Your sacrum is negligible

March 24, 2008

In the spirit of Your neck is pathetic and Your torso is also pretty lame, I note that your sacrum is negligible:

Haplocanthus sacrum; Homo sacrum

We have here the sacrum of the Haplocanthosaurus priscus holotype CM 572, in ventral view with the ilia still in place (so that the slightly hourglass-shaped dark regions you see on either side are the acetabular regions of the ilia, facing downwards). To the right is the sacrum of a good-sized adult male human such as my good self, in dorsal view.

The total length of the five fused sacral vertebrae of Haplo is 79.5 cm (Hatcher 1903:18), compared with about 11.5 cm for the human. Actually, Haplo is not a particularly big sauropod: the sacrum of Brachiosaurus altithorax holotype FMNH P25107, for example, comes in at 95 cm (Riggs 1904:236). But it’s big enough to make your sacrum hang its zygapophyses in shame. I picked Haplo just because Hatcher’s 1903 monograph on it is so beautifully illustrated, and the world is not as plentifully supplied with complete, uncrushed, well-preserved sauropod sacra as we might wish.

This post marks Haplo’s SV-POW! debut, but what kind of sauropod is it? As pointed out by Taylor and Naish (2005:4), various studies have reached different conclusions about this: Riggs (1904:229) classified it as a brachiosaurid; McIntosh (1990:347) as a cetiosaurid; the phylogenetic analysis of Wilson and Sereno (1998:54) recovered it as a non-camarasauromorph macronarian; Upchurch (1998:74) found it to be an “eosauropod” (i.e. a non-neosauropod sauropod); Wilson (2002:240) recovered it as a basal diplodocoid (outside Diplodocimorpha, the clade uniting Diplodocus with Rebbachisaurus); and Upchurch et al. (2004:297) found it in a derived position, as a camarasauromorph closer to Titanosauriformes than to Camarasaurus.

All this disagreement is not as bad as it seems, though. We can discount Riggs’s assignment to Brachiosauridae as this was offered at a time when few sauropods were known. All the other assignments, as disparate as they appear, place Haplo very close to the root of Neosauropoda, that is the divergence between the two great Neosauropod clades Diplodocoidea and Macronaria. Some have it at the base of one branch, some at the base of the another, some just outside; with the exception of Upchurch et al.’s (2004) placement as a macronarian more derived than Camarasaurus, these positions are all only one or two nodes apart on a consensus cladogram.

In fact, the most recent common ancestor of all neosauropods might have been something rather similar to Haplocanthosaurus. It can’t have been Haplo itself, as it came along fifteen million years too late to be the ancestor of early neosauropods such as Atlasaurus, but it’s possible that it’s little changed from that ancestor.

Bibliography

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10 Responses to “Your sacrum is negligible”

  1. Vertebrat Says:

    Haplo’s bones are much bigger than mine.
    Just those five could contain my whole spine.
    But I shouldn’t complain
    “Such a sacrum’s profane!”
    In a sauropod’s back, it’s divine.

  2. Mike Taylor Says:

    Well, I think this is a great week for sauropods in the arts. Just a few days after David Hone’s LOLSAURPODZ popped up in Tetrapod Zoology, here we have what may be the first recorded poem about sauropod vertebrae. Admittedly it’s not exactly Wordsworth, but we have to start somewhere.

  3. Mike from Ottawa Says:

    Not Wordsworth? Thank goodness. The man hardly ever essayed that most sublime of poetic forms, the limerick.

    Vertebrat’s poem is excellent, especially as he gets the rhythm just right, something so many poets fail at (Wordsworth’s limericks were particularly bad on this count), over-concentrating on the rhyme.

  4. Nathan Myers Says:

    Hmm, needs comma.

    My neck is pathetic, I know’t,
    despite ev’ry effort to grow’t.
    With neck-bones pneumatic
    I could swan hieratic
    With an S for the shape of my throat.

  5. Graham King Says:

    (Ahem…)

    Ess-Vee-Pow’s main contributors three
    Could peer through Hap’s portholes with glee
    Their faces, arrayed,
    Through their subject displayed,
    Would be most hip and groovy to see.

    (You could perhaps enlist another three to appear opposite you, in the starboardholes… Boom! Boom!)

  6. Nathan Myers Says:

    I suppose mine would be better as

    My neck is pathetic, I know’t,
    despite ev’ry effort to grow’t.
    With neck-bones pneumatic
    I could swan operatic
    With an S for the shape of my throat.

  7. Nathan Myers Says:

    Speaking of vertebrate spines…

    http://www.aboutcolonblank.com/2008/03/26/the-spine-lamp/

  8. Graham King Says:

    lol! but surely on top of that spine there should be fitted a head-lamp…

    After looking at the pictures on Darren’s blog, I am thinking of a coffee-table modelled on an aetosaur skeleton. They seem to have had such an ideally flat back, with upturned edges.


  9. […] the four posts of axial-anatomy humiliation, Your neck is pathetic, Your torso is also pretty lame, Your sacrum is negligible and Your coccyx is […]


  10. […] which bear mobile ribs, and the lumbar vertebrae which do not); those in the sacrum are called sacral vertebrae and those in the tail are called caudal vertebrae.  But you already know that if you read Tutorial […]


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