What a difference a few years makes (eg., this is a follow-up to an earlier post of mine).
Both the US and the original Czech versions are out there for sale these days (try ebay - and go for the DVD! The Czech version, at least, is cut from a wonderful print).
How the distributors of the US version ever came up with four boys falling asleep in the American Museum of Natural History and transgressing time via an Indian shaman statue is beyond me, but it was a pretty ingenious way of putting a domestic mystical stamp on a foreign film.
The Czech version begins with the character known as "Doc" in the US version recounting his "journey" while reviewing his diary. Before long, the four boys are seen emerging from the cave (which was supposedly located in Central Park in the US version) into the realm of the Ice Age, after which, the film proceeds as the movie we all know with a few notable exceptions: occasional shots of "Doc's" diary written in Czech, and an ending very different from what American audiences have seen - a seashore sequence in which the boys find a living trilobite, and closing shot of the narrator summing up the movie before fading out. (How the boys got back from their 4.5 billion year trip will remain a mystery until I get someone to translate the Czech dialog!) There appears to be no pontificating over how the boys had reached "creation" - and no footage to accompany it (the US version has shots of spouting lava and twisting luminous geometric shapes suggesting not only the beginning of earth but of the universe itself).
Despite extensive credit given to the staff of the American Museum of Natural History in the US version (namely, Edwin Colbert, prominent paleontologist at the time), it's apparent that, after viewing the Czech version, the Museum's input was limited to the museum sequences. The original movie is all Karel Zamen's - along with whichever Czech(s) who served as his paleo-documentarian(s).
Still a mystery, however, is why (as I stated in an earlier post) North American fossil vertebrates feature prominently in the film. The Styracosaur, the Sabertooth cat and, most notably, the grotesque Uintatherium featured are all unique to the American West.
Perhaps Zamen was not as isolated from US influences as life behind the Iron Curtain would have us think.