Brief thoughts on Dreadnoughtus

September 5, 2014

Yay, vertebrae! Lacovara et al. (2014: fig. 1)

Yay, vertebrae! Lacovara et al. (2014: fig. 1)

Mike and I are in York for SVPCA — more on that soonish — and I just wanted to get out some quick thoughts about the world’s newest giant sauropod.

First off, the paper (Lacovara et al. 2014) is open access, which is great. And, hey, 3D PDFs of the whole skeleton and selected elements — I’m going to be having some fun with those.

And given that this is a short initial descriptive paper, I was really happy to see a reasonably detailed table of measurements. The materials and methods section at the end spells out explicitly how the team arrived at their estimates of the animal’s length and mass. All of that looks very solid, and it’s more information that we often get in these short initial descriptions. So although I will look forward to seeing a complete osteological description of Dreadnoughtus in the future, this first paper is better than a lot of similar papers in that it includes a lot of actually useful information.

As for whether Dreadnoughtus was the world’s heaviest sauropod — how could anyone possibly tell? The femur of Dreadnoughtus is 1.9 meters, which is only three-quarters of the estimated length of the largest partial femur of Argentinosaurus. Now, there is plenty of evidence from both histology and macro-level indicators of skeletal age that the holotype individual was still growing, but how much bigger was it going to get, 10%, 25%? I think that given its size, completeness, and immature state it is fair to discuss Dreadnoughtus in the same breath as Argentinosaurus, Puertasaurus, the largest specimens of Alamosaurus, and other giant sauropods. But I think any claim that it is ‘the’ heaviest is premature until we know how big a fully adult Dreadnoughtus was.

Dreadnoughtus and kin. Lacovara et al. (2014: fig. 3)

Dreadnoughtus and kin. Lacovara et al. (2014: fig. 3)

Here’s a weird thing: according to Table 1, the 113-cm cervical vertebra of Dreadnoughtus is the longest known among titanosauriforms. But the longest cervical of Sauroposeidon has a 125-cm centrum, and Sauroposeidon always comes out as a titanosauriform in phylogenetic analyses, including the one in the Dreadnoughtus paper. The estimated 2.5-meter femur of Argentinosaurus reported by Mazzetta et al. (2004) is also not listed in that table, although some estimated lengths for other incomplete elements are given. I don’t think there’s any conspiracy here — it is actually quite a challenge to keep up with all of the relevant numbers — but I would like to have seen a bit more thoroughness in reporting measurements of other sauropods where at least some individual elements are larger than in Dreadnoughtus.

Anyway, as we found for the next-most-recent “world’s largest dinosaur” earlier this year, Dreadnoughtus does not extend the known size range of the largest sauropods. Period. Anyone who says definitively otherwise is actually making assumptions about ontogeny and mass estimation that just aren’t justified.

Does that mean that Dreadnoughtus isn’t interesting? Of course not! For one thing, now we can start talking intelligently about the body proportions of these giant titanosaurs. Up until now we’ve had a good idea of what other, smaller sauropods looked like, things like Mamenchisaurus, Diplodocus, and Giraffatitan, and we’ve had reasonably complete skeletons of small titanosaurs such as Malawisaurus and Rapetosaurus, but we haven’t had a very clear idea of the proportions of the largest titanosaurs (sometimes because of conflicting measurements). So now we can start investigating questions involving the biomechanics and hopefully the growth trajectories of giant titanosaurs, which were more in the realm of speculation until now. There are some tantalizing hints toward this in the current paper — for example, the authors mention that a lot of the bones preserve muscle attachments. That would be a fascinating study in its own right, just knowing what the muscle attachments can tell us about the soft-tissue anatomy of Dreadnoughtus, and in turn what soft tissue can tell us about how the muscles and joints worked.

Big and getting bigger: the limb bones of Dreadnoughtus. Lacovara et al. (2014: fig. 2)

Big and getting bigger: the limb bones of Dreadnoughtus. Lacovara et al. (2014: fig. 2)

There are myriad interesting questions dealing with the ability of the limb bones and vertebrae to support the mass of the body and how that skeletal support changed, both over the lifespan of an animal and over evolutionary time. Now, there is a limit to how much Dreadnoughtus can add here, since it’s only known by two individuals that weren’t radically different in size, but given how bleak the data landscape is for giant titanosaurs, it’s an important addition to our knowledge.

In conclusion, although I have some reservations about overlooked measurements of some other giant sauropods, and although the media-driven Dreadnoughtus-vs-Argentinosaurus pissing contest is pointless, I’m excited about this first paper. And I’m looking forward to more, both more complete descriptive work, and functional and biomechanical analyses building on that. Happy days.

References

Advertisements

13 Responses to “Brief thoughts on Dreadnoughtus


  1. […] Mike Taylor, Matt Wedel, and Darren Naish offered their thoughts on Dreadnoughtus and called into question some of the findings of the original paper. And of course, this is the type of discourse we all […]

  2. Chimu Says:

    From a purely aesthetical standpoint, I find the horizontal (hypothetical) neck rather odd looking when compared to that in relation rather short tail. A more vertical neck would be much vore visually pleasing.

    But besides that and the cringeworthy name, it is of course a astonishing specimen. 2014 shapes up to be a good year for palaentology.

  3. ncmncm Says:

    I notice Diplodocus isn’t in the cladogram. Too distant? It might be pleasant to consider that we know of so many sauropods, we are obliged to omit some for lack of space. But lack of space must be a pretty common problem when reconstructing sauropods.

    Also curious is the gap at the bottom of the Cretaceous. Is that because we don’t have good strata for that span? (Or was Diplodocus ascendant then?)

    I have to agree that the low neck posture looks odd. I am beginning to think maybe they could never lower their necks at all, as adults, getting enough moisture from their diet not to ever need to imbibe. Maybe coprolites can rule on how carefully they conserved water?

    My problem with a neck ever achieving a a horizontal position, as I have mentioned before, is the static compression that the proximal cervical vertebrae would need to endure — many times the full weight of the neck. Static compression calculations are quite easy to do, and they would dictate a lower bound on the amount of cross-sectional bone needed in that vertebra; or, given that quantity, determine an upper bound on neck mass, assuming it had to endure, at least temporarily, a horizontal pose.

    Axial compression can be taken up by circumferential tension — in this case, if we allow supporting the underside with a series of inflated bladders. It would look pretty odd, but that is something sauropods appear not to have worried much about.

    So: 1) especially dense proximal cervical vertebra, or 2) obligate vertical posture, with exclusively dietary hydration, or 3) pneumatic cervical undercarriage? Pick one.

  4. Mike Taylor Says:

    Diplodocus isn’t in the cladogram because this is an analysis of Macronaria only — the other half of Neosauropoda besides Diplodocoidea. So for the same reason, Apatosaurus and many other old favourites are also absent.

    Diplodococids were dominant the end of the Jurassic, but are very rare or unknown in the early Cretaceous. But the sauropod record of the early ages of the EK is poor generally.

    Regarding the neck posture: I think the idea of sauropods never lowering their necks is untenable. But there would be no problem of overbalancing when the neck was low as shown here. The neck is tall in lateral view, but relatively narrow compared with the much more massive torso. Even if their tails were removed completely, all sauropods would have been stable with their CoM well between the two sets of limbs (Henderson and Wedel in prep.)

    I won’t pick one of your three unlikely alternatives until it’s been shown that regular anatomy doesn’t suffice to get the job done. The calculations would be worth doing, for sure.


  5. Oy vey, not again! Another sauropod substantially overestimated in size. There is no way that Dreadnoughtus was 59 tonnes – I’m guessing it was actually about half that, maybe 30 tonnes for the larger individual at best. The femur is only ~1.9 m, which is a bit shorter than in Giraffatitan, and the dorsals are about the same size as Giraffatitan, and are substantially smaller than in Argentinosaurus (the widest dorsals of which are about 129 cm, compare to the widest in Dreadnoughtus of 99 cm). The material actually appears to be close to the same size as Futalognksaurus, which when I did a GDI for that guy based on my own skeletal, only came out to about 25 tonnes. The estimated length of 26 m is also a bit excessive, IMHO, probably about 21 or 22 m – max. A large, but not gigantic, sauropod easily outclassed by Argentinosaurus and Alamosaurus.

  6. ncmncm Says:

    Risk of overbalancing would be the least of its problems.

    “I won’t pick one of your three unlikely alternatives until it’s been shown that regular anatomy doesn’t suffice to get the job done.”

    What is it that you would consider irregular or unlikely about a robust first cervical vertebra? (And, by Newton’s first law, the anterior dorsal.) That *is* regular anatomy’s answer.

    Has anybody actually looked at a cross section of that first vertebra, on *any* sauropod? They all face the same problem. If it doesn’t present enough solid bone to support something like ten times the weight of the whole neck, it will take some pretty creative thinking to work out how they managed without.

    It’s easy to demonstrate the physics with no more than a stick and a length of twine. Attach the twine securely to one end of the stick. That’s the head end. Hold the stick horizontally, with the other end in your navel, held up only by tension in the twine, pulling from directly above your navel.
    As the place where you are holding the twine descends toward the base of the stick, it takes increasing force to keep the end up. The tension in the twine is little more than 0.7 times the weight W of the stick when the angle it makes with the stick is 45 degrees, but it grows toward infinity as the angle decreases toward zero. At zero it doesn’t matter how hard you tug, the stick won’t stay up. At a low angle, it will get pretty uncomfortable, pressing into your navel with many times the weight of the stick.

    In a sauropod neck, the stick represents the vertebral column, and the twine is the muscles and ligatures along their dorsal extrema. The angle corresponds to how high above the centra the neural spines hold these ligaments.

    Seriously, try it. There are sound physical reasons why suspension bridges have high towers and deeply bowed cables. The physics of sauropod necks are the same.

  7. Mike Taylor Says:

    It may surprise you to know that you are not the first person to have applied elementary physics to the problem of sauropod necks. The kind of thing you’re discussing here goes at least back to Alexander 1985:12-14, which includes some calculations for Diplodocus.

    References

    Alexander, R. McNeill. 1985. Mechanics of posture and gait of some large dinosaurs: Zoological Journal of the Linnean Society 83:1-25.

  8. Matt Wedel Says:

    So: 1) especially dense proximal cervical vertebra, or 2) obligate vertical posture, with exclusively dietary hydration, or 3) pneumatic cervical undercarriage? Pick one.

    What? Sorry, you’re thinking about this MUCH too simplistically.

    First, the neck is a segmented beam, not a solid one. The force on the next-to-last cervical is only a little lower than on the last cervical, and it’s a little lower still (not vastly lower) on the one before that, and so on all the way up to the skull. So we shouldn’t expect to see posterior cervicals that are suddenly fantastically large or dense–they should form a continuum of rising ability to resist stress.

    And in fact, that’s pretty much exactly what we see. Look again at the neck of Diplodocus and see how the vertebrae increase in size from just behind the head to the base of the neck (first image here and click through for the whole series).

    Second, people who work on the mechanics of sauropod necks know all of this and have been using it. Pretty much every one of Andreas Christian’s papers on sauropod neck posture has been based on comparing the articular areas of the cervical vertebrae down the neck, to see if the posterior ones are sufficiently bigger to be under about the same stress as the anterior ones.

    Pneumatization helps here by allowing the bone tissue to be more advantageously distributed–something MIke covered in this post and which we talked about in more technical terms in our 2013 PeerJ paper (linked on the sidebar).

    Third, it is very, very common for the muscular forces across a joint to be much greater than the gravitational ones. Every time you take a step, the load on your standing limb is roughly four times your body mass, because the muscles crossing the hip contract that hard to stabilize the joint. So the difference in stress between a horizontal and vertical sauropod neck was probably smaller than the difference between horizontal and the (larger) actual muscular force across the joint in any pose.

    In short, the problem isn’t that we’re ignoring biomechanics, it’s that you seem to be ignoring a lot of the relevant anatomy and physiology.

  9. ijreid Says:

    Hey, Sauroposeidon is a brachiosaurid :)! I agree with the paper that the phylogeny is probably quite a bit off. Did they create their own matrix, or are they just fixing an old one. The position of Euhelopus does not seem to be correct based on all the other analyses I’ve seen, neither does the fact that Epachthosaurus and Argentinosaurus are recovered as non-lithostrotians. I think the reason the cladogram is off is because the analysis didn’t include many titanosaurs known from relatively good remains, such as Diamantinasaurus, Argyrosaurus or Paralititan, all of which would probably greatly change the results.

  10. Mike Taylor Says:

    I wouldn’t necessarily say that the tree in the new paper is “off”, but that it reflects our developing understanding of macronarian phylogeny. There are similar surprises in some other recently published trees, and in others yet to be published.

    The lesson: things aren’t as locked down as a nice, neat tree makes them look!


  11. […] just read Mark Witton’s piece on the new new titanosaur Rukwatitan (as opposed to the old new titanosaur Dreadnaughtus). I was going to write something about it, but I realised that Mark has already said everything I […]

  12. ncmncm Says:

    I labor under no delusion that the final cervical would have any reason to be especially heavier than the next one up. I am also under no delusion that bone stresses are ever limited to just the weights attached. Yes, it’s tapered. Yes, it’s segmented. Yes, it’s pneumatized. Those don’t help much.

    In particular: pneumatization distributes bone over a wider area, which is great for equalizing uneven stress. That is no help at all, here. Howsoever cunningly the bone is distributed, the amount of crushing force it can support is limited by the smallest sum of the cross-sectional area you can discover by slicing at places perpendicular to the force.

    Segmentation allows the more distal verts to carry less load than lower down, but doesn’t change that the final cervical (like the first dorsal) carries the whole load. Segmentation allows the more distal verts to be be lighter, potentially reducing the total load by a factor of up to three.

    But none of that changes that the static load on that final cervical, just because of the geometry, is multiplied many times over before you even start to bring in the other multipliers that apply for other joints, such as would come from the animal actually, you know, moving.

    As always, the numbers matter.

    Has anybody imaged a cross section through the final, or near-final, cervical vertebra of a large sauropod? What is the actual ratio of centrum-to-neural-spine distance at the shoulder vs. total neck length, in any of the larger ‘pods?


  13. […] the paper describing the new giant titanosaur Dreadnoughtus, Lacovara et al. (2014) use the limb bone allometry equation of Campione and Evans (2012) to derive […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: