A lizard’s gotta do what a lizard’s gotta do, as we learn in the animated spaghetti western “Rango,” an agreeably strange concoction full of peculiar lessons.

Arriving as an unexpected combination of genre spoof, existential philosophy and homage to old Warner Bros. cartoons, “Rango” is the b

rainchild of a couple of “Pirates of the Caribbean” collaborators, Johnny Depp and director Gore Verbinski.

Depp inhabits the voice of a pet lizard unceremoniously bounced from the back of a family car and left to fend for himself in the Mojave Desert. Quicker than you can say “Sergio Leone,” he finds himself the newly appointed sheriff of a town where water is more precious than gold.

There’s a reason for that, which the lizard — newly christened Rango, as befits his invented gunslinger identity — will discover. He also meets an independent-minded lizard (Isla Fisher) and a gallery of birds, frogs, rabbits and other varmints.

There characters in this movie do not resemble the cute critters of most cartoons. They are hilariously broken-down and homely, and the digital animation used to bring them to life is amazingly vivid and almost photo-realistic at times.

While not cuddly, the script by “Gladiator” scribe John Logan uncorks both philosophical points and political jibes. The town’s tortoise mayor (Ned Beatty, channeling John Huston) would not have been out of place in the boardroom of Enron or Goldman Sachs, and understands the power of withholding the most prized possession in the desert.

When Rango must wander in the wilderness to answer his oft-repeated question, “Who am I?,” he runs into no less than a vision of “the Spirit of the West,” a recognizable cowboy figure who delivers hard-bitten wisdom.

That scene is typical of the movie’s busy appropriation of pop-culture figures. But somehow this odd mishmash kind of works, even if it overstays its welcome by about 15 minutes or so.

Verbinski directs in his lively style; as usual he creates a diverting surface that falls short of actual movie magic. Depp’s vocals are crazy and without vanity, as befits the mood, and the voice cast also includes Alfred Molina, Bill Nighy and Harry Dean Stanton.

It’s not a musical, but “Rango” does have a great theme song, rendered by a mariachi-singing quartet of birds. The tune would have fit right into a real spaghetti western, but, hey, “Rango” is a real spaghetti western. The sauce just tastes a little funny.