This comes from the director of Jurassic Park III:

http://boxoffice.com/featured_storie...merica-jp4.php
Well, there is going to be a Jurassic Park IV. And it's going to be unlike anything you've seen. It breaks away from the first three—it's essentially the beginning of the second Jurassic Park trilogy. It's going to be done in a completely different way. That's pretty much all I can tell you.