Changmiania liaoningensis

Of course Changmiania liaoningensis was going to get my attention; nearly complete hypsil-grade ornithischians are always welcome here. I had a couple of other topics ahead of it in the queue, but with those out of the way, we can take a few minutes to appreciate this new species and its excellent fossils.

In fact, let's do that right now. Figure 1 from Yang et al. (2020); 1A and 1B are the type specimen, and 1C is the referred specimen. Red arrows indicate gastrolith clusters. CC-BY-4.0.

Genus and species: Changmiania liaoningensis. The genus name is based on "changmian", pinyin for "eternal sleep", while the species name refers to Liaoning (Yang et al. 2020). A loose translation of the name is "eternal sleeper of Liaoning".

Citation: Yang, Y., W. Wu, P.-E. Dieudonné, and P. Godefroit. 2020. A new basal ornithopod dinosaur from the Lower Cretaceous of China. PeerJ 8:e9832. doi:10.7717/peerj.9832.

Stratigraphy and geography: Lujiatun Beds at the base of the Yixian Formation, from Lujiatun, Beipiao City, in western Liaoning, China (Yang et al. 2020).

Holotype: PMOL AD00114 (Paleontological Museum of Liaoning, Shenyang Normal University, Shenyang, Liaoning, China), a skeleton which is more or less complete and articulated. A second nearly complete and articulated specimen, PMOL LFV022, has been referred to the species. The specimens were acquired from local farmers, and had been partially prepared before acquisition, but show no evidence of being augmented (Yang et al. 2020).

If you've been at this for a while, you can probably envision a basic hypsil-type skeleton with little difficulty, and at first glance that's what you're getting here. There's the long tail (lacking abundant ossified tendons, but given some stiffness by the size of the transverse processes and the zygapophyses), the well-developed hind legs, short arms, small hands, light skull between a rectangle and an elongate triangle in shape, and so on. The body size is, unsurprisingly, small: Yang et al. (2020) give the total length of the type specimen as 1,170 mm (a hair over 46 inches), more than half of which is tail (650 mm or 25.6 in), with a skull 110.5 mm long (4.35 in) and a femur 115.5 mm long (4.55 in). The specimens have been left in their slabs, which does obscure some anatomical details but preserves the association of the bones (and the gastroliths, clusters of which are found with both specimens in the right "lumbar"/pelvic region).

The face of Changmiania liaoningensis; not quite as pointy and elongate as Thescelosaurus, but you get the idea. Figure 2 in Yang et al. (2020). CC-BY-4.0.

After finishing admiring the outstanding specimens, one of the first anatomical differences you may notice from the standard model is that C. liaoningensis has no neck. Not literally, of course, but for a dinosaur it's unusually poorly supplied with cervicals, with only six cervicals of no particular length (you yourself have seven). If you're looking closely at the photos, you may also notice that the neural spines of the sacral vertebrae are not separated. This is not an artifact of preparation; the sacral neural spines are in fact fused into a bar. Yang et al. (2020) interpreted these and other features of the skeleton as evidence of adaptation for burrowing. Some of the other features include: fusion of the premaxillae; shortened forearms and hands; relatively large shoulder girdles in which the scapula and coracoid are fused; hips and leg sockets relatively canted, which would make it easier for the animal to assume a stable digging posture; and a well-muscled proximal tail, based on the relatively large processes. However, like other hypsils interpreted as having burrowing habits, the hind legs are still quite well suited for running, making it at most a part-time burrower. Yang et al. (2020) hypothesized that the two specimens of C. liaoningensis represent individuals trapped in collapsed burrows.

This brings us to the evolutionary relationships of C. liaoningensis, and if you've been paying attention to hypsil-grade ornithischians, you're well acquainted with the bewildering range of opinions. Sometimes practically every hypsil is an ornithopod, except Agilisaurus and Yandusaurus, which seem to be permanent outcasts (Dieudonné et al. 2020). Sometimes not even Hypsilophodon is an ornithopod (Madzia et al. 2018). You can find almost every other permutation in between in someone's paper. For the purposes of the paper we are actually looking at (Yang et al. 2020), which includes two of the authors of Dieudonné et al. (2020) and has a similar composition of Ornithopoda, C. liaoningensis ends up as the most basal ornithopod, not in a clade with any other hypsil, burrowing or not. (You may also notice that Nanosaurus agilis continues its astonishing revival.)

References

Dieudonné, P.-E., P. Cruzado-Caballero, P. Godefroit, and T. Tortosa. 2020. A new phylogeny of cerapodan dinosaurs. Historical Biology. doi:10.1080/08912963.2020.1793979.

Madzia, D., C. A. Boyd, and M. Mazuch. 2018. A basal ornithopod dinosaur from the Cenomanian of the Czech Republic. Journal of Systematic Palaeontology 16(11):967–979. doi:10.1080/14772019.2017.1371258.

Yang, Y., W. Wu, P.-E. Dieudonné, and P. Godefroit. 2020. A new basal ornithopod dinosaur from the Lower Cretaceous of China. PeerJ 8:e9832. doi:10.7717/peerj.9832.