Hey Elizabeth, I agree with you. Spinosaurus did not have to be the fastest or the most streamlined predator to thrive in aquatic environments.

The river systems of the Late Cretaceous Kem Kem beds supported coelacanths the size of a car as well as many other giant fish. Dr. Nizar Ibrahim claimed that Spinosaurus only needed to be faster than its prey. The same goes with T.rex which is not a particularly fast animal. Still, it is fast enough to chase down a Triceratops or an Ankylosaurus, its presumed prey.