7. Majungasaurus
Majungasaurs were about 20 feet long, which places them as a predator whose size is in the middle between T-Rex and Velociraptor. Jurassic Park hasn't yet really bothered with these mid-level predators, so the introduction of one here would be a bit of a change in pace. It's an animal that's still significantly bigger than a human and would have no trouble attacking one, without being such a giant monster as the Tyrannosaur. This Madagascan carnivore seems to have fed largely on the enormous sauropods, the biggest of all dinosaurs, so it would make a good scene to see one try and bring down a much bigger animal. When it comes to what makes a creepy monster, however, the real appeal of Majungasaurus is that it is one of the very few dinosaurs known to have been a cannibal. Very little is likely to creep an audience out more about an animal than the sight of it happily devouring its own kind. Perhaps this could be incorporated as one the early problems that the scientists putting together the park had failed to foresee: when Majungasaurs were put in their own enclosure away from other dinosaurs, they preferred to eat each other than the sheep and cattle the park apparently feed the dinosaurs.