Not initially convinced it would work, the director had them do a test and was blown away by what they made, which featured a Tyrannosaurus Rex walking across a still nature image, and then chasing a herd of Gallimimus.
That all changed, however, when Spielberg was asked by artists at Industrial Light And Magic about the possibility of using CGI for the work.
Phil Tippett, who had been hired to do the go motion, quipped that he was about to become extinct, and Spielberg ended up giving that line to Ian Malcolm when Alan Grant talks about living dinosaurs ending paleontology as a study.
When Steven Spielberg started working on Jurassic Park, his plan for photography of full-scale dinosaurs in long shots was to use go motion animation – building on the techniques used in films like the original King Kong (which was a huge inspiration for the director in the making of the movie).