I've rewatched "Supercroc" (expect major edits to some of those dinosaur pages soon, as there are many facts missing) and i realised the REAL reason Parasaurolophus wasn't taken back to the park.
Nigel had just arrived in Cretaceous Texas (despite it being more akin to Alberta) and then he sees two Lambeosaurids. Parasaurolophus. They were running, but now seen calmer. Curiously, they inspect Nigel's Jeep, when Nigel shouts out "Oi! Don't nibble my rope". Like Goats, curious Parasaurs will eat rope.
Why is this so big? Because a fair few fences at Prehistoric park are wooden, with rope holding them up. If the Parasaurs were to nibble at the rope in the park, it could cause the fence to be unstable, and the Parasaurs can roam free. Not that they'll do much damage anyway...
Knowing that the facilities are not yet fit for the Parasaurolophus, Nigel didn't save any on his trip, and would come back when the time is right.
I'm looking into this too much, aren't I? Created a theory out of one sentence. There's more to this theory, that explains the Nyctosaurs in the opening scenes. I'll explain more another time.