SVP Dispatches: The Body of Deinocheirus

It's been a rumor online for years. Hang around the Dinosaur Mailing List or a paleontology forum for long enough, and you'd hear it. Rumors that an old mystery might soon be solved. Rumors that expeditions to the remote Gobi have found a body. Rumors that one of the most enduring riddles of dinosaur paleontology might soon be made clear.

I'm speaking, of course, of Dienocheirus. To a dinosaur enthusiast of a certain age, that name crystallizes the mystery and frustrations of paleontology. "The Terrible Hand" was terrible for its size, terrible for its claws, and terrible because--beyond its long arms and fingers--nothing else remained. 

Copyright Luis Rey

Researchers suspected it to be an ornithomimid, albeit an uncommonly massive one. There were certain diagnostic signs to the hands, the shape of the claws, the structure of the arms, all of which pointed to a kinship with those legendarily fleet-footed animals. But what shape was Dienocheirus? Was it a massive, lumbering browser? A giant, elegant runner? Perhaps even a predator? In the absence of a body, there was no way to be sure. 

Now it seems that the wait is over. According to an abstract recently released at The Society of Vertebrate Paleontology, Dienocheirus was indeed a type of ornithomimid, one displaying skeletal traits previously unknown in that family. The abstract notes that two new specimens were discovered, with material comprising the majority of the postcranial skeleton. Gastroliths were recovered as well, which would imply a herbivorous diet. 

So what did Deinocheirus look like? Apparently it had a heavily built pelvis and hind limbs, adaptations suggesting a slower moving life style than the one practiced by its smaller cousins. Unlike the similarly robust therizinosaurs, though, Deinocheirus was narrow bodied, with tall, straight ribs. By far the most interesting bit of anatomy, however, is the fact that Deinocheirus apparently had long neural spines in the vicinity of its pelvis. The living animal was thus graced with either a sail or a hump, a trait that comes as a complete surprise. 

Copyright http://stygimolochspinifer.deviantart.com

There are still several mysteries about Deinocheirus, and these two skeletons only give rise to new questions--especially ones concerning its somewhat odd anatomy. But rejoice, nonetheless. Deinocheirus has a body, and it's weirder than anybody could have dreamed.  

The complete text of the abstract is below. 

NEW SPECIMENS OF DEINOCHEIRUS MIRIFICUS FROM THE LATE CRETACEOUS OF MONGOLIA

LEE, Yuong-Nam, Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea, Republic of (South); BARSBOLD, Rinchen, Paleontological Center, Ulaanbaatar, Mongolia; CURRIE, Philip, University of Alberta, Edmonton, AB, Canada; KOBAYASHI, Yoshitsugu, Hokkaido University Museum, Sapporo, Japan; LEE, Hang- Jae, Korea Institute of Geoscience and Mineral Resources, Daejeon, Korea, Republic of (South)

The holotype of Deinocheirus mirificus was collected by the Polish-Mongolian Palaeontological Expedition at Altan Uul III in 1965. Because the holotype was known mainly on the basis of giant forelimbs with scapulocoracoids, Deinocheirus has remained one of the most mysterious dinosaurs. Two new specimens of Deinocheirus were discovered in the Nemegt Formation of Altan Uul IV in 2006 and Bugin Tsav in 2009 by members of the Korea-Mongolia International Dinosaur Expedition (KID). Except for the skull, middle dorsal and most of the distal caudal vertebrae, the right forelimb, left manus, and both pedes, the remaining parts of the skeleton (Mongolian Paleontological Center [MPC]-D 100/127) including a left forelimb clearly identifiable as Deinocheirus were collected. The humerus (993 mm in length) is longer than the 938 mm humerus of the holotype. The Altan Uul IV specimen (MPC-D 100/128) is a subadult Deinocheirus (approximately 72% of MPC-D 100/127), which consists of post-cervical vertebrae, ilia, ischia, and hind limbs. Both specimens provide important paleontological evidence for exact postcranial reconstruction of Deinocheirus mirificus. Cladistic analysis indicates that Deinocheirus is a basal member of Ornithomimosauria, but many new unique skeletal features appear to be quite different from other ornithomimosaurs. These include extreme pneumaticity of tall, anterodorsally oriented distal dorsal neural spines (7~8 times taller than centrum height) with basal webbing, fused sacral neural spines forming a midline plate of bone that extends dorsally up to 170% of the height of the ilium, ventrally keeled sacral centra, a well-developed iliotibialis flange, a posterodorsally projecting posterior iliac blade with a concave dorsal margin, a steeply raised anterior dorsal margin of the ilium, an anteriorly inclined brevis shelf, vertically well-separated iliac blades above the sacrum, an completely enclosed pubic obturator foramen, triangular pubic boot in distal view, vertical ridges on anterior and posterior edges of medial surface of the femoral head, and a robust femur that is longer than tibiotarsus. These features suggest that Deinocheirus (unlike other ornithomimosaurs) was not a fastrunning animal, but a bulky animal with a heavily built pelvis and hind limbs. However, the dorsal ribs are tall and relatively straight, suggesting that the animal was narrowbodied. A large number of gastroliths (>1100 ranging from 8 to 87 mm) were collected from the abdominal region of MPC-D 100/127, suggesting Deinocheirus was an herbivore.

This is the first of a few posts about discoveries announced at SVP 2013. Stick around through the rest of the coming week, because there's some cool stuff coming down the pipe.