In a comment on the initial Shunosaurus tail-club post, Jaime Headden pointed out the passage in the Spinophorosaurus paper (Remes et al. 2009) that discusses the club of Shunosaurus (as justification for positioning the Spinophorosaurus osteoderms on the end of its tail):

With the holotypic skeleton, two closely associated dermal  ossifications were found originating from contralateral sides  (Fig. 4A–C). These elements have a subcircular base that is  rugose and concave on its medial side, and bear a caudodorsally  projecting bony spike with a rounded tip laterally. Although these  elements were found in the pelvic region under the dislocated  scapula, we regard it as most probable that they were placed on  the distal tail in the living animal for the following reasons: First,  the close association of the contralateral elements indicates they  were originally placed near the (dorsal) midline of the body.  Second, the stiffening of the distal tail by specialized chevrons is  also found in other groups of dinosaurs that exhibit tail armor  [42,43]. Third, osteoderms of similar shape are known from the  closely related basal eusauropod Shunosaurus [26]. In the latter  form, these elements cover the middle part of a tail club formed by  coalesced distal vertebrae; however, the decreasing size of the distal-most caudal vertebrae of Spinophorosaurus indicate that such a  club was not present in this genus. The right osteoderm is slightly  larger and differs in proportions from the left element, indicating  that, as in Shunosaurus [26], originally two pairs of tail spines were  present (Fig. 5).

— Remes et al. (2009:6-8)

And this gives the reference that I needed for the Shunosaurus tail-spikes (as opposed to the club) — reference 26 is Zhang (1988), which, embarrassingly, we’ve featured here on SV-POW! in our first Shunosaurus post.  Evidently I was so focussed on preparapophyses when I looked at that monograph that I completely failed to register the tail-club spikes — but then, which of us can truly say he has not made that mistake?

Anyway, here’s what Zhang has to show us:

And here’s that tail again, this time from the poorly reproduced photographic plate 12, part 1, and in right lateral view:

It’s apparent that this really is the other side of the distal tail (rather than a reversed image of the same side) because the osteoderms are in front of the club vertebrae in the left-lateral figure, but behind them in the right-lateral plate.

It would be great to say more about these, but the English language summary of Zhang’s monograph is understandably brief, constituting six pages of the 90.  What’s not quite so understandable is that neither the diagnosis of the genus Shunosaurus nor that of the species S. lii mentions the tail-club or spikes, which are arguably the most distinctive features.  The “revised diagnosis” on pp. 78-79 does, however — just:

Posterior caudals platycoelous, with small cylindrical centra; neural spines low, rod-like.  In several last caudals swollen ralidly [sic] and forming “tail-mace”; in addition there are two pairs of little caudal spines, being analogous to that of stegosaurs.

Not much to go on, but something.  That’s all, though — there is no further description, and crucially, no indication of whether the tail elements were found articulated or whether the spikes were found isolated and subsequently moved to the end of the tail.  It may be that Remes at al. know something I don’t, of course — they might have a translation of Zhang (1988) — but if not, then it’s amusing to consider that the spikes on the tail of Shunosaurus may or may not be supported by evidence, and that the inference of tail-spikes on Spinophorosaurus might be based on dodgy premises.

The other thing that struck me forcibly, as I looked at the figure and plate above, is that the caudal vertebrae remain fairly complex all the way to the end: they retain distinct and prominent neural spines, unlike the distal caudal vertebrae of diplodocids and brachiosaurs.  I notice that the distal caudals of Spinophorosaurus also seem to be complex, based on fig. 3H-I and also on the skeletal reconstruction that is fig. 5 — both of which we’ve reproduced before, in our old Spinophorosaurus article.

So what’s going on here?  Are Shunosaurus and Spinophorosaurus unusual in having distal caudals that retain complex neural spines?  If so, is this property correlated with the possession of a tail-club and/or spines?  Is it causally related?  Or could it be that this is normal for basal eusauropods, and my ideas of sauropod tails have been too coloured by extreme neosauropodocentricity?  Clearly I ought to go and look at a lot more basal sauropods’ distal tails before publishing this post.  And prosauropods’, theropods’, ornithischians’, pterosaurs’, crocadilians’ and lizards’ distal tails.

As it happens, the one non-neosauropod group of reptiles whose distal tails I do know something about is monitor lizards, thanks to my adventures with the corpse of “Charlie”.  And those caudals do maintain astonishingly detailed structure right to the end of the tail, with even absolutely tiny caudals having distinct processes.  Here are some photographs that show this.

First, one showing all 56 caudal vertebrae (the 1st is half in frame at top right, next to the sacrum; the rest read from left to right on successive rows, like words on a page).

Now here are five representative caudals from different regions on the tail — the last ones from each row in the picture above, as it happens: caudals 1, 10, 21, 30, 42 and 56.  They are in more or less dorsal view, though caudal 1 has fallen forward onto its anterior face.  In this and subsequent pictures, caudal 10 (the second shown) is  for some reason back to front.

Now here are the same vertebrae, in the same order and orientation, but now in left dorsolateral aspect (except caudal 10 which is of course in right dorsolateral):

Finally, here are the three smallest of these vertebrae (numbers 30, 42 and 56) in close-up, again in left dorsolateral view, so you can more easily see how much structure even the distalmost caudal has:

That last caudal is about 2.5 mm long.

(It’s interesting that caudals 30 and 42 have those cute fused chevrons.)

So anyway: we know that caudal vertebrae retain distinct structure all the way down to the tip of the tail in monitor lizards at least some basal eusauropods: could it be that this is the primitive state, and that degenerate caudals are found only in neosauropods and mammals?  Gotta prep out some more animals’ skeletons and find out!

References

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In a comment on an earlier article, What’s the deal with your wacky postparapophyses, Shunosaurus?, brian engh asked:

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 Omeisaurusand 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.

References

  • 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.

In color, this time, with multiple views, thanks to Xing et al. (2009). They also did a finite element analysis of the tail club and concluded that it was a fairly pathetic weapon. Xing et al. closed by supporting the contention of Ye et al. (2001) that the tail club was a sensory organ. As they stated at the end of the abstract:

The tail club of Mamenchisaurus hochuanensis probably also had limitations as a defense weapon and was more possibly a sensory organ to improve nerve conduction velocity to enhance the capacity for sensory perception of its surroundings.

One thing Xing et al. (2009) cite in support of this is the expanded neural canal inside the club, which they compare to the sacral enlargement in stegosaurs and to the glycogen bodies of birds. They rule out a glycogen body on the grounds that the sacral enlargement in stegosaurs is much bigger than the brain volume, whereas the neural canal enlargement in the M. hochuanensis tail club is much smaller (if you don’t follow that logic, don’t worry, neither do I).

I’m not sure what to make of this thing. On one hand, it would be nice to have more than one club available to rule out the possibility that it’s just a weird paleopathology. On the other hand, it looks oddly regular to be pathological, and the definitive clubs in Shunosaurus and Omeisaurus are at least weak support for this being a genuine feature, although the clubs of the former taxa look very different.

Furthermore, I don’t understand how the authors can rule out the presence of a glycogen body based on the size of the neural expansion alone–especially since the functions of glycogen bodies in extant taxa are very poorly understood (as you may remember from this dustup). Nor can I fathom how a titchy little nerve bundle–if such existed–down at the end of the tail could do much to improve nerve conduction velocity up the rest of the tail. Either my understanding of neuroscience is completely shot, or this hypothesis…lacks support. I am open to being enlightened either way.

Finally, I am disappointed that the authors didn’t pursue the cutting-edge pseudohead hypothesis that has figured prominently here and elsewhere in the blogosphere. There’s a Nobel lurking in there, I just know it.

References

  • Xing, L, Ye, Y., Shu, C., Peng, G., and You, H. 2009. Structure, orientation, and finite element analysis of the tail club of Mamenchisaurus hochuanensis. Acta Geologica Sinica 83(6):1031-1040.
  • Ye, Y., Ouyang, H., and Fu, Q.-M. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica 39(4):266-271.

I am not usually one for field photographs — I am not a geologist, and one bit of rock looks the same as any other to me.  I suffer from a debilitating condition that renders me unable to see fossils in the ground, and am reliant on other people to dig ’em out, clean ’em up and reposit them before I’m able to make ’em into science.

But this … this blew me away:

Spinophorosaurus nigerensis, holotype skeleton GCP-CV-4229 in situ during excavation in the region of Aderbissinat, Thirozerine Dept., Agadez Region, Republic of Niger (Remes et al. 2009:fig. 1)

Spinophorosaurus nigerensis, holotype skeleton GCP-CV-4229 in situ during excavation in the region of Aderbissinat, Thirozerine Dept., Agadez Region, Republic of Niger. (Remes et al. 2009:fig. 1)

It’s the astonishingly complete and well-preserved type specimen of a new basal sauropod, Spinophorosaurus, that came out today in a paper lead-authored by Kristian Remes, previously best known for his work on Tendaguru diplodocines (Remes 2006, 2007, 2009) and for his work on the awesome remounting of the Berlin brachiosaur.

I’m not going to write the new taxon up in detail, but here are the figures of its vertebrae:

Spinophorosaurus nigerensis GCP-CV-4229 (holotype; C, E-I) and NMB-1698-R (paratype; A, B, D). (A, B)— Mid-cervical vertebra in left lateral (A) and ventral (B) views. (C)— Last dorsal and first sacral vertebrae in left lateral view. (D)— Clavicle in cranial view. (E, F)— Proximal caudal neural spines in lateral (E) and cranial (F) views. (G)— Mid-caudal vertebra in lateral view. (H, I)— Distal caudal vertebrae in left lateral (H) and ventral (I) views. Abbreviations: pcdl, posterior centrodiapophyseal lamina; podl, postzygodiapophyseal lamina; spol, spinopostzygapophyseal lamina. Scale bars = 10 cm.  (Remes et al. 2009:fig. 3)

Spinophorosaurus nigerensis GCP-CV-4229 (holotype; C, E-I) and NMB-1698-R (paratype; A, B, D). (A, B)— Mid-cervical vertebra in left lateral (A) and ventral (B) views. (C)— Last dorsal and first sacral vertebrae in left lateral view. (D)— Clavicle in cranial view. (E, F)— Proximal caudal neural spines in lateral (E) and cranial (F) views. (G)— Mid-caudal vertebra in lateral view. (H, I)— Distal caudal vertebrae in left lateral (H) and ventral (I) views. Abbreviations: pcdl, posterior centrodiapophyseal lamina; podl, postzygodiapophyseal lamina; spol, spinopostzygapophyseal lamina. Scale bars = 10 cm. (Remes et al. 2009:fig. 3)

(It’s a shame they didn’t figure more of it, especially as the paper was in PLoS ONE which has no length limits and absolutely stellar figure production, but it would be churlish to complain.)

Finally, here is the skeletal reconstruction: as you can see, it’s a decent size for such a basal sauropod.  Note the freaky all-osteoderm tail-club.

xx

Skeletal reconstruction of Spinophorosaurus nigerensis. Dimensions are based on GCP-CV-4229/NMB-1699-R, elements that are not represented are shaded. Scale bar = 1 m. (Remes et al. 2009:fig. 5)

A truly amazing specimen — I am looking forward to sitting down with the paper and giving it the attention it deserves.

Best of all, you can also sit down with the paper — because, like all PLoS articles, it is freely available to anyone who wants it.  Follow the link below and enjoy!  (Also available from the linked article: super-high resolution images of the figures.)

Timely Discussion From an E-mail Exchange Today

Matt Wedel: That animal is just flat badass.

Zach Miller: It has a goddamn thagomizer!!!

References

Remes, Kristian.  2006.  Revision of the Tendaguru sauropod dinosaur Tornieria africana (Fraas) and its relevance for sauropod paleobiogeography.  Journal of Vertebrate Paleontology 26(3):651-669.
Remes, Kristian.  2007.  A second Gondwanan diplodocoid dinosaur from the Upper Jurassic Tendaguru Beds of Tanzania, East Africa. Paleontology 50(3):653-667.
Remes, Kristian.  2009.  Taxonomy of Late Jurassic diplodocid sauropods from Tendaguru (Tanzania).  Fossil Record 12 (1): 23-46. doi: 10.1002/mmng.200800008
Remes, Kristian, Francisco Ortega, Ignacio Fierro, Ulrich Joger, Ralf Kosma, Jose Manuel Marin Ferrer, for the Project PALDES, for the Niger Project SNHM, Oumarou Amadou Ide, and Abdoulaye Maga.  2009.  A new basal sauropod dinosaur from the Middle Jurassic of Niger and the early evolution of Sauropoda.  PLoS ONE 4(9):e6924. doi:10.1371/journal.pone.0006924