What’s the deal with your wacky tail-club, Shunosaurus?
June 11, 2010
What’s the deal with most Shunosaur “life restorations” showing spikes on the tail club? I can’t find a picture anywhere of a skeleton with any indication of spikes, and yet almost every fleshed-out illustration of Shunosaurs has spikes on it’s tail. Anybody know what that’s about?
It seems we’ve never actually featured the famous Shunosaurus tail-club here before — an amazing oversight, and one that I’m going to remedy right now, thanks to Dong et al. (1989). This short paper is written in Chinese, so I can’t tell you anything beyond what’s in the figures, captions and English-language abstract.
First up, though, here is his illustration of the famed tail-club:
I can’t help noticing, though, that although the fused clump of enlarged distal caudal vertebrae constitutes a nice club, it’s noticably devoid of spikes. So it remains a mystery why so many restorations show a spiked club. Anyone out know why?
Dong et al. (1989) also obligingly includes a figure of the tail-club of Omeisaurus:
And also a photographic plate showing both clubs (though, as is so often the case, the scan has lost a lot of details):
Now, the big question is: why do Shunosaurus and Omeisaurus — and Mamenchisaurus, for that matter — have tail-clubs when they are not closely related, according to modern phylogenies such as those of Wilson (2002) and Upchurch et al. (2004)? [To be precise, Wilson (2002:fig. 13) had Omeisaurus and Mamenchisaurus clading together, but that clade well separated from Shunosaurus; and Upchurch et al. (2004:fig. 13.18) had all three separate, though with the former two as consecutive branches on the paraphyletic sequence leading to Neosauropoda.]
One possibility is just sheer coincidence: but it’s asking a lot to believe that of the 150 or so known sauropods, the only three for which tail-clubs are known just happened to live more or less at the same time and in the same place.
Another option is some oddity in the environment that strongly encouraged the evolution of tail clubs. Yes, this is wildly hand-wavy, but you can sort of imagine that maybe all the local theropods thought it was cool to hunt sauropods by biting their tails, and the clubs evolved in response to that. Or something. There’s a similar, but even more mystifying, situtation in the late Early Cretaceous Sahara, where the theropod Spinosaurus, the ornithopod Ouranosaurus and arguably even the sauropod Rebbachisaurus all evolved sails. Why then? When there? No-one knows and no-one’s even advanced a hypothesis so far as I know.
Getting back to Jurassic Chinese sauropod tail-clubs, though, there is a third option: could it possibly be that Shunosaurus, Omeisaurus and Mamenchisaurus all form a clade together after all, as proposed back in the day by Upchurch (1998:fig. 19)? Upchurch’s pioneering (1995, 1998) analyses both recovered a monophyletic “Euhelopodidae” — a clade of Chinese sauropods that included the three genera above plus the early Cretaceous Euhelopus, also from China. The existence of this clade was one of the two major points of disagreement between Upchurch’s and Wilson’s phylogenies (the other being the position of the nemegtosaurids, Nemegtosaurus and Quaesitosaurus, which Upchurch placed basally within Diplodocoidea but Wilson recovered as titanosaurs).
Upchurch himself has abandoned the idea of the monophyletic Euhelopodidae, as seen in that 2004 analysis and also in Wilson’s and his joint (2009) reassessment of Euhelopus: everyone now agrees that Euhelopus is a basal somphospondyl, i.e. close to Titanosauria, which is a looong way from the basal position that the other Chinese sauropods hold within Sauropoda.) And so the name Euhelopodidae is no longer used. But could it be that Upchurch was half-right, and that when Euhelopus is removed that the group that was named after it, a clade remains?
[If so, then that clade is called Mamenchisauridae: as noted by Taylor and Naish (2007), this name was coined by Young and Zhao (1972) and so has priority over the Omeisauridae of Wilson (2002), as Wilson himself now recognises. Mamenchisauridae was phylogenetically defined (or, as they have it, "diagnosed") by Naish and Martill (2007:498) as "all those sauropods closer to Mamenchisaurus constructus Young, 1954 than to Saltasaurus loricatus Bonaparte".]
As already noted, Omeisaurus and Mamenchisaurus are close together in the recent analyses of both Upchurch and Wilson, so the question becomes: how many additional steps are required to recover Shunosaurus as a member of their clade rather than in its usual more basal position (in the the case of Upchurch’s analysis, to move Omeisaurus up a node)? And to this, I do not know the answer — to the best of my knowledge, it’s never been tested (or if it has, the result has never been published). I’d test it myself, but I need to stop working on this post and watch Inca Mummy Girl soonest. If , say, 20 additional steps are needed, then forget it. But if we only need, say, three steps, then maybe someone should look at this more closely. Back in 2004, when he was Young And Stupid, Matt Wedel wrote to me, in a private email which I now quote without permission because I am pretty sure he’s not going to sue me:
Now that I’ve defended the status quo [of using unweighted characters in cladistic analysis], there are some things I’d be happy to bend the rules for. If an Omeisaurus pops up with a tail club, then Wilson and Sereno be damned, Omeisaurus and Shunosaurus belong in the same clade. [...] So my final word is unweighted characters, please, except for sauropod tail clubs.
Food for thought.
Finally, I leave you with the skeletal reconstruction of Omeisaurus from Dong et al. (1989:fig 3). Long-time readers will notice a more than passing resemblance to the reconstruction from He et al. (1988:fig. 63), which you can see in Omeisaurus is Just Plain Wrong.
It looks very much as though Dong et al. produced their reconstruction by flipping that of He et al. horizontally and pasting on a tail-club. Well, we can’t hold that against them — I’d have done the same.
- Dong Zhiming, Peng Guangzhao and Huang Daxi. 1988. The Discovery of the bony tail club of sauropods. Vertebrata PalAsiatica 27(3):219-224.
- He Xinlu, Li Kui and Cai Kaiji. 1988. The Middle Jurassic dinosaur fauna from Dashanpu, Zigong, Sichuan, vol. IV: sauropod dinosaurs (2): Omeisaurus tianfuensis. Sichuan Publishing House of Science and Technology, Chengdu, China. 143 pp. + 20 plates.
- Naish, Darren, and David M. Martill. 2007. Dinosaurs of Great Britain and the role of the Geological Society of London in their discovery: basal Dinosauria and Saurischia. Journal of the Geological Society, London, 164: 493-510. (Bicentennial Review issue.)
- Taylor, Michael P. and Darren Naish. 2007. An unusual new neosauropod dinosaur from the Lower Cretaceous Hastings Beds Group of East Sussex, England. Palaeontology 50 (6): 1547-1564. doi: 10.1111/j.1475-4983.2007.00728.x
- Upchurch, Paul. 1995. The evolutionary history of sauropod dinosaurs. Philosophical Transactions of the Royal Society of London Series B, 349: 365-390.
- Upchurch, Paul. 1998. The phylogenetic relationships of sauropod dinosaurs. Zoological Journal of the Linnean Society 124: 43-103.
- Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp. 259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria, 2nd edition. University of California Press, Berkeley and Los Angeles. 861 pp.
- Wilson, Jeffrey A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136: 217-276.
- Wilson, Jeffrey A. and Paul Upchurch. 2009. Redescription and reassessment of the phylogenetic affinities of Euhelopus zdanskyi (Dinosauria – Sauropoda) from the Early Cretaceous of China. Journal of Systematic Palaeontology 7: 199-239. doi:10.1017/S1477201908002691
- Young, Chung-Chien, 1954. On a new sauropod from Yiping, Szechuan, China. Acta Palaeontologica Sinica II(4):355-369.
- Young, Chung-Chien, and X. Zhao. 1972. [Chinese title. Paper is a description of the type material of Mamenchisaurus hochuanensis]. Institute of Vertebrate Paleontology and Paleoanthropology Monograph Series I, 8:1-30. English translation by W. Downs.