I know, I know. There are many theories for this. But it's very unclear what happened to Isla Sorna. The Spinosaurus, the Raptors, and the other dinosaurs.
My theory is it's gonna have to do something with Dominion, but idk.
Aktually, the juvenile Spinosaurus killed everything on the island with ease and Masrani couldn't find a way to put it down so he covered it up. Now the adult Spino is the only thing on Sorna.