Third ‘Ice Age’ cracks under weight of its cast

The “Ice Age” series has executed the classic arc of the sequel series: delightful first movie, a second film that’s fun but kind of a place-holder and a No. 3 that feels as if the party guest has overstayed his welcome.

That would be “Ice Age: Dawn of the Dinosaurs,” a movie that bucks most scientific knowledge by putting the mammals from the first two movies together with dinosaurs.

One of the reasons for diminishing returns on sequels is that new characters keep getting introduced in each movie. By movie No. 3, it’s a crowd, and the original mojo of the first movie gets shunted off to the side.

So the original gang of three from “Ice Age” is still around — mammoth Manny (voiced by Ray Romano), cranky tiger Diego (Denis Leary) and klutzy sloth Sid (John Leguizamo).

So are the characters we picked up in the second film, including Manny’s beloved Ellie (Queen Latifah) and her possum posse.

Manny and Ellie are expecting a baby mammoth, Diego is ready to leave the herd for new horizons, and Sid has discovered a couple of very large eggs that he decides to hatch.

Sid’s mothering instinct is strong, but when the hatchlings turn out to be baby dinosaurs with big sharp teeth, the adoption looks more unusual than the latest Brangelina family portrait.

“Dawn of the Dinosaurs” confirms that the hapless, good-hearted Sid has always been the “star” of these movies. Leguizamo’s vocal performance is truly crazed and the character’s stupidity is never ruined by any sudden moments of intelligence.

Along with the big dinosaurs (discovered in a kind of “lost world” environment), the major new character is a weasel, voiced by Simon Pegg, who carries on a never-ending battle with dinosaurs much larger than himself.

There’s nothing terrible about this movie, but the effect overall is blah.

Some of the jokes are good, including a handful of racy ones for the parents in the audience.

And there’s Scrat, of course, the tragically unlucky chipmunk whose adventures have always been the most uproarious parts of the “Ice Age” films.

Here, Scrat meets his perfect mate — or is she?

Their fierce scuffles over an acorn interrupt the movie at regular intervals and provide the most sustained laughs.

If this is the swan song for the “Ice Age” pictures, we trust Scrat will continue to follow his dream, deluded though it is.