Cartilage accounts for nearly a fifth of the length of the neck of a baby giraffe

March 26, 2011

In a comment on the previous post, Dean asked: “What was the difference in length between the neck with its cartilage and the bones flush together?”

I’m glad you asked me that.  You’ll recall from last time that the fully fleshed neck — intact apart from the removal of the skin and maybe some superficial muscle — was 51 cm in length from the front of the atlas to the back of the centrum of the seventh cervical vertebra.  When I pose the cleaned and cartilage-free bones together, the total length of the series is only 41 cm — 10 cm shorter, coming in at just over 80% of the live length.  Don’t believe me?  Here are the photos!

I’m sure I need hardly say, but the top image is the neck as we got it, the second is the cleaned bones posed in more or less the arrangement they must have been in life (both of these taken from the previous post) and the bottom image the bones fully abutting.

So!  The neck of Wallace the baby giraffe was very nearly a quarter as long again as the bones alone suggest.  Does this mean that the neck of Giraffatitan was really 10.6 m long instead of 8.5 m?

It’s an exciting prospect, but I’m afraid the answer is no.  As I hinted last time, while it’s perfectly acceptable, indeed obligatory, to recognise the important role of cartilage in sauropod necks qualitatively, we can’t blindly apply the numbers from Wallace the baby giraffe to adult sauropods for two reasons: 1, Wallace is a baby; and 2, Wallace is a giraffe.

The first of these reasons is part of why I am keen to do this all over again with an adult giraffe when I get the opportunity; but there’s not much we can do about the second.  One might think that a more closely related extant animal such as an ostrich might have a neck that is more homologous with those of sauropods; and that’s true, but my feeling is that the giraffe is more analogous.  That is, although the birds share more recent common ancestry with sauropods, giraffes’ more similar size seem to have encouraged them to evolve cervicals that are in some ways more similar to those of sauropods, most notably in the possession of ball-and-socket intervertebral joints rather than the saddle-shaped joints that are ubiquitous in birds.

How big a deal is Wallace’s juvenile status?  Well, take a look at his fifth cervical vertebra in posterior view:

If this bone were found in 150 million years by competent palaeontologists, in a world where there were no extant artiodactyls to compare with, what would they make of it?  Most of the articular area of the centrum is very obviously damaged, exposing the internal spongy texture of cancellous bone — presumably the bone surface was attached more firmly to the cartilaginous posterior end of the element than to the inner part of the bone, so it came away with the cartilage during simmering.  So it would be obvious to our future palaeontologists that the articular surface was missing, and that the complete vertebra would have been somewhat longer — but it would be hard to judge by how much.

But the state of this bone is particularly interesting because the middle part of the centrum does have a preserved bone surface.  It would be easy to extrapolate that out across the whole area of the posterior end of the centrum, and assume that this was the maximum posterior extent of the element’s functional length in life — an assumption that we know, having taking the neck apart ourselves, would be completely wrong.

Are we making similar incorrect assumptions with our sauropod vertebrae?

An even more interesting case is the postzygapophyses.  The posterodorsal surface of the left postzyg is slightly damaged, but the bone of the right postzyg has a nice, perfectly preserved surface.  But I can tell you that the functional articular surface of the postzyg was totally different from this: different size, different shape, different position, different orientation.  If we tried to calculate range of movement from these zygapophyseal facets, the results we got would be literally meaningless.

The good news is, there’s a clue that would prevent us from making this mistake — a really nice, obvious one.  The texture of the bone on the postzyg is irregularly crenellated in a way that strongly indicates a cartilaginous extension: it’s the same texture you see on the ends of the long-bones of (even mature) birds if you peel off the cartilage caps.  (It’s also what you see, at a much bigger scale, on the ends of the sauropod long-bones.)

But while the presence of this texture indicates the presence of cartilage, I don’t know whether the converse is true.  In the absence of such a texture, can we assume the absence of cartilage?  I just don’t know.  Anyone?

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16 Responses to “Cartilage accounts for nearly a fifth of the length of the neck of a baby giraffe”

  1. Nick Gardner Says:

    A pity I just threw away a deer neck. But if I recall from past cases, adult deer don’t have large amounts of cartilage between their vertebra.

  2. Mike Taylor Says:

    Grargrghrhggh! You threw away a deer neck? For the love of all that is rational, man, what on earth possessed you?

    Is it too late to pick it out of the garbage? You can make some science outta that thing!

  3. Nick Gardner Says:

    I can always go pick up three more that I’m aware of on the side of the road… :)

  4. I assume you have-

    Hoffstetter and Gasc, 1969. Vertebrae and ribs of modern reptiles. in Gans, Bellairs and Parsons (eds.). Biology of the Reptilia, volume 1. London and New York, Academic Press. 201-310.

    Supposedly they find croc intervertebral length is 11.5% of total length, which compares pretty well to the 13.4% in your giraffe.

  5. Mike Taylor Says:

    Interesting, Mickey! No, I don’t have that article, and I can’t find that a PDF even exists, let alone is available. Does anyone have one, or can anyone make one?

    BTW., where do you get the figure 13.4% from?

  6. dmaas Says:

    I’d love to get a copy as well.

  7. Yeah, I don’t know of a pdf version, I just saw reference to it in a ‘Seismosaurus’ article (Herne and Lucas, 2006) while doing my sauropod research.

    As for 13.4%, I divided the difference in lengths between extended and articulated cervical series by the length of the extended series. I suppose I just measured off the screen instead of using the scale provided, so maybe that messed me up.

  8. Dean Says:

    Mike, thanks for the lengthly and well illustrated answer. But jeez, even 10% cartilage must account for some significant underestimation of 100+ foot long sauropod skeletons! Perhaps this excess is already taken into account in skeletal mounts?

    -BTW I’m a High School student hoping to make it into paleontology, and this blog has been a great source of information to me, thanks.

  9. Nathan Myers Says:

    You got three significant figures measuring off the screen? I am impressed.

  10. Mike Taylor Says:

    Dean, it’s long been a source of conflict between Matt and me how we should assemble consecutive vertebrae in line, and how much of a gap to leave between them. In general, I think that physical skeletal mounts are just put together in what feels like the best way, without much concern for cartilage — but this is perfectly reasonable as the amount of distortion in sauropod vertebrae makes it impossible to be very rigorous about this anyway.

  11. [...] compare with the whole-neck length you started with?  [Crib-sheet answer for our baby giraffe: 41 cm vs. a whole-neck length of 51 cm.  Expect a closer match if you're dealing with an adult animal,which will proportionally less [...]

  12. [...] Notify me of follow-up comments via email. Send me site updates « Cartilage accounts for nearly a fifth of the length of the neck of a baby giraffe [...]

  13. [...] must point to SV-POW!’s dissection of a baby Giraffe neck which revealed nearly one fifth of the length was from cartilage. Adults are presumably less extreme than this, but still, wow. Share this:TwitterFacebookLike [...]

  14. [...] die Beiträge auf SV-POW! zum Thema Giraffenhälse und Sauropodenhälse schon gelesen (hier, hier, hier, und hier), einschließlich des letzten Beitrags letzten Beitrags und des wissenschaftlichen [...]

  15. [...] of you have probably read the SV-POW! posts on giraffe and sauropods necks (here, here, here, here), including the latest post and the paper it deals with (Taylor & Wedel 2013 [...]

  16. […] proportional cartilage thicknesses: almost an order of magnitude from the 2.59% of the Rhea up to the 24% of the juvenile giraffe — or, even if you discard that because of its ontogenetic stage, up to 17% for the dog. And […]

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