People are mentioning Jurassic park as a prehistoric fastasy but I disagree, it's an adventure with prehistoric creatures on a modern period so it fits better as a sci-fi adventure (it doesn't need to be on space or laser blasters to be a sci-fi folks)

So in my opinion the Flintstones, Ice age and 10000 BC are good examples of prehistoric fantasy but Jurassic Park, Dinotopia and Encino man aren't.

I'm in doubt about movies where people arrive at a place that is a prehistoric biome thought, it fit both categories

!1UP