Sauroposeidon OMNH 53062 C7-C8 left side

Sauroposeidon holotype OMNH 53062, posterior half of ?C7 and all of ?C8 in left lateral view. Scale bar is in inches.

There’s a lot more Sauroposeidon material these days than there used to be, thanks to the referral by D’Emic and Foreman (2012) of Paluxysaurus and Ostrom’s Cloverly material and the new Cloverly material to my favorite sauropod genus. I’ve seen almost all of this material firsthand, but obviously the specimen I’m most familiar with is the holotype, OMNH 53062. It was the primary thing occupying my mind from the summer of 1996 through the spring of 2000, and it has remained a frequent object of wonder ever since.

The specimen was found lying on its right side in the field, so that side is in better shape, by virtue of having been more deeply buried and thus protected from the ravages of freezing and thawing and other erosional processes. When the jackets were taken out of the ground and prepared, the not-so-well-preserved left sides were prepped first. Then permanent support jackets were made on the left sides, the vertebrae were flipped onto their left sides, the field jackets were removed from their right sides, and the vertebrae were prepped on the right. They’ve been lying in their support jackets, left side down and right side up, ever since. (For more on the taphonomy and recovery of the specimen, see this post and Wedel and Cifelli 2005 [free PDF linked below].)

Now, if I had known what I was doing, I would have photographed the crap out of the left sides before the verts were flipped. But it was my first project and I was learning on the job, and that didn’t occur to me until later.

It also didn’t occur to me that, once flipped, the left sides would be effectively out of reach forever. But the vertebrae are extremely fragile. The bigger verts have cracks running through them, and the jackets flexed noticeably when we took them for CT scanning. I am worried that if we tried to flip the bigger verts today, they might just crumble. Even the surface bone is fragile. I remember once trying to get some dust off one of the verts with a vacuum cleaner hose, and watching in horror as some of the millimeter-thin external bone just flaked off and flew away. That was in the late 1990s, when the verts were still stored in the dusty, drafty WWII-era buildings that had housed the museum collections for ages. Now they’re in what I still think of as the “new” building, which opened in 2000, in a really nice modern collection room with climate and dust control, and I’ve never seen them with any noticeable dust.

Anyway, the left sides are now obscured by their supporting jackets and will remain that way for the foreseeable future. And I don’t have a complete set of photos of the left sides of the verts. But I do have one, of the back half of ?C7 and all of ?C8, and a scan of it appears at the top of this post. It’s a scan of a physical photograph because it was taken in late 1996 or early 1997–no-one I knew had a digital camera, and if you wanted a digital version of a photograph, you shot it on a film camera, had a big print made, and scanned that on a flatbed scanner.

Here’s another version with the vertebrae outlined:

Sauroposeidon OMNH 53062 C7-C8 left side - outlined

When I and everyone else thought that Sauroposeidon was a brachiosaur, I was pretty sure that these were C7 and C8, out of a total of 13 cervicals, just like Giraffatitan. And it still might be so–a future analysis might find that the newly-expanded Sauroposeidon is a brachiosaurid after all, and even if not, Gomani (2005) posited a primitive cervical count of 13 for titanosaurs. If that’s true, then possibly 13 cervicals are primitive for all titanosauriforms, and the increases beyond that–to 17 in Euhelopus and 14-17 in more derived titanosaurs like Futalognkosaurus and Rapetosaurus–were deviations from that primitive pattern.

But.

If Sauroposeidon was a basal somphospondyl, as posited by D’Emic and Foreman (2012) and as found in the phylogenetic analysis of D’Emic (2012), then maybe it was more like Euhelopus than Giraffatitan, and maybe it had more than 13 cervicals. (Note that D’Emic [2012] found Sauroposeidon to be a basal somphospondyl but outside the Euhelopodidae, so even in his analysis, Euhelopus could have gotten its extra cervicals independently of Sauroposeidon.) That’s an interesting prospect, since the 11.5-meter neck estimate for Sauroposeidon I made back in 2000 was based on the conservative assumption of 13 cervicals. If Sauroposeidon had more cervicals, they were probably mid-cervicals (nobody adds more dinky C3s, or stubby cervico-dorsals*–that would be silly), and therefore between 1 and 1.25 meters long. So if the individual represented by OMNH 53062 had 15 cervicals, as Mike hypothetically illustrated in this post, its neck might was probably more like 14 meters long, and if it had 17 cervicals, like Euhelopus and Rapetosaurus, its neck might have topped 16 meters–as long or longer than that of Supersaurus.

Now, I’m not saying that Sauroposeidon had a 16-meter neck. The conservative estimate is still 13 cervicals adding up to 11.5 meters. But the possibility of a longer neck is tantalizing, and can’t be ruled out based on current evidence. As usual, we need more fossils.

Happily, now that Sauroposeidon is known from Oklahoma, Texas, and Wyoming, and is one of the best-represented EKNApods instead of one of the scrappiest, the chances that we’ll find more of it–and recognize it–are looking good. I will keep my fingers firmly crossed–as they have been for the last 17 years.

* Radical pedantry note: of course we have very good evidence of sauropods getting more cervical vertebrae by recruiting dorsals into the cervical series. So, for example, 13 cervicals and 12 dorsals are supposed to be primitive for neosauropods, but diplodocids have 15 and 10, respectively–the obvious inference being that the first two dorsals got cervicalized. So in this narrow meristic sense, sauropods definitely did add cervicodorsals. But my point above is about the morphology of the verts themselves–once diplodocids had those two extra cervicals at the end, the former cervicodorsals were free to become more “cervicalized” in form. So effectively–in terms of the shapes of their necks–diplodocids added mid-cervicals.

References

You may remember this:

Rapetosaurus mount at Field Museum

…which I used to make this:

Rapetosaurus skeleton silhouette

…and then this:

Rapetosaurus skeleton silhouette - high neck

The middle image is just the skeleton from the top photo cut out from the background and dropped to black using ‘Levels’ in GIMP, with the chevrons scooted up to close the gap imposed by the mounting bar.

The bottom image is the same thing tweaked a bit to repose the skeleton and get rid of some perspective distortion on the limbs. The limb posture is an attempt to reproduce an elephant step cycle from Muybridge.

That neck is wacky. Maybe not as wrong as Omeisaurus, but pretty darned wrong. As I mentioned in the previous Rapetosaurus skeleton post, the cervicals are taller than the dorsals, which is opposite the condition in every other sauropod I’ve seen. All in all, I find the reposed Rapetosaurus disturbingly horse-like. And oddly slender through the torso, dorsoventrally at least. The dorsal ribs look short in these lateral views because they’re mounted at a very odd, laterally-projecting angle that I think is probably not correct. But the ventral body profile still had to meet the distal ends of the pubes and ischia, which really can’t go anywhere without disarticulating the ilia from the sacrum (and cranking the pubes down would only force the distal ends of the ilia up, even closer to the tail–the animal still had to run its digestive and urogenital pipes through there!). So the torso was deeper than these ribs suggest, but it was still not super-deep. Contrast this with Opisthocoelicaudia, where the pubes stick down past the knees–now that was a tubby sauropod. Then again, Alamosaurus has been reconstructed with a similarly compact torso compared to its limbs–see the sketched-in ventral body profile in the skeletal recon from Lehman and Coulson (2002: figure 11).

I intend to post more photos of the mount, including some close-ups and some from different angles, and talk more about how the animal was shaped in life. And hopefully soon, because history has shown that if I don’t strike while the iron is hot, it might be a while before I get back to it. For example, I originally intended this post to follow the last Rapetosaurus skeleton post by  about a week. So much for that!

Like everything else we post, these images are CC BY, so feel free to take them and use them. If you use them for the basis of anything cool, like a muscle reconstruction or life restoration, let us know and we’ll probably blog it.

I’ve measured a few necks in my time, including the neck of a baby giraffe. I can tell you from experience that necks are awkward things to measure, even if they have been conveniently divested of their heads and torsos. They have a tendency to curl up, which impedes attempts to find the straight-line length. Even when you manage to hold them straight, you want them maximally compressed end-to-end rather than stretched out, which is hard to achieve without buckling them out of the straight line. And then you need to measure between perpendiculars in a straight line.

Awkward.

Tonight, I needed to measure the mass and length of seven turkey necks. (Never mind why, all will become clear in time.) And I found a way to do it that works much better than anything I’ve done before.

Here’s the equipment:

IMG_0961-equipment

You will need:

  • Kitchen scales (for weighing the necks)
  • Small numbered labels (for the sandwich bags that the necks will go into for the freezer once they’ve been measured)
  • Pen and paper to take down the measurements
  • Translucent ruler
  • Saucepan full of turkey necks
  • Slightly less than one half of a birthday cake decorated like a map of Middle-earth [optional]
  • A Duplo baseboard (double-sized Lego) and about fifteen 4×2 bricks

Use the bricks to build an L-shaped bracket on the board — about half way back, so that can rest your hand in front of it.

IMG_0963-straightened

Now you can push the neck into the angle of the bracket. By keeping it pressed firmly against the back wall (yellow in my construction), you can keep it straight. I find the best way to get the neck exactly abutting the left (red) wall is to start with the neck in its natural position, with the anterior and posterior ends curving towards you, then sort of unroll it against the back wall, and finally push the posterior end into place with your little finger (see below). There is a satisfying moment– almost a click — as the back end pops into place and the neck slides along a little to right as necessary to accommodate the added length.

IMG_0966-blocked

Now use another brick (blue in this photo) as a bracket: slide it along the back wall from right to left until it’s solidly abutting the anteriormost vertebra. If you do this right, there is very little travel: the entire series of vertebrae is lined up and solidly abutted, with bone pushing against the left wall and your new brick. I find there’s less than half a millimeter of variation between the length under gentle-but-firm pressure (which is what I measured) and under the very strongest force you can exert without buckling the neck.

IMG_0967-measured

Once you have found the blue brick’s correct position, you need to hold it firmly in place and measure its position relative the the left wall. (It doesn’t matter if you let the neck re-curl at this point, so long as the blue brick doesn’t shift.)

You need a translucent ruler so that you can lay it across the neck and see where blue brick falls under the scale. (My ruler’s zero is, rather annoyingly, 5 mm from the end; so I needed to subtract 5 mm from the lengths I measured.)

IMG_0969-bagged

Finally, I bagged up each neck in its own sandwich bag, ready for the freezer. Each neck is labelled with a number so that when I take it out for dissection, I will be able to relate the measurements and observations that I make back to these initial measurements.

For the record, here are the measurements:

  • Neck 1: 154 g, 179.5 mm.
  • Neck 2: 122 g, 151 mm.
  • Neck 3: 154 g, 199.5 mm.
  • Neck 4: 133 g, 162.5 mm.
  • Neck 5: 142 g, 169 mm.
  • Neck 6: 80 g, 167 mm.
  • Neck 7: 70 g, 169 mm.

As expected, there is some correlation between neck mass and length; but not as much as you might expect. Naively (i.e. assuming isometric similarity) mass should be proportional to length cubed, but there is a lot of scatter about that line. I don’t know whether that is due to individual variation, or merely because the various necks — all of them incomplete — are different sections of the full neck. Hopefully I will be able to confirm or rule out that possibility when I’ve dissected down to naked vertebrae.

Having taken time to discuss at length why we posted our neck-anatomy paper on arXiv, let’s now return to the actual content of the paper. You may remember from the initial post, or indeed from the paper itself, that Table 3 of the paper summarises its conclusions:

Table 3. Neck-elongation features by taxon.

Needless to say, we puny humans lack all seven of the features that were discussed as contributing to long necks, while sauropods have them all. But it’s interesting to look at the giraffe and Paraceratherium, the two longest-necked mammals, and see what they have in common. They share quadrupedal stance; the giraffe has elongated cervical vertebrae; and Paraceratherium has absolutely large body size. But they both lack all four of the other features:

  • Small, light head
  • Numerous cervical vertebrae
  • Air-sac system
  • Vertebral pneumaticity

And they lack them for the same reason: because they are mammals. The same is true of all mammals, and the individual reasons for those four missing long-neck features are all the same: because mammals have hit local maxima, and can’t evolve away from them.

Mammals’ heads, for example, are all set up for extensive oral processing of food — certainly among large herbivores. (I think pretty much all the toothless mammals are insectivores.) They’ve got very good at it, and there’s no evolutionary pathway that can take a giraffe from its current lifestyle to a sauropod-like crop-and-swallow strategy without passing through an adaptive valley on the way. That means they are stuck with big, solid teeth and heavily engineered jaws, which means they can’t have light heads.

In the same way, mammals have much more efficient lungs than those of their reptile-like forebears, the common ancestors that they share with birds. They have evolved to a point where their lungs are too complex and effective to easily evolve into a different shape — yet by doing so, they have cut themselves off from the yet more efficient avian lung (shared by sauropods) that is capable of extracting twice as much oxygen as our lungs.

And of course in the absence of an avian-style lung, there can be no soft-tissue diverticula or air-sacs, and so no pneumatic invasion of the vertebrae.

A final nail in the coffin of mammal neck length is that we seem to be strongly wired to have exactly seven cervical vertebrae — no more, no less. The exceptions are very few and far between: sloths and sirenians, and even then they don’t vary from the seven-cervical pattern by more than one or two vertebrae.

Skull and cervical skeleton of the three-toed sloth, Bradypus tridactylus, taken at the University Museum of Zoology, Cambridge (UK). Note the nine cervical vertebrae — the most of any mammal.

As for why we can’t get past seven, or at most nine, cervicals — that’s harder to answer. There’s no reason why seven should be an adaptive maximum, so it seems that the reason is genetic: the instructions to produce seven cervicals are part of the same gene complex that gives us an advantage in some other way. I have vague memories of an excellent talk at the Bristol SVP suggesting that cervical-count is linked to cancer resistance, but I can’t remember any of the details.

Anyone able to elaborate?

Anyway: this is how evolution works, and why it doesn’t make organisms (including us) as perfect as we might wish. It has no goal in mind — such as a long neck — and blindly follows the path that at that moment gives the organism the best chance of reproducing successfully. That means an animal like a giraffe, even though it is clearly selecting for neck length, is trapped on an adaptive hill and can’t get down across the valley to a higher peak.

Why giraffes have short necks

September 26, 2012

Today sees the publication, on arXiv (more on that choice in a separate post), of Mike and Matt’s new paper on sauropod neck anatomy. In this paper, we try to figure out why it is that sauropods evolved necks six times longer than that of the world-record giraffe — as shown in Figure 3 from the paper (with a small version of Figure 1 included as a cameo to the same scale):

Figure 3. Necks of long-necked sauropods, to the same scale. Diplodocus, modified from elements in Hatcher (1901, plate 3), represents a “typical” long-necked sauropod, familiar from many mounted skeletons in museums. Puertasaurus modified from Wedel (2007a, figure 4-1). Sauroposeidon scaled from Brachiosaurus artwork by Dmitry Bogdanov, via commons.wikimedia.org (CC-BY-SA). Mamenchisaurus modified from Young and Zhao (1972, figure 4). Supersaurus scaled from Diplodocus, as above. Alternating pink and blue bars are one meter in width. Inset shows Figure 1 to the same scale.

This paper started life as a late-night discussion over a couple of beers, while Matt was over in England for SVPCA back in (I think) 2008. It was originally going to be a short note in PaleoBios, just noting some of the oddities of sauropod cervical architecture — such as the way that cervical ribs, ventral to the centra, elongate posteriorly but their dorsal counterparts the epipophyses do not.

As so often, the tale grew in the telling, so that a paper we’d initially imagined as a two-or-three-page note became Chapter 5 of my dissertation under the sober title of “Vertebral morphology and the evolution of long necks in sauropod dinosaurs”, weighing in at 41 1.5-spaced pages. By now the manuscript had metastatised into a comparison between the necks of sauropods and other animals and an analysis of the factors that enabled sauropods to achieve so much more than mammals, birds, other theropods and pterosaurs.

(At this point we had one of our less satisfactory reviewing experiences. We sent the manuscript to a respected journal, where it wasn’t even sent out to reviewers until more than a month had passed. We then had to repeatedly prod the editor before anything else happened. Eventually, two reviews came back: one of them careful and detailed; but the other, which we’d waited five months for, dismissed our 53-page manuscript in 108 words. So two words per page, or about 2/3 of a word per day of review time. But let’s not dwell on that.)

Figure 6. Basic cervical vertebral architecture in archosaurs, in posterior and lateral views. 1, seventh cervical vertebra of a turkey, Meleagris gallopavo Linnaeus, 1758, traced from photographs by MPT. 2, fifth cervical vertebra of the abelisaurid theropod Majungasaurus crenatissimus Depéret, 1896,UA 8678, traced from O’Connor (2007, figures 8 and 20). In these taxa, the epipophyses and cervical ribs are aligned with the expected vectors of muscular forces. The epipophyses are both larger and taller than the neural spine, as expected based on their mechanical importance. The posterior surface of the neurapophysis is covered by a large rugosity, which is interpreted as an interspinous ligament scar like that of birds (O’Connor, 2007). Because this scar covers the entire posterior surface of the neurapophysis, it leaves little room for muscle attachments to the spine. 3, fifth cervical vertebra of Alligator mississippiensis Daudin, 1801, MCZ 81457, traced from 3D scans by Leon Claessens, courtesy of MCZ. Epipophyses are absent. 4, eighth cervical vertebra of Giraffatitan brancai (Janensch, 1914) paralectotype HMN SII, traced from Janensch (1950, figures 43 and 46). Abbreviations: cr, cervical rib; e, epipophysis; ns, neural spine; poz, postzygapophysis.

This work made its next appearance as my talk at SVPCA 2010 in Cambridge, under the title Why giraffes have such short necks. For the talk, I radically restructured the material into a form that had a stronger narrative — a process that involved a lot of back and forth with Matt, dry-running the talk, and workshopping the order in which ideas were presented. The talk seemed to go down well, and we liked the new structure so much more than the old that we reworked the manuscript into a form that more closely resembled the talk.

That’s the version of the manuscript that we perfected in New York when we should have been at all-you-can-eat sushi places. It’s the version that we submitted on the train from New York to New Haven as we went to visit the collections of the Yale Peabody Museum. And it’s the version that was cursorily rejected from mid-to-low ranked palaeo journal because a reviewer said “The manuscript reads as a long “story” instead of a scientific manuscript” — which was of course precisely what we’d intended.

Needless to say, it was deeply disheartening to have had what we were convinced was a good paper rejected twice from journals, at a cost of three years’ delay, on the basis of these reviews. One option would have been to put the manuscript back into the conventional “scientific paper” straitjacket for the second journal’s benefit. But no. We were not going to invest more work to make the paper less good. We decided to keep it in its current, more readable, form and to find a journal that likes it on that basis.

At the moment, the plan is to send it to PeerJ when that opens to submissions. (Both Matt and I are already members.) But that three-years-and-rolling delay really rankles, and we both felt that it wasn’t serving science to keep the paper locked up until it finally makes it into a journal — hence the deposition in arXiv which we plan to talk about more next time.

Table 3. Neck-elongation features by taxon.

In the paper, we review seven characteristics of sauropod anatomy that facilitated the evolution of long necks: absolutely large body size; quadrupedal stance; proportionally small, light head; large number of  cervical vertebrae; elongation of cervical vertebrae; air-sac system; and vertebral pneumaticity. And we show that giraffes have only two of these seven features. (Ostriches do the next best, with five, but they are defeated by their feeble absolute size.)

The paper incorporates some material from SV-POW! posts, including Sauropods were corn-on-the-cob, not shish kebabs. In fact, come to think of it, we should have cited that post as a source. Oh well. We do cite one SV-POW! post: Darren’s Invading the postzyg, which at the time of writing is the only published-in-any-sense source for pneumaticity invading cervical postzygapogyses from the medial surface.

As for the non-extended epipophyses that kicked the whole project off: we did illustrate how they could look, and discussed why they would seem to make mechanical sense:

Figure 10. Real and speculative muscle attachments in sauropod cervical vertebrae. 1, the second through seventeenth cervical vertebrae of Euhelopus zdanskyi Wiman, 1929 cotype specimen PMU R233a-δ(“Exemplar a”). 2, cervical 14 as it actually exists, with prominent but very short epipophyses and long cervical ribs. 3, cervical 14 as it would appear with short cervical ribs. The long ventral neck muscles would have to attach close to the centrum. 4, speculative version of cervical 14 with the epipophyses extended posteriorly as long bony processes. Such processes would allow the bulk of both the dorsal and ventral neck muscles to be located more posteriorly in the neck, but they are not present in any known sauropod or other non-avian dinosaur. Modified from Wiman (1929, plate 3).

But we found and explained some good reasons why this apparently appealing arrangement would not work. You’ll need to read the paper for details.

Sadly, we were not able to include this slide from the talk illustrating the consequences:

Anyway, go and read the paper! It’s freely available, of course, like all arXiv depositions, and in particular uses the permissive Creative Commons Attribution (CC BY) licence. We have assembled related information over on this page, including full-resolution versions of all the figures.

In the fields of maths, physics and computer science, where deposition in arXiv is ubiquitous, standard practice is to go right ahead and cite works in arXiv as soon as they’re available, rather than waiting for them to appear in journals. We will be happy for the same to happen with our paper: if it contains information that’s of value to you, then feel free to cite the arXiv version.

Reference

  • Taylor, Michael P., and Mathew J. Wedel. 2012. Why sauropods had long necks; and why giraffes have short necks. arXiv:1209.5439. 39 pages, 11 figures, 3 tables. [Full-resolution figures]

In a comment on the previous post, Emily Willoughby links to an excellent post on her own blog that discusses the “necks lie” problem in herons. Most extraordinarily, here are two photos of what seems to be the same individual:

You should get over to Emily’s blog right now and read her article. (Kudos, too, for the Portal reference in the title. I’ve been playing Portal and Portal 2 obsessively for the last week. Quite brilliant, and a very rare example of true innovation in computer gaming.)

Also of interest: this composite of two shoebill (Balaeniceps rex) individuals, which I made from two of the images mentioned in a comment by AL on Emily’s post:

Oh, birds, you crazy creatures!

Back when we were at Cambridge for the 2010 SVPCA, we saw taxidermied and skeletonised hoatzins, and were struck that the cervical skeleton was so very much longer than the neck as it appears in life — because necks lie. At Oxford last week for the 2012 SVPCA, we saw a similar pair of hoatzin mounts (one adult, one juvenile) that clarified the situation:

And here is juvenile in side-view:

As you can see, it’s folding its neck way down out of the way, so that externally it appears much shorter. (And comparing with the Cambridge specimen, you can see that the neck skeleton is proportionally much longer than this in adult.)

Why does it do this? I have no idea.

But I do know it’s not unique to hoatzins. Another nice illustration of how misleading birds’ necks are when viewed in a live animal is this parrot (probably Amazona ochrocephala) in the Natuurhistorisch Museum of Rotterdam (from this Love in the Time of Chasmosaurs post):

One thing that’s not clear to me is how much of the neck the bird can extend in life. If the parrot wants to uncoil all that spare cervical skeleton to reach upwards or forwards, can it? Will the soft tissue envelope allow it? My guess is not, otherwise you’d surely see them doing it. But then … why is all that neck in there at all?