The Shunosaurus tail-club, revisited: spikes, and complex distal caudals

June 21, 2010

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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14 Responses to “The Shunosaurus tail-club, revisited: spikes, and complex distal caudals”

  1. Tracy Ford Says:

    There is also a specimen of Omeiosuarus tianfuensis that has a ‘club’ tail. DONG, PENG & DAXI, 1989, ZDM 5045, 5046, 5048, 5049, 5050, 5052: Distal caudal vertebrae with tail clubs.

    Dong, Z.-M., Peng, G., and Daxi, H., 1989, The Discovery of the Bony tail Club of Sauropods: Vertebrata PalAsiatica, v. 27, n. 3, p. 219-224.

    Also there are several Shunosaurus with a tail club. T5401: Distal end of tail with club
    IVPP V7661, V7662, ZDM 5006, 5007, 5013a, 5035, 5047, 5051, 5053: Distal caudal vertebrae with clubs.

    And interesting enough, all from the same quarry.

  2. Mike Taylor Says:

    We mentioned, and showed the figures of, an Omeisaurus tail-club from Dong et al. (1989) in the original Shunosaurus tail-club article (link above). I didn’t realise there were so many specimens, though.

    It would be great to know the degree of association and articulation of all these elements.


  3. […] This post was mentioned on Twitter by Chris Rowan, JP – Research Lab. JP – Research Lab said: The Shunosaurus tail-club, revisited: In a comment on the initial Shunosaurus tail-club post, Jaime Headden pointe… http://bit.ly/bEXokp […]


  4. Very cool spikes. Obviously, the tail structure Xing et al. describe [1] (as a slub for Mamenchisaurus hochuanensis, ZDM 126) may represent the first part of the club complex observable in Shunosaurus lii (mediolaterally compressed fusion of some vertebrae, followed by an enlarged, swollen element, followed by a “terminal” spike like structure), although the structure in Omeisaurus tianfuensis seems to be as swollen as the succeeding element.

    Has anyone scanned or sectioned one of these swollen elements, in order to observe the substructure? Swollen form through metaplastic reorganization (as in ceratopsian horns, etc.) tends to result in dense, apneumatic bone, while the typical vertebral structure is obvious.

    I should note that these spikes appear symmetrical and more conical than those in Spinophorosaurus nigerensis, which are similar to somne of the spikes in stegosaurs at least. If they were caudal, Remes et al.s taxon would appear to have a different caudal structure than do the Chinese taxa.

    [1] Xing L., Xu X., Shu C.-k., Peng G.-z. & You H.-l. 2009. Structure, orientation and Finite Element Analysis of the tail club of Mamenchisaurus hochuanensis. Acta Geologica Sinica 83(6):1031-1040.

  5. Heinrich Mallison Says:

    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.

    or one is a mirror image of the ohter…..

  6. Mike Taylor Says:

    No, Heinrich: if one was a mirror-image of the other, then the osteoderms would either appear in front of the vertebrae in both figure and plate, or appear behind the vertebrae in both figure and plate. Because they are in front in one, and behind in the other, we know that the two illustrations are from different sides.

  7. Nima Says:

    Very interesting… I’d always illustrated Shunosaurus with the spikes, though I never knew their precise arrangement. But the fact that the two pictures are not mirror images begs a further question:

    Was there a single trio of spikes arranged asymmetrically this way, or were the three spikes in a perfectly symmetrical dorsal arrangement on the club in life, OR were there actually five or six spikes on the club?

    As for Omeisaurus and Mamenchisaurus… I have a suspicion that they were in some way descended from the same ancestor as Shunosaurus. They’re all classified as basal Eusauropods currently, and Shunosaurus just seems to be the most basal of them, a sort of living fossil, a Haplocanthosaurus parallel in the Far East.

    I used to be a firm advocate of a unified Euhelopodidae, not least because the posterior cervicals of Euhelopus had flat-topped neural spines much like Mamenchisaurus and Omeisaurus, as well as similar proportions in the hips and the deep dorsal column. Now that it’s considered a titanosauriform, I don’t know how it fits into this whole story… nobody’s found the tail, which could make things really interesting if there was a club attached…

  8. brian engh Says:

    Hmmm…

    Those osteoderms are much less elongated than what is usually depicted in most paleo-art… Considering the preserved detail of the tiny caudal vertebrae it looks to me like that the ‘spikiness’ has been greatly exaggerated in many depictions.

    Good timing too – I’m just now getting to rendering that illustration.

    Thanks Mike!

  9. Mike Taylor Says:

    Brian, don’t forget that horns are nearly always longer and more pointy than the horn cores, and that we only ever get the cores preserved as fossils. So the traditional level of Shunosaur tail spikiness may not be unmerited.

  10. brian engh Says:

    Oh, for sure, some of the reconstructions do a pretty decent job, but there are some with no spikes and a number of them with more elongated spikes, somewhere between the length they should be, and the length they should be on a stegosaurus. Also, it looks like there is actually only two spikes, located on the dorsal surface of the club, while most shunosaur illustrations have two spikes on both lateral sides of the club (again stegosaur-like).

    haha, this one is particularly terrible:

    … in every way, not just the tail.

    The reason I asked in the first place is because such a huge range is represented in paleo art, and at the same time I couldn’t find any direct skeletal reference.

    To me at least, the osteoderms in the pictures above look much more stud-like, reminiscent of the osteoderms on the back of a crocodile or ankylosaur… I kinda feel like the word ‘spike’ isn’t even the best word for them.

    Anyway, this post provides just the reference I needed! Thanks again Mike!

  11. Aaron Natera Says:

    I look forward to somehow using the word “neosauropodocentricity” in casual conversation at the office today.


  12. […] a theropod with its tail club.  (We’ve previously discussed Shunosaurus tail clubs here and here.)  Brian also chronicled the evolution of his image on his own blog (version 1 [scroll down], […]


  13. […] (Gilmore 1925, one specimen), Mamenchisaurus hochuanensis (Young and Zhao 1972, one specimen), Shunosaurus lii (e.g. Zhang et al. 1984; probably multiple specimens but the paper is in Chinese so I don’t […]


  14. […] observation: Mike noted back when that Shunosaurus and Varanus retain complex caudal vertebrae all the way out to the end. Since in […]


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