Fossil range: Late Cretaceous
Hypothetical restoration of Deinocheirus mirificus, based on a skeletal diagram by Luis V. Rey.
| Scientific classification
Deinocheirus (DYE-no-KYE-rus, Greek: 'terrible hand') was a theropod dinosaur which lived in what is now southern Mongolia, during the Late Cretaceous Period. The only known fossil remains are a single pair of massive, 2.4 m (8 ft) forelimbs, with 25 cm (10 in) long claws and the remains of some ribs and vertebrae. Deinocheirus was named by Halszka Osmólska and Ewa Roniewicz in 1970. The type species and only named species is D. mirificus (Latin: 'unusual', 'peculiar'). Replicas of the fossilized 'arms' are currently on display at the Paleontological Museum of the University of Oslo, Norway, the American Museum of Natural History, New York, the Natural History Museum, London and the Dinosaur Museum, Blanding, Utah.
Discovery and namingEdit
The first known fossil remains are a single pair of massive forelimbs and the remains of some ribs and vertebrae. They were found on 9 July 1965 during a Polish-Mongolian expedition to the Gobi by Professor Zofia Kielan-Jaworowska at the Altan Ula III site in Ömnögovi Province. The find was reported by her in 1966. Deinocheirus was named by Halszka Osmólska and Ewa Roniewicz in 1970. The type species and only named species is Deinocheirus mirificus. The generic name is derived from Greek δεινός, deinos, "terrible", "horrible", and χείρ, cheir, "hand". The specific name is Latin for 'unusual', 'peculiar'.
The holotype specimen, ZPal MgD-I/6, was discovered on the desert surface in sandstone dating to the early Maastrichtian. It consists of a partial, disarticulated skeleton, most parts of which had already weathered away at the moment of discovery. Both forelimbs excluding the right claws, the complete shoulder girdle, centra of three dorsal vertebrae, five ribs, gastralia and two ceratobranchialia, supporting neck bones, could still be recovered. Additional fossils, including fragments of gastralia (belly ribs) belonging to the same specimen, were later found by teams re-examining the original fossil site. Some of these bones contained bite marks made by the contemporary tyrannosaurid species Tarbosaurus bataar, and showed evidence consistent with scavenging. The possibility that the carcass was scavenged by tyrannosaurs may explain why the specimen was preserved in a scattered, disassociated state. Two new specimens of Deinocheirus have been recently discovered and are awaiting publication. One specimen is larger even than the holotype, having a humerus 998 mm long. The other specimen is smaller, and the two together provide a nearly complete skeleton. The skull and foot bones were stolen by looters, but have recently been repatriated to Mongolia.
Deinocheirus is now considered by most paleontologists to be an ornithomimosaur, as the structure of its arms is similar to other dinosaurs of this group. This would make Deinocheirus by far the largest ornithomimosaur, weighing roughly 9,000 kg. Makovicky et al. pointed out that if Deinocheirus is an ornithomimosaur, it is a fairly primitive one, since it lacks some of the features typically seen in ornithomimosaurs. Kobayashi and Rinchen Barsbold added Deinocheirus to several recent cladistic analyses of theropods and were unable to resolve its exact relationships but noted some support for it as a possible ornithomimosaur.
However, over the decades, scientists have not always concurred about the placement of Deinocheirus within Dinosauria. Osmólska and Roniewicz created a new family for Deinocheirus, the Deinocheiridae. The family Deinocheiridae was initially placed in the infraorder Carnosauria, owing to the "gigantic size and thick-walled limb bones", but Osmólska and Roniewicz also speculated that it possibly "constitutes a link between Carnosauria and Coelurosauria". Within Carnosauria, the family Deinocheiridae was tentatively assigned to the superfamily Megalosauroidea, basically because it was obviously not a tyrannosauroid (tyrannosaurids having greatly reduced forelimbs).
Early work generally envisioned Deinocheirus as a carnivore that used its long forelimbs "in tearing dead or weakly agile prey asunder" (Osmólska & Roniewicz 1970: 15). Lambert supported this view, describing the clawed hands of Deinocheirus as "horrifying weapons for attacking dinosaurs of almost any size ... capable of ripping open a sauropod's soft underbelly".Gregory S. Paul disagreed, suggesting that the claws are too blunt for killing but would have been good defensive weapons. The Russian paleontologist Rozhdestvensky compared the forelimbs of Deinocheirus to sloths, leading him to hypothesize that Deinocheirus was a specialized climbing dinosaur, that fed on fruits and leaves and perhaps also eggs and any small animals found in trees. Rozhdestvensky imagined Deinocheirus with the trunk and hind limbs no longer than the fore limbs, but there is no hard evidence for this and the climbing hypothesis has not received much support from other scientists.
- ^ a b c Osmólska, H. and Roniewicz, E. (1970). "Deinocheiridae, a new family of theropod dinosaurs." Palaeontologica Polonica, 21: 5-19.
- ^ Valkenburgh, B. and Molnar, R.E. (2002). "Dinosaurian and mammalian predators compared." Paleobiology, 28(4): 527–543.
- ^ Makovicky, P.J., Kobayashi, Y., and Currie, P.J. (2004). "Ornithomimosauria." In D.B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, Second Edition. University of California Press, Berkeley.
- ^ Kobayashi, Y., and Barsbold, R. (2006). "Ornithomimids from the Nemegt Formation of Mongolia." Journal of the Paleontological Society of Korea, 22(1): 195-207.
- ^ Lambert, D. (1983). A Field Guide to Dinosaurs. New York: Avon Books.
- ^ Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon & Schuster.
- ^ Rozhdestvensky, A.K. (1970). "Giant claws of enigmatic Mesozoic reptiles." Paleontological Journal, 1970(1): 117-125.
- The December 2007 issue of National Geographic contains a brief account of the controversy concerning the classification of Deinocheirus, with illustrations.