Say hello to Oksoko!

I’m very pleased to announce that a major part of my PhD thesis was just published! The paper is Open Access, so you can read it here: Royal Society Open Science

On my very first trip to Mongolia, all the way back in 2014, I was given a young oviraptorid skeleton to work on, which had been excavated illegally but confiscated from the poachers before it left the country. It was my job to figure out what it was, and learn as much about it as I could. It was a real crash course in anatomy for me: I’d only ever worked on isolated bones, never a nearly complete articulated skeleton with a skull!

Over the ensuing years, I would continue to learn more about the specimen and a more spectacular fossil: another confiscated block of three skeletons preserved together that had recently finished preparation. It was early on that we (Phil Currie and I) realized they were the same species as the young oviraptorid, and all of these skeletons were preserved in a very similar way. Plus, they were confiscated at the same time, so it became clear that they had been collected together.

For a few years we spent a month in Mongolia each summer and compared the new skeletons to other known oviraptorids. Based on the skulls, we were able to eliminate many different species, including a superficially similar species called Rinchenia (based on many features of the skull and the rest of the body). But we suspected it could still be an animal called “Ingenia” (its true name is an absolute mess of taxonomy that I won’t get into here).

But “Ingenia” isn’t known from a skull, so we had to compare the hands. Oviraptorid hands have three fingers, and the proportions of these fingers are useful for distinguishing different species. The hands we could see on our specimens were a bit damaged and seemed to be missing parts of the third finger, so in 2018 I started digging out the remaining hand in the block. When I started, only the wrist was showing, and the rest was still encased in rock, so I figured there was a good chance that the whole hand would be there.

But when I uncovered it, I was in for a surprise! The hand was beautifully preserved and completely articulated (all the bones in the right place), but the third finger had only one, tiny, blunt phalanx (finger bone), instead of the complete finger I was expecting to see. This nubbin of bone didn’t have the right joint shape or features to connect to other finger bones, so we could be certain that it was the only remnant of the third finger. Comparing it to the other hands we though were missing bones, it became clear that ALL of the hands had only a stubby little nubbin instead of a third finger. We had just discovered a two-fingered oviraptorid!

This new species is now dubbed Oksoko avarsan (‘Oksoko’ means three-headed eagle, and ‘avarsan’ means “rescued” in Mongolian). It’s one of the most completely known oviraptorids, with multiple skeletons, and literally every bone in the body is known.

As part of our study on it and its relatives, we realized that its two-fingered hand was part of a long trend of digit reduction in oviraptorids, and we were able to map that trend through their evolution. This complicated image summarizes that trend, as well as a bunch of other details. The important part is the colour of the tree branches! It turns out that it was likely an adaptation for living in the Gobi Desert, as it first starts happening when they migrate from southern China into the Gobi Region.

But there are some other really important aspects of the discovery. For one, the confiscated skeletons are all preserved in resting poses, so we have really strong evidence that they were living together in a group before they died (called gregarious or social behaviour). We also have both juvenile and adult skeletons, so we can see the changes that occurred in the skeleton throughout their lives. This first paper is mostly an overview of all these different aspects, and I hope to delve deeper into its anatomy, social behaviour, and biomechanics in future projects!

Copyright Michael Skrepnick 2019

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