Another mystery: embossed laminae and “unfossae”

December 7, 2009

Broadly speaking, pneumatic sauropod vertebrae come in two flavors. In more primitive, camerate vertebrae, modeled here by Haplocanthosaurus, the centrum is a round-ended I-beam and the neural arch is composed of intersecting flat plates of bone called laminae (lam above; fos = fossa, nc = neural canal, ncs = neurocentral suture; Ye Olde Tyme vert pic from Hatcher 1903).

In more derived, camellate vertebrae, the centrum and neural arch are both honeycombed with many small air spaces. This inflated-looking morphology is very similar to that seen in birds, like the turkey we recently discussed. The fossae and foramina on the outside tend to be smaller and more numerous than in camerate vertebrae, as shown here in a titanosauriform axis from India (Figure 3 from Wilson and Mohabey 2006). The green arrows show that the fossae visible on the external surface are excavations or depressions into the honeycombed internal structure of the bone.

External fossae on bones can house many different soft tissues, including muscles, pads of fat or cartilage, and pneumatic diverticula (O’Connor 2006). Pneumatic fossae are often strongly lipped and internally subdivided and may contain pneumatic foramina, which makes them easier to diagnose (but they may also be simple, smooth, and “blind”, which makes them harder to diagnose as pneumatic). But in all of these cases we are usually talking about the same thing: a visible excavation into a corpus of bony tissue, which may have marrow spaces inside if it is apneumatic, or air spaces inside if it is pneumatic (the corpus of bone, not the dent). That’s probably how most of us think about fossae, and it would hardly need to be explained…except that sometimes, something much weirder happens.

Consider this cervical of Brachiosaurus (this is BYU 12866, from Dry Mesa, Colorado). Brachiosaurus and Giraffatitan have an in-between form of vertebral architecture that my colleagues and I have called semicamellate (Wedel et al. 2000); the centrum does have large simple chambers (camerae), but smaller, thin-walled camellae are also variably present, especially along the midline of the vertebra and in the ends of the centrum. As in Haplocanthosaurus, the neural arch is composed of intersecting plates of bone; unlike Haplocanthosaurus, these laminae are not flat or smooth but are instead highly sculpted with lots of small fossae. Janensch (1950) called these “Aussenkaverne”, or accessory outside cavities, because and they are smaller and more variable than the large fossae and foramina that invade the centrum.

And that’s the weird thing. As the red arrows in the above image show, the “Aussenkaverne” are not excavations or depressions into anything, except the space on the other side of the lamina (which in life would have been occupied by another diverticulum). The neural arches of Brachiosaurus and Giraffatitan are not excavated by fossae, they’re embossed, like corporate business cards and fancy napkins.

What’s up with that!? We tend to think of pneumaticity as reducing the mass of the affected elements, but the shortest distance between two vertebral landmarks is a smooth lamina. These embossed laminae actually require slightly more bony material than smooth ones would.

As you can see above, the outer edges of the laminae are thick but the bone everywhere else is very thin. Maybe, like the median septa in pneumatic sauropod vertebrae, the thin bone everywhere except the edges of the laminae was just not loaded very much or very often, and was therefore free to get pushed around by the diverticula on either side, in the sense of being continually and quasi-randomly remodeled into shapes that don’t strike us as being very mechanically efficient. But also like the median septa, the thin parts of the laminae are only rarely perforated (but it does happen), for possible (read: arm-wavy) reasons discussed in the recent FEA post. And maybe the amount of extra bone involved in making embossed laminae versus smooth ones was negligible even by the very light standards of sauropod vertebrae.

Another question: since these thin sheets of bone were sandwiched in between two sets of diverticula, why are the “unfossae” always embossed into them, in the medial or inferior direction? Why don’t any of them pop out laterally or dorsally, looking like domes or bubbles instead of holes, like Mount Fist-of-God from Larry Niven’s Ringworld? Did the developmental program get accustomed to making fossae that went down and into a corpus of bone, and just kept on with business as usual even when there was no corpus of bone to excavate into? I’m only half joking.

I don’t have good answers for any of these questions. I scanned this vert a decade ago and I only noticed how weird the “unfossae” were a few months ago. I’m putting all this here because “Hey, look at this weird thing that I can only wave my arms about” is not a great basis for a peer-reviewed paper, and because I’d like your thoughts on what might be going on.

In Other News

The Discovery Channel’s Clash of the Dinosaurs premiered last night. I would have given you a heads up, except that I didn’t get one myself. I only discovered it was on because of a Facebook posting (thanks, folks!).

COTD is intended to be the replacement, a decade on, for Walking With Dinosaurs. I’m happy to report that one of the featured critters is Sauroposeidon. I grabbed a couple of frames from the clips posted here.

I haven’t seen the series yet, because I don’t have cable. But I’m hoping to catch it at a friend’s place next Sunday night, Dec. 13, when the entire series will be shown again. With any luck, I’ll have more news next week.

Finally, I got to do an interview at Paw-Talk, a forum for all things animal. I’m very happy with how it turned out, so thanks to Ava for making it happen. While you’re over there, have a look around, there’s plenty of good stuff. Brian Switek, whom you hopefully know from this and this, is a contributor; check out his latest here.

References

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31 Responses to “Another mystery: embossed laminae and “unfossae””

  1. Laelaps Says:

    Thanks for the links, Matt! And I enjoyed seeing your contributions to the first 2 episodes of “Clash of the Dinosaurs” (I’ll have to wait for the last 2 – Discovery didn’t send me a second disc). Not like you don’t have enough to cover already, but I would love to see a post with a little more detail about your hypothesis that wee little sauropods munched insects and other protein-rich foods.

  2. William Miller Says:

    Another question: since these thin sheets of bone were sandwiched in between two sets of diverticula, why are the “unfossae” always embossed into them, in the medial or inferior direction?
    …that is weird. And it does sort of imply the diverticula weren’t just doing random weird stuff in the absence of any constraints.

    Also: Ringworld reference! Cool.

  3. William Miller Says:

    Oh, also (can’t edit comment to add this)…

    If the perforate laminae of Giraffatitan HM SII are the same phenomenon (just more so), is this a new synapomorphy, either of the (Brachiosaurus + Giraffatitan) clade or of Brachiosauridae?

    There are no Sauroposeidon dorsals for comparison, sadly … does the Archbishop have embossed laminae or perforate laminae?

  4. Mike Taylor Says:

    William, this is a good question. The vertebrae we’re looking at here are all cervicals, so the lack of dorsal material in Sauroposeidon is not a problem. Hopefully your question will have sent Matt running back to his CT-scan data to check for unfossae in his beast of choice. And I will certainly be looking for them in the Archbishop’s Cervical U scan.

  5. Nathan Myers Says:

    I can’t tell you about unfossae, but I can tell you for certain that all the pure black and white images above are about sex.

    Also, that Haplocanthosaurus was left-handed.

  6. William Miller Says:

    Oops, I was looking at HM SII D8 and somehow forgot/missed that this one was a cervical…

    What about Cedarosaurus? It had dorsals preserved. Are good images of its laminae available?

  7. Mike Taylor Says:

    Sorry to keep disagreeing with you, William, but no cervical material is known from Cedarosaurus. The holotype is listed by Tidwell et al. (1999:22-23) as:

    DMNH 39045, a single specimen consisting of eight articulated dorsal vertebrae, 25 caudal vertebrae, several chevrons, proximal portions of the left and right scapulae, left and right coracoids, left and right sternal plates, right humerus, radius and ulna, metacarpal IV, right pubis, partial left pubis, proximal portions of left and right ischia, partial left femur, right femur, right tibia, three metatarsals, one phalanx, three unguals, ribs, and numerous gastroliths.

    No additional material was reported in that paper, and as far as I know there have been no subsequently referred specimens.

    If I’ve missed something, though, let me know!

  8. Kris Says:

    Matt… in regards to Clash of the Dinosaurs, your referring to baby tyrannosaurs as “little meatballs” was enjoyable.

    The many, many images of Sauroposeidon defecating was, shall we say, less enjoyable ;-)

  9. Nima Says:

    So basically they found just about everything BUT the neck :)

    That’s odd, is there a skull? I’ve seen this skull floating around on the internet, it looks like a brachiosaur and is allegedly from the Early Cretaceous in Utah…

    Here’s the link:

    http://www.sciencedaily.com/releases/2009/04/090429131935.htm

    Is this Cedarosaurus, or any similar species?

  10. William Miller Says:

    Right, I said that it had dorsals (not cervicals).

    I just meant that someone who has access to the specimen should look for HM SII-style perforate laminae on those dorsals.

  11. Matt Wedel Says:

    Sauroposeidon has no unfossae. Its laminae are not flat plates of bone as in Haplocanthosaurus and Brachiosaurus, they are inflated and camellate like the laminae in the titanosauriform axis shown above. “Angloposeidon” shows an intermediate morphology and provides a plausible model of how Sauroposeidon might have evolved from a Brachiosaurus- or Giraffatitan-like ancestor. But that’s a story for another day.

  12. Jamie Stearns Says:

    @Nima:

    The skull is from an as-yet undescribed brachiosaurid from the upper Cedar Mountain formation of Utah. I do not know if is Cedarosaurus or not, but it is apparently a previously-unknown species.

    I have actually been to the site where the material is being excavated (it’s at Dinosaur National Monument within spitting distance of the quarry building), and have learned that there are cervicals there along with no less than four skulls. Unfortunately, we are just going to have to wait for the paper on this beastie before we can say anything about unfossae. The excavated material is being stored at BYU in case anyone is interested.

  13. Jamie Stearns Says:

    PS: The part about it being an unknown species was just what Dan Chure was passing on to the other interpretation people and me, so I really have no idea about what makes it distinctive.

  14. William Miller Says:

    Four skulls! Wow, isn’t that really unusual for sauropods?

    Hmm, since Sauroposeidon has no unfossae, is that another support for a (Brachiosaurus + Giraffatitan) clade, if the perforate laminae really are the same thing?

  15. Mike Taylor Says:

    Four skulls is an unusual morphological adaptation in any vertebrate.

  16. Mike Taylor Says:

    William Miller wrote:

    Right, I said that it had dorsals (not cervicals).

    I just meant that someone who has access to the specimen should look for HM SII-style perforate laminae on those dorsals.

    Ugh, my bad. You were indeed referring to dorsals, I’m not sure how I missed that. Sorry.

    But the broader point is that the kind of sculpting we’re talking about here (including but not limited to unfossae) is never found in dorsal vertebrae — only cervicals. At least, that’s what I’ve observed, and I have spent quite a lot of time gazing at Brachiosaurus and Giraffatitan dorsals. It’s not impossible that I’ve missed something, but I doubt it.

    The reason is that, although dorsals can be highly pneumatic, they are never constructed from sheets of bone such as those that make up our favourite cervical HMN SII:C8, and it’s only by half-punching through a sheet that an unfossa can be made.

  17. William Miller Says:

    OK, so the perforate laminae on HMN SII D8 in this post are not the same thing as the ‘unfossae’?

  18. Matt Wedel Says:

    The reason is that, although dorsals can be highly pneumatic, they are never constructed from sheets of bone such as those that make up our favourite cervical HMN SII:C8

    That’s a courageous assertion, especially in light of the illustrations by Hatcher, Osborn & Mook, Bonaparte, and others, showing that dorsal neural arches are constructed entirely of intersecting sheets of bone. Answer me this: if the dorsal neural arches of Giraffatitan are not composed of intersecting laminae, what are they made of?

  19. Mike Taylor Says:

    Nope. The unfossae are what you’d get if the laminae were made of plasticene and you pushed your finger into them but not far enough to make a hole.

  20. Mike Taylor Says:

    Matt, I’m talking about sheets of bone, such as you get in HMN SII:C8. I’ve never seen anything like that in a dorsal. Yes, there are what we might call plates, but they never extend more than a few inches out from their intersection with the next plate.

  21. Matt Wedel Says:

    I’m sorry, maybe I’m being dense, but I have no idea what you’re talking about. The sheets of bone in the cervicals, like SII:C8, are basically big flat plates (except for the unfossae, etc.) that connect the various apophyses to each other and to the centrum. How is the construction of the dorsals any different? You have all of the same named laminae and then some, and they intersect toward the midline and the top of the neural canal. As far as I can see, other than being anteroposteriorly squashed, the construction of the dorsal neural arches is the same as that of the cervicals. But you’ve looked at a zillion or so dorsals so I have a feeling that we’re somehow talking past each other.

  22. Jaime A. Headden Says:

    Matt,

    Have you traced the thickened edges that seem to persist around any of these embossed fossae, and note whether or not they connect to thicker bone? The reason I ask is that such structures cannot exist in a vacuum, save that something sculpts them out. The resulting unsculpted bone should be connected, laminarly on either side of the embossed “sheet” or plate. It looks like this is occuring in your images, and I wonder if you’ve traced the splines to track the persistence of the thickened rims of each of these areas. If so, then the embossed regions would actually seem to be of diverticular origin, and therefore would be camarate.

  23. Matt Wedel Says:

    Oh, I have no doubt that the embossed regions are pneumatic in origin. No other soft tissue makes tracks like that, end of story. But I’m sorry, I’m not following the connection between the thickened bone and the inference of pneumaticity. Can you please clarify?

  24. Mike Taylor Says:

    Matt, I guess I am talking about a quantitative rather than qualitative difference. Speaking off the top of my head, I guess the greatest breadth:thickness ratio I’ve seen in a lamina of a dorsal vertebra would be about 5-6. In HMN SII:C8, it’s more like 10-20. (Obviously some caliper-and-tape-measure work is needed to do this right.)

  25. Matt Wedel Says:

    Matt, I guess I am talking about a quantitative rather than qualitative difference. Speaking off the top of my head, I guess the greatest breadth:thickness ratio I’ve seen in a lamina of a dorsal vertebra would be about 5-6. In HMN SII:C8, it’s more like 10-20.

    All right, I can buy that. In the cervicals, you’ve got the big not-quite-a-parallelogram bounded by the SPRL, PRDL, PODL, and SPOL on which the diverticula can work their arcane magic. In the dorsals, that space gets divided by the SPDL and frequently an accessory lamina or two, and the spinal laminae often don’t stick out as prominently as they do in the cervicals, so that the canvas available for the diverticula is much smaller and less kite-like.

    They’re all still weird as heck, if you ask me.

  26. David Marjanović Says:

    Janensch (1950) called these “Aussenkaverne[n]”, or accessory cavities

    There’s no “accessory” in that word, just “outside” – “exterior cavern”.

    The n I added is the plural ending.

  27. Matt Wedel Says:

    There’s no “accessory” in that word, just “outside” – “exterior cavern”.

    *embarrassment*

    Thanks, David. I’ll fix the post.

  28. dinochick Says:

    Hi Matt – How many Haplocanthosaurus specimens are there in collections (Carnegie, Cleveland, Vernal?? [have you seen that specimen??], …..???)?

    Thanks!

  29. Matt Wedel Says:

    How many Haplocanthosaurus specimens are there in collections (Carnegie, Cleveland, Vernal??, …..???)?

    The original material (H. priscus and H. utterbacki) is at the Carnegie, and I’ve seen it several times. Irritatingly, I don’t have good photos of anything but the sacrals and first few caudals. There’s H. delfsi on exhibit in Cleveland. There is definitely some Haplocanthosaurus at BYU. Caudals for sure, Brian Curtice identified those in his MS thesis, and I think there are some presacrals as well. Finally, there’s the new specimen and possibly new species that was announced at SVP in a poster about a decade ago. I hear rumblings that that one might be getting close to publication, but who knows. I think that’s the only known Haplocanthosaurus I haven’t seen with my own eyes, unless there is some floating around somewhere that I don’t know about. But I haven’t gotten what you’d call a good look at all of them–my time with H. delfsi, for example, mostly consisted of making funny faces for other people’s photographs while holding a succession of beers.

  30. dinochick Says:

    lol good to know. Do you recollect where the SVP abstract material was at? Is it Sue Ann’s?


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