Hi,
you should use the "glTF" file which is also provided via the download link on sketchfab.
Much more modern file format, which also can be imported and exported from Blender.
I found that it works in 2.81 and 2.91.
Even though the scaling of the bones is off very much (way too big) the orientation and
animation of the "Nile-Crocodile" is imported correctly.
I simply hid the bone structure in the viewport for my test but, I am sure you could downsize the system somehow.
Not a Blender user here so I did not try to find out how.
On the other hand the fbx file loaded into Softimage XSI 2015 flawlessly...nice
Size, orientation and animation working right out of the box in there.
Hope that helps.
CHeers, Klaus