Revealing mistake: In the beginning of the movie where Billy and his female palaeontologist co-worker are working on a Raptor fossil you see him lean on the ground to brush some dirt away. As he leans on the supposedly hard rock you see it give a little, like it was Plaster-of-Paris on top of plywood.
Revealing mistake: In the final showdown with the Spinosaurus in the river it is night time. When the characters get plunged into the river and they have the underwater shots, there is so much light it must be daytime.
Revealing mistake: In the scene where the Spinosaurus is attacking the plane (specifically, the part where it's rolling the plane along the ground), there's a shot in which the plane rolls over the camera, and we see Grant through the window, screaming. At the very end of that shot, the plane rolls completely over and past the camera, and we can see the rest of the clearing behind it...and the Spinosaurus is nowhere to be seen.