
Continuity mistake: When Dieter Stark is about to taze the dinosaur, the guy with the long beard approaches him, telling him what it is. As the bearded man says "They're presumed to be scavengers, like jackals", Stark's taser is closed mostly inwards. In the next shot, the taser is suddenly extended, opened out.
Answer: It's basically about facing one's own mortality. Many humans feel that they 'feel the most alive' when facing (and overcoming) dangerous situations, the more challenging, the better. Roland is a big game hunter, to him, the ultimate challenge would be to hunt the biggest and (presumably) most dangerous predator ever to exist. Facing the danger of the T. Rex would make him feel better and mightier than he had ever felt in his life.
Twotall