Sorry to bump this old topic but there seems to be a huge exaggeration of the size and power of the spinosaurus.
From what I've seen, the spinosaurus's bite force was somewhere between 1000-2000 psi, which isn't weak, but it absolutely PALES in comparison to the 9-10 tons psi that the T-Rex is capable of. Also, compare the teeth, the t-rex has solid banana sized teeth, whereas the spino has smaller, conical teeth (which were also hollow).
Spinosaurus was built to catch fish, that's why it had a long, narrow snout. It wasn't a fearsome predator like many believe, there is fossil evidence of a Carcharodontosaurus feeding on a spinosaurus. Now keep in mind, the cacharodontosaurus was slightly larger than a t-rex, but not nearly as strong and powerful. The t-rex is thought to have the most brute strength of any carnivore that has ever walked the earth, despite not being the largest. In one video I watched somewhere on youtube, it was shown that a T-rex could have potentially lifted a car off the ground with it's mouth. The reason for this is the size of T-Rex's leg muscles, which were probably the largest leg muscles of any animal that has ever lived.
As for the spino's arms, they were relatively weak (actually weaker than a T-rex's, which were actually pretty strong), and were too low on it's body to be used it a fight (it would fracture them if it actually tried to use them in combat).
Let's also not forget the tyrannosaurus's septic bite. One bite means death unless the spino has a ridiculously efficient immune system.
Also, the t-rex had a much more predator-like mentality. It had too because it had to bring down large animals to eat (it wasn't built to catch fish). Spino was larger than t-rex, but it wasn't built to hunt prey larger than itself, it would have likely ran away if challenged by a t-rex (which of course, never actually happened considering they lived on different continents at different times).
I'm done ranting. Sorry, lol.