Fox's CGI feature fails to match the constant visual surprise and teeming invention provided by Disney-Pixar ever since Toy Story, and its uninflected anthropomorphism harks back to a lazier orthodoxy. That said, once you get used to the repetitive, cursorily sketched backgrounds and concentrate on the comic deeds of the central trio - a woolly mammoth, a sloth and a sabre-toothed tiger - there's enough classically derived Road Runner-type fun to keep most family audiences happy. But the characters betray their contrivance. The sloth, Sid, is a hapless orphan abandoned by the migrating herds of the opening sequences. He foists himself on reluctant lone mammoth Manfred with the same blithe insistence that Eddie Murphy's Donkey used to insinuate himself into the company of Shrek, and he cracks a similar brand of self-deprecating gag. Likewise, the screenplay has a magpie lack of discrimination. I liked the goggle-eyed squirrel, but who wouldn't identify with his Sisyphean efforts to secure that damned acorn?