Cavegirl (1985)

Storyline

On a class excursion to a cave with stone age paintings the clumsy Rex gets lost. A mysterious crystal opens a gateway in time and sets him back to the stone ages, where he meets a group of prehistoric fellows and the gorgeous Eba. While teaching her English and doing some pseudo-research on her fellows, his main goal is to get her sleeping with him. However the curiosity of the clan chief disturbs his attempts.

"Rex is taking his first big trip...back 25,000 years!"