The femur of Argyrosaurus, maybe

November 1, 2021

FMNH P13018 with me for scale. Photo by Holly Woodward.

Some of the Burpee Museum folks and PaleoFest speakers visited the Field Museum of Natural History in Chicago after the 2020 ‘Fest. I hadn’t been there since 2012, and a lot had changed. More on that in future posts, maybe. Here I am with FMNH 13018, a right femur referred by von Huene (1929) to Argyrosaurus superbus (note, though, that Mannion and Otero 2012 considered this specimen to be Titanosauria indet., hence the hedge in the title of the post). It’s 211cm long, which is pretty darn big but still well short of the record.

Speaking of the record, here’s a list of the largest sauropod femora (as always, updates in the comments are welcome!):

  1. 250cm – Argentinosaurus huinculensis, MLP-DP 46-VIII-21-3 (estimated when complete)
  2. 238cm – Patagotitan mayorum, MPEF-3399/44
  3. 236cm – Patagotitan mayorum, MPEF-PV 3400/27
  4. 235cm – Patagotitan mayorum, MPEF-PV 3400/27
  5. 235cm – “Antarctosaurus” giganteus, MLP 26-316
  6. 214cm – Giraffatitan brancai, XV1
  7. 211cm – cf. Argyrosaurus superbus, FMNH P13018
  8. 203cm – Brachiosaurus altithorax, FMNH P25107
  9. 200cm – Ruyangosaurus giganteus, 41HIII -0002 (estimated when complete)
  10. 191cm – Dreadnoughtus schrani, MPM-PV 1156

The list is necessarily incomplete, because we have no preserved femora for Puertasaurus, Notocolossus, Futalognkosaurus, or the largest individuals of Sauroposeidon and Alamosaurus, all of which probably had femora in the 210-250cm range. For that matter, most elements of the giant Oklahoma apatosaurine are 25%-33% larger than the equivalent bones in CM 3018, which implies a femur length of 223-237cm (scaled up from the 178.5cm femur of CM 3018). I’m deliberately not dealing with Maraapunisaurus or horrifying hypothetical barosaurs here.

In any case, it’s still a prodigious bone, and well worth spending a moment with the next time you’re at the Field Musuem.


  • Mannion, P.D. and Otero, A., 2012. A reappraisal of the Late Cretaceous Argentinean sauropod dinosaur Argyrosaurus superbus, with a description of a new titanosaur genus. Journal of Vertebrate Paleontology, 32(3):614-638.
  • Von Huene, F. 1929. Los saurisquios y ornitisquios del Creta´ceo Argentino. Anales del Museo de La Plata 3:1–196.

47 Responses to “The femur of Argyrosaurus, maybe”

  1. A few more entries for your list (all over 190 cm):

    Charroud & Fedan (1992) reported a 236cm femur from the Bathonian of Morocco

    A 222cm titanosaur femur (MPM-PV 39) from the Pari Aike (now Cerro Fortaleza) Formation was reported in a 2004 SVP abstract. Maybe it’s a Puertasaurus femur?

    One of the Angeac sauropod specimens, ANG-10-400, is a femur reported to be 220cm (Rozada et al. 2021)

    An Apatosaurus femur was reported in the news to be two meters long.

    Mamenchisaurus jingyanensis allegedly has a femur two meters long, but it’s not clear if it’s complete and the reported humerus and tibia length are not consistent with such a large size.

    The femur of Atlasaurus is probably ~194cm (calculated from a ratio)

    Yunmenglong has a femur 192 cm long.

    Sources for the non-obvious ones:

    Charroud, M. and B. Fedan. 1992. Données préliminaires sur la découverte du gisement de Boulahfa a dinosauriens (SW de Boulemane, Moyen Atlas central). Notes et Mémoires du Service Géologique du Maroc 366:448-449.

    Rozada et al. (2021) A Lower Cretaceous Lagersätte from France: a taphonomic overview of the Angeac-Charente vertebrate assemblage. Lethaia.

  2. DJ Sandy Says:

    I knew this particular femur was big but 211 centimeters was bigger than what I thought it was and I had a particular interest in this specimen since my visit two months ago though the morphology does seem to suggest a fairly large and robust Titanosaur, possibly a Lognokosaur

  3. llewelly Says:

    what an amazing showing by Patagotitan, with 3 entries in this list, numbers 2,3, and 4. I assume 3 and 4 are the left and right of the same individual, based on them sharing the same specimen number.

    Which leads to a question – of all the taxa on this list, which is known from the most material? Patagotitan? Giraffatitan? Dreadnoughtus?

    It’s fascinating to me that some of these animals seem to be so rare (like Brachiosaurus), but others (like Patagotitan) seem to be found more often (Of course they lived at very times and in very different environments – but Brachiosaurus is also rare compared to other saurpods in its environment)

  4. Matt Wedel Says:

    Well, we have more elements of Patagotitan, but AFAIK they all came out of one hole in the ground. We have fewer elements of Brachiosaurus, but it’s known from 7-10 quarries across several US states. So we know more about Patagotitan morphologically, but more about Brachiosaurus in terms of its distribution in time and space. I don’t think we have enough information yet to say which taxon was more widespread or abundant.

    And to back up one step, we have more of Patagotitan and Giraffatitan than of Dreadnoughtus–more elements, from more individuals–but I don’t know which one wins between P. and G.

  5. Ronald Says:

    With regard to Angeac, the French Monster, a fragment of an allegedly larger femur was found, estimated at 2.6 m.

  6. Matt Wedel Says:

    Huh. Gotta say, that photo is not terribly compelling. I mean, obviously the distal end is from a really big sauropod, but it would be trivial to redraw the rest of the bone so that it was 2.4 or 2.3 meters.

  7. Giraffatitan is hands-down the best-represented of these giant sauropods, by a wide margin. Something like 90% of the skeleton is cumulatively represented from several partial skeletons. Of course, there remains the possibility that there’s actually more than one Tendaguru brachiosaurid, but I guess we’ll just have to wait and see how that shakes out, and even then it’s reasonable to expect a decent portion of the current material would continue to reside in Giraffatitan.

    In contrast, Patagotitan is known from two individuals, representing around half the skeleton, plus a handful of isolated bones from other individuals. Dreadnoughtus is roughly comparable to Patagotitan, with two individuals that add up to close to half a skeleton. Dreadnoughtus has more of the hindlimb and tail; Patagotitan has more of the neck and appears to be better-preserved. Futalognkosaurus might be known from the most complete single individual of a giant titanosaur, but it’s still largely undescribed. There is appendicular material that’s been mentioned in a few papers, but it’s not entirely clear to me how much of it there is and if it belongs to the holotype individual.

    It’s also worth considering that all three of those titanosaurs were discovered in the last couple of decades—who knows how much material we’ll have of each thirty years from now?

    There are actually four Patagotitan femora—the fourth, MPEF-PV 3375, is “only” 227 cm long.

    @DJ Sandy: “Robust”, perhaps surprisingly, isn’t really a trait I would associate with lognkosaurs. Mendozasaurus is decidedly on the gracile end for a titanosaur and Patagotitan is fairly middle-of-the-road. In general, femora are not really the most diagnostic of sauropod bones, so I’m not sure how possible it is to classify FMNH P13018 more finely.

  8. DJ Sandy Says:

    @John D’Angelo: Oh 100% however I did refer to it as “fairly robust”, it doesn’t seem to be from an animal of overwhelming girth and I agree the femur isn’t the best bone to diagnose an animal at the genus level but there is still a possibility the animal it belongs to is a Lognkosaur however I do currently agree it is an Indeterminate Titanosaur though I will say I’m not a Sauropod expert like the authors of SVPOW are. I can only dream of being as good as them at classifying Sauropods

  9. Josh Says:

    Actually the latest estimates have the Argentinosaurus femurs at about 255 cm! Of course we have the broken one which I’ve seen the pictures of and also there’s another one listed that was mentioned by Jose Bonaparte that I’ve never seen a picture of! I once had the numbers but have lost them but I remember reading that Argentinosaurus also had the most robust known femur measured by a good margin, maybe someone knows what they are!
    Someone mentioned mpm-pv39 I’ve not seen any measurements of it’s circumference, however just from the pictures you can tell that at 222cm that it’s far more massive than the 235 cm femur of Antarctosaurus giganteus, possibly one of the most robust there is would be cool to get some measurements of it! Another one that could be added to the list is Australotitan which is around 214 centimeters.

  10. Josh: by robustness, I assume you mean absolute circumference? It’s harder to get a list of femoral circumferences, because it’s not reported as often, but these are the largest ones I know of:
    1) Argentinosaurus huinculensis? MLP-DP 46-VIII-21-3: 111–118 cm
    2) Patagotitan mayorum MPEF-PV 3399/44: 101 cm
    3) Titanosauria indet. (Puertasaurus?) MPM-PV 39: 99 cm
    4) Brachiosaurus altithorax FMNH 25107: 94 cm
    5) Patagotitan mayorum MPEF-PV 3400/27: 93.5 cm
    6) Australotitan cooperensis EMF102: 93.3 cm
    7) Dreadnoughtus schrani MPM-PV 1156: 91 cm
    8) Giraffatitan brancai HMN XVI 82 cm
    9) Elaltitan lilloi PVL 4628: 81 cm
    10) Antarctosaurus giganteus MLP 26-316: 80 cm

    Presumably, most of the taxa on the list of the longest femora that aren’t included here would also rank on the list if their circumference were reported.

    The Australotitan paper appears to estimate its femoral length at 189 cm, not 214 cm. Like Ruyangosaurus and Argentinosaurus, it’s incomplete.

  11. Josh Says:

    Yes, I was meaning total circumference! Thanks for that list and wow, I think that kind of cements Argentinosaurus even more as the largest dinosaur known from good material. I knew there was a differential but never knew it was as great as it is compared to second place that is substantially larger!

  12. Mike Taylor Says:

    I have my doubts about circumference as a good measure of robustness, though. Consider three femora, all ellipsoid in cross-section. One is 2 cm x 2 cm (i.e. round), one is 1 cm anteroposteriorly by 4 cm transversely, and the last is 4 cm by 1 cm. The first has circumference 6.28 while both the others have circumference 8.57. On that basis, the round femur would be considered the least robust, although it has the same cross-sectional area as the others. And of the other two, the effective robustness would differ depending on the biomechanics of walking in the animal in question. At best, it’s a rough tool. I imagine engineers would, at this point, start talking about things like second moment of area.

  13. Good point. Of course, it’s hard to measure midshaft cross-section directly, so it’s usually easier to use a proxy such as circumference or diameter—so that just raises the question, what measurement provides the best proxy for the overall robustness of the bone? Midshaft circumference? Midshaft transverse diameter? Something else? A combination of multiple such easily-obtained measurements?

    This all comes back to the classic topic of “measure your damn dinosaur”; it’s unfortunately uncommon for publications to provide all three of the classic measurements of long bone midshaft size (circumference, transverse diameter, anteroposterior diameter). Not that I can blame people for not wanting to mess around with bones of that size more than they have to.

  14. Josh Says:

    It will be interesting to see how Moz-pv 1221 compares when fully excavated!

  15. dimetroblog Says:

    Three things :

    1. The giant turiasaur from Angeac is actually nicknamed “Pépé”, for “Grandad”, and not the “French Monster” or whatever. Like a sympathetic old relative, and not like a terrifying kaiju.

    2. I don’t see the issue with the reconstruction proposed for the giant femur. We got two complete femora. The first that has been found is 220 cm long, but its diaphysis has broken due to compression, so it should have originally been a bit shorter. The second is about 2 m long and is beautifully preserved in volume. The broken femoral distal head has been scaled up using the first femur, which was the only one available at the time for the reconstruction illustrated here. This is a totally legit way to estimate the length of bone, even if its proportions might change a bit now that a better preserved femur has been found.

    3. You may think what you want about femoral robustness, but its mid-diaphysis circumference remains alone a good proxy of the body mass of a tetrapod, as demonstrated by Campione and Evans (2012), available here :

  16. Ronald Says:

    1. I apologize, from now on it will be Pépé.
    2. Do you have an updated insight on the length and proportions of the giant femur, based on the better preserved 2nd femur?
    Thank you.

  17. Matt Wedel Says:

    I don’t see the issue with the reconstruction proposed for the giant femur. We got two complete femora. This is a totally legit way to estimate the length of bone [emphasis added]

    I didn’t say it was wrong, I said it wasn’t terribly compelling. In any population there is variation, and some femora (or any bones) are more slender, and others are more robust. Right now we don’t have any handle on variation in this taxon because we only have two femora. You are correct that this is a totally legit way to estimate the length of the whole bone; indeed, I can’t see any other way to do it. But when the complete bone would be the longest limb bone in existence for any animal, it’s also totally legit to have a healthy respect for the unknowns here (extraordinary claims and all that). Could that be a chunk of the biggest dinosaur femur ever found? Absolutely. But at this point I rate it as more tantalizing than compelling. I’m also not saying that the researchers did anything wrong, or that it’s not the biggest femur ever. I’m just saying it’s not yet conclusively demonstrated. Hopefully more of that individual, or one of equal or greater size, turns up soon.

  18. Matt Wedel Says:

    And belatedly: thank you, John D’Angelo, for bringing more giant femora to my attention, and for providing more info on the preserved elements of Giraffatitan and Patagotitan.

    If my scholarship in this post and this comment thread seems uncharacteristically weak, I can only plead busyness. As always, we’re happy to have sharp commentors on the ball.

  19. LeeB. Says:

    Have you seen this here:

    It looks like there are now three Supersaurus specimens; all large.
    I wonder if there are smaller specimens that have been misidentified.

  20. Mike Taylor Says:

    Yep, we’ve seen it. Brian and Ray have been in touch with us, and we’re discussing together what to do next.

  21. dimetroblog Says:

    To Ronald : Don’t worry about that. It’s just that I am a bit tired of nicknames (e.g., Predator X) and taxa names (e.g., Dreadnoughtus) underlining ginormouness, a trait which is way to hyped to my tastes. Yes, your dinosaur is bigger than mine, and so what ? This is why a simple nickname like “Pépé” was a bit refreshing. :-)

    To Matt : Hm, seems like I have missed the nuance of your reply… Sorry about that ! In turn, I would like some authors estimating sauropod length from fragmentary or specimens to be more careful regarding their proposals. Or proposition ? One of these makes me feel like these authors are trying to get married with a sauropod, which is weird (and probably illegal in some countries). :-|

    Now, Pépé is currently considered as Turiasauria indet. The best femur referred to this taxon is stated to be 2 m long, a value which has likely been rounded, in the caption to figure 27 of the brand new article of Allain et al. (in press) on the Angeac-Charente vertebrate fauna.

    You can find it over here :

    We just have to wait for the full description by Ronan and Rafael Royo-Torres. ^^

  22. Matt Wedel Says:

    No apologies necessary, dimetroblog. I didn’t express myself very clearly the first time around, and conveyed more skepticism than I actually feel. It is clear that Pépé is a legit monster and if does prove to be a turiasaur or some other flavor of non-neosauropod, that’s pretty exciting.

    I admit to being a bit of a neosauropod snob in my early years, and to me one of the most interesting findings of the big Sander et al. (2011) sauropod gigantism paper, as well as Mike’s and my 2013 paper on long necks in sauropods, is that all of necessary pieces for sauropod gigantism and the evolution of long necks were already in place in basal eusauropods. Worth noting in that context: like all omeisaurids and mamenchisaurids, Xinjiangtitan is a non-neosauropod.

  23. Shahen Says:

    There is also very incomplete femur which Lull referred in 1919 to Barosaurus and estimate length – 252.5 cm

  24. Ronald Says:

    I presume people here are aware of this fascinating new paper:
    Climatic constraints on the biogeographic history of Mesozoic dinosaurs.
    It states that sauropods were largely restricted to the warmer regions of the world, indicating a more ectothermic or intermediate metabolism.

  25. Jacek Says:

    What about Plottier Giant which is MCF-PVPH-889/02?its a partial femur which might be ~250cm when complete. Its described in Bellardini et al 2018

  26. Mike Taylor Says:

    Yes, that’s big! Big the femur is very poorly preserved and I wouldn’t put a ton of trust in the “might be ~250cm when complete” estimate. The fibula is in better shape, but at “only” 114 cm, it’s a little shorter than that of the Giraffatitan brancai holotype (119 cm) and decisively shorter than that of the referred specimen XV2 (134 cm). Shame that femur is not better illustrated.

  27. eosinopteryx Says:

    There is a 2.22 m Puertasaurus/Adult Dreadnoughtus femur, and a Plottier Giant with 41.3 cm Femur shaft width, Complete femur could be possibly 2.7 m. Same goes for Argentinosaurus with femur also estimated to be 2.7 m by Molina Perez and Larramendi

  28. eosinopteryx Says:

    If we are talking about femora that arent Complete, Then i have to mention huge YPM 429 femur – it doesnt belong to The same specimen as all of vertebrae, but still its huge at around 2 meters

  29. eosinopteryx Says:

    About Plottier Giant – its femur probably doesnt belong to The same individual as fibula. It Has shaft width 41.3 cm, too big for a fibula slighty bigger than 1 m. About French 2.6 m femur its still huge, Estimated to be 2.55 m by Molina Perez and Larramendi

  30. eosinopteryx Says:

    This is The last femur, i promise
    Lusotitan – 195 cm

  31. eosinopteryx Says:

    Damn i forgot about Futalognkosaurus (198 cm), Fusuisaurus (210 cm) and Apatosaurus (2 m Femur is known)

  32. eosinopteryx Says:

    Ok so this is really The last femur
    A COMPARISON OF THE WORLD’S LARGEST DINOSAURS) There was mentioned a 2.4 m femur of a Titanosaur in MLP

  33. eosinopteryx Says:

    And Australotitan Has 2.146 m femur

  34. Ronald Says:

    @ eosinopteryx: the MLP femur of 2.4m, isn’t that the already mentioned Antarctosaurus giganteus?

  35. Jacek Says:

    Is the MLP-DP 46-VIII-21-3 ~270cm estimate from Molina & Larramendi’s book reliable ?

  36. eosinopteryx Says:

    @Ronald no, that’s different animal, possibly Argentino? Idk
    @Jacek Yes. Using Patagotitans Femur i got almost same results

  37. eosinopteryx Says:

    Isn’t like There a OMNH Apatosaurine caudal 63% bigger than that of louisae?

  38. Matt Wedel Says:

    Yep, OMNH 1331 — your memory is good! See this post.

    I’ll caveat that all the other elements from that quarry suggest an animal 25-33% bigger than CM 3018, and that internal proportions of apatosaurines are all over the map (as the post linked above hints at), so I doubt the whole animal was 63% bigger than CM 3018. But the base of the tail might have been.

    Also relevant: third photo down in this post.

  39. eosinopteryx Says:

    Well, How much bigger (than Louisae) on average are Oklahoma Apato elements?

  40. Matt Wedel Says:

    ?? You’ve lost me. I just answered that question in the previous comment. CM 3018 is the holotype and reference specimen of A. louisae.

  41. eosinopteryx Says:

    About femora: Huene in 1929 mentioned a huge 2.7 m titanosaur femur

  42. Matthew Smith Says:

    I don’t recall ever reading him mentioning this? Where did you read about him describing a 2.7 m titanosaur femur?

  43. eosinopteryx Says:

    Well i misread it and jts actually what news said about size of giganteus femur.

  44. Matthew Says:

    I did read about the new estimate of the Argentinosaurus femur fragment at 2.7 meters, that is one enormous femur! I have seen pictures of it but there has always been another more complete femur referred to Argentinosaurus that is said to be deformed, I’ve always found it odd that I’ve never seen pictures of it anywhere, looks like there would have to be a picture floating around somewhere.

  45. Jacek Says:

    Oh also there is MCF PVPH # Argentinosaurus left femur, said to be 250cm though there is no photos of it

  46. Matthew Says:

    Exactly, that has always seemed so
    strange to me to not have any photos at all of a femur of that class!

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