The good folks at Blue Sky Studios have done it again: yet another brilliant short film starring the bedraggled, hungry Scrat, a sabre-toothed squirrel living in the Pleistocene Ice Age some ten or twenty millennia ago, an unspeaking slapstick comedian whose single skill is hunting for acorns, something he does with great enthusiasm and virtually no success, leading to a series of misadventures that recalls the Golden Age of Tex Avery more than any other contemporary animation has ever managed. In this go-round, we find Scrat (his vocalisations by the series' former director, Chris Wedge) falling in love with a sabre-toothed flying squirrel, Scratté (Karen Disher), their mutual affection conflicting with their mutual desire to own the same nut.

Oh, and once again, the bastards at Blue Sky Studios have chopped their marvelous short up into even shorter chunks, and distributed it throughout a forgettable 90 minute movie about prehistoric animals talking like 21st Century humans.

Really, we all know that Scrat is the best thing about the Ice Age movies. People who don't like the films still like him, people who love the films love him best, and people who haven't seen the films know about them primarily that he is to be found within them. Surely somebody has had the idea to make a Scrat feature; or perhaps judging (correctly, I'd wager), that 90 all-Scrat minutes would be a disaster, they could at least set him loose on an annual or semi-annual series of honest-to-God shorts. "There is no market for animated short films" comes the rejoinder. Yeah? Well, you know who makes an animated short at least once a year? Pixar. And if I were the executives in charge of an animation studio, I think I'd assume that whatever Pixar does, it's probably a smart play. In the meantime, though, the only way we're going to get us any Scrat is to go see Blue Sky's Ice Age features, or partake of the special features on the Ice Age DVDs.

And to be fair, if you're going to drag yourself or be dragged by the young people in your family to see a forgettable movie, Ice Age: Dawn of the Dinosaurs (the third film in the franchise, and the first film of the modern 3-D wave to make the "Part 3-D" connection that resulted in so many wonderfully gaudy movies back in the 1980s) is better than a lot of what's out there. It's even better than the two films preceding it, 2002's Ice Age and 2006's Ice Age: The Meltdown, which might not be the tallest bar to clear, but it's certainly more than I expected. The Shrek movies didn't have that tall a bar to clear, either, and every one of those that comes out is that much more useless than the last.

The latest Ice Age tale returns us once again to the odd family group that formed in the first and expanded in the second: Manny the woolly mammoth (Ray Romano) and his mate Ellie (Queen Latifah), now expecting their first child; Diego the sabre-toothed cat (Denis Leary), growing increasingly frustrated at being a predator in a kids' movie full of silly, endearing anthropomorphic prey animals; and the hopelessly idiotic sloth Sid (John Leguizamo), whose bumbling once again results in the inciting incident that gets the plot a-rolling. Here, he falls into a cavern and finds three large eggs, which he brings home (hoping to start his own family to rival Manny and Ellie's). They hatch, and out pop three plush toy-ready tyrannosaur babies, and a few hours later, their mama comes looking. Yada yada yada, adventure in the underground tropical world where dinosaurs and prehistoric plants still thrive, and a crazed weasel from up top named Buck (Simon Pegg) leads the heroes there and back again.

That the film is not as bad as it could be - that, in fact, it even drifts in to genuine funniness and watchability from time to time - is not a reflection on the plot, which exists solely because after a mere two films, the franchise's handlers had apparently grown bored with ice age fauna and decided that, paleontology be damned, kids these days like the dinos. Nor does it have a single thing to do with the movie's revolutionary ideas that family is a nice thing, even an unconventional family, and that sticking together with the people you love is the best way to face adversity.

No, when Dawn of the Dinosaurs works on absolutely any level other than a safe chance for a parent to grab a 90 minute nap while the little ones stare at the screen wearing amusingly over-sized plastic glasses, it is because after two films of cautiously de-edged characters voiced by semi-famous actors who are not ashamed to be seen cashing a paycheck, the filmmakers have finally cut loose and given a genuinely inventive comic mind a completely loopy madman to play. The pint-sized psychopath Buck, with his leaf eyepatch and a knife almost as big as his body, gets absolutely all of the best lines and situations, and Pegg, unlike everyone else in the vocal cast, actually sees fit to put some energy into his line readings. It's a tonic that the film desperately needs, seeing fit otherwise to bury all of its comedy behind a wall of sitcom clichés, and adding a shockingly high number of dick jokes for a PG family movie.

Take out that character, and Dawn of the Dinosaurs becomes such a routine job that it makes me sleepy just to think about what it might look like; life lessons and musty jokes and action scenes where it seems impossible that the characters are in even the least peril, since they bounce back from every damn thing so readily. Not "bad" - just like the first two weren't "bad" - just profoundly uninteresting. It's frustrating as hell, because the filmmakers obviously know better. After all, they made Buck, and he's funny; a whole movie made at the level of Buck would be, if hardly the masterpiece that Pixar's Up was earlier this summer, at least a fun and engaging adventure movie with a real level of charm and creativity.

And Scrat; they also made Scrat. I can't figure out how a character that great keeps ending up in movies like this. The Ice Age films may not matter, but by God, Scrat matters. He's as good as any comic figure in the movies this decade; and no matter how middling the films where he's stuck may be, they're never going to be completely disposable as long as somewhere, a little squirrel and his acorn will always be playing.