Revealing mistake: When the two dinosaurs are fighting besides the cliff, Malone and Jennifer Holmes hide behind a rock overlooking the cliff. One of the dinosaurs sweeps its tail, and knocks the two lovebirds over the cliff, but they fall onto a rock jutting out from the cliff. After we see them fall, there is a wide shot of the dinosaur swinging its tail. He swings it one way, then the other. After he swings it the first way, the tail freezes in mid-air for a split second, then swings the other way. It's obviously the same shot of the first tail swing, but played in reverse with a pause in between.
Revealing mistake: Whenever the dinosaurs are seen walking on dirt or sand, if you look closely, you can see individual grains of sand and small clumps of dirt. This would not be possible, unless the "dinosaur" was a foot and a half long at the most.
Trivia: In the movie, the native Indians were the bad guys, but in the book, they were the good guys. They were fighting the ape-like species living there, and were helped by the group from England. They however did try to keep the group from leaving the plateau, wanting them to stay.
Challenger: Ah, Professor George H. Challenger and his lost world! Have you got your camera, Malone? I think a photo is in order.
Malone: You're quite right, Professor.
[Snaps a picture of Jennifer Holmes.]