Deinocheirus

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Deinocheirus
Temporal range: Late Cretaceous, 70Ma
Deinocheirusbcn.JPG
Holotype fossil of Deinocheirus
Scientific classification e
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Suborder: Theropoda
Clade: Ornithomimosauria
Family: Deinocheiridae
Osmólska & Roniewicz, 1970
Genus: Deinocheirus
Osmólska & Roniewicz, 1970
Species: † D. mirificus
Binomial name
Deinocheirus mirificus
Osmólska & Roniewicz, 1970

Deinocheirus (/ˌdnɵˈkaɪərəs/ DY-no-KY-rəs; Greek: 'terrible hand') is a genus of large theropod dinosaur, possibly an ornithomimosaurian, which lived in what is now southern Mongolia, during the late Cretaceous Period (Nemegt Formation, dating to around 70 million years ago).

Discovery and naming[edit]

Holotype on display

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. Kielan-Jaworowska published the find in 1966.[1]

Deinocheirus was named by Halszka Osmólska and Ewa Roniewicz in 1970.[2] The type species and only named species is Deinocheirus mirificus. The generic name is derived from Greek deinos (δεινός), meaning "horrible", and cheir (χείρ), meaning "hand". The specific name, mirificus, comes from Latin, meaning "unusual" or "peculiar," and was chosen for the "unusual structure of the forelimbs."[2]

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.[2]

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.[3]

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 (39.3 in) long.[citation needed] The other specimen is smaller, and the two together provide a nearly complete skeleton.[4] The skull and foot bones were stolen by looters, but have recently been repatriated to Mongolia.[5]

Description[edit]

The most well-preserved parts of Deinocheirus are its forelimbs, which measured 2.4 m (8 ft) long — a 938 mm humerus, 688 mm ulna and 770 mm hand — including up to 19.6 cm (8 in) long recurved claws. Each scapulocoracoid of the shoulder girdle has a length of 153 centimetres. The neck must also have been massive with each half of the paired ceratobranchialia measuring 42 centimetres.[2]

The gigantic size of these skeletal elements has generated much speculation about the magnitude of the animal as a whole. Osmólska and Roniewicz thought it could be best compared with the Ornithomimosauria, as the structure of its arms is similar to the members of this group.[2] Should Deinocheirus itself be a member, this would make it by far the largest ornithomimosaur, indeed, one of the largest theropods. The describers estimated its size to be equal to the largest specimens of Tyrannosaurus.[2] Its weight was in 1988 estimated by Gregory S. Paul to have been between six and twelve tonnes.[6] Later estimates confirmed a number of roughly 9,000 kg (20,000 lb).[7] In 2010 Paul revised this to a length of ten metres and a weight of two tonnes.[8]

Restoration showing humped back

In 2010, Phil Senter and H.J. Robins attempted to estimate the total height at the hip of Deinocheirus. By studying more completely known theropods, they found that the length of the scapula (shoulder blade), better than that of the humerus (upper arm bone), could be used to accurately predict hip height. Using the equation found over a range of theropods, Senter and Robins determined that Deinocheirus likely measured 3.3 m (11 ft) to 3.6 m (12 ft) tall at the hip. This would place it as possibly the tallest known theropod, taller than any contemporary predators such as Tarbosaurus.[9]

Though the arms of Deinocheirus have a considerable absolute size, being the longest of any known theropod with the exception of Therizinosaurus, they are not very long relative to the shoulder girdle, the ratio being less than that with most ornithomimosaurs. The shoulder-blade is long and narrow. The humerus is relatively slender. The ulna and radius too are elongated and not very firmly connected to each other in a syndesmosis. The metacarpus is long compared to the fingers. The hand had a good mobility relative to the lower arm but was only capable of a limited flexing motion, unable to close in grasping. The fingers are about equal in length to each other, the first being the stoutest and the second the longest. Only the claw of the left second finger has been preserved in its entirety; it has a diameter of 196 millimetres and a length along its outer curvature of 323 millimetres.[2]

New undescribed specimens show that the animal had a hump on its back and a skull that superficially resembled a cross between an ornithomimosaur and a hadrosaur.[4][10]

Classification[edit]

Deinocheirus is now considered by most paleontologists to be an ornithomimosaur; however, over the decades, scientists have not always agreed about the placement of Deinocheirus within Dinosauria. While Kielan-Jaworowska had initially assigned the find to the Megalosauridae, 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, "faute de mieux", assigned to the superfamily Megalosauroidea, basically because it was obviously not a tyrannosauroid, which have greatly reduced forelimbs endowed with only two extremely small fingers.[2]

Peter 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.[11] Basal traits include the recurved claws, the low humerus/scapula ratio, the lack of syndesmosis, a short posterior process of the coracoid and the combined length of the second and third phalanx of the third finger being greater than the length of the third phalanx. Yoshitsugu 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. Derived traits include the short hand, a flat metacarpus and a relative elongation of the claws.[12]

Paleobiology[edit]

Diet[edit]

Cast of the holotype in Museum of Natural History, London

Early work generally envisioned Deinocheirus as a carnivore that used its long forelimbs "in tearing dead or weakly agile prey asunder".[2]:15 David 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".[13] G.S. Paul disagreed, suggesting that the claws are too blunt for killing but would have been good defensive weapons.[6] 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 hindlimbs no longer than the forelimbs,[14] but there is no hard evidence for this and the climbing hypothesis has not received much support from other scientists.

Paul in 1988 suggested a herbivorous lifestyle for Deinocheirus. It shared its habitat with several other giant, nine to thirteen meter long, herbivores uncovered in the Nemegt Formation, like the small titanosaur sauropod Opisthocoelicaudia, the hadrosaurs Saurolophus and Barsboldia, and the bizarre even longer-clawed Therizinosaurus. Trying to determine the respective niches for these animals Senter & Robins concluded that Deinocheirus due to its hip height had the largest vertical feeding range of them all, specialising in eating high foliage.[9] Paul in 1988 had proposed it would have used its long neck to reach into trees and rip leaves, the arms assisting in pulling down branches.[6] The rock facies of the Nemegt formation suggest the presence of stream and river channels, mudflats, and shallow lakes. Sediments also indicate that there existed a rich habitat, offering diverse food in abundant amounts that could sustain massive Cretaceous dinosaurs.[15]

Paleopathology[edit]

ZPAL Mgd-I/6, the holotype of Deinocheirus mirificus, has abnormal pits, grooves and tubercles on the first and second phalanx of the left second finger that may be the result of injuries to the joint between the two bones.[2][16]

In 2012, Phil R. Bell, Philip J. Currie, and Yuong-Nam Lee identified marks of predation of a specimen from Deinocheirus. Bite marks from Tarbosaurus were found on the Gastralium (lower ribs) of Deinocheirus. The size and shape of the marks made by teeth match Tarbosaurus more than any other tyrannosaur from the region, so it is assumed that it was what bit the Deinocheirus. Five types of marks were analyzed, punctures, gouges, striae, fragmentary teeth, and combinations of the above marks. As only 2% of all theropod feeding trances are bite marks, and as the marks are found on a rare species, the identification of the pathologies are very important.[3]

References[edit]

  1. ^ Kielan-Jaworowska, Zofia (1966). "Third (1965) Polish-Mongolian Palaeontological Expedition to the Gobi Desert and western Mongolia". Bulletin de l'Académie Polonaise des Sciences, C1. II 14 (4): 249–252. 
  2. ^ a b c d e f g h i j Osmólska, Halszka; Roniewicz, Ewa (1970). "Deinocheiridae, a new family of theropod dinosaurs". Palaeontologia Polonica (21): 5–19. 
  3. ^ a b Bell, P. R.; Currie, Philip J.; Lee, Yuong-Nam (2012). "Tyrannosaur feeding traces on Deinocheirus (Theropoda: ?Ornithomimosauria) remains from the Nemegt Formation (Late Cretaceous), Mongolia". Cretaceous Research 37 (2012): 186–190. doi:10.1016/j.cretres.2012.03.018. 
  4. ^ a b Switek, B. (2013). "Mystery Dinosaur Finally Gets a Body", NationalGeographic.com.
  5. ^ "The "horrible hand" Deinocheirus dinosaur's fossils are repatriated to its home country", InfoMongolia.com.
  6. ^ a b c Paul, G.S. (1988). Predatory Dinosaurs of the World. New York: Simon & Schuster.
  7. ^ Valkenburgh, B. and Molnar, R.E. (2002). "Dinosaurian and mammalian predators compared." Paleobiology, 28(4): 527–543.
  8. ^ Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 112
  9. ^ a b Senter, P. and Robins, H.J. (2010). "Hip heights of the gigantic theropod dinosaurs Deinocheirus mirificus and Therizinosaurus cheloniformis, and implications for museum mounting and paleoecology." Bulletin of the Gunma Museum of Natural History, 14: 1-10. [1]
  10. ^ http://www.newscientist.com/article/dn25551-stolen-dinosaur-head-reveals-weird-hybrid-species.html#.U3EwQHbG65K
  11. ^ Makovicky, Peter J.; Kobayashi, Yoshitsugu; Currie, Philip J. (2004). "Ornithomimosauria". In Weishampel, David B.; Dodson, Peter; Osmólska, Halszka. The Dinosauria (2nd ed.) (University of California Press). pp. 137–150. ISBN 978-0520242098. 
  12. ^ Kobayashi, Y., and Barsbold, R. (2006). "Ornithomimids from the Nemegt Formation of Mongolia." Journal of the Paleontological Society of Korea, 22(1): 195-207.
  13. ^ Lambert, D. (1983). A Field Guide to Dinosaurs. New York: Avon Books.
  14. ^ Rozhdestvensky, A.K. (1970). "Giant claws of enigmatic Mesozoic reptiles." Paleontological Journal, 1970(1): 117-125.
  15. ^ Novacek, M. (1996). Dinosaurs of the Flaming Cliffs. Bantam Doubleday Dell Publishing Group Inc. New York, New York. ISBN 978-0-385-47775-8
  16. ^ Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 337-363.