Why no fences in TLW?

Isla Sorna is VERY large... Twice the Size of Nublar, If not more. We only see Two Quarters of Sorna within the two movies... And that's not even a good guess. 

Sorna was a reasearch/breeding station, Designed to breed Dinosaurs for the park at a large level. Originally, They held most of the Dinosaurs within large paddocks on the Island (This evidence being the Cages in the Center in JP3). For monitoring purposes.

But closer to the events of 1993 on Nublar; In efforts to Breed them faster and not have to take care of them for long periods, They began Tagging and releasing into the wild while they were still juvenile. This seemed to work, As the island was still in operation some time after Jurassic Park fell.

It's assumed that That was somewhere inbetween TLW and JP, When ingen had to Liquidate some assests. Theres also a chance that they evacuated when the storm hit in '93, leaving it perhaps with a few staff or none at all. The reason I say a Few, Is because of the Bodies left behind. 

After the Island was evacuated, It's assumed many of the Assest escaped their enclosures/paddocks. A team of Special Operations from the US was sent to control this problem, But they were all killed off, Wether by dinosaurs, Or eachother. 

Which brings us to TLW. most of the movie takes place on one side of the island, Where JP3 Takes place on the other side. 

Now, to your Dinosaur question. 

The spino, Might've been a whole lot more Younger during TLW, It most likely tried to hide or such to avoid predators. Theres also a Chance it was one of the eggs left/layed prior to Evacuation. The real truth is, The writers thought it'd be a Fantastic Idea, something to draw in crowds. As it's said in the new trailer "Corperate noticed that whenever we introduced a new Dinosaur, Park attendance grew," They're applying that but to theaters. (Of course, they did that exactly again with I-rex, But we'll ignore that unitl the movie premieres.)

Again, Two different sides of the islands, That's why there's so many different things. Plus, The islands are based off of Hawaii and Costa Rica, So, with that in mind; There was no grasslands (Most likely, Unless it's in the 1/3 we haven't seen yet), There was mostly just large Clearings.

Hope I helped you out some,

-Paden

X_PADEN_X Thansks for explaining that for me. One thing that doesn't make sense, is in the edition of TLW book that I have, there is a map which shows Isla Sorna to be a lot smaller than the film version.

@JurassicWorld

Keep in mind the films are "Based on the book(s) by Micheal Crichton" So they don't have to be exact. 

In "MC The lost world" I feel like the Greatest problem with it, Was the Size of the island. MC most likely had a concern with this too, As he is the one who helped to write TLW and JP (movies) and decided on going on a larger island. 

I think the map in the book, was just to help visualize what it looked like... Everythings WAAAAY to close together and there in no way should be enough land to support all of the dinosaurs for that long. 

So, In short... The reason the two aren't the same, Is because a choice was made to make the island larger and more "Freedom" like. Writers choice, I suppose. 

However, Another reason is because the movies and the books, are two different Universes. Another notable universe in JP being: Jurassic Park The game. Which takes place in the Movie world, But has very crucial things hinting off to it also having aspects from the Books.