Gillicus

Gillicus was a medium sized fish from the late cretaceous, it was probably a food source for large predators like Tylosaurus,Xiphactinus or Sharks. Gillicus fed on smaller fish or algae. there is a famous fossil of Gillicus after it was eaten by a Xiphactinus. The Gillicus was eaten whole which caused the Xiphactinus' death. If you look at the fossil you can see the Gillicus' skeleton inside the Xiphactinus. Gillicus doesn't appear in the movies or novels but it can be created in Jurassic Park: Builder.