Gigantoraptor was a massive 25-30 foot long oviraptorosaurian theropod dinosaur which lived in eastern Asia (and possibly in North America) during the middle of the Cretaceous Period. The fossils of this enormous bird-like dinosaur, consisting of a partial skeleton, were discovered in the Erlian Basin of “Inner Mongolia” in northern China. This region is home to the Iren Dabasu Formation, dated to the Cenomanian Stage of the late Cretaceous Period, around 95 million years ago. In 2007, the creature was officially named Gigantoraptor erlianensis, “the gigantic robber from the Erlian Basin” (Xu et al 2007, pages 844-847).
95 million years ago, that part of northern China was dominated by a braided river floodplain, and the climate was warm and humid (Van Itterbeeck et al 2005, pages 699-725). Gigantoraptor shared its environment with the 30 foot long titanosaur sauropod Sonidosaurus, the 15 foot long tyrannosaur Alectrosaurus, the large dromaeosaur Achillobator (which might have grown to be the same size as Utahraptor), the ornithomimids Garudimimus and Archaeornithomimus, several species of therizinosaurs, the primitive hadrosaurs Bactrosaurus and Gilmoreosaurus, and the armored ankylosaur Talarurus.
Gigantoraptor is known from a single partial skeleton (collection ID code: LH V0011) composed of a lower jaw, both arms, the right scapula, fragments of a few ribs, some back vertebrae, part of the pelvis, both legs, and most of the tail. Because an upper jaw wasn’t found, we don’t know if Gigantoraptor had a crest or not. Xu and his colleagues estimated that this individual measured 8 meters long (26 feet) and weighed 1,400 kg, making it almost four times larger than the largest oviraptorosaur known during that time. However, an analysis of the bones revealed that this animal was not yet fully grown. Despite the fact that it was already a hefty beast, all indications said that it could grow even larger! The authors also proposed that, due to the animal’s large size, it might have only been partially feathered as a way to prevent over-heating. As to how much or how little feathering Gigantoraptor had, that’s currently unknown (Xu et al 2007, pages 844, 846).
Xu and his colleagues stated in their 2007 paper that Gigantoraptor was a basal member of the family Oviraptoridae (Xu et al 2007, page 846). Then in 2010, it was re-classified as belonging to the oviraptorosaurian family Caenagnathidae, which includes animals like Caenagnathus, Chirostenotes, Conchoraptor, Microvenator, and Anzu (Longrich et al 2010, page 953). This was confirmed in 2014, which determined that Gigantoraptor was not only a caenagnathid, but was also a basal member of this clade (Lamanna et al 2014: e0125843).
In 2015, it was reported that a fragmentary lower jaw (collection ID code: MPC-D 107/17) which was very similar to the one borne by Gigantoraptor had been discovered in 2008 within the Bayan Shireh Formation of Mongolia. The Bayan Shireh Formation spans 102-86 MYA, making it concurrent with northern China’s Iren Dabasu Formation, and some species of prehistoric animals are found in both formations. However, the authors of the 2015 report cautiously identified this jaw as “Caenagnathidae indet.”, meaning “indeterminate caenagnathid” (Tsuihiji et al 2015, pages 60-65). In 2019, it was re-classified as “cf. Gigantoraptor erlianensis“, meaning “similar in shape to Gigantoraptor erlianensis“. Based upon the size of this jaw, and comparing it to the one which is known from Gigantoraptor, it’s estimated that the individual which this jaw belonged to measured 8.9 meters long (29 feet) and weighed 2.7 tons (Molina-Perez and Larramendi 2019, page 54).
Gigantoraptor. © Jason R. Abdale (June 21, 2023).
In addition to fossil bones, there are numerous specimens of fossilized eggs or eggshell fragments from China (Zelenitsky et al 2000, pages 130-131) and South Korea (Huh 2014, page 151) which have been attributed to Gigantoraptor, or possibly to another large oviraptorosaurian. These eggs were given the name Macroelongatoolithus, which literally translates to “huge elongated egg-stone”. As the name suggests, these eggs were very large, measuring almost two feet long, and clearly belonged to a large animal.
Not only have such eggs been found in eastern Asia, but they have also been discovered, amazingly, in North America. During the 1960s, similar eggshell fragments were discovered eight kilometers southeast of the town of Castle Dale, Utah within the rock layers of the Cedar Mountain Formation. A report made in 1970 gave short descriptions of their appearance. In 1975, it was observed that these fragments looked similar to eggshell fragments that had been found in Cretaceous strata within China. More eggshell fragments were found in 1998 within the uppermost strata of the Mussentuchit Member (the uppermost member) of Utah’s Cedar Mountain Formation, dated to approximately 95 MYA, as well as the lowermost layer of the overlying Dakota Formation / Naturita Formation. It was observed that the eggshell fragments occurred in concentrations measuring one square meter, and likely indicated the site of a prehistoric nest. Examination of these fragments, and comparing them to other fossilized eggshells found elsewhere, showed that these Utah eggshell fragments were strikingly similar to Macroelongatoolithus (Zelenitsky et al 2000, pages 130-138). It wasn’t until 2007 that the partial skeleton of Gigantoraptor was made known to the scientific community. The presence of this creature certainly explained the unusually large oviraptorosaurian eggs within eastern Asia, but it also generated controversy concerning the eggshell fragments that had been found in Utah. If these eggshells really did belong to a gigantic oviraptorosaurian, and if such eggs were found in both Asia and North America, then surely that must mean that an animal like Gigantoraptor also lived within North America during that same time!
This prospect remained purely theoretical until 2012. In that year, an expedition conducted jointly by the Field Museum of Natural History and the North Carolina Museum of Natural Sciences to uncover fossils within the Mussentuchit Member of Utah uncovered a partial skeleton which might belong to Gigantoraptor or to a closely-related species. A conference abstract which was presented at a meeting of the Society of Vertebrate Paleontology in Berlin, Germany in 2014 stated the following…
“A partial skeleton of a giant oviraptorosaurian discovered in 2012 is second only to the Chinese oviratorosaur (sic) Gigantoraptor in size. Almost all recovered elements exhibit synapomorphies of Oviraptorosauria. For example, a midcaudal vertebra is highly pneumatic, and a series of four distal caudals form a pygostyle-like structure. Previous evidence of oviraptorosaurs in the CMF was restricted to eggshells referred to the ootaxon Macroelongatoolithus carlylensis. A concentration of Macroelongatoolithus eggshell in situ was discovered 150 meters away from, and at the same stratigraphic level as, the skeleton. This close occurrence, combined with size and character considerations, renders it likely that the new oviraptorosaur taxon is the parent of Macroelongatoolithus carlylensis” (Makovicky et al 2014, page 175).
Regrettably, no further information about this fascinating discovery has been published since then. However, more specimens of the egg form Macroelongatoolithus have been uncovered elsewhere in North America, including in Idaho, Montana, Wyoming, and Nevada (Bonde et al 2008, pages 255, 260; Simon 2014, pages 1-110). This suggests that a large oviraptorosaurian which either may or may not be Gigantoraptor was fairly widespread within the center of North America around 95 million years ago. Just when you thought North American paleontology couldn’t come up with any more spectacular discoveries, these tantalizing hints indicate that there is indeed something remarkable buried underneath the rocks of the American West. Get out there and start digging!
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Bibliography
Bonde, Joshua W.; Varricchio, David J.; Jackson, Frankie J.; Loope, David B.; Shirk, Aubrey M. (2008). “Dinosaurs and dunes! Sedimentology and paleontology of the Mesozoic in the Valley of Fire State Park”. The Geological Society of America Field Guide 11: Field Guide to Plutons, Volcanoes, Faults, Reefs, Dinosaurs, and Possible Glaciation in Selected Areas of Arizona, California, and Nevada (2008). Pages 249-262.
https://www.researchgate.net/publication/275524211_Dinosaurs_and_dunes_Sedimentology_and_paleontology_of_the_Mesozoic_in_the_Valley_of_Fire_State_Park.
Huh, Min (2014). “First Record of a Complete Giant Theropod Egg Clutch from Upper Cretaceous Deposits, South Korea”. Journal of Vertebrate Paleontology, Program and Abstracts (November 2014). Page 151.
https://vertpaleo.org/wp-content/uploads/2021/04/SVP-2014-Program-and-Abstract-Book-10-14-2014.pdf.
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https://vertpaleo.org/wp-content/uploads/2021/04/SVP-2014-Program-and-Abstract-Book-10-14-2014.pdf.
Molina-Perez, Rueben; Larramendi, Asier. Dinosaur Facts and Figures: The Theropods and other Dinosauriformes. Translated by David Connolly and Gonzalo Angel Ramirez Cruz. Princeton: Princeton University Press, 2019.
https://books.google.com/books?id=5m-KDwAAQBAJ&pg=PA54#v=onepage&q&f=false.
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Zelenitsky, Darla Karen; Carpenter, Kenneth; Currie, Philip J. (2000). “The first record of elongatoolithid theropod eggshell from North America: The Asian oogenus Macroelongatoolithus from the Lower Cretaceous of Utah”. Journal of Vertebrate Paleontology, volume 20, issue 1 (March 2000). Pages 130-138.
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