The late 70s was a time for irreverent cartoons aimed at adults. After the success of his X-rated animated film Tarzoon: Shame of the Jungle, French cartoonist Picha created a follow up called The Missing Link. The original was in French, but an English dub was also created. The English version toned down the script in order to avoid the X rating. The soundtrack for the film was done by Leo Sayer, who I know best for his version of "When I Need You." If you're familiar with that song, the style here is fairly similar - that sort of light jazz sound.
The plot of the film is pretty loose, but primarily follows the adventures of O, suggested by the narrator to be the missing link between cavemen and humanity. This is not meant to be any where near historically accurate, as the cavemen live in the same time as the dinosaurs, as well as some made up species like the No-Lobes (bald identical men who speak in cliches) and unnamed female feline creatures who seem to be on the same intelligence level as the cavemen if not a little smarter.
There's also a dragon thrown in for good measure, and in the English version he is voiced by an uncredited Bill Murray.
The humor here, such as it is, depends on raunchiness and shock value. In the beginning, the cavemen, who are fully nude and have their little tiny penises exposed at all times, don't know how to make love to the cavewomen, who all have ginormous breasts, until they view a stegosaurus mount another stegosaurus. The stegosaurus union also results in the male getting cut in half as he humps the female, because her plates are just that sharp, I guess. While the film does get away from this for a while when O goes out on his own, it doesn't really get any funnier.
O wanders the world, first with his brontosaurus dog-like companion Igua, then with a talking pterodactyl named Croak who wants to teach him things and show him the world. O, Croak, the no-lobes, and the dragon are pretty much the only characters who talk - all the other creatures are silent or speak in gibberish. There is a narrator trying to hold it all together, but more often than not this just becomes a bunch of barely connected scenes that are only vaguely interesting.
The dragon is thoroughly ridiculous, and even Murray can't really save it. Apparently, dragons actually shoot fire out of their ass. When O sticks a cork up the dragon's butt, he's able to breathe fire after a bit of indigestion. He also curses a lot, calling O an asshole with just about every sentence he speaks. He eventually gets propelled away from him when the fire shoots from his mouth and he flies off like a rocket.
The point of O's various misadventures is for him to learn about fire, the wheel, clothing, and other such early caveman knowledge. He returns to the other cavemen and teaches them this, becoming their ruler. But it isn't long before they overthrow him, and use the things he taught them to become the most powerful creatures on earth. The dinosaurs commit mass suicide, the once large rats shrink in fear of them, etc. So see, the film wasn't just all shock value, it was about how evil man is and how he's ruining everything. Yeah, sure.
In 1984, another version of the film was released, this time titled B.C. Rock. The footage was re-cut and the audio redone, replacing a few of Leo Sayer's songs with ones by popular musicians of the time including Hall & Oates and Genesis.The narrator was also replaced, this time being O telling us his story, though O is renamed to Stewie Babcock. More of the characters are able to talk, but most of the time they either state the obvious or make some weak jokes. The rock music does help to make some of the previously silent scenes more interesting, but none of the songs really stand out as something strong I'd listen to on their own. The dragon scene is identical, as they clearly just used Murray's previous recording and combined it with the new lead responding to him.
In the end, I can't recommend either version of this movie. The music is uninteresting, the animation is below average, the humor isn't funny, and the story is weak. While it seems to have a small cult following, overall this movie has disappeared into obscurity for a reason.