Jurassic Park broke new CGI ground. Spielberg wasn’t thrilled about the test shots of the dinosaurs- they just weren’t real enough. So Muren and his team showed Spielberg an early CGI dino test of a group of Gallimimus skeletons running through a field. He loved the ease of movement and realism of the effects, but he didn’t think it was good enough still. He pushed Muren to go further, and when they came back with a fully rendered T-rex walking across a field in the daytime, the director decided to go full CGI for certain shots.