Nemegtosaurus = Opisthocoelicauda... probably

[ZoPteryx]

If you're familiar with Nemegtosaurus, than you probably know Opisthocoelicauda and are aware of the interesting history these two have.

For those that aren't familiar, here's a brief recap.  Nemegtosaurus and Opisthocoelicauda are mid-sized titanosaur sauropods from the Late Cretaceous Nemegt Formation in Mongolia.  Both were recovered by the famous joint Polish-Mongolian Palaeontological Expeditions of 1965.  Nemegtosaurus is known only from a well preserved skull and was named first.  Opisthocoelicauda is known from a mostly complete skeleton lacking a head and neck, and was named a few years later.  For a while now, some researchers have suggested that the two may be the same species (they can't be from the same exact specimen because they were found at different sites), in which case Nemegtosaurus would be the valid name.  The waters of this debate have been muddied by the fact that the two taxa have come out as either close or distant relatives in different phyogenetic analyses.  If only we had more remains to clear this issue up...

That's where this new study comes in.  The authors have rediscovered the original locality of the Nemegtosaurus skull and found more remains, post-cranial remains.  While far from complete, there's enough material to confirm that the two are indeed very close relatives, if not the same species.  In particular, Nemegtosaurs possesses Opisthocoelicauda's namesake opisthocoel anterior tail vertebrae, a feature previously considered unique to that genus.

http://www.sciencedirect.com/science/article/pii/S0031018217306909

Imagine this skull on that body.  (If you've got GSP's dino guide, you don't have to imagine.  )

[Sim]

After the latest evidence, I think the two are the same animal.

In particular, Nemegtosaurs possesses Opisthocoelicauda's namesake opisthocoel anterior tail vertebrae, a feature previously considered unique to that genus.

It looks like that might become a unique feature of the genus Nemegtosaurus.

[Halichoeres]

Hey, cool! I slightly prefer the name Opisthocoelicaudia to Nemegtosaurus, but I even more prefer when new remains furnish evidence that two non-overlapping specimens belong to the same taxon. I'll happily accept the priority of Nemegtosaurus for the sake of an almost completely known sauropod.