DreamWorks Animation’s “How to Train Your Dragon” ruled the box office over the weekend with a $43.3 million opening.

The computer-generated fantasy — which is wonderful, by the way — supplants Tim Burton’s “Alice in Wonderland” as the latest gotta-see 3D spectacle. And since 3D screens are fairly limited, with only about 4,000 of them in North America, “Avatar” is now playing almost exclusively in 2D, which explains why it’s finally fallen out of the top ten.

(Well, it’s either that, or last week’s much-ballyhooed announcement of the April 22nd home-video release. Or possibly everyone’s just seen the damn thing by now.)

Next week, Warner’s “Clash of the Titans” will grab most of the 3D screens currently showing “Alice”, which will presumably send that picture spiraling down to the bottom of the charts. Maybe Disney’s decision to shorten its theatrical window wasn’t so crazy after all, huh?