3-D documentary plumbs the ocean depths of the late Cretaceous period to find some truly awesome denizens -- highly unfriendly, computer-generated creatures guaranteed to make one stay on land.

Things that fly at your face, things that eat other things and things you wouldn’t want to meet in 2-D, much less 3-D, are the raison d’etre of giant-screen films. And they all show up in National Geographic’s “Sea Monsters: A Prehistoric Adventure,” which plumbs the ocean depths of the late Cretaceous period to find some truly awesome denizens — highly unfriendly, computer-generated creatures guaranteed to make one stay on land, or at least think about “Jaws.” Pic opened Oct. 5 on 252 bigscreens and giant screens Stateside.

The dilemma of the 3-D format is that when things aren’t leaping off the screen and into your Diet Coke, the films can seem even flatter than their 2-D cousins. But some of the better moments of “Sea Monsters” are actually in the explication: the infant Earth; the North American continent bisected by water; Europe when it was merely a widespread archipelago; and Kansas — where much of what happens happens, or happened — swarming with some of the fiercest reptiles that have ever existed.

CG re-creations of these animals include the tylosaur, the ultimate seagoing carnivore, seemingly capable of ingesting a Lincoln Navigator. When this thing swims toward you, you flinch, while everything around it swims as fast as it can, in the other direction.

Among the swiftest creatures is the dolichorinchops, or Dolly, as she’s called here, who provides the basis for the anthropomorphic drama of “Sea Monsters.” From birth to comfortable death (not to spoil any tension), Dolly’s biography is constructed via the fossils found in either Kansas or central Texas (an explosion that unearths the Texas fossil bed is a spectacular piece of 3-D filming). What happens to Dolly — when, how and why — is based on readings of her and her contemporaries’ bones, but the science seems sound and the story is exciting.

The filmmakers, chiefly helmer Sean Phillips, have actually made the 3-D elements an embellishment to what would have been a fairly riveting drama anyway. The transformation of the earth, the drying up of Kansas, the creation of the continents as we know them and the earth’s surface as it now exists, constitute some very exciting moments. Yes, plenty of things fly at your face, but they’re not the only things worthy of interest.

Production values are superb, with serviceable narration by Liev Schreiber.

Sea Monsters: A Prehistoric Adventure

Production

A National Geographic Giant Screen Films release. Produced by Lisa Truitt, Jini Durr. Executive producer, Timothy Kelly. Directed by Sean Phillips. Written by Mose Richards.

Crew

Camera (color, 15/70 3-D, digital 3-D), T.C. Christensen; editor, Jonathan Shaw; music, Richard Evans, David Rhodes, Peter Gabriel; executive music producer, Gabriel; associate producer, Erica Meehan. Reviewed at Imax Theater, Canada Place, Vancouver, Oct. 8, 2007. Running time: 40 MIN. Narrator: Liev Schreiber.

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