EarthScience Wire

The weird walk of a bizarre dinosaur

For half a century, Deinocheirus mirificus (meaning “horrible hand,” “unusual”) was considered one of the most mysterious dinosaurs in the world. Until now, the enigmatic creature was known only from a pair of enormous 2.4-metre-long forelimbs discovered in the fossil-rich Mongolian Nemegt Formation in 1965. The size of the limbs led some to believe the dinosaur would be some kind of gargantuan theropod, much larger than Tyrannosaurus rex, with its notoriously puny front limbs.

Phil Currie is professor and Canada Research Chair in Dinosaur Paleobiology at the University of Alberta’s Faculty of Science. He said:

We looked for years to find the quarry where the Deinocheirus came from. We had a map, but it was a hand-drawn map—so as you can imagine, it was very difficult to find.

Then, in 2009, Currie and a group of international researchers known as the Korea-Mongolia International Dinosaur Project (KID), uncovered an incomplete skeleton from exposed bones in a quarry at Bugiin Tsav. Evidence in the quarry — isolated bones, broken blocks and some money tucked under a rock as an offering to the gods — suggested that the area had been poached. Currie said:

The fossils in the quarry were in bad shape. The poachers knew what they had, but they only took certain more-saleable parts.

The damaged specimen was missing its skull, hands and feet, but included an easily recognizable hefty left forearm—making it clearly identifiable as Deinocheirus.

Though rich in prehistoric assets, Mongolia suffers from widespread poverty, making it vulnerable to fossil poaching. Poachers often take the bones with the highest value, such as skulls, or those that are easiest to transport, like the claws and teeth. The bones left behind are often mangled—sometimes smashed with crude tools like sledgehammers to get access to the desirable smaller pieces.

The market for poached fossils varies from amateur paleontologists to basement collectors, and there is money in dinosaur bones—ranging in the hundreds of thousands of dollars for popular specimens. The legality of the fossil trade is dubious, and although laws vary from country to country, it has long been illegal to remove fossils from Mongolia for the purpose of selling them.

Lacking its poached bones, the legally collected Deinocheirus skeleton was collected and shipped to Korea for preparation and study. During its preparation, a unique ridge on the femur linked it to another specimen already in the KID collection, now also identifiable as a juvenile Deinocheirus about three-quarters the size of the Bugiin Tsav specimen.

Poached fossils provide missing puzzle pieces

Better yet, word had got out about the find, and Currie was contacted about a fossil dealer in Europe who had what was clearly a Deinocheirus arm, but also feet and, even more incredibly, a skull. Currie said:

What gave us a clue that it was the poached Deinocheirus specimen that we collected was the fact that the hand was divided between the specimen in Europe and the poached specimen we collected in Mongolia.

The skull and other pieces found in Europe fit perfectly with the rest of the specimen that KID had unearthed in Mongolia, nearly completing the skeleton.

Between the two substantial skeletons, it was now possible for the first time to describe the full Deinocheirus in a paper published October 22 in Nature. Currie said:

Deinocheirus is a totally bizarre dinosaur.

At 11 meters long and with an estimated weight of 6.4 tons, Deinocheirus was a behemoth to be sure—but hardly the giant tyrannosaur its massive arms may have suggested. Rather, the apparently disproportionately large forearms were more likely used for digging and gathering plants in freshwater habitats, or for fishing. Among its other unusual attributes are tall dorsal spines, truncated hoof-like claws on the feet to prevent sinking into muddy ground, and bulky hind legs that indicate it was a slow mover. Currie said:

Although the arms have been known since 1965 and have always aroused speculation because of their enormous size and sharp, recurving claws, we were completely unprepared for how strange this dinosaur looks. It almost appears to be a chimera, with its ornithomimid-like arms, its tyrannosaurid-like legs, its Spinosaurus-like vertebral spines, its sauropod-like hips, and its hadrosaur-like duckbill and foot-hooves.

Currie notes that Deinocheirus is a descendant of ostrich-like dinosaurs that were only slightly larger than humans, so its evolution into a giant, multi-ton creature is almost certainly responsible for most of its unusual characteristics. Currie said:

Its great size probably gave it some protection from the tyrannosaurid Tarbosaurus, which appears to have been relatively common in that part of Mongolia some 70 million years ago.

To feed its great bulk, Deinocheirus was apparently an omnivore that ingested both plants and fish, as evident from fish remains found in its stomach contents.

The now near-complete Deinocheirus specimen has been returned to its home for further study in the Mongolia Centre for Paleontology. In support of preserving these assets in Mongolia.

Bottom line: Scientists have created a computer animation of Deinocheirus mirificus walking. The bizarre-looking dinosaur had unusually large forearms and features that seem cobbled together from other dinosaurs.

Read more from the University of Alberta

November 2, 2014

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