The astronauts are forced to take up with primitive (and dumb) cave dwellers played by the great Joe E. Ross as Gronk - with another comedy legend, Imogene Coca (Your Show of Shows) seen as his nagging wife Shadd.
Mid-season the premise was flipped as the cave people and astronauts returned in the space craft to 1967. The focus of the show shifted to stars Coca and Ross as they reacted to the unfamiliar surroundings, setting up home in 20th-century New York City.
Watch the original promo. Watch for the stop-motion dinos.
Thanks to TV Party for this info!