Spinosaurus was a genus of megalosauroid theropod dinosaur that lived during the Middle Cretaceous in what is now North Africa. Based on its snout and tooth morphology alike, we can infer than spinosaurus, like all spinosaurids in general, was primarily piscivorous by nature. Its snout was very thin and specialized, perfect for quickly snatching up fish in water with minimal water resistance (drag). That being said, its snout was actually very robust, as it was very dense (it lacked the impressively-sized fenestrae present in animals with considerably lighter-built rostra, such as carcharodontosaurus, which is evident below. Compared to allosauroids, which killed vertically and possessed exceptionally deep rostra, spinosaurus killed by gripping, which means that its snout as a whole would have to be imperatively strong, as it lacked in any exceptional depth or width), and its post-premaxillary rostrum in general was very heavily-buit and was much more generalized opposed to the very specialized tip which was clearly too gracile in build to be used in macro-predation and was instead designed to hook fish.
Regardless of width, we can safely acknowledge that spinosaurus was at least characterized by jaws that would have faired much better for gripping and resisting lateral forces than carcharodontosaurus (as carcharodontosaurus had a much deeper rostrum relative to width, telling us that it was certainly not very resistant to these kinds of forces) and modern piscivorous crocodilians. A study has even been published regarding multidirectional loads on the skulls of 5 different animals: Spinosaurus Aegyptiacus, Baryonyx Walkerii, American alligator, Indian gharial, and African slender-snouted crocodile. Surprisingly, spinosaurus actually did worse than all of these animals in lateral resistance. Although the main issues with this is that they supposedly used a reasonably more gracile spinosaurus specimen (the largest spinosaurus specimens have very robust rostra in general and were clearly more generalized. Specimens like this include MSNM and MNHM), and they only put the premaxilla area into account for spinosaurus (that area was considerably more gracile than the rest of its rostrum, specifically the area posterior to that, which was a good deal more broadened). Compared to the slender-snouted crocodile and similar piscivorous species, spinosaurus had a much more heavily-constructed central and rear-most rostrum, which means that this area was fundamentally more robust in general and would have been a good deal more resistant than the more specialized region proceeding it.
Spinosaurus clearly had a very powerfully-built post-premaxilla rostrum and mandible alike. Its rostrum, despite lacking in both exceptional width and depth, was still very robustly-built and very dense, making resistance a smaller issue here than many claim. The tests did not account for the region posterior to the specialized premaxilla area of the spinosaurus' rostrum, which means that the full potential of the rostrum's ability to withstand lateral stress was never reached. The majority of spinosaurus' rostrum was very heavily-built and strong, despite being thin in multiple directions. In the event that spinosaurus would be hunting a large terrestrial animal, the more generalized region posterior to its specialized cleft region would most likely be used to bite down, as that area would have the least chance of breaking and the total biting force would be a good deal higher. Spinosaurus would most likely not use its specialized foremost region of its snout in macro-predation, as that area was designed for specialized piscivory.