Jurassic Park- Special Effects

One of the greatest aspects of this whole film is the use of an animatronic Tyrannosaurus Rex. Animatronics is the use of mechatronics to make animals less robotic. In order to make the T-Rex so life like the Stan Winston Studio (well-known for their use of animatronics) went to work making sculptures of a full size and miniature sized T-Rex. This is the point where the creators could decide how realistic the dinosaur actually looked. Stan Winston said that you must have to animatronic as real as possible. That is the most important. If people didn't believe the reality of the dinosaur then even with the best acting the dinosaur wouldn't be real at all. When they finished with making the sculptures look as real as possible they mode molds from them and made skins to place over the robotic skeletal structure of the T-Rex. 
Something else that was really amazing about this scene was the fact that they used small 3-D sculptures or animatics for template that the director Steven Spielberg could use. It's a stop motion type thing that allowed for them to understand the naturalistic movements of the dinosaur and to make them look more like animals rather than a scary monster. 
When they shot this scene they did it on a sound stage in California so that they could control the animatronics of the dinosaur. They also wanted to make sure that the interactions with the breaking of the fence and the tearing of the car was as real as possible. The special effects team went over how the fence would rip if a dinosaur had actually bit down on it. 
Fun Fact
The full-sized animatron of the T-Rex weighed about 9,000 pounds and was 40 feet long. During the shooting of the initial T-Rex attack scene in the downpour, the latex that covered the T-Rex puppet absorbed great amounts of water, making it much heavier and harder to control. Technicians worked throughout the night with blow driers trying to dry the latex out. Eventually, they suspended a platform above the T-Rex, out of camera range, to keep the water off the dinosaur during filming.