Maybe all the camels are wrong

September 27, 2010

Suddenly it’s camel season here at SV-POW! In the last post, Mike was having some doubts about how far back camels could get their heads. That got me curious, so here are the results of 45 minutes worth of Google Image Search.

This live baby camel (source) has its neck extended about as far as the presumably dead juvenile camel from the last post, so that pose is not just mechanically possible, but also achievable in life. Admittedly, this is a baby, so it might have a bit more flexibility than adults. But I doubt if it is really pushing things here, since I’ve seen adults get into more extreme poses than this.

This dromedary Bactrian camel [thanks to John Scanlon for the correction] (source) has its head back pretty close to the hump, but it’s hard to tell with all the hair. People trying to work out the normal neck postures of the members of KISS probably run into the same problem.

I think we should have a caption contest for this one (source). Not terribly informative from a figuring-out-what-the-bones-are-doing point of view, but I like it.

A kneeling camel, from Werner Herzog’s Even Dwarfs Started Small, described as “the only film whose all-dwarf cast gleefully commit acts of arson and vandalism, throw themselves at or on top of moving vehicles, flick through pornographic magazines, stage a mock religious ceremony with a crucified monkey and laugh themselves hoarse at a camel as it takes a dump” (source, for both photo and quote). What’s cool here is that the camel’s back is angled down at the front, but its neck and head posture are unchanged.

Same thing, this time in color, sans dwarf (source).

Now, none of these camels are maxing out because they don’t have their heads laying back on their humps, as shown in slide 9 of this talk by Kent Stevens (thanks to Steve O’C for the link, in a comment on the last post). Which prompted Mike to write:

Yes, I’ve seen the picture you allude to, with the dorsal surface of the camel’s head in contact with the hump. (In fact I am pretty sure that either John or Kent showed that picture at SVPCA.) I initially planned to photoshop the mounted camel’s cervicals into that position, but it just seemed too ludicrous to believe in, and I’ve come to suspect that this picture might itself be the work of photoshoppers.

Look kids, the argument from personal incredulity!

It’s not Photoshop. There are more photos like this, they’re just not easily available online (believe me, I tried). The one shown by Jeff Wilson in his Jobaria talk at SVP ’99 was of a whole live camel on location in the desert, not the same posed camel you can see in Kent’s talk. Also, I’ve seen camels do this at the circus.

And why is it so hard to believe that camels can get their necks back that far? As Mike pointed out in another comment, the anterior verts aren’t extended much at all in his Cambridge camel. If they have anything like the flexibility of the posterior cervicals, getting the head back against the hump ought to be a cinch.

I am starting to think that camels might be the most interesting mammals out there. The neck of the giraffe certainly looks like it is suspended from the withers, whereas camel necks aren’t connected by any straight-line ligament from the back of the head to what pathetic withers they have (meaning that they do have a nuchal ligament, but it can’t be working like a suspension bridge cable inside that curvy neck), and must be held in those ridiculous curvy poses by continuous muscular effort. But when you look at the cervicals, there are no neural spines at all through the middle of the neck! Not to mention the very flat zygs that look like they shouldn’t allow the poses in the first place. It’s like they’re defying us to make any sense of them.

Clearly, what we need to do is visit museums with complete but disarticulated camel necks that we can put in sandboxes and pose, like I did for the chicken and the infamous rabbit way back when. It’s no good taking photos of mounted skeletons and declaring that they’re in ONP. Zyg-by-zyg scrutiny often reveals that one or more joints is not in ONP (usually more, if the animal is mounted in anything like a normal lifelike pose), and the spaces between the centra are often filled with some weird goop that is supposed to look like intervertebral cartilage, or just left open as in the Cambridge camel. Here is another shot from that talk of Kent’s, of a camel neck supposedly in ONP, illustrating both problems.

In the same talk, Kent wrote that the zygs of the camel do allow the head-to-hump posture. That’s backed up by some Photoshopped images of the same mounted camel with the goop in between the verts. I have no doubt that the craniocervical system of the camel allows the head to touch the hump, because I’ve seen it with my own eyes. What I’d like to know is whether you could put a disarticulated camel neck in a sandbox and achieve the same pose without violently disarticulating the cervicals. The photos of the Cambridge camel suggest that either the zygs are going a lot farther past each other than is commonly assumed, or the intervertebral cartilage is allowing more separation of the centra.

In Kent’s talk at SVPCA he cited a pers. comm. from Kent Sanders and me at SVP ’98, that in playing with ostrich necks we could not get the zygs to completely disarticulate, and that the bone would break before that would happen. That’s true, that is what we found. But the really important part of what we found is that the zygs don’t stay parallel to one another. That is, in flexing and extending the neck, the cervical zygs don’t just slide past each other in the same plane, they can also hinge apart like the covers of a book. You’ll recall that the assumption in Stevens & Parrish (1999) was that the zygs maintained 50% overlap, but subsequent work (including work by them) has shown that much smaller overlaps are possible. My work with Kent Sanders on ostrich necks suggests that the problems of determining ROMs from bones are even worse, because the zygs can get to 20-25% overlap and then hinge open, so that only the very edge of one zyg is still in contact with the other. At that point it is meaningless to even talk about overlap. How you constrain that in your model, I have no idea.

Finally, I have a memory of Greg Paul saying years ago, possibly on the DML, that if you fed a camel into DinoMorph, it would crash the program. If anyone can find that quote, I’d be grateful. To my knowledge, that assertion has never been tested, although I think it would be an informative exercise for all parties and I would be most interested in the results.

Bonus Sauropod Image

Because it was a long dry summer (Gilmore 1932:pl. 6):

References

  • Gilmore, C. W. 1932. On a newly mounted skeleton of Diplodocus in the United States National Museum. Proceedings of the United States National Museum 81, 1-21.
  • Stevens, Kent A., and J. Michael Parrish. 1999. Neck posture and feeding habits of two Jurassic sauropod dinosaurs. Science 284: 798-800.
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16 Responses to “Maybe all the camels are wrong”

  1. Heinrich Mallison Says:

    great post (as always)!

    what we found is that the zygs don’t stay parallel to one another. That is, in flexing and extending the neck, the cervical zygs don’t just slide past each other in the same plane, they can also hinge apart like the covers of a book.

    that reminds me of something someone – can’t remember who exactly – kept saying. He used the word “gape”, zygapophyses can gape, as they do in the lower back of human when we bend down to touch our toes. Now who the he*k said that….if I could only remember… ;)


  2. These are awesome photos, Matt. There is a minor caveat in the argument that these reveal much information, as the photos are shown at angles that betray the actual lateral-aspect of the vertebrae in question, and moreover do not show the vertebrae in question.

    However, you note that camel zygapophyses are flat — they are not. The postzygapophyses are ventrolaterally angled, and while they posess virtually none to limited arcs of curvature, it is there (most of in in the coronal plane); the prezygapophyses, on the other hand, are very curved, and very angled relative to the postzygs of the preceding vertebrae, and this is clear in the photo from Kent’s slide. It is also a strong caveat in reconstruction of mobility, as articulation of the intervertebral spaces is not required and in fact doing so (as in Mike’s reconstruction in the previous post) results in less mobility than realistically shown … in mammals. This is due to the concave, flat, or saddle-shaped centra do not lend themselves to neat articulation: avian intervertebral discs are different, very different, from those of mammals, the latter which are large, bulbous, and provide a sort of “ball bearing” between vertebrae, vastly increasing the range of motion. Avian vertebrae get over this advantage:mammal by having many more vertebrae to increase relative arc and torsion in the neck.

    Also, posting actual necks in articulation and not life-postures helps, as it permits noting where the vertebrae are relative to postures improves this discussion. Weren’t there xray studies on neck posture?


  3. Off-topic (sorry): Nima at “the Paleo King” just finished a very good post on the “Archbishop” (plus bonus live restoration!).
    Take a look over there:

    http://paleoking.blogspot.com/2010/09/archbishop-in-first-detailed.html

    Leo A.

  4. Mike Taylor Says:

    Thanks for those photos, Matt. I’ll be happier, though, when we find a convincing one of a camel doing the extreme neck-extension thing. We do have the slide from Kent’s talk, but that is so low-resolution than it’s not really possible to tell even whether it’s a photo or a drawing, so I don’t want to conclude too much from that.

    I trawled some DML archives in search of the Greg Paul quote that Matt was looking for. I didn’t find it, but I did stumble across this very intereresting post by Jerry Harris:

    I’ve also had the pleasure of playing with camel cervicals, and they’re actually peculiar in a number of respects. First, the caudal cotyle isn’t _nearly_ as concave as the cranial condyle is convex — it’s somewhere between stereotypical “opisthocoely” and “having a ball butt up against a flat surface.” I’ve wondered if this is, in part, responsible for the camel’s ability to hyperdorsiflex its neck. Second, the apparent “angle” of the caudal codyle, in lateral view, doesn’t reflect very well the nature of the cotylar surface: we tend to assume that the center of any arcuate surface is the point at which a perpendicular crosses through the apex of the arc (e.g., the umbrella model), and while this may be true geometrically, it isn’t true anatomically all the time. In some opisthocoelous mammals, the caudal cotyle is basically what one would expect except that there’s an extra-long sheet of bone protruding caudally from the ventral margin. In other words, when you look straight into the condyle, along the axis of the vertebra, the concavity seems to be “pointing” more or less along the axis of the vertebra, but when you look at the thing in lateral view, you’d expect that the shaft of the “umbrella” that would hypothetically pierce the arc of the caudal cotyle, you’d think it would be a line that would proceed cranioventrally. I didn’t play very much with how they actually articulated — I was more focused on getting some measurements for other reasons — but it looked as if the vertebrae lined up with the vertebral long axes closer to lining up that one might thing from such “wedge” or “parallelogram”-shaped structures in lateral view. I haven’t thought much about it; it sounds like an interesting adaptation to limit ventral flexion of the neck, but doesn’t necessarily imply that the neck MUST have a sharp upward turn. In some non-opisthocoelous mammals (e.g., a warthog whose skeleton I measured), age produces really ugly exostoses that create caudally-projecting ventral (and sometimes even lateral) sheets from the caudal articular surface; sometimes, these even fuse cervical vertebrae together (i.e., they’re fused along these ventral sheets, but nowhere else), again limiting ventral flexion. I’m not saying that either Kent or Scott is wrong here; just reporting some observations — their applicability to sauropods ought to be investigated.

    All of this, of course, just reinforces the urgency of my getting to a museum with a complete disarticulated camel neck skeleton.

  5. Andreas Johansson Says:

    Humans have pretty pathetic necks, but presumably there must be medical work on neck mobility and the role played by intervertebral cartilages in humans. Might this be something to look at?

  6. Mike Taylor Says:

    Here’s another neat picture that Darren found:

    From “Camel ‘ballet’ in the desert”.

  7. kristina Says:

    “People trying to work out the normal neck postures of the members of KISS probably run into the same problem.”

    Hahaha! Funniest thing I’ve read all week.

  8. Steve O'C Says:

    One thing I haven’t fully understood is how does one decide where the center of rotation between two vertebra is? It’s not like vertebra are parts of a mechanical arm that have a perfectly unchanging center of rotation. It could be that the center of rotation between vertebra is dynamic because of the slightly squishy nature of cartilage and because the vertebra aren’t 100% locked together.

    Anyway, I was searching the net and found some motion x-ray vids with animals. Sadly I’m not sure they are going to answer any questions but they are interesting to watch….There is a human, rabbit, cat and some ducklings.

  9. Mike Taylor Says:

    Steve, you make an important point. Up till now, the way we’ve determined the centre of rotation is to look at lateral-view illustrations and guess. Yes, one of the things we’ll need to do to bring our models up to the ‘merely inadequate rather that almost completely useless” level is to do a better job of understanding how this really works.

    Thanks for the video links — very interesting!

  10. Matt Wedel Says:

    One thing I haven’t fully understood is how does one decide where the center of rotation between two vertebra is? It’s not like vertebra are parts of a mechanical arm that have a perfectly unchanging center of rotation. It could be that the center of rotation between vertebra is dynamic because of the slightly squishy nature of cartilage and because the vertebra aren’t 100% locked together.

    Quite. The fact that zygs can hinge or gape apart, in addition to sliding past each other, suggests that there is an element of dorsoventral gliding in addition to rotation. It’s probably not just for mammals, either. Jaime is correct that mammals tend to have fat, squishy intervertebral discs that potentially allow a lot of motion beyond mere rotation. Birds tend to have a thin skein of articular cartilage over each of the vert, with a synovial capsule between. But many birds also have a cartilaginous meniscus in the joint capsule, between the two vertebrae. Where that’s the case, a single intervertebral joint includes two centra articulating with the meniscus in between. One would think that would potentially increase both the range and kind of motion possible at the joint.

    This is pretty darned interesting stuff. We gotta do more work.

  11. Nathan Myers Says:

    These things poised between the vertebrae might need to be modeled, mechanically, as if they were wee extra vertebrae: an even bony one, then an odd cartilagenous one, then another even bony one, and so on.


  12. [...] The Oxford Camel is Just Plain Cheating and Maybe all the camels are wrong [...]

  13. John Scanlon FCD Says:

    Let me just point out that the picture you refer to as a ‘dromedary’ is a long-haired, two-humped Bactrian camel; the dromedary is the more familiar Arabian job shown in all the other pics.

    I haven’t been out into camel country yet, but will try to do so before the Wet, and will let you know if a neck becomes available.

    On the precedent of Mike’s ostrich dissection, have you tried calling up local llama/alpaca/vicuña farms to see if they have any spare necks?

  14. Mike Taylor Says:

    Thanks for spotting that mistake, John — I fixed the text.

    I was going to respond to your last suggestion by saying “there are no llama farms in Britain”, but thankfully I took ten seconds to Google it, only to find that I was dead wrong. Thanks for the tip — I’ll look into it.


  15. [...] with the vertebrae often held more-or-less straight through the middle section of the neck (camels are an obvious exception [...]


  16. [...] course, here at SV-POW!, we have previous with camels: the Cambridge camel, all the camels, the Oxford camel, the Paris [...]


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