Thursday, October 23, 2014

[Paleontology • 2014] Resolving the Long-standing Enigmas of A Giant Ornithomimosaur Deinocheirus mirificus

 Deinocheirus mirificus
reconstruction: Michael Skrepnick

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.

Altangerel Perle, a Mongolian paleontologist, with the arms of Deinocheirus in Ulaanbaatar State Museum
 Photographer: Louie Psihoyos

Deinocheirus mirificus
from the Greek for “terrible hand, which is unusual”.

Figure 1: Deinocheirus mirificus.
a, MPC-D 100/127. b, MPC-D 100/128. c, Composite reconstruction of MPC-D 100/127 with a simple proportional enlargement of MPC-D 100/128. Scale bar, 1 m. The human outline is 1.7 m tall.
The holotype and the two new specimens provide almost all skeletal information of Deinocheirus.

Figure 2: Skull of Deinocheirus mirificus (MPC-D 100/127).

Figure 3: Postcranial skeletons of Deinocheirus mirificus (MPC-D 100/127, MPC-D 100/128).

Figure 4: Phylogenetic relationships of Deinocheirus mirificus within Ornithomimosauria.
a, Hypothetical fleshed-out reconstruction of Deinocheirus mirificus (by Michael Skrepnick). b, Time-scaled strict consensus tree of the six most-parsimonious trees from our analysis (tree length = 2,927, consistency index = 0.22, retention index = 0.59; Supplementary Information). In this hypothesis Deinocheirus is a derived taxon of the Deinocheiridae, which is the sister-group of the Ornithomimidae.

a, Photo to show in situ gastralia, gastroliths, and stomach contents. Blue and green arrows represent gastralia and gastroliths. Red rectangle is an area of scattered fish remains and gastroliths. Red circle is an area where broken fish bones are aggregated. b, Enlarged photo of scattered fish remains (vertebrae, scales) with gastroliths in a.

Yuong-Nam Lee, Rinchen Barsbold, Philip J. Currie, Yoshitsugu Kobayashi, Hang-Jae Lee, Pascal Godefroit, François Escuillié and Tsogtbaatar Chinzorig. 2014. Resolving the Long-standing Enigmas of A Giant Ornithomimosaur Deinocheirus mirificus.

Deinocheirus Exposed: Meet The Body Behind the Terrible Hand via @ngphenomena
Bizarre dinosaur reconstructed after 50 years of wild speculation