Gigantoraptor

Credit: Mario Lanzas.

*Gigantoraptor* is an extinct genus of caenagnathid oviraptorosaur that lived in Mongolia and possibly Utah during the Late Cretaceous.

## Description

*Gigantoraptor* is a massive oviraptorosaur that lived in Mongolia during the Late Cretaceous, probably having a close relative of equal size surviving into the Latest Cretaceous, North America. Being over 20 feet tall and 30 feet long, it could have weighed over 2-3 tons, being the largest maniraptor. Its claws and very powerful beaked jaw were designed for chopping through tough vegetation, defense, and killing medium-small-sized prey.

## Paleobiology

### Skull

The total length of the mandible is 46 centimeters (460 millimeters), fusing into a broad shovel-like shape, indicating the skull was over half a meter long and toothless, likely having a rhamphotheca. Compared to the right, the left side of the jaws is well-preserved and near-intact. The dentary bones are deep and toothless, having a pair of sharp, relatively flat shelves on the top edges. The anterior dentary is roundedrounds, being more similar to caenagnathids than oviraptorids. From a top, the symphyseal region in the dentary is U-shaped. Along the lateral surfaces of the dentary, nutrient foramina can be found, which probably supported a rhamphotheca.

Both the angular and the articular-surangular-coronoid (ASC) complex are smaller than the dentary. The angular is fused firmly to the ASC complex, giving form to the lower margin in the external mandibular fenestra. The angular is bowed in shape, being mainly forwards-extended with a large, lateral depression that joints the posterior lower process of the dentary. The ASC complex composes of the fused articular and surangular and coronoid process. The ASC extends forwards, articulating with the posterior upper process of the dentary, giving form to the upper margin of the mandibular fenestra. The coronoid prominence is low, being distinctively rounded. On the posterior end of the mandible finds the articular glenoid, who is relatively large, convex, and bowl-shaped.

The anterior caudals have long neural spines, being heavily pneumaticised and having deep pleurocoels. The middle of the (relatively short) tail is stiffened by long prezygapophyses, but not by much. The caudal vertebrae are very pneumatized, having a spongeous-like filling. The forelimbs are long, due to an elongated humerus (73.5 centimeters long) and a slender manus. The humerus bows outwards to a very large extent, having a very rounded head. The first metacarpal is short, adorned with a strongly-diverging thumb. The hindlimbs are well-developed and highly elongate. Of the latter, the femur is slender and has a distinct head and neck, which is 1.10 meters (110 centimeters) long. The tibia has a similar top and bottom border, measuring 1.10 meters (110 centimeters) long. The metatarsus is 58.3 centimeters (583 millimeters) long with metatarsal III as the largest. The pes is robust, with large, strongly-curved pedal unguals.

## Paleoecology

*Gigantoraptor* is known from the Iren Dabasu Formation, Inner Mongolia. dated to 95.8 ± 6.2 million years ago based on U–Pb and stratigraphic analyses. The paleoenvironments that comprise this formation were very humid, being a braided river valley covered in floodplains. A semi-arid climate isindicated by caliche-based sedimentation. It had extensive vegetation, suggested by the paleosol development and many herbivorous dinosaur material found in river channel and floodplain sediment. Diversity of charophytes and ostracods in the floodplain systems are reported.

Dinosaurs include *Alectrosaurus*, *Archaeornithomimus*, *Erliansaurus*, *Neimongosaurus*, *Sonidosaurus*, *Bactrosaurus* and *Gilmoreosaurus*. The Iren Dabasu and Bayan Shireh formations have been correlated based on their similar vertebrate fossils. This may further be supported by a giant, Gigantoraptor-sized caenagnathid in the Bayan Shireh fauna. However, since it is highly fragmentary, its referral to Gigantoraptor remains unknown. The presence of both (supposedly) separate taxa in fluvial-based sedimentation suggest giant oviraptorosaurs preferred mesic habitats rather than xeric habitats. Eggs identified as *Macroelongatoolithus* from the Mussentuchit Member of the Cedar Mountain Formation, Utah are reported. These eggs are traditionally identified as coming from *Gigantoraptor*, so this may indicate *Gigantoraptor* or a *Gigantoraptor*-like taxon in North America. This is hypothesized as a Asian-North American faunal swap

## References

* https://en.wikipedia.org/wiki/Gigantoraptor
* https://www.youtube.com/watch?v=Thhb6Jy-Acw&t=801s&ab\_channel=TateGeologicalMuseum