Xixianykus zhangi – a new alvarezsaur

Xixianykus life reconstruction. Image courtesy of Matt van Rooijen.

Xixianykus life reconstruction. Image courtesy of Matt van Rooijen.

Around the time Haplocheirus hit the journals I commented that this would likely be a good year for Chinese alvarezsaurs. Obviously I rather had some insider knowledge and here’s part of that reason – Xixianykus zhangi. This is a new and really rather small alvarezsaur from Xixa county in Henan, China – a place far more famous for its fossil eggs and isolated baryonychine tooth.

Aside from being the latest taxon in a rather small clade, and having a fair amount of the skeleton intact, Xixinykus has some more interesting things going for it. For a start it does seem to be especially cursorial (that is, adapted for running) which can be seen by a number of anatomical specialisations especially (unsurprisingly) in the legs but also in the body. Despite likely only being likely around half a metre long, the legs on this thing are about 20 cm long. Being fast requires both a long stride length and / or as high stride frequency and Xixianykus as the former in spades at least. This is also combined with proportionally increasing distal parts of the limb (a short femur and a long tibia / metatarsus) which is another good indicator of cursoriality and is higher for Xixianykus than almost all other theropods. Whether or not is did run much is another question entirely, but when it did, it was probably quick. It was also efficient – there are structural adaptations in the body that would have reduced swaying, cutting down energy loss and the short femur also draws muscle mass up the legs making them more efficient (you don’t have to move all that heavy leg muscualture so far than if it was, to take an extreme example, on the foot say).

This is also a fairly old taxon, among the derived alvarezsaurs (the parvicrusorines) this is phylogenetically one of the most basal and the oldest. It’s dated to Santonian-Conacian as opposed to the others which are either Campanian or Maastrichtian. Based on the available material this suggests the possibility of an Asian origin for the group that later dispersed to North America.

Finally, I should add a quick, but large, ‘thank you’ to Matt Van Rooijen author of the Optimistic Painting blog for his reconstruction of the animal. Please don’t rip it off, it’s his artwork, on loan (if you like) to the Musings. If you want to use it, ask him, even if you do see it on various media sites.

A basal parvicursorine (Theropoda: Alvarezsauridae) from the Upper Cretaceous of China

17 Responses to “Xixianykus zhangi – a new alvarezsaur”

  1. 1 Mickey Mortimer 29/03/2010 at 10:50 am

    I commend you on using Parvicursorinae instead of Mononykinae. 🙂

  2. 3 Zach Miller 29/03/2010 at 12:06 pm

    Holy cow, that’s an awesome restoration. I really look forward to reading about this new guy. It certainly is a good year for alvarezsaurs, and I’ll mention Xixiankyus on the podcast next month. Hopefully, I won’t butcher the name.


    • 4 David Hone 29/03/2010 at 1:47 pm

      X is a ‘sh’ in Chinese. So it’s She-she-ah-nye-kuss.

      • 5 Dr. Nick 11/04/2010 at 6:16 am

        The in the syllable xia isn’t a real vowel, more like a “y” sound, so it’s just “shee-shah”

      • 6 Dr. Nick 11/04/2010 at 6:18 am

        Argh. Last comment should read:

        The i in the syllable xia isn’t a real vowel, more like a “y” sound, so it’s just “shee-shah”

  3. 7 Albertonykus 30/03/2010 at 6:40 am

    Another new alvarezsauroid! YES!!!

  4. 8 Roger 30/03/2010 at 8:40 pm

    Very cool—I think I saw the specimen kicking around your office, no? Strange and annoying, though, that neither Bristol nor Monash provide access to _Zootaxa_…

    • 9 David Hone 31/03/2010 at 7:33 am

      You may have done Roger. Errrm, there’s actually several alvarezsaur bits of varying interest and newness kicking around the IVPP at the moment. 😉 I don’t know which one you saw?

  5. 10 Jim Kirkland 03/04/2010 at 12:30 am


    Your cheating, being based out of China 😉

    Give everyone my best and since I’m not coming to China this year, everyone should come over and help out with excavating all our Utah dinosaurs.

    • 11 David Hone 03/04/2010 at 7:43 am

      Silly as it might sound Jim, it’s actually starting to get annoying. I spend too much of my time on descriptions and taxonomy / systematics, when i want to be getting on with my own research themes. I did manage to slip some ecology into the Xixinykus paper, but you should see the list of things I have to describe. It’s getting out of hand. Really.

  6. 12 Dr. Nick 11/04/2010 at 6:14 am

    But, but, the o in onych- ‘nail, claw’ is part of the root, not a connecting vowel, so the name should really be…oh, never mind.

    • 13 David Hone 11/04/2010 at 9:32 am

      Well we don’t pretend to be Latin or Greek scholars, and when combining Chinese with another ancient language, things tend to be a bit fudged, rather by definition. That phonetic explanation I tried to give is based on what Xu Xing wanted it called as best I could manage.

  1. 1 A New Ant-Eating Dinosaur, Xixianykus | Dinosaur Tracking Trackback on 02/04/2010 at 9:52 pm
  2. 2 Musings on 2010 « Dave Hone's Archosaur Musings Trackback on 29/12/2010 at 8:59 am
  3. 3 Linhenykus: the very model of modern Mongol, errr, alverasaur. « Dave Hone's Archosaur Musings Trackback on 24/01/2011 at 8:08 pm
  4. 4 Rychlonohý trpaslík z Číny | DinosaurusBlog Trackback on 01/10/2012 at 4:27 pm
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