Saturday, November 21, 2015

The "Kweichow Sauropod"

"Somebody's got to tell the tale/I guess it must be up to me" — B. Dylan

Among all the other oddities we encountered in the Glut (1982) series in the summer, there was one purported sauropod of particular obscurity, from "Kweichow" (Guizhou). I figured it was the specimen described in Young [Yang] (1948), but was somewhat discomfited to find that it had made itself scarce in the years since 1948. There weren't even any dinosaurs listed in "The Dinosauria" from Guizhou. Had it been re-evaluated as non-dinosaurian, or actually come from a different province? To my surprise, the journal was listed as "in storage" in the University of Minnesota library system, so I fired off an interlibrary loan request and in a few days was the proud owner of a shiny new pdf. Acting on the principle that every dinosaur deserves its day, I present the "Kweichow sauropod".

Conveniently, the article is in English. Somewhat less conveniently, the Romanization is outdated, so I'm not sure of many of the place names, but we can't have everything. The material was found in 1944 by T. H. Yin and I. W. Shen of the Geological Society of China, "about 300 meters NN.W. from the military post at Chingkangsao near a local town called Sungkan, 43 km from the northern gate of Tungtze Hsien [Loushanguan?] right along the Chungking-Kweiyang [Chongqing–Guiyang] High Way." They came up with a dorsal (back) vertebra, a partial sacrum (hip vertebrae), a fragment attributed to the end of a left pubis, and a handful of isolated rib fragments and other bone chunks. The material, described as well-preserved, was thought to represent one individual, and was given the catalog number V361 (institution not specified). Yang was of the opinion that further work would find more of the skeleton, but this does not appear to have been borne out.

Stratigraphically, Yin reported that the specimen came from about 150 meters above the contact with Jurassic rocks, which Yang found interesting because other comparable sauropods were of Late Jurassic age, not Cretaceous. The only other fossil reported was a fish coprolite. By that time, Yang had already worked with what we know as the first representatives of the prolific Jurassic sauropod beds of Sichuan across the provincial border to the north, and it would be easy to suspect that what he had was just one of these sauropods. "The Dinosauria" appears to be of this opinion, because the only place the citation is mentioned in either edition is in a list of papers concerning Yang's sauropods from the Jurassic of Sichuan and Xinjiang. If it weren't for the anatomy of the thing...

The only bone that Yang lingered over was the dorsal, which is an odd piece indeed. Dimensionally, it is at home with the vertebrae of other Middle Jurassic–Lower Cretaceous sauropods from China. The centrum (the cylindrical part) is 150 mm long at its greatest length and 170 mm at its greatest diameter. For comparison, the same figures for comparable vertebrae of compatriot sauropods are given as follows: "Helopus" [Euhelopus], 124 mm and 105 mm; Omeisaurus, 120 mm and 195 mm; Tienshanosaurus (the wallflower of Jurassic Chinese sauropods), 120 mm and 160 mm. The greatest height of the V361 dorsal is 545 mm; the only vertebra of the other Chinese sauropods with a complete height was the Tienshanosaurus specimen, at 370 mm.

For the purposes of the following discussion, here is a brief explanation of the anatomy of sauropod dorsal vertebrae as if scribbled on a napkin. We've already met the centrum, the cylindrical to disc-shaped main body. The rest of the vertebra, festooned with sticking-out bits (processes) and sheets of bone (laminae), is the neural arch. A passage called the neural canal runs through the vertebra at the base of the neural arch; it holds the spinal cord. The neural arch has two processes sticking out laterally, called the transverse processes. On the end of a transverse process is an articulation surface for a rib, called a diapophysis. The part of the neural arch that sticks up, broadly speaking, is called the neural spine. Vertebrae articulate to each other via processes called zygapophyses (the two on the leading side of the vert are prezygapophyses, and the two on the trailing side are postzygapophyses), and also are restricted in movement by the fore and aft surfaces of the centrum (various combinations of concave, convex, and flat surfaces). Hollows in the vertebra are called pleurocoels, sauropod vertebrae being composed partly to mostly of nothing.

Now, back to our sauropod. Yang noticed four unusual features:
  • The neural spine is missing several laminae (for those of you scoring at home, the supraprezygapophysial, suprapostzygapophysial, and supradiapophysial laminae; and yes, after a while the things start sounding like Aztec gods) and is convex-concave;
  • The diapophyses are low, just above the neural canal, with "no constrictional part at the sides of the neural arch between the centrum and the diapophyses". These and some other features led Yang to interpret the vertebra as the last or second-to-last vert before the sacrum, with perhaps no ribs to articulate with it;
  • The  zygapophyses are poorly developed, and there are no parapophyses (processes that would project from the sides of the centrum);
  • The centrum is weakly concave on the leading surface and strongly concave on the after surface, with low pleurocoel openings.
For my money, the most immediately striking feature is the neural spine. Without laminae, it is restored as relatively smooth. It is convex at the front, concave at the back, and arched and rounded along the top. It looks like nothing so much as a shoehorn, at least in the restoration (and we all know how restorations can fudge; in this one, the scale is clearly questionable because it indicates a vertebra about a quarter of the size of the provided measurements). Unless it's really, really heavily restored, it doesn't look like it's saying "Hi, I'm just some other bone that got glued onto this vertebra", if only because so few bones can look like shoehorns.

Yang made some tentative comparisons to the sauropods known at the time, but didn't make any firm conclusions, nor did he name the material. Unfortunately, this odd record slipped through the cracks after his description. The publication has had little impact in the English literature, which makes me worried that somewhere in his later writings he took back the whole thing, but even that should have been mentioned somewhere. Anyway, below is the restoration in all its oddly-scaled glory.

From Young (1948); something is wonky with the scale bar, because it's obviously way too small for the measurements. "16 cm" would provide something closer to what the text cites, but I have no idea what happened here.

References:

Young [Yang], C.-C. 1948. Notes on the occurrence of sauropod remains from N. Kweichow. Science Record 2:200–206.

2 comments:

  1. Cool post. The repository is near certainly the IVPP, as most other stuff Young described was from there, and their numbers start with a V. As for the identification, what do you think of the resemblance between it and Acrocanthosaurus' axis (Harris, 1998)? Same kind of spoon-like neural spine, would explain the lack of neural spine laminae...

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    1. That's an interesting resemblance! (https://books.google.com/books?id=O4wZCgAAQBAJ&pg=PA16#v=onepage&q&f=false for anyone who wants to follow along). On the other hand, if the restoration of our bone is correct, there's no obvious odontoid or axial intercentrum. Wonder how different the next cervical back would be...

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