UPDATE 1-'Horton Hears a Who!' a hit at box office

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By Dean Goodman

LOS ANGELES, March 16 (Reuters) - Move over, Dumbo. Horton is now the big elephant in the room.

The computer-animated adaptation "Dr. Seuss' Horton Hears A Who!" trampled its rivals at the North American box office on Sunday with weekend sales of $45.1 million, the biggest opening of the year.

The $85 million 20th Century Fox release, which boasts the voices of Jim Carrey and Steve Carell, exceeded industry expectations but fell short of the $55.1 million bow of Carrey's previous turn in a Seuss movie, 2000's "How the Grinch Stole Christmas."

It does rank as Carrey's best start since May 2003, when "Bruce Almighty" set a new watermark for the Canadian actor with a $67.95 million opening. Overall, "Horton" stands at No. 4 on Carrey's all-time list.

Carrey voices the title character, a rubbery elephant who stumbles upon a speck that happens to be a tiny planet, home to a city called Who-ville. Carell voices the excitable mayor. In a rare moment of synchronicity with moviegoers, critics were also enthusiastic about the film.

Fox, a unit of News Corp NWSa.N, said "Horton" ranks as the fifth-biggest G-rated opening ever; the top honor is held by 2003's "Finding Nemo" with $70.2 million. The studio expected Easter school vacations to boost the film's midweek performance.

Last weekend's champion, "10,000 BC," slipped to No. 2 with $16.4 million for the three-day period; the 10-day haul for Warner Bros. Pictures' prehistoric epic stands at $61.2 million. The critically maligned saga has also earned $73 million internationally. The Time Warner Inc (TWX.N) unit said the film cost more than $100 million to make.

Opening at No. 3 was "Never Back Down," a mixed martial arts movie targeted at male youngsters. It earned $8.6 million. The $20 million film is the debut production of privately held Summit Entertainment LLC.

Rounding out the top five were the Walt Disney Co (DIS.N) Martin Lawrence comedy "College Road Trip" at No. 4 with $7.9 million, and the Sony Corp (6758.T) (SNE.N) political thriller "Vantage Point" at No. 5 with $5.4 million. Their respective totals rose to $24.3 million after two weeks, and $59.2 million after four weeks.

The top-10 contained one other new release, the action thriller "Doomsday," which opened at No. 7 with a disappointing $4.7 million. The $19 million Rogue Pictures production was released by Universal Pictures, a unit of General Electric Co's (GE.N) NBC Universal Inc. (Reporting by Dean Goodman; editing by Cynthia Osterman)