The last paper from the caenagnathid chapter of my thesis is now out! The paper is open access here.
In 2018, when international travel was still a normal thing, I visited the famous Bugiin Tsav locality in the western Gobi Desert of Mongolia. This spot is famous for producing some of the most gorgeous dinosaur fossils, including a toddler Tarbosaurus and the incredible Deinocheirus specimens that resolved that enigma. Plus, it produced one of the Oksoko specimens!
It also produced the first dinosaur with a pygostyle–a fused set of vertebrae on the tip of the tail that anchored feathers. And that dinosaur just so happens to be an oviraptorosaur, named Nomingia gobiensis. Nomingia has been a bit of a mystery since its discovery, because although it looks in many ways like a caenagnathid, in phylogenies it always came out as an oviraptorid. I discussed why this might be in a 2018 paper, and in drawing comparisons to other caenagnathids like Elmisaurus (which lived nearby), I was surprised by just how similar they were. So similar, I wondered whether Nomingia and Elmisaurus might be the same thing.
So my goal at Bugiin Tsav was to get back to the spot where Nomingia was discovered, to see if I could find more bones and sort out this mess. The old quarry was picked clean, but just a few steps away, I found some other oviraptorosaur bones. “Great!” I thought, “more of the skeleton!” But as I found more bones, it became clear that some of them were duplicates from the skeleton of Nomingia, so they must have been a different individual–“A second Nomingia!”
Back at the lab, I pieced together the bone fragments and was startled to find that the foot bones were identical to Elmisaurus, but the rest of the bones were identical to Nomingia (for which we don’t know the foot bones yet). This skeleton seemed to link the two, and in looking at all of the specimens of both species, it was apparent that there were no differences between them. So, we conclude in this new paper that Nomingia is likely a junior synonym of Elmisaurus, meaning that it’s a second, invalid name for Elmisaurus.
This discovery highlighted the low diversity of caenagnathids in Asia compared to North America. Compared to the multiple species usually found in North American rocks, only a single species was around in Mongolia. And because we’ve found so many specimens of Elmisaurus, we can be fairly confident that this is a true pattern. So it appears that although they were clearly permanent residents of China and Mongolia, they just weren’t as successful as across the pond.
Why was this? We can’t be sure, but we noted a couple key coincidences in our paper that may hold clues. For example, it appears that the later Asian caenagnathids were immigrants from North America, rather than descendants of the giant caenagnathids that had migrated to Asia earlier. Also curious, these giant caenagnathids seem to have disappeared by the Campanian, right when oviraptorids were diversifying. Could it be that earlier endemic Asian caenagnathids were outcompeted by oviraptorids? This might explain why the giant caenagnathids vanished and why all of the later caenagnathids appear to be migrants from North America.