Apatosaurusminimus sacrum/ilia: illustration from forthcoming description

July 1, 2012

I mentioned a few posts ago that Matt and I are working on a redescription of AMNH 675, a sauropod specimen referred by Mook (1917) to “Apatosaurusminimus, but which everyone knows is not Apatosaurus. We plan to share the illustrations from this in-progress paper as we prepare them, so here is perhaps the key one:

Sacrum and fused ilia of AMNH 675, “Apatosaurus” minimus. Top row: left lateral and right lateral; middle row: dorsal, with anterior to top; bottom row, anterior and posterior. Scale bar = 1 m. Click through for very high resolution (6283 x 6479).

The other material comprising this specimen consists of a partial pubis and two ischia, one of which is complete. We’ll show you these once we’ve prepared the illustrations.

What actually is it? Well, we don’t know yet. it has a strange mix of advanced diplodocoid and advanced macronarian features. A preliminary phylogenetic analysis is inconclusive. We have some more approaches to follow up before we’re ready to nail a conclusion to the door.

Reference

Mook, Charles C. 1917. Criteria for the determination of species in the Sauropoda, with description of a new species of Apatosaurus. Bulletin of the American Museum of Natural History 38:355-360.

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25 Responses to ““Apatosaurusminimus sacrum/ilia: illustration from forthcoming description”

  1. anon Says:

    When you say advanced macronarian do you mean advanced for the Late Jurassic in comparison to other Late Jurassic macronarians or do you mean on par with titanosauriforms?

  2. Dino Hunter Says:

    The reason why you guys can’t identify it is because its a segnosaur/therizinosaur…


  3. Maybe a Brachiosaurus humped a Diplodocus.

    *runs

  4. 220mya Says:

    That sacrum could do with a nice new clam-shell fiberglass storage jacket!

  5. Mickey Mortimer Says:

    Ooh, I’m looking forward to this paper. I love redescriptions of old taxa. Do “Morosaurus” agilis next!

  6. Mike Taylor Says:

    anon: by using a term as vague as “advanced Macronarian”, I am hedging my bets. For example, the way the ilia flare out dramatically looks titanosaurian, but the the way the most anterolateral part of the ilial blades are still vertical rather than folding over so that they are directed dorsolaterally does not.

    Tracy, is that a serious suggestion? The “Apatosaurusminimus material does not at all resemble that of Alxasaurus (Russell and Dong 1993:fig. 1) or Enigmasaurus (Zanno 2010:fig. 3).

    Mike Keesey: yes, that is pretty much our current working hypothesis.

    Randy: that would be great! It’s a source of some frustration to me that both Osborn and Mook (13 years later) evidently had access to the ventral aspect of the specimen, as they both mention features only visible in ventral view, but neither of them illustrated it. And now it’s completely inaccessible.

    Mickey Mortimer: of course we can’t do “Morosaurusagilis — it has cranial material!

    References

    Russell, D. A., and Dong, Z.-M. 1993. The affinities of a new theropod from the Alxa Desert, Inner Mongolia, People’s Republic of China. Canadian Journal of Earth Sciences 30:2107-2127.

    Zanno, Lindsay E. 2010. A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology 8(4):503-543. doi:10.1080/14772019.2010.488045


  7. Curious: Were you unable to invert the block for a ventral view? It would make a nice companion image and also help permit access to confirm data on the sacral vertebrae more directly than shown in the current figure.

  8. Mike Taylor Says:

    Nope. Flipping that block would be a major engineering undertaking; doing it without breaking anything would require wizardly skillz. Randy’s clamshell approach would be most promising, but that can’t be done overnight. And even were it done, a lot of prep would be necessary to get rid of all the plaster and wood that currently masks the ventral aspect.

  9. Mickey Mortimer Says:

    I agree with Mike, minimus is unlike therizinosaurids in lacking an obvious antitrochanter and having spinodiapophyseal laminae. Plus the proportions just aren’t right (compare to Suzhousaurus in Li et al., 2008) and this is from the Morrison, when therizinosaurs should be less derived than Falcarius.


  10. This is unfortunately. Matrix appears to obscure the sacral fontanelles and thus regions of the sacral arches that would be of interest to you folks, like more than just substantiating the material in a general cladistic approach. Matrix also seems to obscure the acetabular margins, and so the inner surface is hidden.

  11. grey gryphon Says:

    these are beautiful!

  12. Mike Taylor Says:

    “these are beautiful!”

    They certainly are! Undoubtedly this blog has wandered a long way from its initial intention of displaying a sauropod vertebra picture once a week; but every now and then it’s good just to sit back and admire these gorgeous objects.

  13. Nima Says:

    The more I look at this thing, the weirder it seems…

    What makes this sacrum even more bizarre is that it has six sacrals. The spines look diplodocid but I don’t know of any diplodocid that has six sacrals, and even most Jurassic macronarians had only five. The ilia look roughly like Haplo, but that doesn’t have six sacrals either, and the fusion sequence is completely different, not to mention the shape. My best guess so far is that this beast was a macronarian that converged on diplodocids. Not having a clue where to throw it, I suspect it may belong to a new family…

  14. Mike Taylor Says:

    Nima writes:

    The more I look at this thing, the weirder it seems…

    Exactly!

    What makes this sacrum even more bizarre is that it has six sacrals.

    Well, remember that sacral fusion (unlike, say, neural spine bifurcation) really is an ontogenetic character. It’s not inconceivable that the first or last sacral centrum fused to the others late in ontogeny. But there are two reasons to suspect that’s not the case: first, while centra can fuse progressively, the ribs of all six in “A.” minimus seem to participate in the sacricostal yoke, and I don’t know whether that is something that develops through time. And second, since the sacral ribs of S1 are not fully fused to their centrum (look closely at the bottom-left part of the high-res version of the illustration), it may be that the individual was not fully mature at the time of death anyway.

    The spines look diplodocid but I don’t know of any diplodocid that has six sacrals, and even most Jurassic macronarians had only five.

    Yes, the spines absolutely look diplodocoid; had they been found in isolation, I don’t think there’s much doubt that they would have been so classified. But even ignoring sacral count, the sheer width of the sacrum and the strong flare at the front of the ilia don’t look at all diplodocoid. There are other good reasons for thinking this specimen is different from camarasaurs, brachiosaurs, titanosaurus, mamenchisaurs, etc. It’s a real puzzle.

    The ilia look roughly like Haplo

    In lateral view, yes, they do — a little. But the resemblance is superficial, and it disappears in dorsal view: compare the central part of our illustration with Hatcher 1903:plate V:part 1.

    But that doesn’t have six sacrals either, and the fusion sequence is completely different,

    I wouldn’t set too much store by the sequence of fusion between sacral spines. That seems to have been highly variable between individuals. (McIntosh and Williams 1988:22) rejected Hatcher’s separation of Haplocanthosaurus utterbacki from the type species “H.” priscus because it was based only on this character.)

    My best guess so far is that this beast was a macronarian that converged on diplodocids.

    Sometimes we think that. Then we look at the spines and think, no, it has to be a diplodocid that converged on macronarians.

    Not having a clue where to throw it, I suspect it may belong to a new family.

    … whatever that means :-)


  15. […] I prepared for the forthcoming “Apatosaurus” minimus redescription. Compare this with the sacrum and fused ilia from the previous post. Left ischium of AMNH 675, “Apatosaurus” minimus. Left column: proximal. […]

  16. Nima Says:

    … whatever that means :-)

    Yeah, I’ve been wondering about that too. I have that odd habit of inventing new families for stuff that doesn’t seem to fit well in other places. Antarctosauridae for example (Antarctosaurus + Ampelosaurus + Bonitasaura + Lirainosaurus + Pellegrinisaurus)… or Trigonosauridae (Trigonosaurus, Barrosasaurus, Bonatitan, Narambuenatitan, possibly Muyelensaurus) which both exhibit recurring patterns of diagnostic axial features that look downright bizarre compared to the typical derived lithostrotian.

    I wonder if it’s possible that with “Apatosaurus” minimus we could be looking at a mutant dinosaur here… something where a macronarian’s hox gene’s got all screwy and you end up with diplodocoid-looking sacral spines (but macronarian sacral ribs!) Too bad there isn’t a second specimen of this thing…

  17. Mike Taylor Says:

    (Just a note here to say that we at SV-POW! do not endorse Nima’s driveby “families”. We’d need to see a proper publication that justified them before signing up.)

  18. Nima Says:

    Fair enough :)


  19. […] instructive to compare with the “Apatosaurus” minimus sacrum. Direct comparison is somewhat hindered for two reasons: first, the ilia are fused to that sacrum […]


  20. […] length of 49 m for Amphicoelias fragillimus; but you would hardly use the sacrum illustration from this post in your own work without crediting the […]


  21. […] shown a lot of sauropod sacra around here lately (for example here, here, and here), so here’s a little look back down the […]


  22. […] So I’ve been toying with a different idea: instead of cutting the background out completely, leaving it in place but toning it down. Then the supporting structure is visible, but clearly distinct from the actual bone. (For a more extreme case, see the “Apatosaurus” minimus sacrum.) […]


  23. […] * TNF = Taylor Normal Form, i.e., making multi-view photos like the ones here and here. […]


  24. […] in 2012, when Matt and I were at the American Museum of Natural History to work on “Apatosaurus” minimus, we also photographed some other sacra for comparative purposes. One of them you’ve already […]


  25. […] and I first saw this specimen back in February 2009, when we were mostly there to look at “Apatosarus” minimus (and then again in 2012). As soon as our eyes lit on it, we couldn’t help but be captivated […]


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