Richard Boone (I BURY THE LIVING) is Masten Thrust, the world's richest man who is also a notorious big game hunter. When one of his exploratory oil digging machines uncovers a lost, prehistoric world in the Arctic, where a T-Rex is spotted, he is the first to head a return trip. With him are a female photographer (Joan Van Ark), a geologist, a Japanese scientist, and Masten's African tracker, Bunta.
They encounter a few prehistoric beasts and their camp is trashed by the T-Rex, who also eats one of them. Their means of transportation is also gone and they think that the dinosaur sunk it. They later find out that it carried it back to its den, a canyon littered with the bones of its kill. Not only do they have to deal with the T-Rex trying to eat them, they also have to contend with a tribe of Australopithecines who compete with them for food. One of them, though, a female, tags along with them and soon becomes one of their troupe.
The only survivors end up being the photographer, the geologist and Masten. When they find their machine and get it running to go back to the modern world Masten chooses to stay behind, to hunt the T-Rex, for he truly belongs in a more primitive world.
Sure, the dinosaur effects are along the lines of a Japanese Kaiju movie, with a guy in a T-Rex suit, but the premise and story are cool and it was one of my favorite movies when I was a kid.