Enlarged Reptiles, actually quite effective!
I actually thought the use of photographically enlarged footage of reptiles was very effective in this film. Some have suggested that stop motion effects may have been a better choice. I do wish they had done without the man in the dinosaur suit, and the pig in the triceratops suit. For these sequences, stop-motion would have been preferable. You can tell the filmmakers were uncomfortable with the quality of these effects, since the costume shots are brief and obscure. But I'd rather they'd dispensed with dinosaurs altogether and just gone with the enlarged alligators, lizards and armadillo.
Not only did I find these effects more convincing, they are also more accurate. Whereas humans never coexisted with dinosaurs, anatomically modern humans certainly walked the planet at the same time as giant reptiles. Anatomically modern humans may have encountered giant lizards as late as 40 to 30,000 BC, making the use of giant reptiles quite a bit more convincing than the dinosaurs of One Million Years BC (1966) and When Dinosaurs Ruled the Earth (1970).
I doubt that PETA would agree, but I give the use of real, live reptiles in this film two thumbs up!