There has only been one truly successful animated sequel ever made. And it’s not “Ice Age: The Meltdown.” Disney’s sequel to “The Rescuers” (1977), “The Rescuers Down Under” (1990), remains the only cartoon sequel capable of standing independently as a film, and one of the few sequels (animated or otherwise) that is not a blatant manipulation of viewers to capitalize on the earnings of the original. Admittedly, “Toy Story 2” wasn’t bad, but it remains the exception, not the rule. “The Meltdown” has little in common with 2002’s original, smart and genuinely comical “Ice Age.” The dialogue and humor are forced and the story is boring, a sad contrast to the witty, laugh-out-loud writing of the original that both children and adults could enjoy. And, as a pressing annoyance, the interminable and oddly interspersed scenes devoted to squirrel-rat hybrid Scrat’s unending quest to protect his elusive acorn are tiresome and make the movie disjointed. And to further worsen matters, Queen Latifah has joined the cast.

This time around, Manny the mammoth (voiced by the drawling Ray Romano), Diego the saber-toothed tiger (Dennis Leary) and Sid the sloth (a lisping John Leguizamo) find themselves pressed to outrun melting glaciers and the imminent flooding of the valley they call home — a mass migration plot line that not only mirrors the first “Ice Age,” but is uncomfortably reminiscent of the “Land Before Time,” another animated movie doomed to excessive, and excessively bad, sequels. Bizarrely, director Carlos Saldanha and his writers chose to interject “The Meltdown” with ill-placed and inappropriate Biblical imagery. Awaiting Sid and Co. at the end of their journey is a large ark, illuminated by a beam of light from the heavens, that promises to save all of the prehistoric critters from the catastrophic end of the ice age, yet brings about said results in the audience’s reaction.

But most kiddies will be too distracted by the budding love story between Manny and Ellie (Queen Latifah) to worry about any Biblical allusions or parallels to current worries concerning global warming. Ellie joins up with Manfred and his herd of misfits in their journey towards the ark, and since she and Manny seem to be the last two mammoths alive, isn’t it their duty to repopulate the planet with little woolly pachyderms? But these mildly comical sexual innuendos (the only treat for non-prepubescent viewers) are complicated by Ellie’s identity crisis — she thinks she’s an opossum.

Ellie sleeps hanging upside down from a tree, plays dead when hawks soar overhead and goes nowhere without her brothers at her side (two obnoxious possums created along the same line as the roly-poly twins in “A Bug’s Life”). There is obvious play with the same theme of familial loyalty that dominated the first “Ice Age,” but this time any semblance of sincerity has melted along with the ice.

Also echoing the original, “The Meltdown” creates maudlin back-stories for its characters. Just as Manny is haunted by the loss of his family to human hunters (which fit smoothly into the plot), the reason for Ellie’s mistaken identity proves to be even more melodramatic.

And if audience members are willing to look past these lackluster additions to the cast (and block out Queen Latifah’s unmistakable and over-acted voice) in the hopes that Manny, Diego and Sid will be as entertaining as they were in the original “Ice Age,” they will only be all the more disappointed. Manny’s defining sarcasm has softened beyond recognition, Diego’s defensive inferiority complex and awkward intimacy issues are no more, and even our favorite three-toed friend fails to inspire a gelastic workout. Saldanha and his team tried to rely on the same old jokes, but seem to have forgotten the punch lines.

But the film is not entirely devoid of originality: there is a prolonged musical sequence of vultures singing in formation to a morbid, carnivorous rendition of “Food, Glorious Food” as well as a tribe of pigmy sloths whose cult-like uniformity is clearly intended to be as humorous as the flock of Dodos in the first “Ice Age.”

Needless to say, “The Meltdown” will prove staggeringly disappointing to fans of the original. What’s worse, this subpar sequel almost taints the glory of its precursor. Had it been released directly to DVD, “The Meltdown” could have been filed away and forgotten along with “Beauty and the Beast: The Enchanted Christmas,” “The Little Mermaid II: Return to the Sea” and “The Lion King II: Simba’s Pride” (and let’s not forget “The Lion King 1 1/2”). But, alas! 20th Century Fox refrained from such wisdom, merely cementing the consensus that Pixar — capable of avoiding the animated sequel pitfall — should be the only company allowed to make CGI films.