Gigantoraptor

***Gigantoraptor*** is a genus of giant oviraptorosaur theropod dinosaur that lived 70 million years ago in the later Cretaceous. It was discovered in 2005 in Inner Mongolia.

## Discovery and naming

Since 2001, in a quarry, remains of the sauropod _Sonidosaurus_ had 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 about the size of _Albertosaurus_. He stopped the filming to secure the serendipitous find. This way, the discovery of the _Gigantoraptor_ fossil was captured on videotape.

In 2007 the _Gigantoraptor erlianensis_ was named and described by Xu and colleagues. The type specimen was found in strata dating to about 70 million years ago. It is the remains of a single subadult individual.The partial skeleton lacks the skull but includes the lower jaws, a single neck vertebra, most of the back, tail and leg elements.

## Description

_Gigantoraptor_ belonged to the Oviraptorosauria, a group named after _Oviraptor_. Compared to other known members, _Gigantoraptor_ was much larger, about three times as long and 35 times more massive than the earlier discovered oviraptorosaurid _Citipati_. Xu _et al._ estimated the length at  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. The skull would have been over half a metre long and toothless, probably with a horny beak. 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. It might have been "naked" because it is three hundred times more massive than the smaller feathered species. Very large animals rely more on mass for temperature regulation, losing the insulating coverings found on their smaller relatives. Arm feathers were probably still present on _Gigantoraptor_, since their main functions, such as display and covering the eggs while brooding, are not related to the regulation of body heat.

## Phylogeny

In 2007 Xu _et al._ put _Gigantoraptor_ into the Oviraptoridae family. But in 2010 a second analysis of _Gigantoraptor_ found it was in the  sister group, the Caenagnathidae. This was later confirmed by other studies.

## Paleobiology

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, 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. These fossil eggs were laid in enormous rings with a diameter of three metres.

## Other websites

- _news@nature.com_: "Giant bird-like dinosaur found".
- Wired Science Scientists Discover 3,000-Pound Gigantoraptor Dinosaur in Mongolia
- Fleshed-out restoration of a _Gigantoraptor erlianensis_.  Credit: Julius T. Csotonyi