The data that will be used for the sake of this comparison is found in this study :
https://onlinelibrary.wiley.com/doi/10.1002/jmor.20382
Without further ado, let's get into it!
-Thoracic height/thoracolumbar region length :
Edge: Buffalo (3.86% VS 3.63%)
-Thoracic height/body mass:
Edge: Bison (0.07676 VS 0.06737)
-Thoracic width/thoracolumbar region length:
Edge: Buffalo (3.91% VS 3.57%)
-Thoracic width/body mass :
Edge: Bison (0.0754 VS 0.0681)
-Thoracic area/thoracolumbar length:
Edge: Buffalo (1.34 VS 1.27)
-Thoracic area/body mass:
Edge: Bison (2.69 VS 2.34)
-Thoracic region length/thoracolumbar length :
Edge : Bison (68.8% VS 61.8%)
Overall Edge in Thoracic Robusticity : Buffalo!
-Lumbar height/thoracolumbar length :
Edge: Buffalo (3.86% VS 3.46%)
-Lumbar height/body mass :
Edge: Bison (0.0732 VS 0.0673)
-lumbar width/thoracolumbar length :
Edge: Buffalo (4.61% VS 4.24%)
-lumbar width/body mass :
Edge: Bison (0.0896 VS 0.08)
-lumbar area/thoracolumbar length :
Edge: Buffalo (1.60 VS 1.46)
-lumbar area/body mass :
Edge: Bison (3.083 VS 2.785)
-Lumbar region length/thoracolumbosacral length :
Edge : Bison (26% VS 31.2%) because lower score is better in this case.
NOTE: Another study also mentions that Bison have proportionally wider, more ventro-cranially and less cranially oriented lumbar processes with larger endplates and more anteriorly positioned spinous processes due to having more negative PC1 and PC2 scores. These features would play a role in strengthening the Bison's back. The Buffalo's positive PC1 and PC2 scores would grant it taller neural spines which is an advantage but also more cranially oriented processes :
https://academic.oup.com/biolinnean/article/116/3/721/2440504
Overall Edge in Lumbar Robusticity : Bison!