Ibrahim et al. (2014) shift the tall-spined "caudal" vertebrae back to being a posterior dorsal, and they move the next tallest caudal almost all the way to the anterior part of the tail, in contrast to the positions that have been recently suggested. This results in a much shorter "retro-look" sail and a rather skinny but flexible tail. That may well be correct, but what I want to focus on is the pelvis and hindlimb proportions. The authors' provide a wonderful table (S2) with measurements of individual elements of the neotype specimen, which is naturally the first thing I went to check when I saw how radical the new interpretation was. And that's where we run into trouble.

How can we know how large the pelvis and the hind limbs are relative to the rest of the animal in a composite skeleton? The best way to tell is to scale them against the dorsal column, and luckily the neotype specimen (FSAC-KK 11888) has several vertebrae. Table S2 in the supplemental data section reports that D8 is 18 cm long. It also reports that the length of the ilium is ~71 cm in length, or nearly 4 times the length of D8 (3.94 to be precise).

As it happens you can use ImageJ or Photoshop to check the linear proportions of those elements with their respective measurement tools, and here is where something fishy happens, as the ilium in the reconstruction from the paper is much too small relative to the vertebrae from the same specimen. In fact it needs to be increased about 27% (e.g. x 1.27) to match the published length. And it's not just the ilium that is wrong; the rest of the pelvis and the entire hindlimb is off, and they are off by about the same amount, suggesting it's the reconstruction and not the measurements that are in error.

I've "corrected" the size of the pelvis and hind limb so that they match their published size relative to the dorsal vertebrae, and it makes a pretty big difference. Not only do the hindlimbs look more in line with other theropods, but the deeper pelvis would also impact the center of gravity calculations (by shifting them back). I haven't had a chance to look at the scaling of the cervical or caudal series in depth, but assuming that Table S2 is correct then the appendicular skeletal proportions published in the paper cannot be right. At the very it least it calls into question the idea that Spinosaurus was an obligate quadruped on land.