>>16715336
>>16715362

I'm not married to any one hypothesis since it's an extinct animal and I'm not sure how many bones we have of the creature yet, but: I think I lean more towards Hypothesis B, assuming it does indeed have stubby legs.
In that I would perhaps compare the Spinosaurus to a Cormorant: stubby legs, diving, they even share the same hooked snout. The tail is also far too 'flippy' for it to be a mostly land creature.