About eleven minutes into the movie, Professor Challenger is addressing the Royal Zoological Society and is approaching the speakers table from the back of the room. Looking over his shoulder you can see the ceiling on the underside of the balcony at the back of the room. There are modern (1980's to 1990's) fluorescent lighting fixtures on that ceiling, even though the movie is set in 1912.
The Plateau in the film has been described as a world that is "cut off from evolutionary development." If that were true then dinosaurs from different eras would not be in the same place, nor would there be any ape-men or humanoids.
It should be pointed out however that some of the goofs (the mixture of creatures from different eras, the professor turning up at exactly 12.00 in the amazon) are taken direct from the original novel.
Challenger gives Summerlee a note with "directions" on it to The Lost World. He then shows up at 12:00 when the expedition is supposed to start. How would Challenger guarantee himself that he would show up exactly at that time? Plus, if he did it would mean that he would have to be on the same boat, which he wasn't. He couldn't have been on a different boat and left at the same time for the same place either. That is a waste of resources and a transportation company would not do it.