LOS ANGELES--"Shrek Forever After," the first 3-D sequel for the lovable ogre, opened this weekend at the top of the North American box office, ending "Iron Man 2's" two-week reign, preliminary figures showed Saturday.

The fourth of the Mike Myers-voiced animated series raked in $71.3 million, well short of the record $121.6-million opening set by its previous installment, "Shrek the Third," according to data released by box office tracker Exhibitor Relations.

Higher-priced, 3-D theater tickets likely deterred some moviegoers, observers noted.

The superhero sequel "Iron Man 2" fell to second place with $26.6 million, bringing its three-week total to $261.3 million.

In third place was "Robin Hood", director Ridley Scott's latest historical epic starring Russell Crowe as the famous English outlaw. The film took $18.7 million, with a two-week total of $66.1 million.

The romantic drama "Letters to Juliet" opened took fourth place, with $9.1 million, ahead of romantic comedy "Just Wright," with a duo of rapper-actors Queen Latifah and Common, at $4.2 million.

Saturday Night Live-inspired "MacGruber" opened at number six on the box office charts with $4.1 million, followed by "Date Night" with Tina Fey and Steve Carell with $2.8 million.

Eighth place went to fright flick "A Nightmare on Elm Street" with $2.3 million.

Trailing ninth and tenth place were "How to Train Your Dragon," which took in $1.9 million, and Bollywood musical "Kites," about a dance-teacher who marries women to provide them with green cards, which opened with $1 million.