Amphicoelias fragillimus - smaller than you think
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Amphicoelias fragillimus is often listed as one of the largest dinosaurs, if not the largest. Size estimates are usually superlative, and often includes mass estimates well over 100 tonnes, with the most commonly cited estimates usually around 120-150 tonnes; and length estimates in the 50-60 meter range.

I myself at one point gave a mass estimate of 150-250 tonnes and length of about 70 meters.

I think I was probably wrong, and a recent size comparison with Argentinosaurus demonstrates why:



Since my GDI mass estimate for Argentinosaurus is about 64 tonnes, I knew 100+ tonnes estimates for Amphicoelias had to be wrong.

I did a completely new reconstruction of Amphicoelias fragillimus, with missing parts restored after Amphicoelias altus and compared that to a reconstruction of a posterior dorsal of Argentinosaurus. As you can see, in both total width and centrum length, Argentinosaurus just edges out A. fragillimus in size. I should also point out that the posterior dorsals of diplodocids are usually taller than the anterior dorsals, while the opposite is the case in at least some titanosaurs:


Diplodocus dorsal sequence

Malawisaurus dorsal sequence

This means, of course, that we are not comparing apples and oranges and therefore, the absolute size of a vertebra can be misleading, especially when comparing taxa that are not closely related. There are several things one needs to keep in mind, then, when trying to get an idea of overall size of a sauropod based on vertebral size (or indeed, any animal):

1. Serial position of vertebra (i.e., the 1st dorsal, 5th dorsal, 8th dorsal, etc.)
2. Proportions (length to width, etc.)
3. Phylogeny (diplodocid, brachiosaur, etc.)
4. Absolute size

These points may seem obvious, but often times it appears only absolute size is discussed. In fact, this is probably the least important factor in determining the total size of the animal. An example to compare would be Giraffatitan and Diplodocus. Both Giraffatitan and Diplodocus each have a dorsal vertebra that measures 107 cm in total height. If one were to study these vertebra in isolation without respect to points #1, #2 and #3 that I listed, and only compared absolute size (point #4), one might get the impression that both taxa were approximately the same size. In fact, they are not, as you may well be aware. Rigorous reconstructions show that Giraffatitan is consistently estimated to have been about 25-30 tonnes and about 23 meters long, whereas Diplodocus is usually estimated to be about 10-15 tonnes, and about 25 meters long. Clearly, Giraffatitan was bigger in mass than Diplodocus.

Focusing on points #1, #2 and #3 show why, even though both Giraffatitan and Diplodocus have a dorsal vertebra of the same height, one is clearly larger.

First, the serial position of the vertebrae are different. In Giraffatitan, it is the 4th dorsal that is 107 cm tall, while it is the 10th dorsal in Diplodocus. In Giraffatitan the anterior dorsals are taller than the posterior dorsals, while the opposite is the case in Diplodocus.


Giraffatitan dorsal (top right)

Second, consider the proportions. The dorsal of Giraffatitan is considerably wider proportionally (and in absolute terms) than the dorsal in Diplodocus. In Giraffatitan the width of the diapophyses is the same as the height of the entire vertebra, over 107 cm wide (Janensch, 1950). In Diplodocus, the widest dorsal (the 4th) is only 75 cm across the diapophyses, and is only 49.5 cm in the 10th dorsal (Lull, 1919).

Third, consider the phylogeny. We can use phylogenetic bracketing to get a rough idea of the proportions of an animal, even if known from incomplete material. We know, for instance, that diplodicids tend to be long and skinny, whereas brachiosaurs tend to be shorter in total length, but also more robust and therefore heavier than a diplodocid of the same length.

So what does this all mean for Amphicoelias fragillimus, especially in comparison to Argentinosaurus?

First, consider the serial position of the vertebra. The dorsal of Amphicoelias fragillimus appears to be one of the last, if not the last dorsal, and is commonly cited as the 10th (Carpenter, 2006). The vertebra of Argentinosaurus I have chosen to compare it with was originally described as the 2nd (Bonaparte and Coria, 1993), but subsequent analysis suggests it is a posterior dorsal, possibly the last or penultimate dorsal (Novas and Ezcurra, 2006; Salgado and Powell 2010).

Second, consider the proportions. Amphicoelias is clearly much more gracile than Argentinosaurus. In fact, it appears likely that the centrum would have been shorter and skinnier than in Argentinosaurus. Even the diapophyses appear to be not to have been as wide. Obviously, Amphicoelias is considerably incomplete, even the lone dorsal. This is where the third point comes into play.

Phylogenetically A. fragillimus was a diplodocid, and appears to be close to A. altus. This gives us a way to confidently restore the missing bits. The parts in gray were restored after A. altus (Osborn and Mook, 1921). Also, we can compare it to more complete diplodocids, like Diplodocus itself and compare proportions with it.

Restoring the incomplete vertebra of A. fragillimus off of A. altus, gives these estimated measurements:

* Total height: ~2400 mm
* Diapophyses width: ~1070 mm
* Centrum width (posterior face): ~600 mm
* Centrum length (total): ~490 mm

In Diplodocus, these measurements are (10th dorsal; from Lull, 1919):

* Total height: 1070 mm
* Diapophyses width: 495 mm
* Centrum width (posterior face): 325 mm
* Centrum length (total): 290 mm

Here are some ratios of Amphicoelias to Diplodocus:

* Total height ratio: ~2.24
* Diapophyses ratio: ~2.16
* Centrum width: ~1.84
* Centrum length: ~1.69

Taking the average of these ratios, we get that, on average, A. fragillimus was "only" 1.9825 times larger than Diplodocus in linear dimensions, which would suggest being about 7.79 times heavier, or approximately 78 tonnes, assuming Diplodocus was 10 tonnes (a mass estimate I got by doing a GDI of Gregory S. Paul's multi-view Diplodocus reconstruction). My own mass estimate for Argentinosaurus is about 64 tonnes, and for the largest Alamosaurus specimen about 74 tonnes. This means that there are no sauropods yet known that we can confidently say are heavier than 100 tonnes. Amphicoelias fragillimus still was possibly the largest sauropod, although not nearly by the margin often claimed: only by a few tonnes. Since any mass estimates are imprecise, I'd say it is approximately a tie for first place between Alamosaurus and Argentinosaurus for the largest known sauropod.

So, the whales win - by a wide margin*. ;)

*There are at least 4 living whale species for which specimens are known that reach over 100 tonnes: the blue whale, fin whale, bowhead whale, and Northern Pacific right whale.

References:

Bonaparte, J. F., and R. A. Coria. 1993. Un nuevo y gigantesco sauropodo titanosaurio de la Formacion Rıo Limay (Albiano–Cenomaniano) de la Provincia del Neuquen. Ameghiniana 30:271–282.

Carpenter, K. 2006. Biggest of the big: a critical re−evaluation of the mega−sauropod Amphicoelias fragillimus Cope, 1878. New Mexico Museum of Natural History and Science Bulletin 36: 131–137.

Janensch, W. 1950 Die Wirbelsäule von Brachiosaurus brancai ("The vertebral column of Brachiosaurus brancai") Palaeontographica Supplement VII (1), teil 3, leif 2:31-93

Leonardo Salgado & Jaime E. Powell (2010): Reassessment of the vertebral laminae in some South American titanosaurian sauropods, Journal of Vertebrate Paleontology, 30:6, 1760-1772

Lull, R. S. 1919. The sauropod dinosaur Barosaurus Marsh. Memoirs of the Connecticut Academy of Arts and Sciences 6:1–42.

Novas, F. E., and M. Ezcurra. 2006. Reinterpretation of the dorsal vertebrae of Argentinosaurus huinculensis (Sauropoda, Titanosauridae). Ameghiniana 43(4, Supplement):48R–49R.

Osborn, H. F., and C. C. Mook. 1921. Camarasaurus, Amphicoelias and other sauropods of Cope. Memoirs of the American Museum of Natural History, n.s. 3:247–387.
Comments48
anonymous's avatar
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bricksmashtv's avatar
bricksmashtvHobbyist General Artist
Could you by any chance email me the Argentinosaurus dorsal paper? I'll PM you my email.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
Sure, let me know which one you want.
bricksmashtv's avatar
bricksmashtvHobbyist General Artist
okay sent! Thanks in advance!
TheDubstepAddict's avatar
TheDubstepAddictHobbyist Traditional Artist
Astonishing
SameerPrehistorica's avatar
SameerPrehistoricaProfessional Digital Artist
Fin whale, bowhead whale, and Northern Pacific right whale doesn't weigh
100 tonnes on average.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
That is true, and I never said that they did.
SameerPrehistorica's avatar
SameerPrehistoricaProfessional Digital Artist
Yes,i know.I just wanted to mention it. If it was about fragmentary prehistoric animals size,i won't talk about anything as those things are not easy to accurately estimate.Different people make their estimates and i don't take any of those seriously.
          Whales are living animals and they were weighed.Quite a longtime before i searched in some genuine whale websites.In all those sites,only blue whale was given an average weight of 100 tonnes /100 tonnes plus.Those 3 other Whales where given the 60 - 70 tonne range which is the same i have heard in videos.
            Except Cope,how many people have seen the real partial vertebra of Amphicoelias fragillimus before it was lost ?
I'm having a doubt if it was real.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
While it's true that they don't weigh on average a 100 tonnes, all of those species are known from individual specimens that weigh over 100 tonnes. For instance, the bowhead is known from specimens that weigh up to 160 tonnes. See some of the references from this journal entry (at the bottom) for more info: palaeozoologist.deviantart.com… . The point is, we don't have any convincing evidence of sauropods that were larger than the largest whales, even when comparing average whale sizes. There are no known sauropod specimens that, when accurately restored, even hint of a sauropod in the 100 tonne range. For instance, my restoration of Argentinosaurus comes in at about 60+ tonnes using GDI estimation. The largest specimen of Alamosaurus might have reached ~70 tonnes or so, but it is based on a sole tibia that may or may not be properly referred to Alamosaurus. And with Amphicoelias fragillimus restored as a rebbachisaur or basal diplodocoid we are talking only ~55 tonnes.


I don't know how many people saw the real vertebra of Amphicoelias fragillimus. Many people have your skepticism about its existence. However, Kenneth Carpenter noted, "The immense size of the measurements given by Cope and the inferred vertebra size have been met with skepticism (several individuals, verbal to Carpenter), with typographical errors in the measurements being the most commonly assumed explanation. There is, however, every reason to accept Cope at his word. First, Cope never made any subsequent corrections in his publications; furthermore, his reputation was at stake. Marsh, who was ever so ready to humiliate Cope, never called into question the measurements. Marsh is known to have employed spies to keep tabs on what Cope was collecting, and it is quite possible that he had independent confirmation for the immense size of A. fragillimus. Osborn and Mook (1921) accept Cope’s measurements without question, as does McIntosh (1998). Thus, there is historical precedence for accepting the measurements as correct." (www.gardenparkdinos.com/wp-con… The particular fact that Marsh and Cope had such a big rivalry, and that Marsh employed spies, and that Marsh never called into question the specimen strongly indicates that it was real and that the measurements were accurate.
Stuchlik's avatar
And how long was Amphicoelias ? 1,69 x 25= 42,2 m. Over 40 m ?

Best
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
If it was similar to Diplodocus, then possibly, yes. If it was actually a rebbachisaur-grade diplodocoid, then it may have been shorter.
TitanoRex's avatar
WHAAALLESSS! D:<
SpinozillaRex's avatar
so how big is it exactly?
pilsator's avatar
pilsatorHobbyist Traditional Artist
Nice rundown. Not sure about the diplodocoid in-group inference (IIRC, A.? fragilimus has ever been included in a published phylogenetic analysis but I may be wrong), but with such limited material, that's the least of the problems it has left us with.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
Thanks!

Actually, I just found out (after I did this post) that Amphicoelias has been included in two published phylogenetic analysess: Whitlock (2011) & Rauhut et al. (2005). Whitlock (2011) found it to be a basal diplodocoid more derived than Amazonsaurus and Haplocanthosaurus (successively), but less derived than the rebbachisaurids (with the most basal rebbachisaur being Histriasaurus, followed by Rebbachisaurus). I believe only A. altus is scored.

However, it's position is not well resolved, and depending on which other taxa they include it results on an unresolved polytomy, so I'd say the results are very tentative.

If we take these results as valid, then Amphicoelias may have looked more like a cross between Amazonsaurus and Histriasaurus, unfortunately both are terribly incomplete, so it doesn't help much with trying to estimate size.

Refs--

Rauhut O, Remes K, Fechner R, Cladera G, Puerta P. 2005. Discovery of a short-necked sauropod dinosaur from the Late Jurassic period of Patagonia. Nature 435: 670–672.

Whitlock, J.A. 2011. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society 161:872–915.
pilsator's avatar
pilsatorHobbyist Traditional Artist
The only thing that might help would be looking for character polarity down there. I would have sworn that I had a copy of Whitlock (2011) on my machine, but I don't, so no idea what his Amphicoelias OTU consists of.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
Yes, the polarity of the characters would make a difference. I'll only point out that out of the total characters scored, 86% could not be scored in A. altus in Whitlock (2011).
liej's avatar
What about Puertasaurus for that title ? It seems to me Shartman suggested it as a very serious contender ?

Excellent article, you're going to disappoint a lot of dreamers, even though Amphicoelias is still an absolute giant.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
Puertasaurus is an example of points #1 and #2 that I describe above not being taken into consideration.

The sole dorsal vertebra (either the 1st or 2nd) is exceptionally wide at 168 cm across the diapophyses, but it is much shorter than the dorsals of Argentinosaurus in both total height and centra length. Also, since the positions of the dorsal vertebrae of Argentinosaurus have been reconsidered, we don't have any anterior Argentinosaurus dorsals, so the width comparisons could be misleading.

The height of the dorsal of Puertasaurus is only 106 cm tall (Novas et al., 2005), compared to at least 145 cm for the known dorsals of Argentinosaurus (see above).

The total centra length for Puertasaurus is not mentioned, but based off of the published drawings, it looks to be about 42 cm, which is significantly shorter than the 50 cm + lengths in Argentinosaurus. Of course, those are posterior dorsals, but the thing to remember is that in many titanosaurs, the anterior dorsals are generally longer than the posterior dorsals, which means the posterior dorsals of Puertasaurus were likely shorter than 42 cm, meaning they were potentially 10 cm shorter than in Argentinosaurus.

Also, consider the width of the diapophyses. In a juvenile specimen of Alamosaurus, the anterior dorsals are 50 cm wide across the diapophyses, and the posterior dorsals are 32 cm (Lehman and Coulson, 2002). Which means the anterior dorsals are more than 50% wider. If this was true in Argentinosaurus, than the anterior dorsals might be ~175 cm wide (based off of 116 cm wide posterior dorsal I reconstructed above), which would be wider than Puertasaurus. This ratio is even more extreme in Opisthocoelicaudia (Borsuk-Bialynicka, 1977), where the 2nd dorsal is 66 cm wide across the diapophyses, and the 11th dorsal is 41 cm wide, for a ratio of more than 60% wider, which would lead to an estimated anterior dorsal width of Argentinosaurus of ~185 cm. So my guess is that the anterior dorsals of Argentinosaurus would actually be wider than Puertasaurus.

Taking these things into consideration, Puertasaurus was probably smaller than Argentinosaurus, Alamosaurus and Amphicoelias.

Refs--

BORSUK-BIALYNICKA, M. 1977. A new camarasaurid sauropod Opisthocoelicaudia skarzynskii gen. n., sp. n. from the Upper Cretaceous of Mongolia. Palaeontologia Polonica, 37:5–64.

Lehman, T.M. and Coulson, A.B. 2002. A juvenile specimen of the sauropod dinosaur Alamosaurus sanjuanensis from the Upper Cretaceous of Big Bend National Park, Texas. Journal of Paleontology 76: 156–172.

Novas, F.E., Salgado, L., Calvo, J., and Agnolin, F. 2005. Giant titanosaur (Dinosauria, Sauropoda) from the Late Cretaceous of Patagonia. Revista del Museo Argentino de Ciencas Naturales 7: 37–41.
liej's avatar
Thank you very much for these explanations.

Actually, your older estimate of Amphicoelias was the basis for a number of enthusiasts on the web for stating that Amphicoelias indeed was potentially heavier than the largest whales. But I'm not surprised of your revision, as this has been usually the case with almost all giants sauropods, with the notable exception of Alamosaurus due to the later findings.

Whatever, Amphicoelias was a absolute giant. But is it really valid ? I've heard several times that the lost bone itself could have been doubtful and/or the measurements off. Just like even a well known fossil, the skull of Sue, has been revised in size.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
You're welcome.

Yes, you are correct, generally size estimates are over-inflated when initially reported (unfortunately). I'm sorry to hear that a number of people have taken my older estimate too seriously :( Oops. Hopefully that will now be corrected.

As for the validity of A. fragillimus, I'll let Carpenter (2006) explain: "The immense size of the measurements given by Cope and the inferred vertebra size have been met with skepticism (several individuals, verbal to Carpenter), with typographical errors in the measurements being the most commonly assumed explanation. There is, however, every reason to accept Cope at his word. First, Cope never made any subsequent corrections in his publications; furthermore, his reputation was at stake. Marsh, who was ever so ready to humiliate Cope, never called into question the measurements. Marsh is known to have employed spies to keep tabs on what Cope was collecting, and it is quite possible that he had independent confirmation for the immense size of A. fragillimus. Osborn and Mook (1921) accept Cope’s measurements without question, as does McIntosh (1998). Thus, there is historical precedence for accepting the measurements as correct."

Ref--

Carpenter, K. 2006. Biggest of the big: a critical re−evaluation of the mega−sauropod Amphicoelias fragillimus Cope, 1878. New Mexico Museum of Natural History and Science Bulletin 36: 131–137.
liej's avatar
Thank you ! Indeed we have all reasons to think the measurements as trustable then.

That's not your fault, people enthusiasm is there and then they go with their own calculations more or less flawed. I've seen several posts where they came up with weights figures over 300 tonnes.

There are the dinos enthusiasts who are happy with rigorous estimates hinting on the biggest land animals ever, and there are those who wish absoutely to get an animal bigger than the (boring ?) B. musculus.
palaeozoologist's avatar
palaeozoologistHobbyist General Artist
You're welcome, glad I could be of service!

"I've seen several posts where they came up with weights figures over 300 tonnes."

Oh jeez, 300 tonnes?! That's definitely absurd :D

"There are the dinos enthusiasts who are happy with rigorous estimates hinting on the biggest land animals ever, and there are those who wish absoutely to get an animal bigger than the (boring ?) B. musculus."

Haha, very true...we need more of the former ;)
Spinodontosaur4's avatar

I believe Hartman stated he felt Puertasaurus and Alamosaurus (he also tentatively put Argentinosaurus into the same category) are in the same size class after he restored both of them, but who is actually larger isn't certain. Nima Hassani's Puertasaurus seems a lot bigger though...

I don't think 4 tonnes here or there in animals this large fragmentary are _that_ significant either, it's pretty much the equivalent of only 400 kg difference in an 8 tonne animal.

liej's avatar
Sort of compi Tyrannosaurus/Giganotosaurus...
anonymous's avatar
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