Here’s a dorsal vertebra of Camarasaurus in anterior view (from Ostrom & McIntosh 1966, modified by Wilson & Sereno 1998). It is one of the most disturbing things I have ever seen in a sauropod. It makes my skin crawl.

Here’s why: the centrum and the thing we habitually call the ‘neural arch’ aren’t fully fused, and as this modified version makes clear, the ‘neural arch’ is neither neural nor an arch. Instead of being bounded ventrally by the centrum and dorsally and laterally by the neural arch, the neural canal lies entirely below the synchondrosis between the not-really-an-arch and the centrum.

Why?! WHY WOULD YOU DO THAT, CAMARASAURUS? This is not ‘Nam. This is basic vertebral architecture. There are rules.

Look at c6 of Apatosaurus CM 555 here, behaving as all good vertebrae ought to. Neural arch be archin’, as the kids say.

And if you are seeking solace in the thought that maybe the artist just drew that Cam dorsal incorrectly, forget it. I’ve been to Yale and examined the original specimen. I’ve seen things, man!

Camarasaurus isn’t the only pervert around here. Check this out:

Unfused neural arch of a caudal vertebra of a juvenile Alamosaurus from Big Bend. And I mean, this is a neural arch. This may be the most neural of all neural arches, in that it contains the entire neural canal. It’s more of a neural…ring, I guess. That’s right, this Alamosaurus caudal is batting for the opposite team from the Cam dorsal above. And it’s a team that neither you nor I play on, because we have well-behaved normal-ass vertebrae with neural arches that actually arch, and then stop, like God and Richard Owen intended.

Scientifically, my question about these vertebrae is: well, that is, I mean to say, what!? I think they have damaged me in some fundamental way.

If you have anything more intelligent to add (or even less intelligent – consider the gauntlet thrown down!), the comment thread is open.

References

  • Ostrom, John H., and John S. McIntosh. 1966. Marsh’s Dinosaurs. Yale University Press, New Haven and London. 388 pages including 65 absurdly beautiful plates.
  • Wilson, J. A. and Paul C. Sereno. 1998. Early evolution and higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.

So, this happened today

March 28, 2013

Big Bend Alamosaurus cervical J with Matt for scale

Mounted Alamosaurus in Dallas 1

Next week I’m going to visit the Perot Museum of Nature and Science in Dallas, Texas, to see their big Alamosaurus (these photos were kindly provided by Ron Tykoski of the Perot Museum, with permission to post). See that sweet string of cervical vertebrae in front of the mounted skeleton? A photo of those same vertebrae when they were still in the ground was featured in the post “How big was Alamosaurus?” three and a half years ago. Happily now they are out of the ground, prepped, and on display, and Tony Fiorillo and Ron Tykoski are working on getting them and some other new Alamosaurus material described.

Mounted Alamosaurus in Dallas 2

Here’s another view of that mount. You may be wondering, first, how legit is it, and second, how big is it? Happily, I have answers for you. In email messages with permission to cite, Ron Tykoski wrote,

The Alamosaurus skeletal mount by RCI  in the photos is based upon scaling the Smithsonian and UT Austin material to match the size of our cervicals here in Dallas.  There were enough overlapping parts between the pieces at the three institutions to get the proportions pretty nicely supported.

I ran across your SV-POW thread on ‘How big was Alamosaurus?’ back when you first posted it in ‘09.  You ought to be pleased to know that you came remarkably close to the eventual size of the skeleton we wound up with.  The full skeleton RCI generated (again, based off scaling to the Dallas verts) is 84ft long, about 16ft at the shoulder (I dropped a tape measure from the 1st dorsal neural spine to the floor during skeleton construction and got 480cm-490cm), and a neck + head of about 25ft.  The overall length and neck length were provided by RCI after fabrication and assembly.   That shoulder height is a bit suspect though based on the positioning of the pectoral girdle in the mount, relative to the ribcage and vert column.   I think the head currently is posed about 25ft or so off the floor, but I can’t verify that (I didn’t get into the scissor-lift to check that at the time).  This skeleton actually played a role in determining the size of the hall in which it is installed.  We decided early in the planning phase for the building that this skeleton would be the centerpiece for the hall.  As a result, the ceilings for this floor had to be made extra-high, and the mid-room support pillars designed out to accommodate the skeleton and still clear all the HVAC, sprinkler heads, and other necessities.

That’s all pretty fantastic–both that we have enough of Alamosaurus to do a pretty rigorous full skeletal mount, and that the beast was legitimately pretty darned big. Ron goes on:

One correction to the story on SV-POW, the Dallas cervical series consists of only 9 verts, not 10.  There may have been frags or something that made folks think there was a 10th at the anterior end of the series when first found, but I’ve never seen evidence of it in our collection.  This may be supported by the fact that the verts were given letter designations in the field (that we still use), and are identified as verts B through J, from anterior to posterior.

I later learned from Tony Fiorillo that the vertebrae were labelled B through J in the field in case anything anterior to B turned up, but nothing did, so the ‘A’ placeholder went unused. That reminds me of the search in the mid-1800s for the hypothetical planet Vulcan (not the one you’re thinking of) between Mercury and the Sun, which I bring up for no reasons other than that hypothetical planets are cool, and if you’re exploring, it’s worth keeping an open mind about what might yet turn up.

There’s more to say about the size of Alamosaurus–we haven’t even covered the big material described by Fowler and Sullivan (2011) yet–but I’m not going to say a whole lot right now, since I’m going to see the Big Bend material in Dallas in just a few days. Watch this space.

Reference

Fowler, D.W. and Sullivan, R.M. 2011. The first giant titanosaurian sauropod from the Upper Cretaceous of North America. Acta Palaeontologica Polonica 56 (4): 685–690.

I was cruising the monographs the other night, looking for new ideas, when the humerus of Opisthocoelicaudia stopped me dead in my tracks. I think you’ll agree it is an arresting sight:

Opisthocoelicaudia right humerus in lateral, anterior, medial, and posterior views, from Borsuk-Bialynicka (1977: figure 7)

Opisthocoelicaudia right humerus in medial, anterior, lateral, and posterior views, from Borsuk-Bialynicka (1977: figure 7)

I’d seen it before, but somehow I had never grokked its grotesque fatness. I mean, damn, Opisthocoelicaudia, you really let yourself go. Especially compared to the slenderness and grace of this juvenile Alamosaurus humerus:

Alamosaurus left humerus in anterior and posterior views, from Lehman and Coulson (2002: figure 7).

Alamosaurus left humerus in anterior and posterior views, from Lehman and Coulson (2002: figure 7).

Now, I realize that part of the slenderness of this Alamosaurus humerus might be because it’s a juvenile–other alamosaur humeri are a bit more robust–but it’s still a striking contrast. I couldn’t help but superimpose them, scaled to the same midshaft width:

Alamosaurus and Opisthocoelicaudia humeri superimposed

I flipped the Alamosaurus humerus left-to-right to match that astonishing lump of Opisthocoelicaudia. The result reminds me of one of Abrell and Thompson’s Actual Facts:

If you put Woodrow Wilson inside William Howard Taft, he would have stuck out by a good 18 inches.

None of that probably signifies anything more than that I am easily amused. And also,  Opisthocoelicaudia is Just Plain Wrong. You hear me, Opisthocoelicaudia? Don’t make me make you cry mayonnaise!

References

Sorry for the very short post. We have some longer stuff planned, but we’ve been too busy to kick it out this week, and I wanted to leave you with something cool to ponder over the weekend. Here’s the ilium of Giraffatitan overlaid on that of Brontomerus, scaled to the same acetabulum diameter (Giraffatitan is HMN J1, left ilium, modified from Janensch 1961: pl. E, fig. 2; Brontomerus is of course OMNH 66430 from Taylor et al. 2011:fig. 2).

And here’s the same thing comparing Rapetosaurus and Brontomerus (Rapetosaurus is holotype FMNH PR 2209, left ilium, modified from Curry Rogers 2009: fig. 39B). This one was tricky to scale because the ilial margin of the acetabulum is so different in the two taxa.

Here is the same trick performed with the ilium of the canonical pretty basal neosauropod Camarasaurus — specifically, Camarasaurus supremus AMNH 5761 Il. 1, left ilium, modified from Osborn and Mook (1921: fig. 87).  In this case, the proportions are so very different that it’s hard to make a meaningful superimposition: we tried to scale to equal acetabulum size, but probably that of the Camarasaurus was proportionally larger than in the other taxa illustrated in this post.  Still, here it is:

Finally, in response to Paul Barrett’s comment on a subsequent article, here is a superimposition of the ilium of Alamosaurus on that of Brontomerus:

(Sorry about the poor quality of this one, but the only figure I could find of a complete Alamosaurus ilium was the line-drawing in Lehman and Coulson (2002:fig. 8) — none of the standard descriptive works seem to illustrate a complete or near-complete ilium.)

We had a figure like these in an early draft of the paper, but we ditched it because we felt that doing a broader comparative figure would be more valuable. But I like the kick in the brainpan that these overlays provide.

References

A section of the cotyle of a presacral vertebra of Alamosaurus (Woodward and Lehman 2009:fig. 6A).

The last time we talked about Alamosaurus, I promised to explain what the arrow in the above image is all about. The image above is a section through the cotyle (the bony socket of a ball-and-socket joint) at the end of one of the presacral vertebra. The external bone surface would have been over on the left; it was either very thin (which happens) or a bit eroded, or both. The arrow is pointing at something weird–a plate of bone inside the vertebra that forms a sort of shadow cotyle deep to the articular surface.

This is weird for a couple of reasons. First, once camellate (small-chambered) vertebrae get above a certain level of complexity, it’s hard to make any sense of the orientation of individual bony struts. Possibly I haven’t seen enough vertebrae, or played with enough 3D models, to figure it out. You would certainly expect that the struts would be oriented to resist biomechanical loads, just like the struts in the long bones of your limbs; the fact that sauropod verts were filled with air whereas your long bones are filled with marrow shouldn’t make any difference. Back in the day, Kent Sanders–who is second author on that super-important paper on unidirectional air flow in croc lungs that you’ve probably heard about (Farmer and Sanders 2010)–speculated to me that the complex of laminae we see in the vertebrae of most sauropods are still there in the inflated-looking vertebrae of titanosaurs and birds, they’re just incarnated in internal struts rather than external laminae. Cool hypothesis for somebody to test.

The other reason that this is weird is that the plate of bone is parallel to the articular surface. One place where I have seen some regularity in terms of strut orientation is in zygapophyses, where in both camerae and camellate vertebrae the internal struts are oriented at right angles to the articular surfaces of the zygs, like beams propping up a wall. In this Alamosaurus section, there are indeed smaller struts that run at right angles to both the cotyle and the internal plate, but I have no idea why they’re so wimpy and the plate is so thick; a priori I would have expected the reverse.

It turns out that this isn’t even the first time that an internal “shadow” of the cotyle has been figured–check out this figure that I redrew from Powell’s (1992:fig. 16) Saltasaurus osteology. But don’t credit me with the discovery. I’d looked at this section a hundred times and even drawn it and never noticed the shadow cotyle, until it was pointed out by Woodward and Lehman (2009)–another reason to read that paper if you haven’t yet. Kudos to Holly Woodward for spotting this and making the connection.

Now that I’ve drawn attention to the weirdness and given credit where it’s due, this is one of those times I’m going to throw up my hands in confusion and open the floor for comments.

References

  • Farmer, C.G., and Sanders, K. 2010. Unidirectional airflow in the lungs of alligators. Science 327:338-340.
  • Powell, J.E. 1992. Osteologia de Saltasaurus loricatus (Sauropoda – Titanosauridae) del Cretacico Superior del noroeste Argentino; pp. 165-230 in J.L. Sanz and A.D. Buscalioni (editors), Los Dinosaurios y Su Entorno Biotico: Actas del Segundo Curso de Paleontologia in Cuenca. Institutio Juan de Valdes.
  • Woodward, H.N.,  and Lehman, T.M. 2009. Bone histology and microanatomy of Alamosaurus sanjuanensis (Sauropoda: Titanosauria) from the Maastrichtian of Big Bend National Park, Texas. Journal of Vertebrate Paleontology 29(3):807-821.

ASPs for Alamosaurus

January 4, 2010

A section of the cotyle of a presacral vertebra of Alamosaurus (Woodward and Lehman 2009:fig. 6A). The arrow will be explained in a future post!

Last year was good for sauropod pneumaticity. In the past few months we’ve had the publication of the first FEA of pneumatic sauropod vertebrae by Schwarz-Wings et al (2009), as well as a substantial section on pneumaticity in the big Alamosaurus histology paper by Woodward and Lehman (2009). I won’t repeat here everything that Woodward and Lehman have to say about pneumaticity, I just want to draw attention to a little piece of it. Their work is observant, up-to-date, and worth reading, so if you can get access to the paper, read it.

The major brake on the growth of our knowledge and understanding of pneumaticity is sample size. I harped on this in 2005 (Wedel 2005), and Mike just brought it up again in a comment on a previous post. In fact, what he had to say is so relevant that I’m going to just cut and paste it here:

How does degree of pneumatisation vary between individuals? Here are three more: how does it vary along the neck, how does it vary long the length of an individual vertebra, and how does it vary through ontogeny? Then of course there is variation between taxa across the tree. So what we have here is a five-and-half-dimensional space that we want to fill with observations so that we can start to deduce conclusions. Trouble is, there are, so far, 22 published observations (neatly summarised by Wedel 2005:table 7.2), which is not really enough to let us map out 5.5-space! That’s one reason why, at the moment, each observation is valuable — it adds 4% to the total knowledge in the world.

To be fair, there are a few more published observations. Schwarz and Fritsch (2006) published ASPs for cervicals of Giraffatitan and Dicraeosaurus, and I have a gnawing feeling that there are a couple here and there that I’ve seen but not remembered. I’ve got some more of my own data in the as-yet-unpublished fourth chapter of my diss, which I failed to get out as part of the Paleo Paper Challenge. And, getting back to the subject of the post, Woodward and Lehman (2009:819) have some tasty new data to report:

Digital images of sections of vertebrae and ribs were imported into ArcGIS 8.1 (Dangermond, 2001; for methods see Woodward, 2005). A unitless value for the total area of the image was calculated, using the outline of the bone as a perimeter. Subtracted from this was the area value taken up by bone, as determined by color differences (lighter areas are camellate cavities, darker areas are bone). Using this method, longitudinal sections of centra are estimated to be roughly 65% air filled. The amount of open space similarly calculated for the pneumatic proximal and medial rib sections is about 52%, whereas the cancellous spongiosa in distal rib transverse sections yields an average estimate of about 44% of their cross sectional area. Hence, the camellate cavities result in an appreciably lower bone volume compared to spongiosa.

The ASP of 0.65 for centra is right in line with the numbers I’ve gotten for neosauropods, and with the results of Schwarz and Fritsch (2006) for Giraffatitan (Dicraosaurus had a much lower ASP, around 0.2 IIRC). The stuff about the ribs is particularly interesting. Using densities of 0.95 for bone marrow, 1.8 for avian (and sauropod) compact bone, and 1.9 for mammalian compact bone we get the following:

  • Pneumatic Alamosaurus vertebrae – ASP of 0.65, density of 0.63 g/cm^3.
  • Pneumatic Alamosaurus ribs – ASP of 0.52, density of 0.86 g/cm^3.
  • Apneumatic Alamosaurus ribs – MSP (marrow space proportion) of 0.44, density of 1.43 g/cm^3.
  • Pneumatic bird long bones – ASP of 0.59, density of 0.74 g/cm^3.
  • Apneumatic bird long bones – MSP of 0.42, density of 1.44 g/cm^3.
  • Apneumatic mammal long bones – MSP of 0.28, density of 1.63 g/cm^3.

ASPs and MSPs of bird and mammal bones are calculated from K values reported by Cubo and Casinos (2000) for birds and Currey and Alexander (1985) for mammals. I don’t know what the in vivo density of sauropod compact bone was; changing it from the avian value of 1.8 to the mammalian value of 1.9 would have a negligible effect on the outcome.

At least with the data in hand, we can make the following generalizations:

  • The apneumatic bones of birds are thinner-walled than those of mammals, on average. (This has been known for a long time.)
  • The apneumatic ribs of Alamosaurus were more similar in density to apneumatic bird bones than to apneumatic mammal bones.
  • In both birds and Alamosaurus, pneumatization reduces the amount of bone tissue present by 15-30% in the same elements (long bones for birds, ribs for Alamosaurus). Pneumatic bones are light not just because the marrow is replaced by air, but because there is less bone tissue than in apneumatic bones, as bird people have been observing for ages.

There’s loads more work to be done on this sort of thing, so I’m going to stop blogging now and get back to it. Stay tuned!

References