WASHINGTON - Rest in peace, dear Diplodocus. So long, Stegosauruses, you strange, beautiful beasts.

The Fossil Hall at the Smithsonian National Museum of Natural History is now closed for a long-planned - and, officials say, long-overdue - five-year, $48 million renovation.

Most of its specimens won't reappear until 2019, when the massively popular exhibition space is scheduled to reopen at the world's second-most-visited museum.

"Five years feels short, to be honest," said Siobhan Starrs, the Natural History Museum's exhibition project manager, whose team will start taking down the first of more than 2,000 specimens Monday morning.

Before closing time Sunday, a few thousand final visitors squeezed through the hall amid much paleobiological pageantry: "Red carpet" photo ops with the fossils, a dino-themed film festival and experts posted everywhere to discuss all things Dinosauria.

"Stand there and look up at his mouth," a father told his daughter, who obliged by staring - mouth dramatically agape - at the banana-sized teeth of a T. rex cast. She pulled in her arms to mimic the king carnivore.

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"It's an iconic, favorite space," museum director Kirk Johnson said. "People have made a lot of memories here."

The Fossil Hall - actually a suite of smaller halls, including the one dedicated to dinosaurs - was "mobbed" on Sunday, according museum officials.

As the clock wound down on the dated hall's final day, Johnson snapped photos of a soon-to-be-(temporarily)-extinct species.

"Tomorrow, when people come here and try to see the dinosaurs, they'll wish they came today," he said. "This is a historic moment."

During the renovation, the rest of the signature items in the museum's enormous collection will remain on display - including the Hope Diamond, which sits on a rotating pedestal behind bulletproof glass, and Henry, the African bush elephant that towers over visitors in the rotunda.

And there will be some dinosaurs on display throughout the kid magnet on the Mall, which trails only the Louvre in museum visits, according to a 2013 report from the Themed Entertainment Association.