Daniel Vidal et al.’s new paper in Scientific Reports (Vidal et al. 2020) has been out for a couple of days now. Dealing as it does with sauropod neck posture, it’s obviously of interest to me, and to Matt. (See our earlier relevant papers Taylor et al. 2009, Taylor and Wedel 2013 and Taylor 2014.)

Overview

To brutally over-summarise Vidal et al.’s paper, it comes down to this: they digitized the beautifully preserved and nearly complete skeleton of Spinophorosaurus, and digitally articulated the scans of the bones to make a virtual skeletal mount. In doing this, they were careful to consider the neutral pose of consecutive vertebrae in isolation, looking at only one pair at a time, so as to avoid any unconscious biases as to how the articulated column “should” look.

Then they took the resulting pose, objectively arrived at — shown above in their figure 1 — and looked to see what it told them. And as you can well see, it showed a dramatically different pose from that of the original reconstruction.

Original skeletal reconstruction of Spinophorosaurus nigerensis (Remes et al. 2009:figure 5, reversed for ease of comparison). Dimensions are based on GCP-CV-4229/NMB-1699-R, elements that are not represented are shaded. Scale bar = 1 m.

In particular, they found that as the sacrum is distinctly “wedged” (i.e. its anteroposterior length is greater ventrally than it is dorsally, giving it a functionally trapezoidal shape, shown in their figure 1A), so that the column of the torso is inclined 20 degrees dorsally relative to that of the tail. They also found lesser but still significant wedging in the last two dorsal vertebrae (figure 1B) and apparently some slight wedging in the first dorsal (figure 1C) and last cervical (figure 1D).

The upshot of all this is that their new reconstruction of Spinophorosaurus has a strongly inclined dorsal column, and consequently an strongly inclined cervical column in neutral pose.

Vidal et al. also note that all eusauropods have wedged sacra to a greater or lesser extent, and conclude that to varying degrees all eusauropods had a more inclined torso and neck than we have been used to reconstructing them with.

Response

I have to be careful about this paper, because its results flatter my preconceptions. I have always been a raised-neck advocate, and there is a temptation to leap onto any paper that reaches the same conclusion and see it as corroboration of my position.

The first thing to say is that the core observation is absolutely right, — and it’s one of those things that once it’s pointed out it’s so obvious that you wonder why you never made anything of it yourself. Yes, it’s true that sauropod sacra are wedged. It’s often difficult to see in lateral view because the ilia are usually fused to the sacral ribs, but when you see them in three dimensions it’s obvious. Occasionally you find a sacrum without its ilium, and then the wedging can hardly be missed … yet somehow, we’ve all been missing its implications for a century and a half.

Sacrum of Diplodocus AMNH 516 in left lateral and (for our purposes irrelevant) ventral views. (Osborn 1904 figure 3)

Of course this means that, other thing being equal, the tail and torso will not be parallel with each other, but will project in such a way that the angle between them, measured dorsally, is less than 180 degrees. And to be fair, Greg Paul has long been illustrating diplodocids with an upward kink to the tail, and some other palaeoartists have picked up on this — notably Scott Hartman with his very uncomfortable-looking Mamenchisaurus.

But I do have three important caveats that mean I can’t just take the conclusions of the Vidal et al. paper at face value.

1. Intervertebral cartilage

I know that we have rather banged on about this (Taylor and Wedel 2013, Taylor 2014) but it remains true that bones alone can tell us almost nothing about how vertebrae articulated. Unless we incorporate intervertebral cartilage into our models, they can only mislead us. To their credit, Vidal et al. are aware of this — though you wouldn’t know it from the actual paper, whose single mention of cartilage is in respect of a hypothesised cartilaginous suprascapula. But buried away the supplementary information is this rather despairing paragraph:

Cartilaginous Neutral Pose (CNP): the term was coined by Taylor for “the pose found when intervertebral cartilage [that separates the centra of adjacent vertebrae] is included”. Since the amount of inter-vertebral space cannot be certainly known for most fossil vertebrate taxa, true CNP will likely remain unknown for most taxa or always based on estimates.

Now this is true, so far as it goes: it’s usually impossible to know how much cartilage there was, and what shape it took, as only very unusual preservational conditions give us this information. But I don’t think that lets us out from the duty of recognising how crucial that cartilage is. It’s not enough just to say “It’s too hard to measure” and assume it didn’t exist. We need to be saying “Here are the results if we assume zero-thickness cartilage, here’s what we get if we assume cartilage thickness equal to 5% centrum length, and here’s what we get if we assume 10%”.

I really don’t think it’s good enough in 2020 to say “We know there was some intervertebral cartilage, but since we don’t know exactly how much we’re going to assume there was none at all”.

The thing about incorporating cartilage into articulating models is that we would, quite possibly, get crazy results. I refer you to the disturbing figure 4 in my 2014 paper:

Figure 4. Effect of adding cartilage to the neutral pose of the neck of Diplodocus carnegii CM 84. Images of vertebra from Hatcher (1901:plate III). At the bottom, the vertebrae are composed in a horizontal posture. Superimposed, the same vertebrae are shown inclined by the additional extension angles indicated in Table 2.

I imagine that taking cartilage into account for the Spinophorosaurus reconstruction might have given rise to equally crazy “neutral” postures. I can see why Vidal et al. might have been reluctant to open that can of worms; but the thing is, it’s a can that really needs opening.

2. Sacrum orientation

As Vidal et al.’s figure 1A clearly shows, the sacrum of Spinophorosaurus is indeed wedge-shaped, with the anterior articular surface of the first sacral forming an angle of 20 degrees relative to the posterior articular surface of the last:

But I don’t see why it follows that “the coalesced sacrum is situated so that the posterior face of the last sacral centrum is sub-vertical. This makes the presacral series to slope dorsally and the tail to be subhorizontal (Figs. 1 and 4S)”. Vidal et al. justify this with the claim by saying:

Since a subhorizontal tail has been known to be present in the majority of known sauropods[27, 28, 29], the [osteologically induced curvature] of the tail of Spinophorosaurus is therefore compatible with this condition.

But those three numbered references are to Gilmore 1932, Coombs 1975 and Bakker 1968 — three venerable papers, all over fifty years old, dating from a period long before the current understanding of sauropod posture. What’s more, each of those three was about disproving the previously widespread assumption of tail-dragging in sauropods, but the wedged sacrum of Spinophorosaurus if anything suggests the opposite posture.

So my question is, given that the dorsal and caudal portions of the vertebral column are at some specific angle to each other, how do we decide which (if either) is horizontal, and which is inclined?

Three interpretations of the wedged sacrum of Spinophorosaurus, in right lateral view. In all three, the green line represents the trajectory of the dorsal column in the torso, and the red line that of the caudal column. At the top, the tail is horizontal (as favoured by Vidal et al. 2020) resulting in an inclined torso; at the bottom, the torso is horizontal, resulting in a dorsally inclined tail; in the middle, an intermediate posture shows both the torso and the tail slightly inclined.

I am not convinced that the evidence presented by Vidal et al. persuasively favours any of these possibilities over the others. (They restore the forequarters of Spinophorosaurus with a very vertical and ventrally positioned scapula in order to enable the forefeet to reach the ground; this may be correct or it may not, but it’s by no means certain — especially as the humeri are cross-scaled from a referred specimen and the radius, ulna and manus completely unknown.)

3. Distortion

Finally, we should mention the problem of distortion. This is not really a criticism of the paper, just a warning that sacra as preserved should not be taken as gospel. I have no statistics or even systematic observations to back up this assertion, but the impression I have, from having looked closely at quite a lot of sauropod vertebra, is the sacra are perhaps more prone to distortion than most vertebrae. So, for example, the very extreme almost 30-degree wedging that Vidal et al. observed in the sacrum of the Brachiosaurus altithorax holotype FMNH PR 25107 should perhaps not be taken at face value.

Now what?

Vidal el al. are obviously onto something. Sauropod sacra are screwy, and I’m glad they have drawn attention in a systematic way to something that had only been alluded to in passing previously, and often in a way that made it seems as though the wedging they describe was unique to a few special specimens. So it’s good that this paper is out there.

But we really do need to see it as only a beginning. Some of the things I want to see:

  • Taking cartilage into account. If this results in silly postures, we need to understand why that is the case, not just pretend the problem doesn’t exist.
  • Comparison of sauropod sacra with those of other animals — most important, extant animals whose actual posture we can observe. This might be able to tell us whether wedging really has the implications for posture that we’re assuming.
  • Better justification of the claim that the torso rather than the tail was inclined.
  • An emerging consensus on sauropod shoulder articulation, since this also bears on torso orientation. (I don’t really have a position on this, but I think Matt does.)
  • The digital Spinophorosaurus model used in this study. (The paper says “The digital fossils used to build the virtual skeleton are deposited and accessioned at the Museo Paleontológico de Elche” but there is no link, I can’t easily find them on the website and they really should be published alongside the paper.)

Anyway, this is a good beginning. Onward and upward!

References

  • Bakker, Robert T. 1968. The Superiority of Dinosaurs. Discovery 3:11–22.
  • Coombs, Walter P. 1975. Sauropod habits and habitats. Palaeogeography, Palaeoclimatology, Palaeoecology 17:1-33.
  • Gilmore, Charles 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.
  • Hatcher, John Bell. 1901. Diplodocus (Marsh): its osteology, taxonomy, and probable habits, with a restoration of the skeleton. Memoirs of the Carnegie Museum 1:1-63.
  • Osborn, Henry F. 1904. Manus, sacrum and caudals of Sauropoda. Bulletin of the American Museum of Natural History 20:181-190.
  • Taylor, Michael P. 2014. Quantifying the effect of intervertebral cartilage on neutral posture in the necks of sauropod dinosaurs. PeerJ 2:e712. doi:10.7717/peerj.712
  • Taylor, Michael P., and Mathew J. Wedel. 2013c. The effect of intervertebral cartilage on neutral posture and range of motion in the necks of sauropod dinosaurs. PLOS ONE 8(10):e78214. 17 pages. doi:10.1371/journal.pone.0078214
  • Taylor, Michael P., Mathew J. Wedel and Darren Naish. 2009. Head and neck posture in sauropod dinosaurs inferred from extant animals. Acta Palaeontologica Polonica 54(2):213-230.
  • Vidal, Daniel, P Mocho, A. Aberasturi, J. L. Sanz and F. Ortega. 2020. High browsing skeletal adaptations in Spinophorosaurus reveal an evolutionary innovation in sauropod dinosaurs. Scientific Reports 10(6638). Indispensible supplementary information at https://static-content.springer.com/esm/art%3A10.1038%2Fs41598-020-63439-0/MediaObjects/41598_2020_63439_MOESM1_ESM.pdf
    doi:10.1038/s41598-020-63439-0

 

Hello, ladies!

March 28, 2019

To my shock, I find that we seem never to have posted Bob Nicholls’ beautiful sketch Hello, ladies! on SV-POW!. His recent tweet reminded me about this piece, so here it is!

Like so many classic sauropod sketches, this was executed during a mammal-tooth talk at SVPCA: this one back in 2013, the year of our first Barosarus talk. (Our second was in 2016.)

Bob’s sketch shows speculative sexual display behaviour. We have no direct evidence for (or against) such behaviour; but while we don’t believe sexual selection was the main reason for sauropods evolving long necks, it seems inevitable that long necks evolved for other purposes would be exapted for sexual display.

I always love Bob’s sketches — in fact, for most palaeoartists, I tend to like their sketches more than their finished pieces. Among the many things about this one that make me jealous is all the females in the background admiring the male: the economy of line where Bob can not only summon up a perfectly cromulent diplodocid head in a few strokes, but imbue it with a sense of being inquisitive about the display. It’s magical.

 


Whatever happened to that 2013 Barosaurus project?, you may ask.

Well, the first thing that happened is that after we submitted the abstract, entitled Barosaurus revisited: the concept of Barosaurus (Dinosauria: Sauropoda) is based on erroneously referred specimens, we realised that there was a tiny, tiny mistake in our work. So by the time I gave the talk at the actual conference, the title slide was this:

Then you will recall we did an efficient job of converting the conference presentation into a manuscript, which we submitted as a preprint less than a month after the conference. The preprint quickly garnered amazingly helpful comments, which we used to extensively revise the manuscript.

For reasons we don’t understand, there was a three-year delay before we got it submitted for peer-review in 2016; but when we did finally submit, we did it in the confident hope that it would sail through peer-review, having already been extensively reviewed and revised.

But it was not to be. When we got the reviews back, they asked for a ton of changes, and that process was just too dispiriting to face having already made a ton of changes based on the first set of comments just prior to the submission. So the tedious process got back-burnered, and the suddenly three more years passed.

The upshot is that I still need to handle the reviews on the 2nd version of the paper, and shove the blasted thing through the peer-review process. I will, to be frank, be glad to get it out of my POOP chute, so I can think about other things — not least, the 2016 Barosaurus project.

Just got the APP new issue alert and there are three papers that I think readers of this blog will find particularly interesting:

That’s all for now, just popping in to let people know about these things.

Back in 2013, when we were in the last stages of preparing our paper Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus (Wedel and Taylor 2013b), I noticed that, purely by chance, all ten of the illustrations shared much the same limited colour palette: pale brows and blues (and of course black and white). I’ve always found this strangely appealing. Here’s a composite:

wedel-taylor-2013b-all-figures

I’m really happy with this coincidence. In fact I think I might get it printed up as a poster for my office.

(Thought: if I did, would anyone else be interested in buying it?)

Update (a couple of hours later)

At Matt’s suggestion, I switched the order of figures 7 and 8 (the last two on the third row) to get the following version of the image. It breaks the canonical order of the figures, but it’s visually more pleasing.

wedel-taylor-2013b-all-figures-v2

Now we should write an updated version of the paper that reverses the order in which we refer to figures 7 and 8 :-)

References

  • Wedel, Mathew J., and Michael P. Taylor. 2013. Caudal pneumaticity and pneumatic hiatuses in the sauropod dinosaurs Giraffatitan and Apatosaurus. PLOS ONE 8(10):e78213. 14 pages. doi:10.1371/journal.pone.0078213

A few bits and pieces about the PLOS Collection on sauropod gigantism that launched yesterday.

2013-10-29-SauropodEbook1-thumb

First, there’s a nice write-up of one of our papers (Wedel and Taylor 2013b on pneumaticity in sauropod tails) in the Huffington Post today. It’s the work of PLOS blogger Brad Balukjian, a former student of Matt’s from Berkeley days. The introduction added by the PLOS blogs manager is one of those where you keep wanting to interrupt, “Well, actually it’s not quite like that …” but the post itself, once it kicks in, is good. Go read it.

Brad also has a guest-post on Discover magazine’s Crux blog: How Brachiosaurus (and Brethren) Became So Gigantic. He gives an overview of the sauropod gigantism collection as a whole. Well worth a read to get your bearings on the issue of sauropod gigantism in general, and the new collection in particular.

PLOS’s own community blog EveryONE also has its own brief introduction to the collection.

And PLOS and PeerJ editor Andy Farke, recently in these pages because of his sensational juvenile Parasaurolophus paper, contributes his own overview of the collection, How Big? How Tall? And…How Did It Happen?

Finally, if you’re at SVP, go and pick up your free copy of the collection. Matt was somehow under the impression that the PLOS USB drives with the sauropod gigantism collection would be distributed with the conference packet when people registered. In fact, people have to go by the PLOS table in the exhibitor area (booth 4 in the San Diego ballroom) to pick them up. There are plenty of them, but apparently a lot of people don’t know that they can get them.

References

This is an exciting day: the new PLOS Collection on sauropod gigantism is published to coincide with the start of this year’s SVP meeting! Like all PLOS papers, the contents are free to the world: free to read and to re-use. (What is a Collection? It’s like an edited volume, but free online instead of printed on paper.)

There are fourteen papers in the new Collection, encompassing neck posture (yay!), nutrition (finally putting to bed the Nourishing Vomit Of Eucamerotus hypothesis), locomotion, physiology and evolutionary ecology. Lots for every sauropod-lover to enjoy.

x

Taylor and Wedel (2013c: Figure 12). CT slices from fifth cervical vertebrae of Sauroposeidon. X-ray scout image and three posterior-view CT slices through the C5/C6 intervertebral joint in Sauroposeidon OMNH 53062. In the bottom half of figure, structures from C6 are traced in red and those from C5 are traced in blue. Note that the condyle of C6 is centered in the cotyle of C5 and that the right zygapophyses are in articulation.

Matt and I are particularly excited that we have two papers in this collection: Taylor and Wedel (2013c) on intervertebral cartilage in necks, and Wedel and Taylor (2013b) on pneumaticity in the tails of (particularly) Giraffatitan and Apatosaurus. So we have both ends of the animal covered. It also represents a long-overdue notch on our bed-post: for all our pro-PLOS rhetoric, this is the first time either of has had a paper published in a PLOS journal.

Wedel and Taylor (2013b: Figure 4). Giraffatitan brancai tail MB.R.5000 (‘Fund no’) in right lateral view. Dark blue vertebrae have pneumatic fossae on both sides, light blue vertebrae have pneumatic fossae only on the right side, and white vertebrae have no pneumatic fossae on either side. The first caudal vertebra (hatched) was not recovered and is reconstructed in plaster.

It’s a bit of a statistical anomaly that after a decade of collaboration in which there was never a Taylor & Wedel or Wedel & Taylor paper, suddenly we have five of them out in a single year (including the Barosaurus preprint, which we expect to eventually wind up as Taylor and Wedel 2014). Sorry about the alphabet soup.

Since Matt is away at SVP this week, I’ll be blogging mostly about the Taylor and Wedel paper this week. When Matt returns to civilian life, the stage should be clear for him to blog about pneumatic caudals.

Happy days!

References

My hobby:

October 17, 2013

oh crap im part furry

Fear and Loathing dinosaur tail 2

Relic cover

polar dinosaur babies

convincing genetic engineers that everyone would look better if they had sauropod tails.

If you have no idea what I’m on about, go check out XKCD.