How long was the torso of Dreadnoughtus?

September 15, 2014

In a comment on the last post, on the mass of Dreadnoughtus, Asier Larramendi wrote:

The body mass should be considerably lower because the reconstructed column don’t match with published vertebrae centra lengths. 3D reconstruction also leaves too much space between vertebrae. The reconstruction body trunk is probably 15-20% longer than it really was. Check the supplementary material: http://www.nature.com/srep/2014/140904/srep06196/extref/srep06196-s1.pdf

So I did. The table of measurements in the supplementary material is admirably complete. For all of the available dorsal vertebrae except D9, which I suppose must have been too poorly preserved to measure the difference, Lacovara et al. list both the total centrum length and the centrum length minus the anterior condyle. Centrum length minus the condyle is what in my disseration I referred to as “functional length”, since it’s the length that the vertebra actually contributes to the articulated series, assuming that the condyle of one vertebra sticks out about as far as the cotyle is recessed on the next vertebra. Here are total lengths/functional lengths/differences for the seven preserved dorsals, in mm:

  • D4 – 400/305/95
  • D5 – 470/320/150
  • D6 – 200/180/20
  • D7 – 300/260/40
  • D8 – 350/270/80
  • D9 – 410/ – / –
  • D10 – 330/225/105

The average difference between functional length and total length is 82 mm. If we apply that to D9 to estimate it’s functional length, we get 330mm. The summed functional lengths of the seven preserved vertebrae are then 1890 mm. What about the missing D1-D3? Since the charge is that Lacovara et al. (2014) restored Dreadnoughtus with a too-long torso, we should be as generous as possible in estimating the lengths of the missing dorsals. In Malawisaurus the centrum lengths of D1-D3 are all less than or equal to that of D4, which is the longest vertebra in the series (Gomani 2005: table 3), so it seems simplest here to assign D1-D3 functional lengths of 320 mm. That brings the total functional length of the dorsal vertebral column to 2850 mm, or 2.85 m.

At this point on my first pass, I was thinking that Lacovara et al. (2014) were in trouble. In the skeletal reconstruction that I used for the GDI work in the last post, I measured the length of the dorsal vertebral column as 149 pixels. Divided by 36 px/m gives a summed dorsal length of 4.1 m. That’s more than 40% longer than the summed functional lengths of the vertebrae calculated above (4.1/2.85 = 1.44). Had Lacovara et al. really blown it that badly?

Before we can rule on that, we have to estimate how much cartilage separated the dorsal vertebrae. This is a subject of more than passing interest here at SV-POW! Towers–the only applicable data I know of are the measurements of intervertebral spacing in two juvenile apatosaurs that Mike and I reported in our cartilage paper last year (Taylor and Wedel 2013: table 3, and see this post). We found that the invertebral cartilage thickness equaled 15-24% of the length of the centra.* For the estimated 2.85-meter dorsal column of Dreadnoughtus, that means 43-68 cm of cartilage (4.3-6.8 cm of cartilage per joint), for an in vivo dorsal column length of 3.28-3.53 meters. That’s still about 15-20% shorter than the 4.1 meters I measured from the skeletal recon–and, I must note, exactly what Asier stated in his comment. All my noodling has accomplished is to verify that his presumably off-the-cuff estimate was spot on. But is that a big deal?

Visually, a 20% shorter torso makes a small but noticeable difference. Check out the original reconstruction (top) with the 20%-shorter-torso version (bottom):

Dreadnoughtus shortened torso comparison - Lacovara et al 2014 fig 2

FWIW, the bottom version looks a lot more plausible to my eye–I hadn’t realized quite how weiner-dog-y the original recon is until I saw it next to the shortened version.

In terms of body mass, the difference is major. You’ll recall that I estimated the torso volume of Dreadnoughtus at 32 cubic meters. Lopping off 20% means losing 6.4 cubic meters–about the same volume as a big bull elephant, or all four of Dreadnoughtus‘s limbs put together. Even assuming a low whole-body density of 0.7 g/cm^3, that’s 4.5 metric tons off the estimated mass. So a ~30-ton Dreadnoughtus is looking more plausible by the minute.

For more on how torso length can affect the visual appearance and estimated mass of an animal, see this post and Taylor (2009).

* I asked Mike to do a review pass on this post before I published, and regarding the intervertebral spacing derived from the juvenile apatosaurs, he wrote:

That 15-24% is for juveniles. For the cervicals of adult Sauroposeidon we got about 5%. Why the differences? Three reasons might be relevant: 1, taxonomic difference between Sauroposeidon and Apatosaurus; 2, serial difference between neck and torso; 3, ontogenetic difference between juvenile and adult. By applying the juvenile Apatosaurus dorsal measurement directly to the adult Dreadnoughtus dorsals, you’re implicitly assuming that the adult/juvenile axis is irrelevant (which seems unlikely to me), that the taxonomic axis is (I guess) unknowable, and that the cervical/dorsal distinction is the only one that matter.

That’s a solid point, and it deserves a post of its own, which I’m already working on. For now, it seems intuitively obvious to me that we got a low percentage on Sauroposeidon simply because the vertebrae are so long. If the length-to-diameter ratio was 2.5 instead of 5, we’d have gotten 10%, unless cartilage thickness scales with centrum length, which seems unlikely. For a dorsal with EI of 1.5, cartilage thickness would then be 20%, which is about what I figured above.

Now, admittedly that is arm-waving, not science (and really just a wordy restatement of his point #2). The obvious thing to do is take all of our data and see if intervertebral spacing is more closely correlated with centrum length or centrum diameter. Now that it’s occurred to me, it seems very silly not to have done that in the actual paper. And I will do that very thing in an upcoming post. For now I’ll just note three things:

  1. As you can see from figure 15 in our cartilage paper, in the opisthocoelous anterior dorsals of CM 3390, the condyle of the posterior vertebra is firmly engaged in the cotyle of the anterior one, and if anything the two vertebrae look jammed together, not drifted apart. But the intervertebral spacing as a fraction of centrum length is still huge (20+4%) because the centra are so short.
  2. Transferring these numbers to Dreadnoughtus only results in 4.3-6.8 cm of cartilage between adjacent vertebrae, which does not seem unreasonable for a 30- or 40-ton animal with dorsal centra averaging 35 cm in diameter. If you asked me off the cuff what I thought a reasonable intervertebral spacing was for such a large animal, I would have said 3 or 4 inches (7.5 to 10 cm), so the numbers I got through cross-scaling are actually lower than what I would have guessed.
  3. Finally, if I’ve overestimated the intervertebral spacing, then the actual torso length of Dreadnoughtus was even shorter than that illustrated above, and the volumetric mass estimate would be smaller still. So in going with relatively thick cartilage, I’m being as generous as possible to the Lacovara et al. (2014) skeletal reconstruction (and indirectly to their super-high allometry-derived mass estimate), which I think is only fair.

References

 

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22 Responses to “How long was the torso of Dreadnoughtus?”


  1. I feel very flattered that you took time to write a post from one comment of mine. Happy to make a contribution.

    By the way, how did you estimate the torso dorsal view max breadths (pelvis and belly region) in order to apply GDI?

    Thank you Matt

  2. Matt Wedel Says:

    how did you estimate the torso dorsal view max breadths (pelvis and belly region) in order to apply GDI?

    I used the dorsal view of the reconstructed skeleton from the 3D PDF. Comparing to the lateral view, I found that the width and depth of the torso were pretty close to equal at the front of the ilium, at mid-torso (position of the longest preserved rib), and at the shoulder girdle. So I felt comfortable assigning the GDI model a circular cross-section through the torso.

    My GDI torso model is admittedly pretty crude–basically two truncated cones sitting base-to-base. But giving it a more realistic profile (say, by integrating across elliptical lateral and dorsal profiles) would introduce more guesswork, especially in the front half of the torso where the anterior dorsals are missing. And it would not radically change the answer. My goals for the GDI were modest–basically to test whether the 59-ton allometric mass estimate was volumetrically plausible, according to Lacovara et al.’s own skeletal reconstruction.

    I feel very flattered that you took time to write a post from one comment of mine. Happy to make a contribution.

    And we are happy to have such insightful commenters. Good spot on the torso length–I think you nailed it.


  3. Ok, I see, thank you for your explanations.

  4. engh Says:

    Ahhh, now it actually looks like a titanosaur torso. When I first saw their skeletal recon my thought was “huh, looks like a diplodocid torso.”

  5. eotyrannus Says:

    I agree with Brian — the more ‘compact’ version makes it looks more like a happy titanosaur (based on what we think we know about titanosaur proportions).

  6. Mike Taylor Says:

    Huh? Diplodocids have tiny short torsos.


  7. Hi, gang! I feel kind of diffident commenting here under this nym, because in this crowd it seems kind of cheeky — I’ve got an MA in Bio, theoretical population genetics, which in most places makes me “Doctor Science” but here, not so much.

    In any event, I came here because, like everyone else this week, I saw news stories about Dreadnoughtus. I started chasing links because, to my sauropod-naive eye, the Dreadnoughtus images going around look fundamentally unbelievable. The neck looks extremely thick (and thus heavy) compared to the body, as though it would have a huge moment arm and putting the animal’s center of gravity close to the forelimbs. Basically, the reconstruction looks as though it’s going to tip forward any minute.

    Your short-torso reconstruction, then, looks even *worse*. I’m trying to get a sense, from the layperson’s point-of-view, of what this creature looked like and maybe how it moved.

    Dr. Google-Scholar led me to Taylor & Wedel on sauropod neck anatomy. Does this imply that the average density of Dreadnoughtus‘ neck was lower than that of its torso, moving the center of gravity back toward the middle of the body?

    Modern animals with necks as long as the torso keep the head back toward or above the center of gravity much of the time, usually by bending the neck or by stretching it straight up. Giraffes of course don’t have very bendable necks, and their sloping backs certainly look as though designed to keep the center of gravity under the head as much as possible, and to reduce the neck’s moment arm. Brachiosaurs look like they’re constructed using basically similar principles, so my imagination doesn’t rebel

    Dreadnoughtus et al. don’t have the built-up forelegs and sloping backs of giraffes or brachiosaurs, yet the spines on the ventral sides of their caudal vertebrae don’t make their necks look as bendy as a swan’s or an ostrich’s. Do you think Dreadnoughtus‘s neck would have been more flexible than e.g. a Gerenuk’s?

    So far, I am finding it literally impossible to imagine how this creature balanced and moved, if it habitually had a neck 1.5-2 times the length of the torso stretched out in front of it yet no tail to counterbalance. Can you guys explain it to me?

  8. Matt Wedel Says:

    Hi Dr. Science, you have come to the right place.

    The neck looks extremely thick (and thus heavy) compared to the body, as though it would have a huge moment arm and putting the animal’s center of gravity close to the forelimbs. Basically, the reconstruction looks as though it’s going to tip forward any minute.

    Two things here. First, you’re probably right about the neck being drawn too fat. I think the fleshy envelope around the vertebrae was probably much less voluminous.

    BUT, with that said, necks and tails are very, very misleading. I explained in my first post on the mass of Dreadnoughtus, even assuming a circular cross-section and a fat neck, the neck volume is less than half that of the torso. The torso and limbs together still account for about 2/3 of the volume of the animal. And because the neck widens toward its base, the center of gravity of the neck would not have been very far out in front of the front legs, so the moment arm is actually pretty small. Don Henderson and Heinrich Mallison have independently done a ton of relevant work with 3D volumetric models of sauropods, and they’re all pretty stable.

    Does this imply that the average density of Dreadnoughtus‘ neck was lower than that of its torso, moving the center of gravity back toward the middle of the body?

    Hard to say. I mean, the center of gravity was probably square in the middle of the body no matter what. But the neck might have been pretty light. There are links to some published figures for the density of various birds in that previous post. One thing I didn’t mention in that post is that there is a published measurement of the density of the neck of a goose of only 0.3 g/cm^3. Even I find that very hard to accept for sauropods, but who knows. One of our long-delayed projects around here is to do a realistic mass estimate of the neck of a sauropod, taking into account bones, muscles, air sacs, and all the rest.

    Modern animals with necks as long as the torso keep the head back toward or above the center of gravity much of the time, usually by bending the neck or by stretching it straight up.

    Yes, that’s true, and we think the same was probably true for sauropods. In fact, we wrote a whole paper on that very subject: Taylor et al. (2009).

    the spines on the ventral sides of their caudal vertebrae don’t make their necks look as bendy as a swan’s or an ostrich’s. Do you think Dreadnoughtus‘s neck would have been more flexible than e.g. a Gerenuk’s?

    You are either psychic or superhumanly insightful: as luck would have it, Mike and I are right now working on two different projects that bear on that very question. I can’t tell you what our results will be since they’re not in yet, but we think that sauropod necks may have been more flexible than sometimes supposed. At the risk of beating you to death with references, here’s a paper we published last year on estimating the thickness of articular cartilage in the necks of sauropods: Taylor and Wedel (2013c).

    So far, I am finding it literally impossible to imagine how this creature balanced and moved, if it habitually had a neck 1.5-2 times the length of the torso stretched out in front of it yet no tail to counterbalance. Can you guys explain it to me?

    Mostly, it came down to the neck being a big visual fake-out: it looks big, but the actual volume was pretty small compared to the body. Even in the fat-necked Dreadnoughtus model, and assuming overly-fat circular cross-sections through the neck, the neck and head made up a smaller proportion of the whole-body volume than in a giraffe. And that’s before taking into account air spaces in and around the neck vertebrae.

  9. Mike Taylor Says:

    One thing I didn’t mention in that post is that there is a published measurement of the density of the neck of a goose of only 0.3 g/cm^3. Even I find that very hard to accept for sauropods, but who knows.

    I find it hard to accept for geese, too. [citation needed]

  10. Matt Wedel Says:

    Oh, I just remembered something that may make the very low goose neck density more palatable: a lot of birds have huge tracheae. IIRC in one of Andreas Christian’s papers there is a cross-section of an ostrich neck, and the trachea is almost as big as the vertebrae+muscle section. That could bring the density of the intact neck waaay down.

  11. Mike Taylor Says:

    Super-fat tracheae will make a big difference, yes. I suppose the problem of stating the density of a bird’s neck depends in part on what you count. If it has big, fluffed up neck feathers, trapping lots of air, then the volume of the neck increases. These issues are always fuzzier than we’d like.


  12. Thanks so much for your reply, Dr. Wedel! I’ve continued reading, and I find that Preuschoft & Klein (2013, from the PLOS Collection) make predictions that align with my instincts as a birder and naturalist. That is, NO WAY was the sauropod alert resting posture one where the neck extended in front of the body — even though that’s what’s shown in most illustrations. I also reject images of them moving long distances with necks in front, such as this one of Alamosaurus.

    In fact, I’ll go further. If the resting position of sauropod necks was forward — as argued by Stevens (2013) in the Collection — they couldn’t have evolved to be hyper-long. The energetic burden of supporting a horizontal neck goes up as some exponent (2? 3?) of its length, even if weight is held steady, and would quickly become evolutionarily prohibitive. In other words, the fact that sauropod necks could be 1.5-2x the length of the torso is evidence that their resting posture must have been low-energy: mostly vertical, like a giraffe, or a relaxed S-curve, like a bird. Or, heck, coiled on the back — that was a lot of neck to store!

    This in addition to the fact that a hyper-long neck basically comes with a sign, Predators Bite Here. A creature like Mamenchisaurus would *have* to rest with the vulnerable neck back near the body, otherwise they’re basically a buffet. For predator defense, I think hyper-long necks would also need to be relatively fast-moving, especially for the part more than a leg-length away from the body.

    As I think about it, it seems to me that pneumaticized cervical vertebrae are a necessary pre-adaptation for hyper-long necks (defined as “longer than needed to reach the ground” — in which case I wonder if any mammal has ever had one). Only if the bones are pneumaticized can you evolve a neck light enough to be supported and moved without prohibitive energy expenditure and predator risk. That’s (one reason) why hyper-long necks could evolve repeatedly in the archosaur lineage, but not in mammals — though I guess that pesky 7-cervical-vertebrae-or-maybe-8 limit is the other reason.

    The mammals most ecologically similar to sauropods are the elephants, who use an out-and-out tentacle to collect food and bring it back to the huge torso for processing. I’m basically saying that sauropod heads and necks were converging on tentacles — and it’s kind of amazing how far they got, given the design problems raised by putting your command & control center at the end of a tentacle some distance from your body mass.

    I’ve been a science writer, and I suspect that one reason sauropod weight estimates are played up is also why they’re illustrated with out-stretched necks: because the press is far more likely to pick up an article using superlatives: “largest”, “heaviest”, “longest”, etc.

  13. Mike Taylor Says:

    That’s (one reason) why hyper-long necks could evolve repeatedly in the archosaur lineage, but not in mammals.

    For many more reasons, see yet another of our papers, Taylor and Wedel 2013a, Why sauropods had long necks; and why giraffes have short necks.


  14. Andreas Christian always says that he doesn’t care about density, because you can simply stick a huge trachea (example of choice: ostrich) on any neck and cut the density in half ;)


  15. Dr. Taylor:

    Yes, I had already read that paper, but my own take tends to be a bit heavier on ecological factors. In fact, my only course in paleo was paleoecology from Peter Dodson, back when I was a grad student and he was junior faculty (a looooooong time ago).

    Re-reading your paper and thinking about it some more, I now conclude that giraffes don’t merely have *short* necks, they have necks that are *too short*.

    Everyone thinks of the giraffe as “the mammal with the longest neck”, but I suggest they are more accurately “the mammal with the longest *legs*” — plus a barely-adequate neck.

    Giraffes are the only animals I know of in any taxon that have necks too short to easily reach the ground. The splay-legged posture they need to take while drinking is bound to be costly, putting them at increased risk from predators (because it takes them a precious half-second longer to take that first step running away).

    It looks to me as though a giraffe’s neck length is at a hard limit, and that it’s maybe not coincidence that the neck of Paraceratherium was approximately the same length.

    I don’t think giraffes “relatively small torsos and large, heavy heads” (which you cite) are really what limits evolution of longer giraffe necks.

    The Platonic form sauropods were aiming for is a creature with a very large but movable torso where vegetation is processed and fermented after ingestion, served by one or more long tentacles that can sweep out a huge feeding envelope.

    Sauropods were limited by the fact that their head was on the end of the tentacle, limiting how long and flexible it could be. They lightened their teeth (which meant they had to replace them very frequently) and reduced their brain size to the point that I wonder how they could function at all.

    There’s no reason a priori that a mammal couldn’t lighten its head that way: reducing teeth (or possibly having them grow continuously, as in Rodents) and having most food processing taking place post-orally. But I wonder if it’s actually possible for a large animal as dumb as a sauropod to survive, in the Cenozoic.

    It may also be that the “eat ’em all and let the gut flora sort them out” approach doesn’t work all that well on Cenozoic vegetation, due to a higher average content of cellulose and/or secondary compounds. Elephants, which are the closest mammal to sauropods ecologically, do a lot of picking & choosing (Owen-Smith & Chafota, 2012). But then, they can grow enormous brains because their tentacle really is a tentacle, so they can actually think about what they eat.

  16. sublunary Says:

    Is Cenozoic vegetation really worse for a herbivore than Mesozoic? Cycads and such are pretty tough, horsetails have silica like grasses (although I do remember a post on Tet Zoo about them being nutritious for rapid sauropod growth – is that right?), conifer needles aren’t exactly tender…

    As for the intelligence thing… it always seemed odd to me that in all the Mesozoic, we don’t have any evidence of any really large-brained critters, whereas we have several separate lines evolving really big brains in the Cenozoic (primates, dolphins, and IIRC parrots and corvids). What was different in the jungles and oceans of the Mesozoic vs the Cenozoic ones to discourage/encourage brain development?

  17. Mike Taylor Says:

    Lots to get our teeth into here!

    Giraffes are the only animals I know of in any taxon that have necks too short to easily reach the ground. The splay-legged posture they need to take while drinking is bound to be costly, putting them at increased risk from predators (because it takes them a precious half-second longer to take that first step running away).

    It’s worse than that. It takes a giraffe longer than half a second to get into our out of that splayed-forelimb posture, and it’s not unknown for them to slip while in that posture, get into a position where they’re unable to get up at all, and die. So, yes, their necks really are too short.

    It looks to me as though a giraffe’s neck length is at a hard limit, and that it’s maybe not coincidence that the neck of Paraceratherium was approximately the same length.

    Could be. Of course the Paraceratherium neck is built very differently: much more robust, and proportionally less elongate, vertebrae, so it’s not obvious why it would run into the same limit. But as a matter of observation, it, and three theropod lineages, and pterosaurs, all ran into the same 2.5-meters-or-so limit. So maybe there’s something going on here that’s more fundamental than we realise.

    I don’t think giraffes “relatively small torsos and large, heavy heads” (which you cite) are really what limits evolution of longer giraffe necks.

    See our Table 3. We give these as two of five factors that limited the lengths of their neck.

    The Platonic form sauropods were aiming for is a creature with a very large but movable torso where vegetation is processed and fermented after ingestion, served by one or more long tentacles that can sweep out a huge feeding envelope.

    Never forget that evolution doesn’t aim for anything. All it does is move slightly from where it is into the direction that looks most advantageous at the time. It can’t plan. Which is why …

    There’s no reason a priori that a mammal couldn’t lighten its head that way.

    Actually, there is. Mammals are locked into local maxima. Because evolution can’t plan to switch to a sauropod-style small-head strategy, all they can do is evolve fitter versions of the heads they have now. For a giraffe to evolve toward the sauropod condition, it would need first to be a giraffe with weedy teeth — which would immediately get out-competed by the better-equipped giraffes.

    So my tentative conclusion is that in general, all the most important evolutionary innovations happen down at the bases of trees where they’re barely perceptible. When the ur-sauropodomorph (and its ur-theropod cousin) diverged from the ur-ornithischian, the differences in dentition would have been all but undetectable. But once those early forms had started down the path of respectively reducing and enhancing the dental batteries, their ingestive fates were as good as sealed.

    It may also be that the “eat ‘em all and let the gut flora sort them out” approach doesn’t work all that well on Cenozoic vegetation, due to a higher average content of cellulose and/or secondary compounds.

    Unlikely: see Hummel et al. 2008, which analysis the nutritional value of ancient plants and concludes they’re not all that different from modern ones.

    Elephants, which are the closest mammal to sauropods ecologically […]

    I am always suspicious of this kind of statement, because it equates a whole gigantic clade to two species of extant animal. No doubt some sauropods were ecologically close to elephants. Others were closer to giraffes, hippos, zebras, what have you. But anyway …

    [elephants] do a lot of picking & choosing (Owen-Smith & Chafota, 2012). But then, they can grow enormous brains because their tentacle really is a tentacle, so they can actually think about what they eat.

    Also because they waste so much time orally processing food that they have to pick and choose to a certain extent. For sauropods, it didn’t matter. You (excellent) phrase “eat ‘em all and let the gut flora sort them out” is dead on. If a sauropod happened to ingest something of little value, it wouldn’t really make any difference: it would just poop it out, not having wasted any time chewing it.

    (It would be interesting to know how much time elephants spend actually putting food into their mouths compared with how long they spend chewing it.)


  18. I believe the Hummel and Clauss group looked at grabbing versus munching time in several animals.

  19. Mike Taylor Says:

    Are you referring to Sauropod feeding and digestive physiology in the first DFG book?

  20. bricksmashtv Says:

    Is the image of the two Dreadnoughtus skeletals side-by-side CC-BY? I would like to use it for my paper I’m working on ATM.

  21. Matt Wedel Says:

    Seems to be, in that according to this page the Nature Publishing Group journals that are open access use the CC-BY 4.0 license, and we also use CC-BY here on the blog. So you’d need to credit Lacovara et al. for the original, unmodified skeletal, and me for the one with the shortened torso (“as modified by Wedel…” etc). Good luck with your paper!

  22. bricksmashtv Says:

    No problem. Thanks again!


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