Well, not Xenoposeidon, anyway

November 27, 2007

After eight consecutive posts on Xenoposeidon, I have to admit that even I am getting just a tiny bit bored of it, so I can only imagine how the rest of you feel. So now for something completely different:

BMNH 96 “Chondrosteosaurus”

You see before you a badly battered cervical vertebra, BMNH R96, which if I remember correctly is catalogued as belonging to “Chondrosteosaurus“. That genus, like so many from the Wealden, was erected on non-diagnostic material, and there is really no reason to think that R96 belongs to the same taxon as the Chondrosteosaurus type specimen BMNH R46869. It’s best regarded as Neosauropoda indet. (and, no, before you ask, we will not be naming it and promoting it as “The world’s second most amazing sauropod”).

The interesting thing about this specimen is that its condyle is completely eroded away. We’re looking at it in anterior view, right into the front of the centrum, and we can see a classic camellate pattern. The network of thin lines is bone; everything in between, now filled with matrix, used to be filled with air when the animal was alive. A while back, Matt ran the number on this photo and concluded that this vertebra was 78% air — a very high proportion even by sauropod standards, exceeded only by Sauroposeidon (the world’s third most amazing sauropod).

Of course it’s a shame that this bone is so poorly preserved; on the other hand, if it were complete, we wouldn’t be able to see the internal structure. Matt’s firmly of the opinion that bone not broken is a bone wasted, and I sometimes think that if he had his way, he’d go through the world’s sauropod collections with a sledgehammer, smashing all the vertebrae open in search of pneumaticity. (Note to collections staff: Just kidding! Har har!) It’s certainly true that more is known about the “Angloposeidon” vertebra than would be known if it weren’t snapped in two; and of course, we’d not have known about the internal structure of the Xenoposeidon vertebra were the condyle not blasted off.

Up till now, internal structure has been badly neglected in terms of informing sauropod phylogeny, despite Matt’s work on its evolution and distribution (Wedel 2003a, 2003b). The analyses of Wilson (2002) and Upchurch et al. (2004) each included just a single character for presacral bone texture in their matrices; and the Grand Unified Analysis of Harris (2006), which merged the Wilson and Upchurch matrices, discarded even this one character, as discussed in the supplementary data. That may be fair enough: we might not yet know enough about vertebral bone texture to code it well. But hopefully that will soon change, because there is a lot of information out there that’s not getting used.


21 Responses to “Well, not Xenoposeidon, anyway”

  1. Nick Gardner Says:

    I like the free article plugging in the references section. There should be some kind of index of authors who host their articles on their personal Web spaces.

  2. Mike Taylor Says:

    Thank, Nick. We like Open Access, too — in fact, we think any other kind of access is iniquitous. The current situation has been brilliantly skewered by Scott Aaronson in a short article that every academic author should read.

    There should be some kind of index of authors who host their articles on their personal Web spaces, you say? Ladies and Gentlemen, I give you: Open Access Biology and Paleontology, Part II: Individual researchers’ pages, from the blog of Dr. Vector.

    Although now that you come to mention it, a more visible location right here on SV-POW! would not be such a bad idea.

  3. Mike from Ottawa Says:

    Until I saw the scale bar I thought ‘Who knew a morel could fossilize.’

    Can CT scanning get at the air spaces in a sauropod vetebra? Seems it would be a little more respectful than a sledgehammer, though sledgehammers are cheaper than CT scanners, unless you’re a rockstar like Paul Sereno.

    Other questions: do you know enough about the internal structure of the vertebrae of any particular sauropods to know to what extent variability in the internal spaces is an individual characteristic as opposed to a species characteristic. It seems like something that would have involved exploratory development (showing off having read ‘The Plausibility of Life) and, so, be quite variable within a species and even, perhaps within the vertebrae of a single animal. If that was the case, it wouldn’t be a very useful measure for cladistic analysis would it? I’m hoping I’m out to lunch and will get the error of my ways shown to me.

  4. Matt Wedel Says:

    Hi Mike from Ottawa,

    Mike Taylor was joking about the sledgehammer. This January will be the tenth anniversary of my first sauropod vertebra CT scan. So not only can it be done, it’s been the cornerstone of my career to date. And I got the idea from Brooks Britt, who was doing it a decade and a half ago. The papers linked above include some CT images. Not enough–never enough–but hopefully sufficient to make a few points.

    Your second question is extremely perceptive. Pneumaticity is inherently variable, so there is little reason to get all worked up about some kinds of differences–say, the specific location of an accessory lamina, or the exact pattern of spaces inside a bone. But there are broad regularities that seem to hold up across fairly large clades (see the papers above for details). Those regularities aren’t hard to identify, but whether they are suitable cladistic characters is another question. We’d prefer for cladistic characters to have discrete states, so we know we’re coding real differences and not just our subjective views of things. The trouble with pneumatic internal structures is that there are pretty finely-graded series of intermediates between most or all of the known ‘states’, which makes coding those things as discrete characters difficult or impossible. That’s the very reason that Jerry Harris tossed pneumatic internal structure out of his Suuwassea analysis: it’s not that it wasn’t evolving, or that we don’t see regular differences among clades, it just wasn’t suitable for phylogenetic analysis–given the current level of understanding.

    I actually think there is a way to sort this stuff out discretely, but that’s based on some ideas I haven’t written up yet, so I’m going to keep mum for now. One of these days…

    Anyway, a point to keep in mind is that characters that don’t show discrete states might not be great for phylogenetic analysis, but they still evolve, and we can still learn a lot about evolution from them.

  5. Mike from Ottawa Says:

    Thanks, Matt. I should have perused the papers first, you being so kind as to have made them available – even if I’ll have to be googling half the words in them. :-)

  6. Matt Wedel Says:

    Nah, a seasoned SV-POW! veteran such as yourself will be fine. Or, if you get stuck, let us know. Any sticking points might be good fodder for future tutorials.

  7. Mike from Ottawa Says:

    Actually, I am stuck, but not on the pneumaticity papers, but on the term “embolomerous” that lards Clack’s Gaining Ground. Even googling I can’t find anything that does more than describe this condition of vertebrae in terms that involve 43 more terms of equal obscurity (to me). You guys, though, honchos in all things vertebral, I hope can give me an explanation that can cut through my ignorance. A picture would be even better, if there’s one out there on the web.

  8. Mike Taylor Says:

    “embolomerous” — what the heck?

    Sorry, never heard of it.

  9. Mike from Ottawa Says:

    That makes me feel better. Especially since I think I’ve now got it figured out, after going over several pages that come later in Clack’s book, bouncing back to illustrations early in the book, I’ve got it figured out. If you ever need to know, LMK, and I can give you guys a tutorial about vertebrae. :-)

  10. Randy Says:

    A great story (or debacle?) about the importance of seeing the cross sections of fossil bones via breaks is recorded in this reference:

    White, T.D. 2006. Early hominid femora: the inside story. Comptes Rendus Palevol 5:99-108.

    Hopefully the sauropod gods won’t smite me for referencing a paper that is about neither sauropods or vertebrae.

  11. Darren Naish Says:

    ‘Embolomerous’ is one of several terms used to describe the vertebral configuration of early tetrapods (‘early’ in the loosest sense of the term: we’re talking about all those tetrapods that aren’t amniotes and used to be called ‘amphibians’). In these animals, there are various vertebral elements that no longer exist as discrete elements in adult amniotes – namely intercentra and pleurocentra (I’ll avoid discussing the fate of these elements in amniotes.. anyone else want to do it?).

    — In the rhachitomous condition, the pleurocentra are small, paired structures tucked under the neural arch.

    — In the gastrocentrous condition, the intercentra alone support the neural arch (the pleurocentra are tiny).

    — In the schizomerous condition, intercentra and pleurocentra are about equal in size, both forming the anterior and posterior parts of the vertebral body respectively.

    Embolomeres – a group of long-bodied, mostly aquatic tetrapods that were around from the Carboniferous to the Permian (some were huge, exceeding 4 m) – might be described as schizomerous, but I suppose the intercentrum and pleurocentrum are both so big in these forms that a different descriptive term is warranted, and this is where the embolomerous condition comes into it.

    I admit that I’ve always struggled with these terms because they’re virtually never explained in the literature, and there are further terms – like prorhachitomous and lepospondylous – that I’ve ignored here. No doubt an expert on the animals concerned would explain things better. Have you thought of asking Dr Clack?

  12. Darren Naish Says:

    Har har – you funny! :)

  13. Mike from Ottawa Says:

    Cruel to get our hopes up for BTV-POW! like that Mike. The moment of anticipation, though, gives me a good opening to say how excellent SV-POW! is. I look for opportunities to tout it to people because I think that the enthusiasm and good cheer you guys show in a blog with such a narrow focus says something very positive about the nature of doing science and the power of the sense of wonder.

    “Have you thought of asking Dr Clack?”

    I almost did, but I found enough scattered about her book to figure it out to my (current) satisfaction.

    I’m finding Gaining Ground truly fascinating. It is my commute reading and I find that I get through just a few pages, with much referring to images and re-reading bits in order to actually understand something, and there I am at my destination with the feeling that it’s only been a couple of minutes not 40. As a book for the layman, though, it has some problems that are more a matter of organization than anything else.

    Though this may be more a question for TetZoo (which, like the rest of ScienceBlogs, I can’t access here at work), is there anything good that’s similar to Gaining Ground regarding the evolution of the whales? Or of sauropods, to bring us a bit closer to the topic and not turn this into the BTV-POW! or the CV-POW!

  14. Darren Naish Says:

    People are always asking about a good review volume on whale evolution.. and the answer it that there is no such volume, yet. The closest thing to it is Berta et al.’s Marine Mammals: Evolutionary Biology (here on Amazon), but it’s more of a textbook than a good read. There’s a new semi-popular book out on the evolution and fossil history of marine animals, called Neptune’s Ark, but I know nothing about it and have yet to see it.

    As for a good book on sauropods, I’ll let Mike or Matt answer that one.

  15. Mike Taylor Says:

    I don’t think there is a good semi-technical book about sauropods as a group. In the last couple of years, two all-sauropods-all-the-time volumes have come out, Thunder Lizards edited by Carpenter and Tidwell and Sauropods: Evolution and Paleobiology edited by Wilson and Curry Rogers; but while both of these books have lots of good stuff in, they are essentially compendia of random technical papers, and have nothing to offer in the way of tutorials or a coherent journey through their subject.

    My best recommendation would by The Complete Dinosaur, edited by Farlow and Brett-Surman. It’s about all dinosaurs, not just sauropods (as the name kind of implies), but it does a great job of laying out what’s known for an intelligent layman — and it’s absurdly cheap for such a hefty tome. Chapters are contributed by many different authors, but their subjects are such that the book makes a coherent whole which I found very helpful a few years back and still occasionally refer to.

    But if you want a whole book just about sauropods, then I think you’ll have to wait for SV-POW!: The Book. No, just kidding, we have no such plans.

  16. Mike Taylor Says:

    Dude, of all the people in the world who know how dispiriting it is to have Book Plans and then watch them fall to pieces under your feet, I’d have thought you’d be first in the line shouting “No SV-POW! book, not now, not never!”

  17. Darren Naish Says:

    I’m a slow learner. But good point…

  18. […] by Mike’s recent post on the interior of Chondrosteosaurus from the Isle of Wight’s Wessex Formation, what could I do […]

  19. […] another shard of excellence, referred to Chondrosteosaurus, NHM 96. As Mike had discussed here before, there’s no good reason to believe that it actually is Chondrosteosaurus, and the internal […]

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