The Astonishing Case of HMN SII:D8, part 1: Spinoparapophyseal Laminae!

May 26, 2008

Of all the sauropod vertebrae in the world, perhaps the single most intriguing is a dorsal vertebra of the Brachiosaurus brancai type specimen HMN SII. It was designated the 20th presacral (i.e. 7th dorsal) by Janensch (1950), but that was on the assumption that the dorsal column consisted of 11 vertebrae. Since Janensch never had any actual reason for assuming 11 dorsals, and Migeod’s (1931) Tendaguru brachiosaurid had 12 dorsals, it seems best to assume for now that brachiosaurids in general had 12 dorsals, so that the vertebra Janensch thought was D7 (i.e. the fifth-last dorsal) was more likely D8. Anyway, that’s what I’ll be calling it.

Here is that vertebra in right anterodorsolateral view — that is, from above, in front, and to the right.

Brachiosaurus brancai type specimen HMN SII, dorsal vertebra 8 in right anterodorsolateral view

It’s a bit of a close-up, so you can hardly see the centrum down there, and only the bottom half of the neural spine is included. On the positive side, you get a good view of those honking great prezygapophyses and the nice, big gap between them. You also see the neat, parallel spinoprezygapophyseal laminae (SPRLs) running up the front of the neural spine.

But I want to draw your attention to that lamina coming down towards us from the side of the SPRL. What is it? It can’t be a nice, well-behaved spinodiapophyseal lamina (SPDL), because we already have one of those over on the left-hand side, coming down from the side of the neural spine and flaring out laterally towards the diapophysis. No indeed: the lower end of the lamina I’m interested in here is actually running towards the parapophysis. OK, it’s broken off, but you can see where it would be if it was there. So this thing is a spinoparapophyseal lamina, or SPPL for short.

Well, this is weird. Wilson (1999) listed, illustrated and discussed nineteen different vertebral laminae, but there is no hint of an SPPL anywhere in that paper. So far as I’m aware, this feature is unique to this one vertebra. So is it just a one-off freak? I don’t think so, because on the other side of the neural spine, you see its mate, the left SPPL, heading off towards its parapophysis. But then why don’t we see this on any of the other dorsals of the same specimen? Well, it might have been there in life. The truth is that the B. brancai dorsals are rather more smushed up than you’d gather from the rather lovely drawings in Janensch (1950) — remind me some time to show you my photos of the co-ossified D11/D12 pair — and the relevant portion is only really preserved in D8. It’s possible that it was SPPLs all along the dorsal sequence.

Stay tuned for more hot news about how weird HMN SII:D8 is!

References

Update

To help you get your bearings, here is a photo that I should have included in the original post: the same vertebra from nearly the same angle, but taken from further out so that you can see the whole thing. The big photo was taken from a little higher up, looking slightly down on the vert.

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17 Responses to “The Astonishing Case of HMN SII:D8, part 1: Spinoparapophyseal Laminae!”

  1. Mike from Ottawa Says:

    OK, I’m a bit thick tonight, so what angle are we viewing the thing from? Is the centrum that bit in the lower right hand corner?

  2. Adam Says:

    Isn’t this the same as the “accessory spino-diapophyseal lamina” mentioned by Salgado, Coria and Calvo (1997)? According to them it occurs in at least Argentinasaurus and Opisthocoelocaudia amongst other titanosauriforms, though they failed to notice its occurence in the D8 of B. brancai. Are the dorsals of B. altithorax good enough to determine its presence?

    cheers

    Adam Yates

  3. Mike Taylor Says:

    There you go, MfO, hope that helps.

  4. Mike Taylor Says:

    Hi, Adam, good to hear from you. Looking up my trusty Salgado et al. 1997, I see an “accessory supradiapophyseal lamina” or ASDL in Figure 6 (on page 11) — I assume this is the lamina you mean?

    I’ve looked up the relevant papers, and found the figures that Salgado et al.’s line drawings are based on in Bonaparte and Coria 1993:fig. 2A and Borsuk-Bialynicka 1977:fig. 2B3 — unfortunately, the photographic plates in BB77 don’t really help, so those illustrations are all we have to go on.

    First, it’s clear that in both Argentinosaurus and Opisthocoelicaudia, the ASDLs, though originating on the neural spine (such as it is in Opistho) do not get close to the parapophyses — in both of the illustrated vertebrae, the parapophyses are some way ventral to the point where the laminae are heading. So these are not SPPLs.

    But that raises the question: are the laminae on HMN SII:D8 really SPPLs? Could it be that both they and the ASDLs of Salgado et al. are homologous, being really just accessory spinal laminae that could end up anywhere, amd that just happen to end up in the region of the parapophyses in HMN SII:D8?

    I can’t prove it convincingly, but I don’t think so: the Putative SPPLs of HMN SII:D8 (hereafter PSoHSII:D8 ) really do seem to be headed straight for the parapophyses on both sides of the vert — if anything, it’s even clearer on the left side.

    Salado et al.’s figured Brachiosaurus brancai dorsal is not from the type specimen, but is a referred isolated element (No 8, I think) which is different in several respects from the vertebrae of the type specimen and whose referral I am not 100% convinced by.

    Finally, do the Brachiosaurus altithorax dorsals have SPPLs? Sir, they do not! The horizontal laminae around the prezygs, parapophyses and diapophyses form a pretty featureless apron, and there is not so much as a hint of anything like an SPPL even on the well-preserved 7th presacral. You can see this pretty well in a previous SV-POW! post here: https://svpow.wordpress.com/2007/10/11/brachiosaurus-altithorax-last-four-dorsals/

    Hmm. Makes you think, doesn’t it …

  5. Adam Says:

    Yes, it was the ASDL I had in mind. I was thinking along the lines that you clearly spelt out as your alternative hypothesis, ie. that the ASDL and the SPPL are homologous structures, that they simply terminate somewhere on the dorsal surface of the plate formed by the prezygodiapophyseal lamina and that it is conicidental that it lies close to the parapophysis in vertebrae where the parapophysis is placed high on the neural arch. To test this we’d need a nice series of well-preserved dorsals of a taxon that has such laminae. Trigonosaurus might do the trick, it clearly has ASDLs in more anterior dorsals, but sadly the illustrations of the posterior dorsals just don’t show the area in front of the spinodiapophyseal laminae (Campos et al. 2005, fig. 19-20).
    Thanks for clearing up the condition in B. altithorax.
    Oh well, back to the basal guys where there are at most four laminae to worry about

  6. Mike Taylor Says:

    Hmm, I don’t see what you see in Trigonosaurus. The only anterior dorsal shown in anterior view is D4 (Campos et al. 2005:fig. 16), in which the only apparent laminae are a prespinal, an intraprezygapophyseal and, you might argue, a very very robust pair of PRPLs. Lateral views such as fig. 19 are no use here, as the diapophyses are inclined so dorsolaterally, and the neural spine is so short, that any ASDL or SPPL would be obscured.

    What am I missing?

  7. Adam Says:

    I was looking at the dorsal view of D5 in figure 18. I interpret the spinodiapophyseal laminae as forming the lateral margins of the reclined neural spine in dorsal view and the shorter additional set of laminae that branch off the prespinal ridge/lamina and end near the base of the transverse processes as the ASDLs.
    Of course, I could be making a boneheaded error here.

  8. Mike Taylor Says:

    Hmmm, good spot on figure 18. That certainly does look like an ASDL; but its strange that D4 doesn’t have it. Still, it’s a million miles away from being spinoparapophyseal — the parapophyses on that baby are the most anterior visible part of the vertebra. splayed out nice and wide (whereas in D4 they are presumably lower down and less prominent, so that they are obscured by the prezygs).

    I think it all comes down to whether the laminae in question on HMN SII:D8 really are headed for the parapophyses, and doing so “deliberately” rather than just landing up there through randomness. And my photos seem to say yes. But I should be back over in Berlin in November, so hopefully I’ll be able to reach a firmer conclusion.

  9. Matt Wedel Says:

    I think it all comes down to whether the laminae in question on HMN SII:D8 really are headed for the parapophyses, and doing so “deliberately” rather than just landing up there through randomness.

    For the record, this is my favorite comment on any blog, anywhere, ever. I’m not biased, it just is. Anytime you can say “It all comes down to…” and then launch into that much arcane anatomy, you know you’re in a happy place. And one with, ahem, limited practical applications.

    Other than forwarding the march of science. Adding to the store of human knowledge. That’s practical enough for me.

  10. Graham King Says:

    Hi Mike! (since we last conversed over dinner in the Hereford Arms at the dino conference.)

    and doing so “deliberately” rather than just landing up there through randomness

    Just as well you put those “” around deliberately, Mike, as the concepts of deliberateness-or-otherwise get a bit mind-boggling when the item in view is a sub-section of a part of the skeleton of a long-dead creature which even when entire and alive may have had a rather different capacity for ‘deliberation’ than you or I. However, I quibble… purely for the sake of it, really…

    What I really want to say is thanks for your very welcome and welcoming comment to me, on that first day of the conference: about palaeontology being open to anyone. As a newbie and non-professional that helped me feel quite equally a part of the gathering thru the following days, which were very happy friendly ones.

    And I guess our pre-conf exchanges on SVPOW helped too. Cheers!


  11. […] Just when you thought it was safe to go back into the Humbold bone-room … hot on the heels of Part 1: Spinoparapophyseal Laminae!, comes another dose of terror thanks to everyone’s favourite mid-to-posterior brachiosaurid […]

  12. Mike Taylor Says:

    Hi, Graham, nice to hear from you. Yes, palaeo really is open to anyone who’s prepared to do the work — as I discovered to my own pleasant surprise. As Matt pointed out to me many years ago, the only difference between people who have written published papers and people who haven’t is that the latter have written published papers. Profound. Anyway, glad you enjoyed the conference, I just wish I’d been able to stay for more of it myself.

  13. Matt Wedel Says:

    As Matt pointed out to me many years ago, the only difference between people who have written published papers and people who haven’t is that the latter have written published papers. Profound.

    I believe I said the former have written published papers, although your version is possibly more profound, in a Zen koan sort of way.

    Anyway, Graham, we all start somewhere. Even the likes of Charles Whitley Gilmore and Alfred Sherwood Romer were once n00bs attending their first conferences, measuring their first fossils, writing their first papers, etc. They were brilliant and talented, to be sure, but this field has seen a lot of brilliant comets who flare for a time and then burn out. Gilmore, Romer, Simpson and the rest of the little-g gods of paleontology* attained that status mainly because they never quit working. I find a lot of comfort in that fact. It’s awfully hard to be brilliant on command–or ever. Simply not quitting is a much more attainable goal.

    * The Big-G Gods of Paleontology are Taphonomy and…uh…well, the more I think about it, just Taphonomy (he’s a jealous god–try not to piss him off). Although he frequently appears in his Trickster avatar and gives us otherwise complete sauropods with no heads, and way too many titanosaur caudals. All you can do to appease him is arrange to be buried in a depositional environment, and even then there are no promises. The big earthen bastard.


  14. […] 3, 2008 Welcome to the third and climactic episode in my HMN SII:D8 trilogy. If the unique spinoparapophyseal lamina and total lack of infradiapophyseal laminae featured in the first two episodes were not enough to […]


  15. […] pure on this: for example, I have a paper on Brachiosaurus in press that mentions in passing the spinoparapophyseal laminae, absence of an infradiapophyseal laminae and perforate anterior centroparapophyseal laminae of the […]


  16. […] vertebra of the same specimen, which we’ve discussed in detail here on account of its unique spinoparapophyseal laminae, its unexpectedly missing infradiapophyseal lamina and its bizarre perforate anterior […]


  17. […] to but to acknowledge its recognition of the spinoparapophyseal lamina (SPPL) that occurs in D?8 of the Giraffatitan paralectotype MB.R.2181 (formerly HMN SII) and has now been recognised also in […]


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