The creature in the lagoon is indeed a Mosasaur (albeit stupid large) and not a dinosaur (marine reptiles and pterosaurs were not dinosaurs by definition). I thought it looked great up until RAPTOR ASSAULT COMBAT TEAM GO GO! I will see it anyhow as I am a huge paleontology nerd. Considering some of the original scripts had like laser beam military trained dinosaurs as the bad guy, I will take their snake/raptor/trex/cuttlefish hybrid that the design docs said they are going for. I just hope they don't try to do the same thing like they did with the Spinosaurus and have it fight and kill a Rex just to show how badass it is.
That fight was retarded, and if it happened like it did in the movie, the Rex won that fight in the first five seconds. T-Rex teeth are serrated and if it got its jaws around the relatively thin Spinosaurus neck, it wasn't coming back off without ripping out its throat at the least. Also, the entire strength of a Rex is its head musculature (obviously). The Rex would have crushed the backbone and/or windpipe of the Spinosaurus and that shit was done. Otoh, Spinosaurus teeth were not serrated to hold onto the T-Rex's neck, and it has no where near the strength in its jaws to snap the neck of such a heavily muscled creature like a T-Rex. Spinosaurus was not built to be an alpha predator in the sense it was depicted, it was an extremely large specialist dinosaur that while physically large than a Rex, was no where near as heavily built. /dinosaurnerdrantoff
Also, as I have been following this story for a while, the premise here, is it is 20 years later (which it pretty much is in real life since JP1), the park was eventually reclaimed/rebuilt. They have released a photo of a statue dedicating the new park to John Hammond (dead in both real life and the movie). Chris Pine trained raptors, which is a fairly feasible concept due to their intelligence, however they are still obviously using Utahraptor sized dinosaurs, and calling them Velociraptors (and not giving them any feathers....). Calling it 6 months early, they lure the super dino near the lagoon, the Mosasaur kills it, movie ends.
Edits cause I loveJurassicPark: The third movie was Isla Sorna not Isla Nublar which is JP 1 and JP 4, thus no Spinosaurus anywhere. While they did deviate heavily in Lost World from the book (events from book 1 made it to movie 2 for some reason), they could pull the scene from the end of the first book where they firebomb the island to kill all the escaped dinosaurs to try and reclaim it, then use that as a premise for rebuilding the park. I believe foreign investment is supposed to be the reason they rebuilt it, cause corporate profits >>> people's lives yo.
Also from wikipedia:
In an interview with Empire, Trevorrow confirmed that the production had hired Legacy Effects (formerly Stan Winston Studios) to create animatronic dinosaurs for the film, as they had in the previous three films.[127] Visual effects supervisor Phil Tippett and Industrial Light and Magic are also set to return
