The opening few minutes of "Ice Age" include the much-seen but still very clever sequence used in the film's trailer about a prehistoric squirrel trying to store a nut — with nearly disastrous results.

That would probably present something of a problem for your ordinary, run-of-the-mill animated comedy, which would have trouble topping that dazzling little gag. But fortunately, there's more to "Ice Age" than that sequence.

Actually, there's a whole lot more, including a pro-animal-rights stance that's surprisingly subtle (despite its pungency, the message is never forced down our throats).

This computer-animated feature — taken as a whole, at least — may not be quite as memorable as the collaborations between Disney and Pixar, but it's still head and shoulders above most of the animated competition, including the traditional cel-animated films coming from the Mouse House these days. (It should be noted, though, that some of the animated violence is pretty intense, and as such, may be a little much for extremely young audiences; note the PG rating.)

The plot takes place during the title era, a time when most prehistoric mammals have headed for warmer climes. However, a sloth named Sid (voiced by John Leguizamo) has gotten a late start. Worse, he's made some very powerful enemies.

So he's fortunate to find a protector in the form of Manfred, or Manny (Ray Romano), a woolly mammoth who doesn't seem to care about joining the southern migration.

Manny doesn't care too much for wisecracking Sid, either, but he reluctantly partners up with him to return a human child who has become lost from his father and is being pursued by a pack of saber-toothed cats.

Speaking of thesaber-tooths, one of them, Diego (Denis Leary), offers to lead the duo to a human settlement. But as it turns out, he's leading them into a trap, and it's not just the child who's in danger.

Admittedly, the plot does bear some superficial resemblances to "Monsters, Inc." And director Chris Wedge (an Oscar-winner for his 1999 animated short "Bunny") employs some irritating gimmicks, such as his unnecessary use of animated "slo-mo."

But neither of those problems is completely insurmountable, and it's clear that the voice cast is having a ball, particularly the low-key Romano. In fact, Leguizamo is so funny here that one could conclude he's better heard and not seen.

The creative animation work may not look as fully "rendered" as Pixar's industry standard, but it uses lighting effects and innovative backgrounds to an equally impressive degree.

"Ice Age" is rated PG. It contains scenes of animated violence (prehistoric animal battles, some of which are done in slapstick style) and a couple of vulgar jokes involving bodily functions of prehistoric animals. Running time: 81 minutes.

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