The revisionist version of natural history offered up in the Ice Age movies gets yet another twist in the fourth instalment, 10 years after Manny the woolly mammoth, Diego the sabre-toothed tiger, Sid the sloth, and Scrat the squirrel made their chilly debut to hot box-office receipts. The lessons of family and loyalty in Continental Drift may seem a little warmed over, but the creatively constructed laughs, amusing voice characterisations, and inventive CGI animation are reason enough to keep the series viable for kids to giggle about and grown-ups to belly laugh over--sometimes for exactly the same reasons.

Once again, acorn-addicted Scrat is the cause of some pretty important behind-the-scenes machinations. His dialogue-free antics also serve as a stand-alone subplot that could easily be a very clever short film of its own. This time the weasely rodent's addled obsession with the fruit of the oak is revealed as the cause of the formation of the world's continents as we now know them. He sets the story--and planet Earth--in motion while pursuing a little nut in a hyperactive prologue that causes underground rifts that in turn form the famous shapes of Australia, Africa, North America, and the outline of Italy (which it turns out is shaped like a boot for a very good reason). Above ground this means more global chaos for the herd of animals we've come to know so well. All the familiar voices reprise their wonderful roles as fissures in earth and ice separate Manny (Ray Romano) from his woolly wife Ellie (Queen Latifah) and boy-crazy teenager Peaches (Keke Palmer). With a killer continental shelf bearing down on them, mother and daughter lead the madcap pack of animal characters toward a safe meeting place while Manny, Diego (Denis Leary), Sid (John Leguizamo), and Sid's crazy granny (Wanda Sykes) drift away on an iceberg schooner into a newly vast open ocean. While floating into oblivion, the mismatched pack encounters a band of animal pirates piloting another slab of ship-shaped ice, captained by a crazed baboon named Gutt (Peter Dinklage), who's bent on resentment-based revenge. The motley crew provides a plethora of comic encounters and a new raft of excellent voice actors. Running a close second to Dinklage in ingenious casting is Jennifer Lopez as Shira, a sultry tiger who, don't cha know, ends up on the good ship and falling for Diego in the end.

The adventures of both the land- and sea-based creatures are full of clever gags and densely constructed set pieces that may not be quite up to Pixar story standards, but are certainly always on the ball and executed with computer-animation acumen that is astonishingly lifelike for such an unreal-looking world. Scrat's misadventures act as interstitial connectors to the parallel heroes' journey stories until they ultimately intersect in a massively scaled finale. Even after all the melting and refreezing, the Ice Age world is still a hot commodity in the animated-franchise business and remains a good investment despite the constancy of global rifts in entertaining family fare. --Ted Fry