How did aquatic dinosaurs go extinct?
Spinosaurs (like Spinosaurus) are currently only known from 112-97 million years ago, although isolated teeth push the origin possibly back to ~150 Mya. At least now, there isn't any definite spinosaur material younger than 97 Mya.

So spinosaurs were already extinct when the rest of the non-bird dinosaurs went extinct at the end of the Cretaceous, whether by meteor impact, volcanism, a combination, or something else completely.