Temporal range: Late Cretaceous, 70Ma
|Gigantoraptor with Oviraptor (below)|
Xu et al., 2007
|Species:||† G. erlianensis|
Xu et al., 2007
Gigantoraptor is a genus of the giant oviraptorosaurian theropod dinosaur. It was discovered in 2005 in the Iren Dabasu Formation, Erlian basin, in Inner Mongolia. The age of the Iren Dabasu formation is controversial. Based on ostracods, Godefroit suggested the unit was Nemegt equivalent or about 70 million years old, although some dinosaur remains suggest an older Baynshirenian age c 85-90 Ma.
Discovery and naming
Since 2001, in a quarry at Saihangaobi, in Sonid Zuoqi, numerous remains of the sauropod Sonidosaurus have been uncovered. In April 2005 Chinese paleontologist Xu Xing was asked to reenact the discovery of Sonidosaurus for a Japanese documentary. Xu obliged them by digging out a thighbone. As he wiped the bone clean, he suddenly realized it was not from a sauropod, but from an unidentifiable theropod in the size class of Albertosaurus. He then stopped the filming to secure the serendipitous find. This way, the discovery of the Gigantoraptor holotype fossil was documented on film.
In 2007 the type species Gigantoraptor erlianensis was named and described by Xu, Tan Qingwei, Wang Jianmin, Zhao Xijin and Tan Lin. The generic name is derived from Latin gigas, gigantis, "giant" and raptor, "seizer". The specific name refers to the Erlian Basin.
The only known type specimen, LH V0011, was found in layers dating to the Campanian-Maastrichtian, about seventy million years old. It consists of is the incomplete and disassociated remains of a single subadult individual, a partial skeleton lacking the cranium but including the lower jaw, a single neck vertebra, most of the back and tail and the majority of the frontlimb and hindlimb elements.
It was clear to Xu et al. that Gigantoraptor belonged to the Oviraptorosauria, a group named after Oviraptor, but compared to other known members, Gigantoraptor was much larger, approximately three times as long and 35 times more massive than the heaviest earlier discovered oviraptorosaurid Citipati. Xu et al. estimated the length at 8 metres (26 ft) and the weight at 1400 kilogrammes. In 2010 Gregory S. Paul even gave an estimate of two tonnes (2.2 tons).
The toothless lower jaws of Gigantoraptor are fused into a broad shovel-like mandibula. They indicate that the unknown skull was over half a metre long and toothless also, probably equipped with a horny beak. The front tail vertebrae have very long neural spines and are heavily pneumaticised with deep pleurocoels. The middle section of the relatively short tail is somewhat stiffened by long prezygapophyses. The back tail vertebrae are lightened by spongeous bone. The front limb is rather long because of an elongated slender hand. The humerus is bowed outwards to an exceptionally large extent and has a very rounded head. The first metacarpal is very short and carries a strongly diverging thumb. The hindlimb is also long because of an elongated lower leg. The thighbone is relatively slender and short with a distinct head and neck. The foot is robust with large and strongly curved toe claws.
No direct evidence of feathers was preserved with the skeleton, but Xu et al. (2007) discussed their likely presence on Gigantoraptor. They admitted that despite Gigantoraptor being a member of the Oviraptorosauria, a group that includes the feathered species Caudipteryx and Protarchaeopteryx, it might have been "naked" because it is three hundred times more massive than these species, and very large animals may rely more on mass for temperature regulation, losing the insulating coverings found on their smaller relatives. However, they suggested that at least arm feathers were probably still present on Gigantoraptor, since their primary functions, such as display and covering the eggs while brooding, are not related to the regulation of body heat.
In 2007 Xu et al. assigned Gigantoraptor to the Oviraptoridae, in a basal position. The anatomy of Gigantoraptor includes the diagnostic features of the Oviraptorosaurs. However, it also includes several features found in more derived eumaniraptoran dinosaurs, such as a frontlimb/hindlimb ratio of 60%, a lack of expansion of the distal scapula and the lack of a fourth trochanter on the thighbone. Despite its size, Gigantoraptor would thus have been more bird-like than its smaller oviraptorosaurian relatives.
The diet of Gigantoraptor is uncertain. Although some oviraptorosaurs such as Caudipteryx and Incisivosaurus are thought to have been mostly herbivorous, Gigantoraptor had long hind legs with proportions that allowed for fast movement (it was probably more nimble than the larger and less agile Tarbosaurus), and large claws, a combination that is not usually found in herbivores of this size. Paul suggested that Gigantoraptor also was a herbivore and used its speed to escape predators.
The specimen has advanced ossification and growth rings in the fibula that indicate it was likely eleven years of age when it died. It appears to have reached an early young adult stage at age seven, and probably would have grown much larger when it reached the adult stage. This indicates a growth rate that is faster than in most large non-avian theropods.
The existence of giant oviraptorosaurians as Gigantoraptor explains several earlier Asian finds of very large, up to 53 centimetres long, oviraptorosaurian eggs, assigned to the oospecies Macroelongatoolithus xixiaensis. These were laid in enormous rings with a diameter of three metres.
- Xu, X.; Tan, Q.; Wang, J.; Zhao, X.; Tan, L. (2007). "A gigantic bird-like dinosaur from the Late Cretaceous of China". Nature 447 (7146): 844–847. doi:10.1038/nature05849. PMID 17565365.
- "Remains of giant bird-like dinosaur unveiled". CBC News. Last updated 13 June 2007. Retrieved 29 October 2011.
- Paul, G.S., 2010, The Princeton Field Guide to Dinosaurs, Princeton University Press p. 153
- Nicholas R. Longrich, Philip J. Currie, Dong Zhi-Ming (2010). "A new oviraptorid (Dinosauria: Theropoda) from the Upper Cretaceous of Bayan Mandahu, Inner Mongolia". Palaeontology 53 (5): 945–960. doi:10.1111/j.1475-4983.2010.00968.x.
|Wikispecies has information related to: Gigantoraptor|
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- Fleshed-out restoration of a Gigantoraptor erlianensis. Credit: Julius T. Csotonyi
- Yahoo! News: China finds new species of big, bird-like dinosaur
- Description: Factsheet with picture English/German at Dinosaurier-Web