Essentially a CGI version of the venerable Three Godfathers, with digitized mammals subbing in for John Wayne and company, this Fox foray onto Pixar/PDI terrain boasts some ingenious gags, but too much of the nagging smart-ass tone that has marred a lot of recent children's movies. (Needless to say, the tots who loved Shrek will eat this up.) As millions of mammals migrate south away from the coming Ice Age, three head north: a morose mammoth (voice of Ray Romano), his chatterbox tree-sloth sidekick (John Leguizamo), and a conniving saber-toothed tiger (Denis Leary) whose fellow cats expect him to deliver the trio's latest find--a delectable human baby separated from his parents. The unusually hard-edged humor hints at a darker, less kid-friendly comedy that may have been softened during development: Most of the jokes involve the scarcity of food, the savagery of the food chain, and the tough luck of evolution. That tone results in some big laughs (especially at the expense of the ill-fated dodo bird), but it clashes sharply with the sentimental story. (Jim Ridley)