title: Resolving the long-standing enigmas of a giant ornithomimosaur Deinocheirus mirificus.
abstract: The holotype of Deinocheirus mirificus was collected by the 1965 Polish-Mongolian Palaeontological Expedition at Altan Uul III in the southern Gobi of Mongolia. Because the holotype consists mostly of giant forelimbs (2.4 m in length) with scapulocoracoids, for almost 50 years Deinocheirus has remained one of the most mysterious dinosaurs. The mosaic of ornithomimosaur and non-ornithomimosaur characters in the holotype has made it difficult to resolve the phylogenetic status of Deinocheirus. Here we describe two new specimens of Deinocheirus that were discovered in the Nemegt Formation of Altan Uul IV in 2006 and Bugiin Tsav in 2009. The Bugiin Tsav specimen (MPC-D 100/127) includes a left forelimb clearly identifiable as Deinocheirus and is 6% longer than the holotype. The Altan Uul IV specimen (MPC-D 100/128) is approximately 74% the size of MPC-D 100/127. Cladistic analysis indicates that Deinocheirus is the largest member of the Ornithomimosauria; however, it has many unique skeletal features unknown in other ornithomimosaurs, indicating that Deinocheirus was a heavily built, non-cursorial animal with an elongate snout, a deep jaw, tall neural spines, a pygostyle, a U-shaped furcula, an expanded pelvis for strong muscle attachments, a relatively short hind limb and broad-tipped pedal unguals. Ecomorphological features in the skull, more than a thousand gastroliths, and stomach contents (fish remains) suggest that Deinocheirus was a megaomnivore that lived in mesic environments.
authors.affiliation: Geological Museum, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, South Korea.
authors.forename: Yuong-Nam
authors.initials: YN
authors.lastname: Lee
authors.affiliation: Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar 210-351, Mongolia.
authors.forename: Rinchen
authors.initials: R
authors.lastname: Barsbold
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada.
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Currie
authors.affiliation: Hokkaido University Museum, Hokkaido University, Sapporo 060-0810, Japan.
authors.forename: Yoshitsugu
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Geological Museum, Korea Institute of Geoscience and Mineral Resources, Daejeon 305-350, South Korea.
authors.forename: Hang-Jae
authors.initials: HJ
authors.lastname: Lee
authors.affiliation: Earth and History of Life, Royal Belgian Institute of Natural Sciences, Rue Vautier 29, 1000 Bruxelles, Belgium.
authors.forename: Pascal
authors.initials: P
authors.lastname: Godefroit
authors.affiliation: Eldonia, 9 Avenue des Portes Occitanes, 3800 Gannat, France.
authors.forename: François
authors.initials: F
authors.lastname: Escuillié
authors.affiliation: Paleontological Center, Mongolian Academy of Sciences, Ulaanbaatar 210-351, Mongolia.
authors.forename: Tsogtbaatar
authors.initials: T
authors.lastname: Chinzorig
mesh_terms: D000818:Animals; D049628:Body Size; D025061:Dinosaurs / Q000033:anatomy & histology* / Q000145:classification*; D005580:Fossils; D008986:Mongolia; D010802:Phylogeny; D012863:Skeleton; D012886:Skull / Q000033:anatomy & histology; D013131:Spine / Q000033:anatomy & histology