Accidentally Correct Writing: The Spinosaurus swimming in the river scenes (and also at the sea, if you accept the implicationsnote Listen carefully when the boat disappears on the mist, you can hear the same growl heard just before the river attack that it was him the one who attacked the boat at the beginning), when it was discovered that it was an aquatic creature. Not to mention it being bigger than Tyrannosaurus.
Refitted for Sequel: Many scenes in the film are from the books: The river chase and aviary from the first and the cloning lab from The Lost World. It's been joked that III exists mainly to use up all the bits from the books they couldn't fit into the first two movies.
The incorrectness of the Jurassic Park dinosaurs is Handwaved and Justified by Grant in that these dinosaurs are mutants, not real dinosaurs (thanks to having their DNA spliced by frog DNA.) One of the changes includes putting some feathers on the head of the raptors.
Around the time this film was made, it was not yet known that pterosaurs didn't rear their young like birds.
In 2014, a more complete skeleton of Spinosauruswas found, which showed that while still a big carnivore, in fact the movie incarnation might be shorter lengthwise and lighter in weight than the actual creature, the Spinosaurus had an even more bizarre shape and was suggested to have been quadrupedalnote or at least semi-quadrupedal, since the forelimbs seem to lack the adaptations for a fully quadrupedal movement, and some have suggested that even with the super-short hind limbs, Spinosaurus would have still been capable of bipedalmovement. More data is needed to clarify this situation. and adapted for an aquatic lifestyle, as its hind legs were unconventionally short and possessed webbed feet, much like a duck or a pelican. This new reconstruction has not gone withoutcriticism, although the researchers have also responded to the detractors.
A Baryonyx◊ had Spinosaurus' role in the original script. This was referenced in-movie. Billy guesses the dinosaur that attacked the plane is a Baryonyx, but Grant corrects him, saying Baryonyx didn't have that impressive sail on the back.
The ending was changed a lot; in the original script, the Spinosaurus was attacked by raptors and killed at the end; this was probably changed because in the first movie, the raptors were no match for the T. rex, and having them bring down an even bigger carnivore that actually killed a T. rex earlier in the film wouldn't seem realistic. note To be fair, the T. rex only fought one raptor, having killed the second one by surprise. Also, the helicopter was to be attacked by Pteranodons. And they also considered having the Spinosaurus attack the marines.
One of the first scripts was about a group of teens stranded in the island and being eaten one by one. It was described as Friends with dinosaurs... and quickly dropped.
The infamous T-Rex vs Spinosaurus fight was originally much longer and more even, but the Spinosaurus animatronic was a newer model and far more powerful than the T-Rex one, which was a repurposed one from the previous film. They underestimated exactly how powerful the machine was and during the fight a swipe from it decapitated the T-Rex animatronic in a single swipe, damaging it beyond repair. As a result, the battle had to be cut severely shorter than intended.