spinosaurs are definaltey the longest predator on eatrh, bu the LARGEST goes to t rex. is't more massive and heavily built than spinos. 12 tons is totally unrealistic. the most recent evudence suggest something more like 6-7 tons.
we know therapods walked horizontally because of the placement and architecture of the hip socket. if they walked "belly out", like we do, the hips would face moer out to the side and forward than they do and the knees would bend the other diection, towards the body. also the tails and vertibrae sections do not alight to support the estimated weights of most therapods, even the new, more conservative ones.