Posts Tagged 'Haplocheirus'

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

Haplocheirus on the wires

Given that the dinosaur colours story broke the day before, I thought that the Haplocheirus story might struggle to make the press, especially as it is quite a complex story to cover. Nevertheless, plenty of places picked it up an a few of them are rounded up here. You can judge for yourself how successful or otherwise they were (especially in light of my recent ‘guide‘). Do take special note of the audio slide show at NSF’s website and from GW university that have lots of detail, including a video interview with Jonah Choiniere.

ABC news

AFP news

BBC online

Live Science

Scientific American

Discovery News

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Guest post: Haplocheirus – the skilful one

Jonah Choiniere continues his guest spot on the Musings with the news of the fascinating Haplocheirus, a basal alvarezsaur from the Jurassic that tells us quite a bit about theropod diversification and alvarezsaur evolution. If you have missed out, my brief review of alvarezsaurs is here, with a more detailed one by Jonah here.

I started working with Dr. Clark in 2004 when I entered the Ph.D. program at George Washington University. Dr. Clark set me up with a project working on the systematic relationships of basal coelurosaurs, a big group of theropod dinosaurs that includes things like Tyrannosaurus, Velociraptor, and of course birds. I began work on this project in the summer of 2005, on my first visit to China. One of the first fossils I looked at was the theropod skeleton unearthed in 2004. On first glance, the skull looked like an ornithomimosaur, but Dr. Xu and Dr. Clark bade me to carefully consider the specimen. We began to notice similarities between the skeleton and that of alvarezsaurids, and a large phylogenetic analysis confirmed that many of these similarities were shared, derived characteristics – this was an alvarezsaur. The paper released today is a first look at these characteristics. After toying with some other names, we finally settled on Haplocheirus sollers as the scientific name for the new animal. The name means “simple-handed skilful one,” in reference to the fact that Haplocheirus has a simple (plesiomorphic) hand relative to the derived hand of other alvarezsaurids, and that it may have used this hand in ways that other alvarezsaurids couldn’t have (i.e., grasping prey rather than merely digging). Because Haplocheirus slots in at the base of Alvarezsauridae, we elected to call this larger group (i.e., Alvarezsauridae plus Haplocheirus) the Alvarezsauroidea, which is consistent with some other larger groups of theropods (eg., Spinosauroidea, Tyrannosauroidea) and reflects the increased diversity of this clade.

The specimne of Haplocheirus (less the skull). Image courtesy of Jonah Choiniere.

The specimen of Haplocheirus (less the skull). Image courtesy of Jonah Choiniere.

I present the details of why we think Haplocheirus is an alvarezsauroid in the paper, so I’ll let the reader look there, but below I’ll talk a bit about some of the neater features of the skull and the forelimb.

Continue reading ‘Guest post: Haplocheirus – the skilful one’

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