The Story (contains spoilers if you care about such things)
We're not really looking at plots here, as we are only interested in cavegirls in bikinis, and this film isn't exactly The Maltese Falcon but some idea may be helpful.
A portentous narration (the only English in the film) describes the origins of the world against lots of pictures of smoke, flame and stock footage of molten lava while Mario Nascimbene's music thunders on in full Soloman and Sheba mode.
Fade through smoke to a red dawn and a parched landscape (filmed on location in the Canary Islands and adding a sheen of quality to the whole production) where grubby, unkempt dark-haired prehistoric men from the Rock People trap a warthog (which does look appropriately prehistoric) in a pit. Our hero Tumak (John Richardson, later to make lots of bad Italian films) heroically kills the creature in the pit winning the favour of his father, tribal leader Akhoba (Robert Brown, later to play "M" in four James Bond films) and the hatred of his brother, Sakana (Percy Herbert-who also apprered in a James Bond film but as "first piper" in the original Casino Royale).
That night they all return to their very spacious, artistically-lit, split-level cave and meet up with the women folk. Here we see our first cavegirl in fur bikini, Nupondi, (Martine Beswick-who was John Richardson's wife for some years). Fortunately, it is raining so not only is she in a fur bikini but she is wet as well allowing us to enjoy her glistening cleavage. Sakana pushes her around a bit in a very caveman-like way but is not nearly as unpleasant as his father who gets very annoyed when others in the tribe try to grab their bits of roast warthog first. The whole tribe generally has dreadful table manners and shows us how primitive they all are. Eventually Tumak tries to grab some of his father's dinner. Father really loses it and they fight with big sticks until, forced up some rock steps, Tumak finds himself at a cliff edge, tries to hit his father with a rock and tumbles over the edge, fortunately bouncing on some trees on the way down. The lovely Nupondi looks distraught and tries to peer over the cliff but is manhandled away by Sakana.
Tumak wakes up the next day, looks back up at his former home with some annoyance and then treks away over the stark but beautiful Lanzerote landscape. He walks past a dinosaur skeleton so it is something of a disappointment to find him facing a photographically enlarged Iguana which makes horrible roaring noises and chases him (very slowly) around the landscape. In an interview included on the DVD Ray Harryhausen explains that the thinking behind using a real lizard for this first encounter was that when the stop motion dinosaurs appear people would find them more believable. Sadly, the opposite is true and the dynamation dinos look much better than the iguana. It was actually the original version of this film, One Million BC (1940), that first had the idea of sticking spikes and frills on lizards and using them for dinosaurs. There was such an uproar over the way the lizards were treated that it led to the formation of the American Humane Association which monitors the welfare of animals in films. Again, the original footage from the 1940 film turned up in many other films over the next three decades.
Grabbed by the "dinosaur's" tongue Tumak excapes by chopping the end of the tongue off and fleeing into another convenient cave which he soon runs from at the sight of a much more primitive ape-man. He resumes his trek across the increasingly sulphurous landscape.
Back in the Rock Tribe's cave Nupondi gets into more trouble with Sakana for mooning over a warthog tusk given to her by Tumak. But the father stares him down.
Meanwhile Tumak has a scary encounter with the "moving mountain" that is our first Harryhausen dinosaur and a nasty looking giant tarantula. He flees and gradually gets exhausted staggering across the desert landscape in the heat. Suddenly he reaches the seashore..
We now cut to our first sight of a bevy (well eight) of fur clad lovelies from the Shell tribe running through the surf with their spears on a fishing expedition. Teasingly, Loana, (Raquel Welch) does not appear in this very first shot. Instead we see her artistically squatting down on some rocks by the seashore.
If this film were made today there would be lots of intercut close ups of flexing tanned muscles, smooth tummies and plunging cleavage (not to mention having them run in slow motion through the surf) but here there is actually hardly any of this sort of thing and the female characters are presented in a rather straightforward way
The girls run out of the sea and Loana spots a Tumak up on the cliff and rushes up to him only to be chased away by a giant turtle.
She calls for help on her horn and the men of the shell people rush in from their studio bound village.
Loana drags the unconscious Tumak away from the turtle and the men and women of the village drive it into the sea. Loana's rather foxy number 2, tries to look after Tumak as well but Raquel soon shoos her off.
They return to their cave, which is obviously superior to the other two we have seen on account of the cave paintings, taking Tumak with them.
Meanwhile Akhoba, Sakana and the Rock tribe are hunting. Sakana helps Akhoba fall off a cliff and takes over leadership of the tribe.
Tumak wakes up in the Shell People's cave, eyes up Loana doing a bit of sewing and eats his dinner from a turtle shell. He makes a terrible mess and looks downright primitive compared with the blonde haired Shell People.