As can be seen here, Amphicoelias is recovered more derived than Amazonsaurus, but more basal than the most basal rebbachisaur, Histriasaurus. This placement has weak support, and as Whitlock comments, "The recovery of Amphicoelias as a basal diplodocoid agrees with the findings of Rauhut et al. (2005), although the latter result may hinge on one or two key scorings. As mentioned above, re-scoring Amazonsaurus in Rauhut et al.’s (2005) matrix results in the placement of Amphicoelias in a large polytomy with essentially all other eusauropods."
On top of that, it is unclear from Whitlock's (2011) analysis, whether A. altus is only scored, or if A. fragillimus is included as well. So this analysis may only apply to A. altus. But no matter, as when I did some comparisons of the overall morphology and proportions of A. fragillimus, it turns out it agrees quite well with rebbachisaurs.
One of things I have noticed about A. fragillimus was that its neural arch is proportionally tall when compared to diplodocids such as Diplodocus, Barosaurus, Apatosaurus and others, as well as in comparison to the dicraeosaurs. Using the dorsal of Rebbachisaurus garasbae, I completed a new reconstruction of the dorsal of A. fragillimus (see above). The gray parts are directly traced from Rebbachisaurus and you can see how well the neural arch proportions match. Obviously, the neural spine in Rebbachisaurus is considerably wider proportionally than that of A. fragillimus, but the neural spine of Limaysaurus tessonei matches quite well, being remarkably thinner side-to-side than in Rebbachisaurus. A thinner neural spine is also seen in Amazonsaurus.
Amazonsaurus dorsal from Carvalho et al (2003)
Another thing that seems to support the hypothesis that A. fragillimus was a rebbachisaur or rebbachisaur-grade diplodocoid is the apparent extreme pneumaticity of the vertebra, with the etymology of its species name meaning "very fragile". Rebbachisaurs such as Nigersaurus and Tataouinea demonstrate extreme pneumaticity in their skeletons, for instance.
How big is a rebbachisaur-ized A. fragillimus?
As shown in the second image above, the reconstructed total height of the vertebra of A. fragillimus is just under 243 cm tall (this happens to be quite close to the reconstructed height when I previously used Diplodocus as a comparison). Compare this to the dorsal vertebrae height of Limaysaurus, at just over 121 cm tall. Assuming fairly similar proportions, A. fragillimus is about twice as large as Limaysaurus in linear dimensions. My recent reconstruction of Limaysaurus gives a total length of 14.3 m, and a mass of about 6.2-6.5 tonnes (depending on the assumed tissue density). This means a total length of about 28.6 m for A. fragillimus, and a mass of about 51-53 tonnes.
Key: blue figure -A. fragillimus, yellow figure - Supersaurus, green figure - Rebbachisaurus, gray scale figure - Limaysaurus
As seen in this comparison I mocked up, A. fragillimus was probably only slightly shorter in length than Supersaurus (silhouette of Supersaurus based on skeletal from Scott Hartman: www.palaeocritti.com/_/rsrc/12…). The lengths come out the same in the image, but in a fair comparison, the neck and tail would be horizontal (with no dorsal or ventral bending) in the Supersaurus outline, which would probably "add" a few more meters to the "length" of the Supersaurus. For comparison, Supersaurus was estimated to be 33-34 m long and mass 35-40 tonnes by Lovelace et al. (2007), but a GDI mass estimate based on the multi-view skeletal therein gives me a volume of about 32.6 m^3 and a mass of about 26 tonnes (assumed the same density they did of 0.8).
So, a rebbachisaur-like A. fragillimus was probably the biggest diplodocoid, but not the longest, and is smaller than the largest titanosaurs, although not by much. (Also note that the length of the hindfeet of a scaled of rebbachisaur-like A. fragillimus are about 144 cm long, which is only slightly shorter than the biggest Broome & Plagne sauropod tracks which are up to 150 cm long, meaning they might not have been record-breakers either, possibly 60 tonnes or less if they were rebbachisaurs.)
Carvalho IDS, Avilla LDS, Salgado L. 2003. Amazonsaurus maranhensis gen. et sp. nov. (Sauropoda, Diplodocoidea) from the Lower Cretaceous (Aptian-Albian) of Brazil. Cretaceous Research 24: 697–713.
Lovelace DM, Hartman SA, Wahl WR. 2008. Morphology of a specimen of Supersaurus (Dinosauria, Sauropoda) from the Morrison Formation of Wyoming, and a re-evaluation of diplodocid phylogeny. Arquivos Do Museu Nacional, Rio De Janeiro 65: 527–544.
Whitlock, JA. A phylogenetic analysis of Diplodocoidea (Saurischia: Sauropoda). Zoological Journal of the Linnean Society, 2011, 161, 872–915.
Some more thoughts on theropod lips
Thoughts about the size of Dreadnoughtus
A new year, a new blog
How big are blue whales? And what does 'big' mean?
I don't know if this (size estimate) is outdated or whether you have seen the link to be written below, but if neither is true, I'd like to ask the following:
What do you think about Greg Paul's take on the size of the animal? On Page 18, he gives an estimate of 80000 to 120000 kg with the same base as herein, and also says this:
"Accommodating such a tremendous vertebra within a smaller-bodied sauropod is implausible, and in the less likely but not impossible event that Maraapunisaurus had a lower, more typical (for sauropods) dorsal vertebral height/body size ratio, it might have been even larger."
Limaysaurus is not a basal rebbachisaurid as stated in the newest thesis. So SpinoInWonderland used other rebbachisaurid ( for example, Demandasaurus) as the model basis of Maraapunisaurus. So it's not very reasonable to use Limaysaurus to calculate Maraapunisaurus's mass. For other Besides, body mass listed in the Princeton Field Guide is often underestimated since Argentinosaurus was given a "50 tonnes" in the book.
Rebachisaurids seem to be absent from North America while Dicreasaurids are there more often. The problem with this reconstruction is that large sauropods tend to naturally be orientated towards higher browsing, and have had proportionally longer necks as a result, rather than a simple scale up. Plus even in your graph, it is outside of the rebachisaurid and Dicreasaurids groups, so it doesn't guarantee similar proportions. I agree that it was more basal than the competition, but I doubt the idea of such a huge beast having proportions similar to a far smaller one, especially when other basal sauropods are known that didn't have such specialisations. For now Tornieria does seem a plausible comparison.
The large Apatosaurus and Barosaurus notably do not differ much in the proportions of the preserved material.
Confirmed rebbachisaurs are so far absent from N. America. Note that I did say "or rebbachisaur-grade diplodocoid". It may not be a rebbachisaur 'proper' (all rebbachisaurs are known from the Cretaceous) but likely a basal diplodocoid of some sort. Since rebbachisaurs are the only basal diplodocoids (except Haplocanthosaurus) that have decent material preserved, I use them as a guide. Notably, Haplocanthosaurus has somewhat similar proportions overall to rebbachisaurs, so I think it is reasonable.
Please remember, that this was a thought experiment. Until more material is preserved, all such estimates are speculations of course. That said it is informed speculation, and data-driven and much more likely than scaled up apatosaurs or diplodocus.
At its size, even with a short neck, it would still be a 'high-browser', so not sure that point makes my reconstruction less likely. Even doubling the size of the neck would not affect the mass much.