Wing-like transverse processes, pneumatic caudals and all that…

June 9, 2008

NHM Diplodocus caudals

Just to break the stranglehold that titanosauriforms clearly have on SV-POW! (kidding), every now and again we need a diplodocoid or mamenchisaurid. And here’s another pic of the CM84/CM307 cast of Diplodocus carnegii as displayed at London’s Natural History Museum (photo © NHM). Again, we’re looking at the tail, but this time at the proximal part, and there’s a lot of neat stuff here to pay attention to…

— Note that laminae are present all over the place. Though it’s not totally obvious in this photo, ACDLs and PCDLs are present on the centra, PRDLs and PODLs are at the base of the neural arch, and SPRLs and SPOLs are present on the neural spines. I forget if we’ve gone through the acronyms for all the laminae – someone remind me. ACDLs are commonly present on sauropod proximal caudals, but are particularly prominent in the first 15 caudals of diplodocids. ACDLs, PCDLs, PRDLs and PODLs are absent from more distal caudals (Wilson 1999).

— Secondly, pneumatic foramina are present on the sides of the centra. It’s been said that pneumatic foramina are also present in at least some titanosaurs (specifically Neuquensaurus: Upchurch et al. 2004), but this isn’t evident in the primary description of this taxon (Powell 2003) nor coded for by Wilson (2002). Anyway, pneumatic foramina in the caudal vertebrae are a well known characteristic feature of diplodocids and even isolated centra have been identified as belonging to diplodocids on the basis of their presence (Gabunia et al. 1998). They aren’t present in dicraeosaurids (the sister-taxon to Diplodocidae within the diplodocoid clade Flagellicaudata).

— Perhaps the best known unusual feature of diplodocid caudals concerns the transverse processes. Ordinarily in sauropods (and in other dinosaurs) these are dorsoventrally compressed, laterally projecting processes that emerge from the approximate area of the neurocentral suture. In diplodocids (and dicraeosaurids) however, these are massive, dorsoventrally deep, wing-like structures: you can see in CM84/CM307 here that they are particularly massive and wing-like on the most proximal four or five of the caudals. Presumably these had – to use the technical terminology – some big-ass muscles attached to them. What does this tell us about tail function? Well, that’s a very very good question.

Another thing worth noting is that – if we were able to see the articular surfaces of the centra – we would note that diplodocids have procoelous proximal caudals. This contrasts with the usual sauropod condition, where proximal caudals are amphiplatyan or amphicoelous. Caudal procoely is seen in a few other sauropod groups (notably mamenchisaurids… and, err, titanosaurs!), but that of diplodocids is only mildly developed by comparison.

That’ll do for now, consider this an introduction.

References

  • Gabunia, L. K., Mchedlidze, G., Chkhikvadze, V. M. & Lucas, S. G. Jurassic sauropod dinosaur from the Republic of Georgia. Journal of Vertebrate Paleontology 18, 233-236.
  • Powell, J. E. 2003. Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogoegraphical and phylogenetic aspects. Records of the Queen Victoria Museum 111, 1-173.
  • Upchurch, P., Barrett, P. M. & Dodson, P. 2004. Sauropoda. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds). The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 259-322.
  • Wilson, J. A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19, 639-653.
  • Wilson, J. A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136, 217-276.
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15 Responses to “Wing-like transverse processes, pneumatic caudals and all that…”

  1. Mike Taylor Says:

    Odd to talk of anterior caudal procoely in connection with diplodocids and mamenchisaurids, but not mention titanosaurus. Is this part of a Grand Plan?

  2. Graham King Says:

    Those are very interesting bones. I stood looking up at them myself, on a busy Bank Holiday Monday this 5th May.

    I see lots to comment on and ask, so moving from the top down (dorsoventrally; I’m practising the terminology here, I hope I do ok!):

    The neural spines are… odd. Wider from side to side (‘dextrosinistrally’?) – and bifid – rather than anteroposteriorly. Which seems mechanically weak for lever-arms helping to support that long tail aloft (in its updated remounted posture off-ground).
    So I am wondering if in Diplodocus the wide and dorsoventrally deep transverse processes served that role instead, with strong paired muscle-masses dorsolateral to the tail-base, rather than mostly-just-dorsal muscle and ligaments doing it. That may imply either a freeing of the neural spines for some other purpose, or a special need for mobility (especially lateral flexure) at the tail-base… or both.
    (May I just say ‘shake your booty’ here before someone else does?)
    I guess there would be similar muscle attached under those ‘wings’ (are there any clues to muscularity, above or below them, from degree of scarring – or is the original bone surface not well enough represented to tell?)

    It would be great to see a series of caudal cross-sections, a reconstruction of that tail anatomy!

    The chevrons: would they have been attached below each vertebra, or below the intervertebral discs (as they seem to be mounted here)? How were they oriented in life (orthogonal to tail axis or oblique)? This bears on tail dorsoventral thickness, and on…

    The cloaca (excuse me): am I right in picturing the gut opening in that quite restricted space under the chevrons and above where the ischia meet? seems small… Since some of the more distal chevrons seem to be missing, are the chevrons’ exact placement wrt vertebrae well-known in this area?

    Finally, those ischia. I noted on my visit in May that this pair seems quite asymmetric: is that an artefact of preservation and/or mounting, or likely a real-life condition? it might be interesting to compare series of cow and elephant pelvises for symmetry
    (I have seen a grossly deformed cow pelvis, in the Dorling Kindersley book Eyewitness:Skeleton. Broken in a fall, it had healed, but with the parts displaced and askew, evidently forming a ‘new’ acetabulum for the head of the femur… Respect!)

    Did sauropods lie down resting weight on their ischia and pubes?

    Could asymmetries in this area indicate: natural variation; asymmetric gait/stance; left-or-right-tailedness (in whatever they did with their tails); trauma; or a habit of laying down sideways?

  3. Matt Wedel Says:

    The neural spines are… odd. Wider from side to side (’dextrosinistrally’?) –

    Mediolaterally or simply transversely. Although dextrosinistrally has a certain panache.

    and bifid – rather than anteroposteriorly. Which seems mechanically weak for lever-arms helping to support that long tail aloft (in its updated remounted posture off-ground).

    Keep in mind that the neural spines were connected to one another by sheetlike interspinous ligaments, which transmitted forces from one vert to the next all the way back to the sacrum, from which the tail was ultimately cantilevered. Spines that were anteroposteriorly long and narrow had less area available for the attachment of those tendons, compared to transversely wide spines. Works for muscles, too–strength correlates with cross-sectional area, not length, so a broad spine has more room around the edges for muscle attachment.

    I’m going to pass on the ischium question, although without having looked at them closely my knee-jerk reaction is to blame Taphonomy. That Eyewitness Skeleton book is a little gem; I use it all the time in my anatomy labs.


  4. Not a regular reader (nor a palaeontologist), but I’ve seen mention of this blog on Darren’s TetZoo, and when I saw this photo of Charles Gilmore and some sauropod (?) vertebrae at the Smithsonian in 1924, I figured it would be good for my karma to point you to it.

    http://www.shorpy.com/node/3541?size=_original

    cheers,

    George

  5. Graham King Says:

    Cheers Matt!

    ’dextrosinistrally’?

    Mediolaterally or simply transversely. Although dextrosinistrally has a certain panache.

    ;-D I knew that simpler word ‘transversely’… there it is in the title, ‘transverse processes’… but obviously forgot it!

    …mechanically weak for lever-arms helping to support that long tail aloft (in its updated remounted posture off-ground).

    Keep in mind that the neural spines were connected to one another by sheetlike interspinous ligaments, which transmitted forces from one vert to the next all the way back to the sacrum, from which the tail was ultimately cantilevered.

    (Lightbulb goes on over head!) Cantilevered… I see… I was thinking of the tail having to be actively hauled up to support it mid-air, but a passive ribbon of ligament with the spines embedded in it would save effort. Do I infer correctly then that the tail in life would likely have little flexure in the vertical plane but be rather mobile laterally?

    (Like those toy snakes or lizards I’ve seen – and hope you have too or this illustration won’t help much! – where a median strip of leather or somesuch standing on edge holds the whole assemblage of rigid body segments together, and each segment has bevelled-off faces, or gaps between it and adjoining segments, thus allowing wiggle in horizontal plane only).

    A tail swung much to the side would apply axial torsion to the vertebral column; I wonder if those transverse processes signify a substantial swing (to a large angle and/or forceful)?

  6. Darren Naish Says:

    Thanks for comments Graham (and others). Some select responses to points not already answered: the CM84 mount doesn’t make sense in terms of relative size of the ischia relative to the vertebrae and chevrons, and this is almost certainly because it includes material from more than one individual. Ordinarily there would be/is a pretty sizeable space between the ventral tips of the ischia and the first chevron, so plenty of room for the cloaca thank you very much… (peruse our archives and look for other mounted skeletons to see what I mean).

    Q: Did sauropods lie down resting weight on their ischia and pubes?

    A: We know nothing of what sauropods could and did do as goes this sort of thing, but it seems ok to me to imagine that they might have occasionally rested, belly to the ground, and used their pubes, ischia, knees and elbows to support their weight. Computer modelling has now been used to examine possible resting postures in theropods and Triceratops, but sauropods remain untested as goes this sort of thing so far as I know… it’s only a matter of time however.


  7. […] revision of the genus’ (p. 7). You might recall that we looked at Diplodocus caudal vertebrae quite recently, and on that occasion the vertebrae belonged to D. carnegii. If you compare the D. carnegii caudals […]

  8. Matt Wedel Says:

    Whoa, something just struck me as odd. Why are there no chevrons under the vertebrae on the left?

  9. Darren Naish Says:

    Knowing the way the great British public behave in museums, someone probably reached up and nicked them. I admit I hadn’t even noticed this before, duh.

  10. Dave Godfrey Says:

    They’d have needed a stepladder to do it though, they’re a good way off the ground. I wonder if they ever had chevrons on the cast, even before the remount?

    Part of me is still inclined to believe that there’s no real evidence for this mount, and its all done to stops people nicking bits of the cast. :)


  11. […] done diplodocine caudal vertebrae before but, what the hell, you can never have too many of them. Here’s the tail base of the […]


  12. […] an extremely rare condition in sauropods, in fact unique as far as I know.  As we’ve shown here and here, among other places, the chevrons are usually separate bones from the […]

  13. Adrian Baker Says:

    As a newbie (as such) I don’t know what the abbreviations mean, i.e. PRDLs, PODLs, SPRLs, SPOLs,ACDLs & PCDLs.
    Can you please either tell me their meanings or let me know where to find them?
    Fantastic Blog by the way, it will keep me busy for hours.

    Many thanks
    Ade

  14. Matt Wedel Says:

    Hi Adrian,

    The abbreviations all refer to laminae, the thin sheets of bone that connect the various landmarks in sauropod vertebrae. We have a tutorial about laminae, but I don’t think it covers all of the 19 named ones. At the time we wrote it, the one-stop-shopping-for-laminae-paper–Wilson (1999)–was still freely available on Jeff Wilson’s website, but that appears not to be the case anymore. We should probably go back and update that tutorial with a canonical list of laminae and their abbreviations. [20 minutes later] Okay, tutorial updated.

    Thanks for the kind words about the blog, btw.

  15. Adrian Baker Says:

    Many thanks for that Matt, very much appreciated.

    Ade


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