The Bizarre Deinocheirus.....

 

Deinocheirus mirificus – a dinosaur that we are all familiar with and now, thanks to the disclosures at this year’s SVP meeting in Los Angeles, an animal that we are now much more able to visualise in life. I first learnt about Deinocheirus as a kid and I was mystified by the huge arms of the type specimen. For me, at the time, it represented the ultimate theropod but for palaeontologists it was inconceivable that the rest of the animal could be simply scaled up from the huge arms as you might restore a conventional theropod - it was just too big.

There was even a train of thought that Deinocheirus was a kind of giant reptilian sloth using its arms to pull down vegetation. Eventually, as the science of phylogenetics came to the fore, we got nearer to the truth and Deinocheirus was generally regarded as a basal ornithomimosaur but even then there were still discussions about whether this diagnosis was accurate and a few of us were always secretly hoping that it would indeed turn out to be some kind of super predator. One thing that everybody agreed on – we needed more fossils.

Eventually they were found and Yuong-Nam Lee, of the Korean Institute of Geoscience & Mineral Resources, and colleagues presented their findings to a large and expectant audience. Two specimens were displayed – MPC-D 100/127 and MPC-D 100/128 – recovered from the Upper Cretaceous Nemegt Formation at Altan Uul IV and BuginTsav in 2006 and 2009 respectively. Much of the missing post cranial material that had eluded fossil hunters of the years was recovered although one of the specimens had already been illegally plundered which is both disturbing and unfortunate to say the least.

Of the material that was displayed there were a series of cervical vertebrae in full articulation complete with the atlas vertebra (C3 – C10) which are very ornithomimosaur-like and a similar series of dorsal vertebrae which display tall anterodorsally facing and highly pneumatic neural spines. The dorsal ribs are fairly straight and are indicative of a narrow body.  The sacral vertebrae (S1 – S6) also demonstrate tall neural spines and are fused (except for sacrals S1 and S6) and form a strong plate of bone.  This appears to demonstrate the presence of a hump in Deinocheirus akin to those found in other dinosaurs and is somewhat unexpected in this taxon.

There is also a series of caudal vertebrae preserved whilst the ilium is quite distinct and displays a raised anterior dorsal margin. The pubic region, as a whole, is strongly developed. The femur is well developed, robust and longer than the tibia and is clearly both unique and diagnostic of Deinocheirus.  Also of interest is the presence of gastroliths in the gastralia of MPC-D 100/127 (well over a 1000) and this is indicative that the animal was probably herbivorous.

Despite the fact that there is still no skull material for Deinocheirus, this new post cranial material looks wonderfully preserved and has allowed us to confirm that Deinocheirus is indeed a basal ornithomimosaur and is, therefore, a stunning vindication and endorsement of phylogenetics – a real triumph. The real surprise, however, is the visual reconstruction of the animal that drew audible gasps from the enthralled audience. There are a number of reconstructions already circulating but, in my opinion, not one of these has got the proportions or appearance of the animal correct.

I do not intend to add further fuel to the fire, and I am certainly not talented enough to produce my own image but if I said to you that Deinocheirus looks like a cross between an ornithomimid, a therizinosaur and Concavenator then you will appreciate just what a bizarre animal this really is. We all look forward to the paper which, at time of writing, still unfortunately appears to be some way off.

Next up - tyrannosaurids but before that I will be publishing a guest post which is a terrific article about the filming at the Natural History Museum in London for David Attenborough’s new programme, David Attenborough’s Natural History Museum Alive 3D, to be broadcast on New Year’s Day so watch out for this one.

Reference

Lee, Y., Barsbold, R., Currie, P., Kobayashi, Y. & Lee, H. 2013. New specimens of Deinocheirus mirificus from the Late Cretaceous of Mongolia.  Journal of Vertebrate Paleontology, SVP Program and Abstracts Book, 2013, pp161.