Marine reptile from Yunnan

[Crazyhen]

This is an incomplete specimen of marine reptile from Luoping, Yunnan Province of China.  Triassic.  Any idea what is the species? It looks like Diandongosaurus.

[Crazyhen]

[pachy-pleuro-whatnot-odon]

I wouldn't really know, unfortunately. Never heard of Diandongosaurus before, and there doesn't seem to be to much easily accessible information available on that genus on Google or Wikipedia either. Beautiful skull, though! 

 

Actually, based on the skull along, my first impression would've been some type of nothosauroid sauropterygian, to which Diandongosaurus doesn't appear to be affiliated, however. I did manage to find the below image at the Institute of Paleontology and Paleoanthropology, though, which illustrates the holotype for Diandongosaurus:

 

 

Based on this, I'd say that, although very similar to Keichousaurus in appearance, there are three distinguishing characteristics that jump out at me: 1) shorter neck, 2) wider rib cage and 3) expanded/wider base of the tail. As these features seem to be present in the photographs above, I'd say there's a good chance if the specimen being Diandongosaurus. However, I feel I should point out that the last two characters I listed appear to be present in Keichosaurus, where they may be sexually dimorphic, belonging to the male morphotype - at least insofar as the below image suggests (source: Wikipedia after Xue et al., 2015, "New information on sexual dimorphism and allometric growth in Keichosaurus hui, a pachypleurosaur from the Middle Triassic of Guizhou, South China"; A = female morphotype, B = male morphotype):

[Crazyhen]

There is not much information on Keichousauridae other than Keichousaurus hui.  There are two other species: Diandongosaurus acytidentatus and Dianopachysaurus dingi .  The one shown in your picture is an D. acutidentatus.  The attached photo is Dianopachysaurus dingi.  I do not possess the expertise to tell them apart.

[Crazyhen]

It’s interesting to note that while K. hui is so numerous in the area, other Keichousauridae species are very rare and only a few specimens have ever been found.

[pachy-pleuro-whatnot-odon]

2 hours ago, Crazyhen said:

There is not much information on Keichousauridae other than Keichousaurus hui.  The Diandongosaurus has two known species.  The one shown in your picture is an D. acutidentatus.  There is another one, D. dingi.  See the attached photo.  I do not possess the expertise to tell them apart.

Hmm, interesting. Not that I did a very thorough search, but I only found reference to the one species, D. acutidentatus. As to telling the two apart, that information should be available in their systematic descriptions - and then probably in that of D. dingi, rather than that of D. acutidentatus (although the latter might describe features that distinguish Diandongosaurus from nothosauroids). My suggestions above are simply based on quick observations. As to telling the two species apart: keep in mind that not all body parts may differ to the extent that those parts would differ between species. That is, you might not be able to tell them apart based on skull, but might need to have the arm and leg bones available for that - as seems to be the case concerning the sexual dimorphism of K. hui referred to above. Generally the more complete individuals have been found to base the systamic description of the species upon, the more of a skeleton you'll need to find to be able to identify one species of a genus over another. In addition, things like lumping and splitting species don't make differentiation any easier either, as having a whole skeleton available for diagnosis makes it easy to split species based on tiny differences, but makes it harder to do so on fragmentary evidence, since you might not have exactly those pieces that are diagnostic available to you. Nothosaurs can, as I understand, reasonably be differentiated based on their cranial morphology, for instance. But I'm not sure whether the same would be true for other nothosauroid genera, let alone sister clades (for an example, see Rieppel & Wild, 1994, "Nothosaurus edingerae SCHULTZE, 1970: Diagnosis of the Species and Comments on its Stratigraphical Occurrence").

 

2 hours ago, Crazyhen said:

It’s interesting to note that while K. hui is so numerous in the area, other Keichousauridae species are very rare and only a few specimens have ever been found.

In that respect, the paucity of other species of Keichousaurus in the deposits is very interesting, as it may very well be that - if contemporaneous - these species represent different ontogenetic stages (with the other species representing life stages an animal quickly passes through or is less likely to obtain, such as juvenile or old-age) or anagenetic evolution. An interesting article that goes into such differences between related species is Zietlow (2020), "Craniofacial ontogeny in Tylosaurinae".

[Crazyhen]

12 hours ago, pachy-pleuro-whatnot-odon said:

I wouldn't really know, unfortunately. Never heard of Diandongosaurus before, and there doesn't seem to be to much easily accessible information available on that genus

The papers on the two species are listed below:

https://www.researchgate.net/profile/Jonathan_Aitchison/publication/261740145_A_New_Pachypleurosaur_Reptilia_Sauropterygia_from_the_Lower_Middle_Triassic_of_Southwestern_China_and_the_Phylogenetic_Relationships_of_Chinese_Pachypleurosaurs/links/5553ebd208ae980ca60866dd/A-New-Pachypleurosaur-Reptilia-Sauropterygia-from-the-Lower-Middle-Triassic-of-Southwestern-China-and-the-Phylogenetic-Relationships-of-Chinese-Pachypleurosaurs.pdf?origin=publication_detail

 

 

http://www.ivpp.cas.cn/cbw/gjzdwxb/xbwzxz/201105/P020110530511087154324.pdf

 

 

 

[pachy-pleuro-whatnot-odon]

Thanks! Unfortunately, I won't be able to work my way through them any time soon, but I'm happy to add them to my library

[piranha]

Liu, X.Q., Lin, W.B., Rieppel, O., Sun, Z.Y., Li, Z.G., Lu, H., Jiang, D.Y. 2015
A New Specimen of Diandongosaurus acutidentatus (Sauropterygia) from the Middle Triassic of Yunnan, China.
Vertebrata PalAsiatica, 53(4):281-290  PDF LINK

 

Sato, T., Cheng, Y.N., Wu, X.C., Shan, H.Y. 2014
Diandongosaurus acutidentatus Shang, Wu & Li, 2011 (Diapsida: Sauropterygia) and the Relationships of Chinese Eosauropterygians.
Geological Magazine, 151(1):121-133  PDF LINK