Thunk (Clarke Duke), Gran (Cloris Leachman), Sandy (Randy Thom), Ugga (Catherine Keener), and Eep (Emma Stone) and Grug (Nicolas Cage) in “The Croods.” (DreamWorks Animation)

Think of “The Croods” as the back story of “The Flintstones,” before that modern Stone Age family got, well, modern.

Like Fred, Wilma and Pebbles, the heroes of this cute animated comedy are animal-pelt-wearing proto-humans. Unlike the protagonists of the old Hanna-Barbera cartoon, however, hunter-gatherers Grug Crood (voice of Nicolas Cage) and his wife, Ugga (Catherine Keener), don’t live in an amenity-filled house but in a dark, depressing cave. They’re raising their kids — Eep (Emma Stone), Thunk (Clark Duke) and Sandy (Randy Thom) — as best they can, considering there’s no Internet.

Rounding out the clan is Ugga’s elderly, unpleasant mother. Voiced by Cloris Leachman, the character contributes nothing to the evolution of the shrewish mother-in-law stereotype of sitcom fame.

This world is a scary place, filled with saber-toothed tigers and other dangerous beasties. That’s one nice thing about this film. Because of the prehistoric setting, the filmmakers were free to imagine all sorts of wondrous, extinct critters, of which there is no evidence in the fossil record.

A swarm of tiny red birds, for example, whose carnivorous appetites seem to place them as closer cousins to piranhas than to parakeets, figures prominently in the plot and is a visual treat. So is a colony of angry blue monkeys. At times, the film’s 3-D vision of the so-called “Croodaceous Era” resembles the fantastical, candy-colored jungle of “Avatar.” When the Croods, who have spent too much time in a cave, discover rain and stars for the first time, there’s a sense of discovery for us, too.

In other words, it’s a good-looking story.

Driving that story forward is the character of Eep, a restless teen who chafes at her father’s dictum, “Never not be afraid.” Sneaking out of the cave one night, Eep encounters Guy (Ryan Reynolds), a more advanced, Homo-sapiens-like adolescent who has already discovered such conveniences as fire, shoes, pants and a belt.

Actually, that’s Belt, a sloth-like pet whose long, lithe arms Guy uses to keep his pants from falling down.

Guy has discovered something else, too: The world as Eep knows it is coming to an end, thanks to shifting continental land masses. That leads the sloping-foreheaded Grug and his family of knuckle-draggers — for whom brawn has always compensated for their distinct lack of brains — to throw in their lot with the more fearless Guy, after an earthquake destroys their home.

Off they all go, in search of the Dawn of Man.

“The Croods” is light fare, but it explores a serious theme, if only superficially. That’s the importance of cooperation — and the evolutionary advantage of altruism — in the formation of human society.

Will that notion occur to anyone among the film’s target demographic of crumb-snatchers and rug rats? Probably not. “The Croods” is also just good, goofy fun, for a generation too young to have met Bamm-Bamm. But for those of more precocious intellects, it offers a little something extra to chew on besides rock-smacking slapstick and a brontosaurus burger.

PG. At area theaters. Contains mild peril. 92 minutes.