Mamenchisaurus tail club, again

March 30, 2010

In color, this time, with multiple views, thanks to Xing et al. (2009). They also did a finite element analysis of the tail club and concluded that it was a fairly pathetic weapon. Xing et al. closed by supporting the contention of Ye et al. (2001) that the tail club was a sensory organ. As they stated at the end of the abstract:

The tail club of Mamenchisaurus hochuanensis probably also had limitations as a defense weapon and was more possibly a sensory organ to improve nerve conduction velocity to enhance the capacity for sensory perception of its surroundings.

One thing Xing et al. (2009) cite in support of this is the expanded neural canal inside the club, which they compare to the sacral enlargement in stegosaurs and to the glycogen bodies of birds. They rule out a glycogen body on the grounds that the sacral enlargement in stegosaurs is much bigger than the brain volume, whereas the neural canal enlargement in the M. hochuanensis tail club is much smaller (if you don’t follow that logic, don’t worry, neither do I).

I’m not sure what to make of this thing. On one hand, it would be nice to have more than one club available to rule out the possibility that it’s just a weird paleopathology. On the other hand, it looks oddly regular to be pathological, and the definitive clubs in Shunosaurus and Omeisaurus are at least weak support for this being a genuine feature, although the clubs of the former taxa look very different.

Furthermore, I don’t understand how the authors can rule out the presence of a glycogen body based on the size of the neural expansion alone–especially since the functions of glycogen bodies in extant taxa are very poorly understood (as you may remember from this dustup). Nor can I fathom how a titchy little nerve bundle–if such existed–down at the end of the tail could do much to improve nerve conduction velocity up the rest of the tail. Either my understanding of neuroscience is completely shot, or this hypothesis…lacks support. I am open to being enlightened either way.

Finally, I am disappointed that the authors didn’t pursue the cutting-edge pseudohead hypothesis that has figured prominently here and elsewhere in the blogosphere. There’s a Nobel lurking in there, I just know it.

References

  • Xing, L, Ye, Y., Shu, C., Peng, G., and You, H. 2009. Structure, orientation, and finite element analysis of the tail club of Mamenchisaurus hochuanensis. Acta Geologica Sinica 83(6):1031-1040.
  • Ye, Y., Ouyang, H., and Fu, Q.-M. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica 39(4):266-271.
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21 Responses to “Mamenchisaurus tail club, again”

  1. Zach Miller Says:

    Yeah, I’ve never thought much of Mamenchisaurus’ tail club. Looks too much like a pathology, especially when you compare it to other, ACTUAL tail clubs. It’s also not very big or imposing to function as a decent tail club, is it? Isn’t this animal something like 60 feet long?

  2. William Miller Says:

    I don’t entirely understand how it would function as a sensory organ: what does it sense and what does the nerve conduction velocity have to do with it? Maybe I’m just dense…

  3. Nathan Myers Says:

    The placement of this neuroanomaly reveals its true purpose. We finally know the true reason why sauropods were so all-fired long: it was to provide room to generate series electrical potential. Allow an attacker to complete the circuit between highly-charged head and tail-tip, and said attacker, convulsing on the ground, can attack no sauropod more. Stepping on it afterward probably helped some.

  4. Mike Taylor Says:

    Wait, there’s a definitive tail-club in Omeisaurus? Somehow I never registered that. Maybe you could write it up next time around. (Er, after I’ve posted one, I mean.)

  5. William Miller Says:

    Speaking of Mamenchisaurus: a comment on the ODP website just linked to these Gregory S. Paul mass estimates – http://www.gspauldino.com/data.html – which puts M. sinocanadorum at 75000 kg! (And Argentinosaurus at only 55000, which is smaller than I’d ever heard suggested…) Is that the accepted value now?

  6. Mike Taylor Says:

    Not yet accepted by anyone other than Greg, as far as I know. Mazzetta et al.’s (2004) paper estimated 73 tonnes and explained how they reached that figure — it was pretty convincing. We’ll wait for Greg to show his own working before leaping on board his much lower estimate.

    Oh, and you can add me in with those who find the 75 tonne estimate for M. sinocanadorum perplexing. Having seen casts of the holotype of M. hochuanensis many times, I can tell you confidently that that animal is Diplodocus-sized, i.e. may have massed around 15 tonnes, probably less. Russell and Zheng’s (1993) description of M. sinocanadorum is AFAIK still the only published work on that species, and says of its size that “Cervicals 2-4 in the type of M. sinocanadorum are, on the average, 1.19 times longer than those in the type of M. hochuanensis, yielding an estimated skeletal length of 26 m”. If the two mamenchisaurus species were isometrically similar, that would make M. sinocanadorum 1.19^3 = 1.69 times as massive as M. hochuanensis, which would come to about 25 tonnes. Unless he’s referring to a new, unpublished, and MUCH bigger specimen, I don’t at all understand how Greg got a figure three times that.


  7. I myself was wondering about Greg Paul’s mass estimate, and I have even posted a question about this to the DML thinking it was a typo, and Greg Paul informed me it was not. I even discussed this with Tim Williams on the DML (who also kindly supplied me with a pdf of the original description of M. sinocanadorum, giving an length estimate of 26 meters).

    Greg Paul said this was based off a new mount (and presumably, a new specimen) that was 35 meters long! He said the proportions of this species were quite similar to other Mamenchisaurus species, and from the photos I’ve seen, it looks quite similar to M. youngi. Let us assume Paul’s estimate for M. youngi at 6,700 kg is correct (this is from his website), as it seems reasonable. Wikipedia gives an estimated length of this species of 16 meters. So, this means M. sinocanadorum was 35/16=2.1875 times the length of M. youngi. Since volume is the cube of length, (2.1875)^3=10.4675 times the volume. So, 6,700 kg*10.4675=70,132 kg. This is just 5,000 kg shy of Paul’s estimate.

    Here is the issue: Paul’s length is based off a museum mount that is indeed 35 meters long, according to news reports I read about a year ago (I think some are still up if you do a Google search). Now, museum mounts are notorious for being inaccurate (especially so when dealing with Chinese dinosaurs: mamenchisaurs especially are often articulated horribly, for some unknown reason they tend to look like prosauropods!), so I take this length of 35 meters with much skepticism.

    Case in point: the Fernbank Museum’s mount of Argentinosaurus is over 37 meters long! ON the other hand, based of isometric scaling from Malawisaurus, I get a length estimate for Argentinosaurus somewhere between 28-30 meters long (with 29 meters probably being the safest bet, IMO). Based off a multivew skeletal of Uberabatitan (which off the skeletal is 17 meters long from here), I did a GDI (Graphic Double Integration) estimate of its volume (~13.6 m^3), and thus got a mass estimate of ~10,457 kg. Going off the mount of Argentinosaurus, we have 37/17=2.1764 times the length, which is (2.1764)^3=10.31 times the volume, and thus a mass estimate of 10.31*10,457 kg=107,812 kg. Going off scaling from Malawisaurus we have 29/17=1.70588 times the length, and thus (1.70588)^3=4.96418 times the volume, and thus a mass estimate of 4.96418*10,457 kg=51, 910 kg, less than half from going off the mount (which is reasonably close to Paul’s estimate of 55,000 kg for Argentinosaurus, largely due to the fact I used a density of 300 kg/ m^3 for the neck and 800 kg/m^3 for the rest of the body, compared to 600 kg/m^3 and 900 kg/m^3 respectively in Paul’s estimate; and the fact that I forgot to incorporate the limbs (!))!

    Using the original length estimate for Mamenchisaurus sinocanadorum from the paper of 26 m, we have 26/16=1.625 times the length of M. youngi, and thus (1.625)^3=4.29102 times the volume, for a mass estimate of 4.29102*6,700 kg=28,749 kg, which is close in size to Brachiosaurus or Giraffatitan in mass.

  8. William Miller Says:

    >>300 kg/ m^3 for the neck and 800 kg/m^3 for the rest of the body

    Isn’t this kind of low for titanosaurs? Weren’t they less pneumatic than e. g. Sauroposeidon – or am I wrong on that? (probably am)

    PS: does anyone know if there are fairly recent published mass estimates for Lambeosaurus magnicristatus or L. lambei?


  9. You may be right, over here, Matt Wedel discusses ASPs for Alamosaurusu (a titanosaur) and gives a density of 0.63g/cm^3 for its vertebrae (which is equivalent to 630 kg/m^3). Problem is, can we extrapolate the density of the bone to the rest of the neck, which had airsacs? The reason I used a density of 300 kg/m^3 was because Henderson (2006) gave that as a density estimate for the necks of Brachiosaurus and Diplodocus (based off the density in bird necks). Whether such a low density estimate is justifiable in sauropods is debatable, but not entirely unreasonable and may be quite likely. The point of my mass estimate is to give a minimum mass estimate, since most tend to give over estimates.

    It should be noted, that all the dorsal vertebrae of titanosaurs that I have seen have pneumatic fossae (i.e., Argentinosaurus has them), so the density of the the torso was probably still around 800 kg/m^3. The neck may have been closer to 600 kg/m^3, but this doesn’t affect the mass much for Argentinosaurus, going from ~51,900 kg in my previous estimate to ~52,900 kg. For kicks, if we increase the density of the rest of the body to 900 kg also (thus, using the same density as Paul), I get an estimate of ~58,500 kg (again this is not including the limbs which would probably each weigh close to 1,000 kg each in large titanosaurs; since the bones in the limbs were apneumatic). In my opinion, a mass estimate in the range of 50-60 tonnes for Argentinosaurus is the most likely. I don’t trust Mazzetta et al.’s (2004) estimate, because it is based off of logarithmic-based regression analyses of certain bone lengths, which a recent paper by Packard et al. (2009) have shown to overestimate the mass by as much as 100 percent! This would mean the estimate of 73 tonnes given my Mazzetta would be reduced to 36 tonnes. I am of the opinion that these equations, no matter how mathematically sound, can not give accurate mass estimates for dinosaurs since they differ in many respects from large mammals, from which the equations are based.

    Greg Paul, in his study on iguanodont taxonomy (2007), gave a mass estimate of 2.4 tonnes for Lambeosaurus lambei based off of the ROM 1218 specimen. The mass estimate was based of a volumetric model (presumably done in clay).

    Refs–

    Henderson, Donald M. BURLY GAITS: CENTERS OF MASS, STABILITY, AND THE TRACKWAYS OF SAUROPOD DINOSAURS. Journal of Vertebrate Paleontology 26(4):907–921, December 2006.

    Packard, G.C. et al. ALLOMETRIC EQUATIONS FOR PREDICTING BODY MASS OF DINOSAURS. Journal of Zoology 279 (1):102-110, June 22 2009.

    Mazzetta, G.V. et al. GIANTS AND BIZARRES: BODY SIZE OF SOME SOUTHERN SOUTH AMERICAN CRETACEOUS DINOSAURS. Historical Biology 16, Issue 2-4:71-83, June 2004.

    Paul, G.S. A REVISED TAXONOMY OF THE IQUANODONT DINOSAUR GENERA AND SPECIES. Cretaceous Research 29 (2):192-216, April 2008.

  10. William Miller Says:

    Hmmm. So is your Argentinosaurus estimate assuming a smaller body volume than the 73-tonne one?

    >>Greg Paul, in his study on iguanodont taxonomy (2007), gave a mass estimate of 2.4 tonnes for Lambeosaurus lambei based off of the ROM 1218 specimen.

    Thank you. I had seen that (the estimate is in the same document) and was wondering if there were any others. (The reason I was wondering is that in looking at stuff for the Open Dinosaur Project I found some incredibly enormous estimates for the giant Baja California lambeosaur (?Lambeosaurus laticaudus); one of the WJ Morris papers estimated 23 tonnes, but by extrapolating from Paul’s 2430 kg estimate for L. lambei ROM 1218 (56 cm humerus ROM 1218; 95 cm largest Baja humerus LACM 26757; 1.696 times longer in linear dimension, thus 4.88 times heavier) I get an estimate of under 12 tonnes, so I wanted to see if there were estimates high enough to make the “23 tonne lambeosaur” reasonable.

    (Sorry for the ornithischian diversion!)

  11. Mike Taylor Says:

    Zach, Mazzetta et al. used a variety of different techniques in arriving at their Argentinosaurus mass estimate, cross-checked them against each other and tested their lines for quality of fit. I am not saying their work is perfect (whose is?) but I would certainly not write it off as readily as you seem to have.

  12. Steveoc Says:

    For what it’s worth you can see images of the Mega-Mamenchisaur here,

    Mamenchisaurus - 05

    Mamenchisaurus - 02

    Mamenchisaurus - 01

    There is flash sequence with some images here: http://www.kyoryu.jp/midokoro/1/1off.swf

    The press reports claimed it was discovered in 2001 so I doubt it’s M.sinocanadorum. The Expo web site simply called it Mamenchisaurus sp. I’d be really interested to know how much is known.
    The reconstructed neck is about 16 m long!!!

    http://www.kyoryu.jp/midokoro/m02.html


  13. @ William Miller: I don’t know my body volume estimate compares to Mazzetta et al.’s 73 tonne estimate, because they only give a mass estimate for Argentinosaurus, not a volume estimate.

    @Mike: You may be right–I may have been hasty in my rejection of Mazzetta’s estimate. In fact, a new paper on the topic has recently been published in the Journal of Zoology, as a rebuttal to the Packard et al. (2009) study cited above. Of particular note, the abstract, in part, says “Their [Packard et al. (2009)] proposed approach is thus unduly sensitive to small relative errors for large mammals; as the largest (the elephant) is comparatively light for its large-bone circumference, the resulting model grossly overestimates the body mass of small mammals and is likely to substantially underestimate the body mass of dinosaurs. It is also important to note, however, that the error bars for the conventional model already indicate substantial uncertainty in body mass, such that for example, the body mass of Apatosaurus louisae may be as high as 63 metric tonnes, or as low as 23 metric tonnes, with a modal value of 38 metric tonnes.”

    Unfortunately, I do not have access to the entire paper so I cannot discuss the specifics. However, assuming that the conventional model is accurate, there is still a wide error bar to consider in regards to Mazzetta’s estimate; furthermore, assuming Mazzetta et al. (2004) estimate is accurate in every other respect, their density is off. They assumed a density of 950 kg/m^3 for their sauropods. It is likely they were significantly less dense as both you and Matt Wedel have pointed out many times on this blog. If we assume a density of 800 kg/m^3 instead, the 73-tonne estimate is reduced to roughly 61 tonnes. Take into account the wide error bar, and we are talking a likely weight estimate between 40 and 80 tonnes, which encompasses the values that I think are most likely (i.e., 50-60 tonnes). Having said that, the fact that my GDI estimate and Paul’s volumetric estimate are within a few tonnes of each other would suggest they are more accurate, and I would therefore still suggest that Mazzetta’s estimate is too high as an average weight. Certainly some individuals probably reached that weight, but as an average weight representative of the species it is probably too high.

    It’s worth to point out that Henderson’s (cited previously) mass estimate for Apatosaurus was around 16 tonnes (depending on the specimen, Paul gives between 7 and 20 tonnes), which is still significantly below the lowest estimate in the new J. of Zoology paper gives of 23 tonnes, and far below the modal estimate of 38 tonnes. Speculating based off of the figures given by Mazzetta, the lowest estimate was 60 tonnes for Argentinosaurus, so a mass estimate given by a 3D model like Henderson of a clay model like Paul would probably be below 60 tonnes.

    @Steveoc: awesome, thanks for pointing us to the pics of this incredible animal! Suffice to say, it does not looked “restored” in the way that the Argentinosaurus skeleton does, so I’m (tentatively) thinking it may be the real deal. Hooray for 70-tonne mamenchisaurs!

    Refs–

    Cawley, G.C., Janacek, G.J. On allometric equations for predicting body mass of dinosaurs. Journal of Zoology 280 (4):355-361, April 2010.

  14. LeeB Says:

    Steveoc,
    at http://dml.cmnh.org/2006Aug/msg00502.html
    there are listed news reports of some sauropod dinosaurs found in china.
    One discusses a huge sauropod found in Changji, S.E. Junggar basin in Xinjiang in 2006 which was excavated a few hundred metres from sauropod remains found in 2001.
    Perhaps the 2001 material relates to the huge Mamenchisaurus in the pictures.
    These remains are near where M. sinocanadorum was excavated so may be the same species.

    LeeB.


  15. Quasi-recantation: I completed the GDI on Uberabatitan (from which I scaled up Argentinosaurus) to include the limbs. The hindlimbs had a volume of 1.94 m^3 each and the forelimbs had a volume of )0.41 m^3 each. Thus the total mass of the limbs together (assuming a density of 1000 kg/m^3) of ~4700 kg, which increases the total mass of Uberabatitan from ~10,400 kg to ~15,100 kg. Assuming Argentinosaurus was 29 meters long can be isometrically scaled up from Uberabatitan, which was possibly 17 meters long, then Argentinosaurus would mass (29/17)^3=4.96 times Uberabatitan for a total mass of 74,959 kg, which is roughly 20 tonnes heavier than Paul gets, but only about 2 tonnes heavier than Mazzetta et al. This means then, since I used a much lower density than Paul did, that my volume is quite a bit higher than Paul’s model was, which leads to some sort of contradiction, as it means Argentinosaurus massed equally with or more than the giant mamenchisaur (assuming my GDI was accurately done).

    Caveats: (1)Argentinosaurus may not necessarily be accurately scaled isometrically from Uberabatitan, (2)My GDI may be in error (although I have re-checked everything thoroughly, and have found no errors as of yet), and (3) GDI estimates are known to be off by up to 20% off in either direction from the actual weight (based of living animals), giving a range of equally likely weights of 59-89 tonnes for Argentinosaurus.

    Moral of story: doing (accurate) mass estimates of extinct animals (especially giant ones, known from incomplete and/or poorly described remains)is fraught with difficulty and is not for the faint-of-heart, as there is much room for error and no real degree of certainty.

    Refs–

    Chapter 10 on body mass estimations from “Magnificent mihirungs: the colossal flightless birds of Australian dreamtime”, by Peter Murray and Patricia Vickers-Rich, 2004.

  16. William Miller Says:

    1)Argentinosaurus may not necessarily be accurately scaled isometrically from Uberabatitan

    True. Is the Argentinosaurus material good enough to nail down its body volume very closely? There aren’t complete ribs, right?


  17. [...] deserving a post of its own. In this case, I’m talking about the thread following the recent Mamenchisaurus tail club post, which got into some interesting territory regarding mass estimates for the largest sauropods. This [...]

  18. Nima Says:

    Whatever species that new mamenchisaur is, it’s crazy huge and easily dwarfs diplodocus… That thing almost reminds me of Huanghetitan in an odd way…

    The tail club is just weird, I concur that if it’s a normal structure then it was probably a sensory organ rather than a weapon. It looks to me like it MAY also be a pathology of an otherwise normal weaponized tail club, sort of like how ostromyelitis caused one of a stegosaurus specimen’s thagomizer spikes to lose its conical shape and compress into a shriveled squashed mess covered in little infected pits…


  19. [...] the big question is: why do Shunosaurus and Omeisaurus — and Mamenchisaurus, for that matter — have tail-clubs when they are not closely related, according [...]

  20. Trevor Says:

    How does Puertasaurus figure in these discussions?

  21. Mike Taylor Says:

    How does Puertasaurus figure in these discussions?

    Er. It doesn’t. Not unless a new specimen of Puertasaurus has been discovered that we’ve not heard about, and the tail tip is preserved in that specimen and has a club. It’s only very distantly related to Mamenchisaurus and there is absolutely no a priori reason to expect it to have a club.


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