This one, obviously, is a follow-up to this one. Mark drew the picture, Mike had the idea, Mark gave the go-ahead, and here we are. Cry havoc and let slip the azhdarchids of war!

Who’s next? Who wants some? You want a little? Huh? Huh?

One of our great palaeontological heroes (well, one of mine anyway) is Charles Whitney Gilmore (1874-1945), former curator of the Division of Vertebrate Paleontology at the United States National Museum (USNM), successful monographer of stegosaurs, ornithopods and theropods, and prolific describer of ceratopsians, crocodilians, ichthyosaurs… and sauropods. But like oh so many late great palaeontologists, I previously had no idea what he looked like and had never seen a photo of him. Well, here he is and, to boot, he’s posing with some sauropod vertebrae: specifically, caudals of Diplodocus.

Gilmore named one of the best known of titanosaurs, Alamosaurus, in 1922, and in 1932 described a Diplodocus specimen collected from Uinta County, Utah, in 1924 and mounted in the USNM eight years later (it is specimen USNM 10865). After comparing the four Diplodocus species (D. longus Marsh, 1878, D. lacustris Marsh, 1884, D. carnegii Hatcher, 1901 and D. hayi Holland, 1924) Gilmore (1932) concluded that USNM 10865 couldn’t be referred to any one ‘until there has been a thorough revision of the genus’ (p. 7). You might recall that we looked at Diplodocus caudal vertebrae quite recently, and on that occasion the vertebrae belonged to D. carnegii. If you compare the D. carnegii caudals with the USNM 10865 vertebrae shown in the photo above, you’ll note that the neural spines of the CM 84 D. carnegii specimen appear more posteriorly inclined than do those on USNM 10865.

As Gilmore explained, D. carnegii has more inclined neural spines than D. longus, so perhaps USNM 10865 is a D. longus (you can clearly see the different neural spine orientations depicted in Scott Hartman’s skeletal reconstructions of D. carnegii and D. longus in Lovelace et al.’s (2007) recent Supersaurus paper, shown below: click to enlarge. Image copyright Scott Hartman). However, Gilmore also noted that some of the USNM neural spines are posteriorly inclined, and as much as are those of D. carnegii. He ended up labelling the specimen D. longus, and this is what it remains today, but further study is needed…. in fact, we probably need a good, specimen-level analysis of the different alleged Diplodocus species. Upchurch et al. (2004) recently did exactly this with Apatosaurus.

Anyway, the photo used above comes from here on Shorpy, the ‘100-year-old photo blog’, and thanks to both George Hammond and Jacob Kesinger for bringing it to our attention – it’s a nice one to have added to the site. Palaeo-mammal fans might note the panel-mounted Phenacodus on the wall.

References

  • Gilmore, C. W. 1932. On a newly mounted skeleton of Diplodocus in the United States National Museum. Proceedings of the United States National Museum 81, 1-21.
  • Lovelace, D. M., Hartman, S. A. & Wahl, W. R. 2007. Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny. Arquivos do Museu Nacional, Rio de Janeiro 65, 527-544.
  • Upchurch, P., Tomida, Y. & Barrett, P. M. 2004. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs 26, 1-108.

SuperCroc’s sidekick

June 15, 2008

Paul Sereno’s Project Exploration has a traveling exhibit called The Science of SuperCroc, which I recently visited at my old stomping grounds, the Oklahoma Museum of Natural History. The exhibit focuses on Sarcosuchus, the improbably large and possibly Kryptonian crocodilian from the Cretaceous of Niger, but it also includes nice mounted skeletons of the spinosaur Suchomimus and–relevant to our purposes here–the just plain improbable sauropod Nigersaurus.

At least one of my co-bloggers probably thinks I should stop pandering to the crowds with my mounted skeleton posts and get back to hardcore vertebral anatomy. After all, that’s the raison d’etre of SV-POW!, and I have been falling behind a little lately. Still, I’m going to risk the Wrath of Mike and go ahead and post about the mounted Nigersaurus skeleton, and why you should definitely go see it if you get the chance.

Here are my reasons for doing so:

1. It is a demonstrated scientific fact, as rock-solid as the value of c or the proposition that the Amazon basin is damp, that Nigersaurus is Damn Weird. In a clade of little-known weirdos (Rebbachisauridae), it promises to be an exceedingly well-known ultra-weirdo, thanks to (1) the large number of skeletons that have been discovered, including both juveniles and adults, and (2) the sheer vastness of its weirdness, which you can sample immediately and without charge courtesy of Sereno et al. (2007) and the kind offices of the Public Library of Science (translation: free paper here).

2. Although Nigersaurus was named in 1999 and has been the subject of three peer-reviewed publications, not much of the skeleton has been figured to date. So the opportunity to see the whole critter up close is pretty remarkable. If sauropods were heavy metal, the traveling Nigersaurus mount would be an evening backstage getting high with Led Zeppelin, circa 1973. Certainly if you work on sauropods, the morphology of Nigersaurus will make you think that someone has been under the influence of powerful illicit substances, and that someone is Mother Nature (or Gaia, or the overused/sexist/quasi-pantheistic biosphere personification of your choice).

3. It’s a really nice mount. It’s fiberglass, but the quality of the casts is first rate. I have seen a lot of traveling skeletons that looked like they were made out of Play-Doh by speed-sculpting chimps, but the mounts in the SuperCroc exhibit are all well cast, gracefully mounted, and nicely displayed, by which I mean that you can get up close to them and walk most or all of the way around them, which is my major pet peeve about mounted skeletons: I want to be able to see them from any angle, or at least many angles. SuperCroc delivers.

4. The exhibit includes a lot of display cases that explain the detailed anatomy of the beasts. For Nigersaurus alone, there were cases on vertebral pneumaticity (yay!), the vertebrae themselves (real bones), the detailed anatomy of the jaws (real bones, from the holotype!), the head and neck skeleton plus life sculpture (shown at the top), adult and baby femora (real bones), probable feeding ecology, and maybe one or two others I can’t remember, plus a giant wall hanging of the full-color life restoration painting that came out with the 2007 paper.

So if you get a chance to see SuperCroc, it’s worth it just for the sauropod.

I’ll have tons more to say about the Nigersaurus vertebrae in future posts, but the short version is that they are small and unbelievably delicate. Mike and I always characterize Camarasaurus vertebrae as coarse, fat, and kind of ugly; the vertebrae of Nigersaurus are the aesthetic opposite. They look like they might have been constructed out of toothpicks and white glue. And they are crazy pneumatic. In one of his essays, outdoor humorist Patrick F. McManus characterized a poorly-maintained country bridge as consisting mostly of holes that were elevated and loosely defined by a few rotting beams. Similarly, the skull and cervical vertebrae of Nigersaurus seem to be mostly holes, with just enough bone around them to suggest the form of a sauropod. One more half-baked comparison: the mounted Nigersaurus looks like the skeleton of a skeleton, at least in the craniocervical region.

I want to make a final point that is not really about vertebrae. As you can see in the photo above, and to beat a dead thunder-lizard, sauropods had erect limbs, compact feet, and deep, slab-sided bodies. You don’t have to be a zoologist to see that this is a body-form made for roaming the land, not for bobbing around slurping up pond scum. That’s not to say that sauropods didn’t go into the water. They probably did so all the time. Elephants do, almost every chance they get. Heck, elephants may even be descended from aquatic ancestors. But no one would characterize elephants as aquatic or even semi-aquatic. Sauropods weren’t elephants, and they weren’t giraffes, and facile comparisons of sauropods to big mammals have probably done more harm than good to sauropod paleobiology. But sauropods weren’t hippos or manatees, either, despite decades of ecological characterization as such. The Aquatic Sauropod era officially ended the same year I was born, so you may rightly wonder why I am tilting at this particular windmill. It’s because ideas are seductive, and sometimes we allow them to make us blind to the obvious. I don’t know of any way to fight that tendency other than to keep asking questions.

And I don’t know of a sauropod that is more likely to provoke questions than Nigersaurus. Go see it if you can.

NHM Diplodocus caudals

Just to break the stranglehold that titanosauriforms clearly have on SV-POW! (kidding), every now and again we need a diplodocoid or mamenchisaurid. And here’s another pic of the CM84/CM307 cast of Diplodocus carnegii as displayed at London’s Natural History Museum (photo © NHM). Again, we’re looking at the tail, but this time at the proximal part, and there’s a lot of neat stuff here to pay attention to…

– Note that laminae are present all over the place. Though it’s not totally obvious in this photo, ACDLs and PCDLs are present on the centra, PRDLs and PODLs are at the base of the neural arch, and SPRLs and SPOLs are present on the neural spines. I forget if we’ve gone through the acronyms for all the laminae – someone remind me. ACDLs are commonly present on sauropod proximal caudals, but are particularly prominent in the first 15 caudals of diplodocids. ACDLs, PCDLs, PRDLs and PODLs are absent from more distal caudals (Wilson 1999).

– Secondly, pneumatic foramina are present on the sides of the centra. It’s been said that pneumatic foramina are also present in at least some titanosaurs (specifically Neuquensaurus: Upchurch et al. 2004), but this isn’t evident in the primary description of this taxon (Powell 2003) nor coded for by Wilson (2002). Anyway, pneumatic foramina in the caudal vertebrae are a well known characteristic feature of diplodocids and even isolated centra have been identified as belonging to diplodocids on the basis of their presence (Gabunia et al. 1998). They aren’t present in dicraeosaurids (the sister-taxon to Diplodocidae within the diplodocoid clade Flagellicaudata).

– Perhaps the best known unusual feature of diplodocid caudals concerns the transverse processes. Ordinarily in sauropods (and in other dinosaurs) these are dorsoventrally compressed, laterally projecting processes that emerge from the approximate area of the neurocentral suture. In diplodocids (and dicraeosaurids) however, these are massive, dorsoventrally deep, wing-like structures: you can see in CM84/CM307 here that they are particularly massive and wing-like on the most proximal four or five of the caudals. Presumably these had – to use the technical terminology – some big-ass muscles attached to them. What does this tell us about tail function? Well, that’s a very very good question.

Another thing worth noting is that – if we were able to see the articular surfaces of the centra – we would note that diplodocids have procoelous proximal caudals. This contrasts with the usual sauropod condition, where proximal caudals are amphiplatyan or amphicoelous. Caudal procoely is seen in a few other sauropod groups (notably mamenchisaurids… and, err, titanosaurs!), but that of diplodocids is only mildly developed by comparison.

That’ll do for now, consider this an introduction.

References

  • Gabunia, L. K., Mchedlidze, G., Chkhikvadze, V. M. & Lucas, S. G. Jurassic sauropod dinosaur from the Republic of Georgia. Journal of Vertebrate Paleontology 18, 233-236.
  • Powell, J. E. 2003. Revision of South American titanosaurid dinosaurs: palaeobiological, palaeobiogoegraphical and phylogenetic aspects. Records of the Queen Victoria Museum 111, 1-173.
  • Upchurch, P., Barrett, P. M. & Dodson, P. 2004. Sauropoda. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds). The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 259-322.
  • Wilson, J. A. 1999. A nomenclature for vertebral laminae in sauropods and other saurischian dinosaurs. Journal of Vertebrate Paleontology 19, 639-653.
  • Wilson, J. A. 2002. Sauropod dinosaur phylogeny: critique and cladistic analysis. Zoological Journal of the Linnean Society 136, 217-276.

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 creep you out, then this ought to do it: the ACPLs of this vertebra have great big holes in them!

Unfortunately, my photos of this are terrible. In some of my general shots of the vertebra, the perforations are visible if you already know what you’re looking for, but the only photos I have that really make the point are two where I shoved rolled-up pieces of paper through the holes. (NOTE TO HUMBOLDT CURATORS: I did this really, really carefully.) Those photos did not come out well (stupid autofocus), but here is one of the neural arch, taken from just below the level of the horizontal lamina complex, on the right-hand side:

D8 neural arch in right lateral view, showing perforate ACPL

The ACPLs of this vertebra are distinctly odd. Most ACPLs are fairly low, and directed straight out from the vertebra, in a lateral direction. These are way broader than your average ACPL in the street, and their orientation coming out of the vert is more anterolateral. Plus uh, they have these holes in them.

Are the holes damage? Nope. Sadly, I don’t have photos that demonstrate this, but as I recall from my visit, the holes are lined with finished bone. Plus the fact that the same morphology is seen on both sides makes that unlikely. I think they are a genuine osteological feature.

So what are we to make of all this? A single vertebra seems to have not one, not two but THREE osteological features not seen (or at least not recognised) in any other vertebra from any sauropod (including the other dorsals of the same specimen). What are the options?

1. This vertebra is damaged or diseased. I don’t think so: the fact that all three features (SPPLs, absence of IDLs and perforate ACDLs) are preserved on both sides makes this seem very unlikely.

2. Brachiosaurus brancai is much weirder than anyone, Janensch included, has given it credit for. I think that holds water if you buy the idea that the reason none of the other B.b dorsals have these features is poor preservation. I’ll need to look closely at the material in November. (I did look at it closely when I was there before, of course, but I didn’t know what I was doing back in my young-and-foolish days.)

3. This vertebra does not actually belong to Brachiosaurus brancai but to another animal. It’s an interesting possibility, and not one I would want to dismiss out of hand. Quarry S, whence HMN SII was excavated, contained at least two individuals which Janensch (1914) initially placed in two different species (B. brancai and B. fraasi) before changing his mind. What if he was right the first time round, and the “SII” specimen is a chimera? Unfortunately we’re not likely ever to know (unless new and better material is found) as Janensch’s quarry map as reproduced by Heinrich (1999) doesn’t give any clues. It is a mystery to both my family and the rest of the planet.

I wish I knew.

Well, that’s it from HMN SII:D8.  No doubt Matt will soon be back with some more blatant playing-to-the-gallery-posts comparing the sizes of whales and sauropods (I ask you, how off-topic is that?)  I know it’s been a bit hardcore, but, hey, that’s what we’re here for, right?

References

  • Heinrich, Wolf-Dieter. 1999. The taphonomy of dinosaurs from the Upper Jurassic of Tendaguru, Tanzania (East Africa), based on field sketches of the German Tendaguru expedition (1909-1913). Mitteilungen aus dem Museum fur Naturkunde in Berlin, Geowissenschaftliche Reihe, 2: 25-61.
  • Janensch, Werner. 1914. Ubersicht uber der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden. Archiv fur Biontologie, Berlin, III, 1 (1): 81-110.
Follow

Get every new post delivered to your Inbox.

Join 395 other followers