Sauroposeidon proteles

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Figure 1: A reconstruction by Mike Taylor, Matt Wedel and Darren Naish[1]

Cladistics:
Saurischia
Sauropodomorpha
Sauropoda
Somphospondyli
Sauroposeidon
S. proteles[2]

Time: Lower Cretaceous, Aptian-Albian[2]

Location: Oklahoma, USA, Antlers Formation[2]

Description: The Holotype (OMNH 53062) is known from the 5th, 6th, 7th und 8th cervical vertebra[2] and belongs to one of the worst preserved sauropods of the lower Cretaceous of the USA.[1] The vertebrae are highly elongated. The elongation can be measured by the EI value which designates the length to width ratio. In Sauroposeidon, this value is higher than 5 which is exceptional for a sauropod.
The longest vertebra is the 8th cervical vertebra (C.8) with a length of 1,4 m. The 6th and the 7th are 1,35m (C.6) and 1,37m (C.7) long. For the C.8, there are neither total length nor centrum length estimates. For the others, centrum length estimates of 1,22m (C.6), 1,23m (C.7) and 1,25 (C.8) exist.

Table 1[2]
The vertebrae's Vertebra pneumaticity is interpreted as evidence of an air sack system as observed in modern birds. Moreover, it reduces the weight of the neck and allows lifting it in a higher position. It is unclear why Sauroposeidon would require such a reach though since Brachiosaurus had a shorter neck despite comparatively higher competitive pressures from other sauropods. It has been suggested that the neck acted as a compensation for its inflexible massive body body[2].

Size estimates: The neck length was calculated using the measurements of the Giraffatitan specimen in Berlin (HM SII). Extrapolating from the latter's 9 m long neck and taking into account that Sauroposeidon's vertebrae are 25-33% longer, yields a neck length of 11,5-12m, assuming similar proportions. To compare them, here the measurements of the Giraffatitan in Berlin (aswell from my second source):

Table 2: Table containing data on Giraffatitan's measurements.[2]
Due to Giraffatitan's lower EI, the width disparity between the two taxa is not as great as the length disparity. Consequently, estimates based on the width yield an animal only marginally larger than Giraffatitan.[2] Due to the lack of leg or torso material, mass estimates are based on isometric scaling from Brachiosaurus, ranging from 15[3] to 78 t[4]. However, these are regarded as outliers[2]. Other estimates yield 29[5], 32[6] and 46 t[7]. Wedel at al. calculate it at 50-60 t whilst noting that the animal was likely slimmer than Brachiosaurus due to the more elongated neck. Thus, isometric scaling might produce inflated figures. The height is estimated at 17-18m[2][8].

Classification: This animals shows that sauropods of the lower Cretaceous in the USA were not as reduced in their diversity as previously suggested[9]. In the year Wedel et al. (2000) classified Sauroposeidon as a close relative of Brachiosaurus. In the year 2012 however, Wedel regarded it as a basal Macronaria, citing similarities in the cervical vertebrae of Sauroposeidon to other basal Macronaria, like Erketu and Qiaowanlong[1]. DÂ’Emic, M.D., and B.Z. Foreman (2012) treated Paluxysaurus and Sauroposeidon as synonymous[10].

Figure 2: Paluxysaurus material now assigned to Sauroposeidon. ©Mike Taylor, Matt Wedel and Darren Naish[1]
A more recent publication treats Sauroposeidon as a sister taxon to Paluxysaurus and places both taxa closer to Saltasaurus than Brachiosaurus, thus assigning them to a group called Somphospondyli.

Figure 3: Phylogenetic tree by Mannion et al. (2013)[11]


Sources:
[1] svpow.com/2012/09/05/hot-sauropod-news-part-2-a-new-look-for-sauroposeidon/
[2] Mathew J. Wedel, Richard L. Cifelli, R. Kent Sanders (2002): Osteology, paleobiology, and relationships of the sauropod dinosaur Sauroposeidon
www.app.pan.pl/archive/published/app45/app45-343.pdf
[3] Russell. D.A., Beland, P., & McIntosh, J.S. 1980. Paleoecology of the dinosaurs of Tendaguru (Tanzania). Memoirs de la Societe' Geologique Fran~ais5 9, 169-175.
[4] Colbert, E.H. 1962. The weights of dinosaurs. American Museum Novitates 2076, 1-16.
[5] Anderson, J.F., Hall-Martin, A,, &Russell, D.A. 1985. Long-bone circumference and weight in marnmals, birds, and dinosaurs. Journal of Zoology 207,53-61.
[6] Paul, G.S. 1988. The brachiosaur giants of the Morrison and Tendaguru with a description of a new subgenus, Giraffatitan, and a comparison of the world's largest dinosaurs. Hunteria 2, 1-14.
[7] Alexander, R.McN. 1989. Dynamics of dinosaurs and other extinct giants. 167 pp. Columbia University Press, New York.
[8] Holtz, Thomas R., Jr., and Luis Rey. 2007. Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages. Random House, New York. 428 pages.
[9] Philip D. Mannion, Paul Upchurch: A re-evaluation of the ‘mid-Cretaceous sauropod hiatus’ and the impact of uneven sampling of the fossil record on patterns of regional dinosaur extinction. In: Palaeogeography, Palaeoclimatology, Palaeoecology. 299, Nr. 3–4, 2011, Abstract, S. 529
www.sciencedirect.com/science/article/pii/S0031018210007078
[10] DÂ’Emic, M.D., and B.Z. Foreman. 2012. The beginning of the sauropod dinosaur hiatus in North America: insights from the Lower Cretaceous Cloverly Formation of Wyoming. Journal of Vertebrate Paleontology 32(4): 883-902.
[11] Philip D. Mannion, Paul Upchurch, Rosie N. Barnes, Octávio Mateus, Osteology of the Late Jurassic Portuguese sauropod dinosaur Lusotitan atalaiensis (Macronaria) and the evolutionary history of basal titanosauriforms, Zoological Journal of the Linnean Society, Volume 168, Issue 1, May 2013, Pages 98–206, doi.org/10.1111/zoj.12029

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Predicted body temperature:

Predicted body temperature for the largest dinosaur ( Sauroposeidon proteles at about 60 tons) was about 118 °F—just past the limit for most animals, suggesting that body temperature may have prevented dinosaurs from becoming even bigger.

www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.0040255