CHICAGO -- Sometimes a natural history institute as colossal as Chicago's Field Museum digs up some of it best finds in its own storage vaults.

It happened recently when the staff rediscovered fossils of a young dinosaur -- perhaps Albertosaurus -- lurking in plaster casing. They decided it was time to examine the cousin to Tyrannosaurus Rex.

The pieces were crated up and marked "51-22" because they represented the 51st find of the museum's 1922 dig in Canada.

Museum officials aren't embarrassed that they forgot about the dinosaur so long: That's life at a facility that takes in more specimens than it can handle at once. And they say sometimes the fossils get better with age because of new scientific information.

"Beyond dinosaurs, we have far more fossil mammals still in their field jackets, still in storage and never looked at," said Bill Simpson, the museum's chief fossil preparer. Most seem like known species, but new ideas or research tools could prove that wrong in the future, he said.

"That's why we rarely throw things away," Simpson said. "We're good at taking care of things for a long time. It's what we do."

In recent years the museum has learned about ancient agriculture from corncobs it found in storage. And the museum pulled a carved plaque from decades of storage to find that pre-Columbian nobility may have exchanged gifts.

The fossilized tyrannosaurid is an important find because it died young and could offer a unique view of its species, said resident dinosaur expert Peter Mackovicky, who will start research on the bones this year.

"It is not even half-grown, so it gives us a good idea of what an Albertosaurus child would have looked like," Mackovicky said.

"It is going to tell us some things we don't know about the growth cycles of these kinds of animals."

It is an almost perfectly preserved rear end, including an 8-foot tail and right leg and foot, and an almost complete left leg and foot.

The animal is estimated to have lived 70 million to 75 million years ago.

Museum paleontologist Elmer Riggs brought it to Chicago in 1922 among other fossils and marked its crate "partial skeleton of a carnivorous dinosaur."

Museum officials at the time focused their time and money on removing the rock around another of that dig's specimens -- a duckbill dinosaur that remains on display at the Life Over Time Exhibit.