NEW YORK (AP) _ The dinosaur-loving public packed into the American Museum of Natural History's newly renovated dino halls this weekend to find changes as drastic as those that killed the beasts 65 million years ago.

Apatosaurus, who used to be called Brontosaurus, has a new skull and a tail 20 feet longer. Tyrannosaurus, who used to pose upright like Godzilla, is crouched over like Road Runner. And the exhibit says dinosaurs aren't really extinct; birds are a kind of flying dinosaur.

These revelations, however, were still in the future at 9:56 a.m. Friday as 4-year-old Ari Butowsky stood outside the great closed doors of the museum's Central Park entrance.

The world's greatest dinosaur collection, shuttered for more than three years, would reopen to the public at 10. And Ari was waiting at the head of the line.

Waiting may be the wrong word. Ari actually was using his 40 pounds to try to slide open one of the 10-foot high metal doors.

Taking pity, the guards rolled the door open and admitted Ari, his mother, Elise, and his stroller-bound, 1 1/2-year-old brother Jared two minutes early.

``Gonna be a busy day,'' said the guard, rolling his eyes.

The Butowskys followed the 2-foot-long dinosaur footprints and boarded an elevator car that soon became as crowded as a raptor nest and as humid as a Mesozoic swamp.

They got off on the fourth floor, where everyone had to wait some more while the mayor's wife snipped a ceremonial ribbon.

Then Ari joined the land rush into the first of the two reopened galleries, the Hall of Saurischian Dinosaurs. The computer-savvy preschooler headed not toward the big bone statues off in the distance, but to a computer console dispensing information about ornithomimids, a word he was able to read and pronounce accurately.

``Wanna see the dinosaur bones?'' his mother asked after he had spent what seemed like a long time using the interactive program. She led him off, and suddenly there, looming above the swelling first-day crowd, was the skeleton of his favorite dinosaur: T. Rex.

This was not the lumbering beast of the museum's 1917 installation, a monarch who had to stoop to conquer. This was a sleek, stalking hunter, his spine and tail parallel to the ground.

The informed eye saw one of the century's great archaeological finds, a skeleton with hundreds of real bones (not plaster casts) that had to be taken apart, cleaned and carefully reglued in the new posture.

But Ari's eye saw a killing machine with a head the size of a piano and teeth like pirate daggers.

``He's a little scared,'' Mrs. Butowsky said of her suddenly speechless son.

He backed across the aisle toward what stupid adults still call Brontosaurus and what Ari and his ilk call by its scientific name, Apatosaurus. It stretched 86 feet, almost the length of the room.

Mounted in 1905, this was the first large dinosaur skeleton ever put on public display. But for some reason it had the wrong skull, and it was missing a few neck bones _ mistakes corrected in this installation.

Next door was the Hall of Ornithischian Dinosaurs, the ones with the ``backward pointing extension of pubis bone,'' a crucial feature shared by such disparate creatures as the Triceratops and the sparrow.

``The dinosaurs displayed here are more closely related to chickens, pigeons and gulls than to any of the other dinosaurs in these galleries,'' the label explained.

Most museums organize their fossil exhibits chronologically, oldest to youngest. But the Museum of Natural History's are arranged to form a giant family tree that emphasizes dinosaurs' evolution and their relationship to other invertebrates.

The new exhibit's conclusions are not written in stone. In fact, the museum has included surgeon general-style warnings if an issue, such as why the dinosaurs died off, remains in dispute. In fact, some parts of the text panels can be detached and changed.

A central theme of the exhibit is how what we know or think we know about the dinosaurs has changed in recent years.

And about how much is still in doubt: Were the dinosaurs warmblooded or coldblooded? Social or solitary? How did they raise their young? And why did Stegosaurus have those plates on its back? (Maybe for temperature control, maybe for attracting mates.)

Even Ari didn't have the answers.