Slender Giants

8th September 2014

Mike Taylor1 & Mathew Wedel2

1University of Bristol, Bristol, UK.
2Western University of Health Sciences, Pomona, USA.

The giant sauropod dinosaurs are often perceived as having a single uniform body plan: in fact there is great variation between different sauropods. For example, Apatosaurus has much more robust limbs than the closely related Diplodocus. The brachiosaurids Brachiosaurus and Giraffatitan have disproportionately narrow dorsal centra compared with diplodocids. They also have the slenderest humeri of all sauropods -- both by length:width ratio, and in proportion to their own femora, which are about 50% bigger in cross-sectional area. This is surprising, as their tall, broad torsos and small tails meant they carried more of their weight on their forelimbs than other sauropods. Exacerbating this paradox, the coracoid of Brachiosaurus has a unique ventrolaterally oriented glenoid articulation -- perhaps suggesting a mechanically inefficient sprawled posture, putting the slender humeri under great stress.The femora of brachiosaurids pose another puzzle, being more eccentric than those of other sauropods: the mediolateral width is more than twice the anteroposterior diameter for most of the length of the shaft. The humerus of Giraffatian is 5% longer than the femur; the humerus of the Brachiosaurus altithorax holotype is eroded at its distal end, but reasonable reconstructions suggest that it too was longer than its femur when complete. The radius and ulna of Giraffatitan are also longer than the tibia and fibula, and the forefoot much taller than the hindfoot. These proportional differences show that the shoulders of brachiosaurs were even higher, relative to the hips, than most current restorations show.

[Slides PPT] [Slides PDF]

The abstracts volume for SVPCA 2014 can be downloaded. Note that this abstracts booklet PDF is of a provisional version, differently paginated from the final version.

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