There is no real evidence that shows T-rex being semi-aquatic... although it is possible it is unlikely. It could be very dangerous for it. It might have gone though water if needed.(many non-aquatic animals cross through rivers etc..) As I said before dinosaurs most likely evolved from crocodilians so it could be a left over. Theropods had nostrils in that area from before Coelophysis down.
Spinosaurus (avatar), Baryonyx ,Suchomimus, and others on the other are all thought to have been semi-aquatic.
Spinosaurus
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