Several months away from opening its new dinosaur hall -- hoped to be a top-tier cultural attraction in the city -- the Carnegie Museum of Natural History is losing its director to a new museum in Arizona.

Natural History Museum Director Billie R. DeWalt announced yesterday he is leaving the 112-year-old Oakland facility at the end of February to be president and director of the Musical Instrument Museum in Phoenix. The new museum, spearheaded by Target department stores CEO Bob Ulrich, is not yet built but supposed to open in fall 2009.

Mr. DeWalt's departure comes just as the Carnegie is completing its $36 million "Dinosaurs in Their World" exhibition. Set to open in November, it will display the world's third-largest collection of dinosaur fossils, many of them purchased by Andrew Carnegie himself.

The renovation has shut down the museum's traditional dinosaur spaces for nearly two years while they were reconstructed and expanded, and the museum's dinosaur bones cleaned and remounted by technicians in New Jersey.

The timing of his departure, Mr. DeWalt said yesterday, "is a little awkward, but I'm the kind of person who empowers my staff. I give them both the direction and responsibility, and they are fully capable of bringing all the projects to completion on their own."

Taking the job in Phoenix will allow Mr. DeWalt to return to his roots as a cultural anthropologist, he said, and again work side-by-side with his wife, Sylvia Keller, a former Carnegie Natural History Museum deputy director who will be leaving her current post as director of Pittsburgh Arts & Lectures, which runs the Drue Heinz Lecture Series.

Construction of the new dinosaur hall is basically complete -- museum staffers are concentrating on building exhibits that will display the dinosaur skeletons in natural habitats and positioned in lifelike poses. The Carnegie Museums system is planning a major publicity, education and fund-raising drive to match the debut of the hall.

The museums must now add a national search for a new natural history director to that to-do list, which Carnegie President David Hillenbrand said will start immediately.

Mr. Hillenbrand praised Mr. DeWalt, saying initiatives he started will make it "a wonderful job and a wonderful opportunity" for someone new.

Besides nearly completing fund-raising for "Dinosaurs in Their World" -- with $32.5 million raised so far -- in his five years in the job Mr. DeWalt has overseen renovations for the Hillman Hall of Minerals and Gems and the Powdermill Nature Reserve, the Carnegie's biological field station in Westmoreland County, and a new education center for the two Oakland museums.

Filling leadership positions in the cash-strapped museum world is not easy, as they require managers with business and budgeting abilities, in addition to cultural or scientific ones. The four Carnegie Museums (science center, natural history, art and Andy Warhol) experienced system-wide budget cuts in 2003 and have constraints on their endowment spending this year.

Mr. Hillenbrand, a former Bayer executive who has run the museums since 2005, said he will be meeting with Carnegie Museums board chair Suzy Broadhurst and natural history chair Jack Barbour to address the vacancy, but that he was leaning toward a replacement with museum experience, as opposed to one from the private sector.

The Carnegie tapped Mr. DeWalt in February 2001, nearly a year after the resignation of his predecessor, former astronaut Jay Apt. Mr. DeWalt, former director of Pitt's Center for Latin American Studies, came to Pitt from the University of Kentucky in 1993.

The Musical Instrument Museum is planned to be the largest instrument museum in the world, addressing the importance of music in shaping cultures worldwide. Plans are for a $60 million budget, with instruments from more than 250 countries. Its offices are currently in Minneapolis -- the home base of Target -- but the museum will be built in Phoenix to draw a diverse tourist base.

Mr. DeWalt, 60, met with MIM officials in December and told Mr. Hillenbrand of his departure Sunday.

He has many reasons for taking the job -- including the growing city of Phoenix, a supportive and resourceful museum board and a chance to build a museum from the ground up -- but chief among them is the chance to work alongside his wife. She left the museum after the pair developed a personal relationship, and they were married in 2005.

"It allows me to go back to my roots as an anthropologist but it also allows me an opportunity to work with Sylvia. We met at the museum, worked together and were a great dynamic team, so I think we're going to have that opportunity at the new museum," he said.

Mr. DeWalt said he expects to remain in Pittsburgh through the summer and his wife plans to continue through May in her job with Pittsburgh Arts & Lectures, to help with succession there.