Jurassic Park fell on a particular interesting time where animatronics, stop motion, and CGI were starting to shift of on who got the spotlight. The film originally called for the T-Rex to be a completely animatronic creature with some stop motion bits mixed in. Of course, if you follow movies you know that this became an iconic use of full CGI creatures, groudbreaking in the fidelity they achieved.
There are obviously still scenes where the animatronic is present, which means there had to be some fun times on the set playing with it!
