Actors (from L) Josh Duhamel, Tyrese Gibson, Megan Fox, film director and executive producer Michael Bay and Shia Labeouf pose for a picture as they arrive for the Russian premiere of "Transformers: Revenge of the Fallen" in Moscow June 16, 2009.[Agencies]

LOS ANGELES  - The 'bots are still on the trot.

The mega-successful bow last week by Paramount's action sequel "Transformers: Revenge of the Fallen" has so transformed the competitive box-office landscape, it's hard to see either of two rival movies opening at No. 1 this weekend.

Just a few weeks ago, 20th Century Fox's 3-D animated three-quel "Ice Age: Dawn of the Dinosaurs" seemed to have a shot at debuting atop the Fourth of July weekend rankings. But despite continued prospects of a healthy bow, it's highly unlikely that "Dawn" will capture session bragging rights.

Like Universal's Johnny Depp-starring "Public Enemies," "Dawn" entered wide release Wednesday. But its real showdown will come this weekend. With the Independence Day holiday falling on Saturday, box-office rankings will be based on a three-day span.

Comparing "Dawn of the Dinosaurs" to its 800-pound holdover rival on that basis, the Fox family film should open in the $45 million-$50 million range, while Paramount's Michael Bay-directed blockbuster could get enough of a boost from the box-office-friendly holiday to keep its sophomore-session drop to a modest 50 percent. That would give it a Friday-Sunday tally of $55 million or more this session.

Playing in 3,319 locations, "Enemies" looks likely to ring up $25 million over the weekend and perhaps $40 million for its first five days. "Dawn" is set for a record 1,606 3-D auditoriums, with a total of 3,993 opening playdates and 4,093 engagements starting Friday; its five-day projection hovers at $60 million-$65 million.

The midweek opening for both pictures was designed to stimulate word-of-mouth while maximizing box-office grosses during a week when most students are off from school. But the "Transformers" sequel could take its biggest bite out of the new films on Wednesday and Thursday, as its marketplace momentum remains strong.

Happily for the new releases and holdovers alike, the Fourth of July session is generally one of the year's more lucrative frames. So a rising tide of holiday business should lift all box-office boats once the weekend arrives -- provided the battling 'bots don't hugely exceed expectations again.

One unknown is whether a significant number of theater operators will keep their "Transformers" moneymaker on more screens and in bigger auditoriums during its second weekend than originally planned. In any event, distribution executives at Fox and Universal expressed calm resolve in the face of the looming clash with the behemoth holdover.

"I think we're as well positioned as any picture can be in this marketplace," Fox distribution chief Bruce Snyder said. "People are ready for a new family movie."

The R-rated "Enemies" ought to hold its own by appealing to a distinctly older audience, Universal distribution president Nikki Rocco said. Prerelease interest appears solid.

"The tracking looks good," Rocco said. "I'm feeling really good about that."

Among the weekend's notable expansions, Sony Pictures Classics plans to broaden Woody Allen's "Whatever Works," starring Larry David, to more than 300 screens from 35.