1993), p. 78
  15. ^ Osborn (1917), p. 735–736
  16. ^ Carpenter et al. (2005a), p. 58
  17. ^ Carpenter et al. (2005a), p. 49, 69
  18. ^ Ostrom (1969), p. 146; Paul (2002), p. 236
  19. ^ Osborn (1917), p. 738; Carpenter et al. (2005b), p. 45
  20. ^ Carpenter et al. (2005a), p. 60, 62
  21. ^ Senter (2006), p. 1030
  22. ^ Senter (2006), p. 1030
  23. ^ Paul (1988a), p. 306
  24. ^ Osborn (1917), p. 737
  25. ^ Carpenter et al. (2005a), p. 67
  26. ^ Osborn (1903), p. 463
  27. ^ Ostrom (1969), p. 161
  28. ^ Ostrom (1969), p. 161; Paul (1988b), p. 6
  29. ^ Osborn (1903), p. 459
  30. ^ Osborn (1917), p. 735; Paul (1988b), p. 3
  31. ^ Norman (1985), p. 39; Foster (2007), p. 178
  32. ^ Paul (1988a), p. 305
  33. ^ Paul (1988a), p. 305; Foster (2007), p. 178
  34. ^ Long and Schouten (2008), p. 73
  35. ^ Fastovsky and Weishampel (2005), p. 291
  36. ^ Osborn (1903), p. 459
  37. ^ Osborn (1903), p. 459–464
  38. ^ Osborn (1903), p. 459; Osborn (1917), p. 733
  39. ^ Osborn (1903), p. 459
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