Long-Standing Deinocheirus Enigma Solved

A reconstruction of the dinosaur Deinocheirus mirificus. (Photograph: Yuong-Nam Lee/KIGAM)
22/10/2014
Long-Standing Deinocheirus Enigma Solved
post by
Reinout Verbeke

Paleontologists have exhaustively described one of the most mysterious dinosaurs after tracing stolen fossils. The dinosaur, Deinocheirus mirificus, appears defy previous presumptions: he had huge grasping arms and claws, but was a non-dangerous omnivore. The research, to which Belgian paleontologist Pascal Godefroit (RBINS) contributed, has been published in Nature this week.

On July 9 1965, Zofia Kielan-Jaworowska, a member of the Polish-Mongolian Paleontological Expedition, discovered very strange fossils in the latest Cretaceous (about 70 ma) Nemegt Formation at Altan Uul III, a remote area from the Gobi Desert in Mongolia: a pair of gigantic (2.4 m!) forelimbs, armed with impressive claws, belonging to a mysterious theropod dinosaur. For nearly 50 years, this dinosaur, named Deinocheirus mirificus ("unusual terrible hands"), remained one of the most stubborn enigmas in paleontology. Nothing except its huge arms and a handful of other bone fragments had been found.  Two new specimens of Deinocheirus were finally discovered in the Nemegt Formation of the Gobi Desert, respectively in 2006 and 2009, by members of the Korea-Mongolia International Dinosaur Expedition (KID). But the excavation team got a shock when they noticed that the skull and other parts of the skeleton of both specimens were missing, apparently poached by dino-hunters who roam the Gobi desert.

By chance, the skull and feet of the largest specimen were discovered in a private collection by Pascal Godefroit, a palaeontologist at the Royal Belgian Institute of Natural Sciences (RBINS). After negotiation with the owner of the specimens and Oyungerel Tsedevdamba, Minister of Culture, Sport and Tourism of Mongolia, the poached fossils were finally returned to Mongolia on the 1st of May, 2014. After nearly 50 years, palaeontologists are finally able to reconstruct the whole skeleton of Deinocheirus, to resolve its phylogenetic status and to infer its ecology in a paper published on the 22nd of October in the prestigious scientific journal Nature.

Slow mover

With a body length of 11m and an estimated body weight of 6.4 tons, Deinocheirus is by far the largest known dinosaur to belong to the ornithomimosaurs (‘ostrich-like’), a group of omnivorous or herbivorous theropod dinosaurs that flourished during the Cretaceous. Although ornithomimosaurs were usually small to medium-sized fast-running dinosaurs, Deinocheirus was a slow mover, as is indicated by its massive hind limbs and feet and its hip adapted to support a heavy body.

More than 1,100 gastroliths were found inside its belly, together with fish remains, showing that Deinocheirus actively visited the meandering river systems of the Nemegt Formation. The blunt tips of its pedal claws would have prevented its feet from sinking down into wet substrates. Teeth are absent and the adductor chambers for the masticatory musculature are strikingly small compared with its huge lower jaw; it is therefore clear that Deinocheirus was not capable of powerful mastication. It is hypothesized that it may have fed on relatively soft understory vegetation, or possibly herbaceous water plants. The duck-like bill of Deinocheirus may be ecologically tied to water-based food as in water-fowl. Its long forearms with giant claws may have been used for digging and gathering herbaceous plants.

Bony sail

The long neural spines of the dorsal and sacral vertebrae created a sloping, bony sail in the middle of the dinosaur's back. No other ornithomimosaur has been found with such a structure, but other unrelated dinosaurs — such as the semi-aquatic Spinosaurus and the iguanodontids Ouranosaurus have been found with similar sails. Some paleontologists hypothesize that these structures supported fleshy sails that may have helped dinosaurs regulate their body temperature, while others suppose that the vertebrae supported a structure resembling a camel's or bison's thick hump.

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