The life and times of Oyster Bay's Theodore Roosevelt, the nation's 26th president and foremost 20th-century conservationist, were commemorated Thursday with the unveiling of a $40-million face-lift of the American Museum of Natural History.

This weekend, for the first time in three years, visitors will enter the museum's main 100-foot rotunda entrance and see its restored vaulted ceiling supported by eight 48-foot-high marble columns, along with a freshly painted 5,200-square-foot mural that depicts Roosevelt's life as president, conservationist and world traveler.

A new permanent exhibit examines Roosevelt as a "young boy and naturalist" living on Long Island, where he captured and mounted his first "specimen" -- a snowy owl in Oyster Bay in 1876. His journals in his own handwriting as a 13-year-old boy are also on display. Roosevelt's writings document his observations of insects and bird drawings on Long Island.

"He was an amazing man," said Douglas G. Brinkley, a professor of history at Rice University, and author of "The Wilderness Warrior: Theodore Roosevelt and the Crusade for America."

Brinkley, who consulted on the new exhibit, said that Roosevelt's career as a conservationist started at the museum.

"The exploration of nature and his love of nature is here," Brinkley said of the iconic museum on Central Park West, founded in 1869.

"That is why kids respond to this museum . . . This museum is the cradle of conservation."

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In tribute to Roosevelt, an exhibit shows the wonders of the Grand Canyon -- an effort to remind visitors that he saved the 800,000-acre Arizona landmark from ranching and mining interests by making it a national park.

Museum president Ellen V. Futter said the exhibits "are essential destinations for all who are passionate about preserving wildlife and wild lands."

The museum's famous dioramas in the Hall of North American Mammals that depict the bison in its natural habitat on the nation's grassy prairies and the North American grizzly and bighorn sheep have all been cleaned, buffed and refurbished.

Another addition is a bronze sculpture of Roosevelt when he was on a 1903 camping trip to Yosemite National Park. Visitors can now sit and put their arm around the nation's pioneering conservationist.