What’s the deal with your wacky postparapophyses, Shunosaurus?
March 8, 2010
Shunosaurus lii is a basal eusauropod from the Middle Jurassic of China. Outside of palaeontological circles, it’s not at all well known — which is kind of surprising, as it’s one of the best represented of all sauropods. It’s known from numerous complete skeletons, including skulls, and has been described in detail in Zhang’s (1988) monograph: 89 pages and 15 plates. Here’s a skeleton of one individual, as found in the ground:
Apart from being so well represented, Shunosaurus is known mostly for its tail club, which at the time of its discovery was unique among sauropods. Despite recent discoveries of Mamenchisaurus hochuanensis individuals with preserved tail-clubs, and of Spinophorosaurus, the Shunosaurus tail-club is the best developed and best preserved.
But I don’t want to show you that. I want to show you something I’ve been wanting to see for many years, and today finally saw for the first time: a feature of the dorsal vertebrae totally unique to Shunosaurus, known as postparapophyses.
Sadly, these are the only figures in the paper that show the postparapophyses (and as far as I know the only published figures anywhere). So we have them in lateral view only, and lack what would be an informative posterior view. Plate 10, part 1, supposedly shows one of the posterior dorsals in posterior view, but in my PDF at least the reproduction is so poor as to be wholly uninformative.
What makes things even worse is that the extended English-language abstract on pages 86-91 of Zhang (1988) does not mention this feature at all — in fact it occurs only in the list of anatomical abbreviations on page 6. So, to the best of my knowledge, here is the entirety of what has been published in the English language about this feature based on observation of the material:
Wilson and Sereno (1998:14-15) expanded a little on this, but it’s not clear that what they wrote was based on anything more than the figure above. Here it is anyway, for completeness:
Comments–Zhang’s (1988:78-79) diagnosis listed numerous features, only a few of which appear to be autapomorphies of Shunosaurus lii. One of the more striking autapomorphies is an unusual articulation between the ribs and the posterior dorsal vertebrae. The parapophyseal articulation is split between adjacent vertebrae, with a portion of the articulation in its usual position by the prezygapophyses and an anterior extension located near the postzygapophysis on the preceding vertebra (Zhang, 1988:figs. 31, 32; “postparapophysis”).
That’s your lot.
So if we’re to make anything at all of the PPPs, it will have to be on the basis of the figure reproduced above. And I don’t really know how much we can say. The PPPs look sort of like postzygapophyses, havng a distinct ventrally oriented facet. This makes me wonder whether they are in fact lateral extensions of the postzygapohyseal facets, perhaps connected by a lamina that would be visible in posterior view.
The bottom line is, I don’t know, and I would greatly appreciate comments (or better still, photos!) from anyone who has seen the material first-hand.
I leave you with Zheng’s (1988:fig. 57) skeletal reconstruction of this distinctively dumpy-looking sauropod. Note by the way that the plantigrade manus reconstruction is almost certainly wrong: the metacarpals should be held in a more or less vertical arcade as in other sauropods.
- Wilson, Jeffrey A. and Paul C. Sereno. 1998. Early evolution and Higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.
- Zhang Yihong. 1988. The Middle Jurassic dinosaur fauna from Dashanpu, Zigong, Sichuam, vol. 1: sauropod dinosaur (I): Shunosaurus. Sichuan Publishing House of Science and Technology, Chengdu, China.
Update (9 March 2010)
Rob Taylor found this nice photograph of what is apparently a skeletal mount of Shunosaurus: the original is here. Any information about this mount will be gratefully received: please comment below if you know anything.