A 66-million-year-old dinosaur is being readied for exhibition in Los Angeles. Mike O'Sullivan reports, visitors can watch scientists as they work on the remains of the Tyrannosaurus rex known as Thomas.

Using brushes, dental picks and small power tools, workers at the Natural History Museum of Los Angeles County remove debris from the bones of the dinosaur, a process that will take several years to complete.

The object of their study is a Tyrannosaurus rex, nicknamed Thomas. It is one of a few dozen substantially complete T. rex skeletons worldwide. Thomas weighed as much as 3,600 kilograms and had teeth 30 centimeters long. He stood three meters high at the hip and was nine meters long from head to tail.

Discovered in Montana, the dinosaur was excavated between 2003 and 2005. It is being prepared for display in 2011, when the skeleton will be moved to the new Dinosaur Hall in the museum's refurbished original 1913 building. In the meantime, visitors can watch the painstaking process of preparation.

Luis Chiappe, director of the museum's Dinosaur Institute who excavated Thomas, says scientists are sharing the excitement of discovery.

"We want to show to people that we do a lot of research," he said. "Behind the scenes, this is a research institution that has a number of experts that go out and collect fossils, bring them here, prepare them and study them. And that what you see here on display is just the tip of the iceberg."

Thomas is being prepared in a special exhibit space, a glass-and-steel clean room, built so the public can look on. The skeleton will be mounted to show the modern understanding of dinosaurs as active, lively creatures.

Phil Fraley, who will oversee the mounting, says dinosaurs were once thought to be lumbering and sluggish, and were shown with tails dragging on the ground. That view has changed.

"So what we're doing now and has been an ongoing process over the past several years has been an updating of the scientific exhibits, especially dinosaur paleontological exhibits to reflect current scientific thought," he said.

This dinosaur skeleton is two-thirds intact, making it one of the top five T. rex specimens in collections anywhere.

Simon Adlam of the natural history museum says the study of dinosaurs tells us what the world was like tens of millions of years before humans arrived.

"It's part of our origins. We learn a lot about the way the habitats were, through the fossils themselves," he said. "We learn about migration of how species traveled."

Thomas was found in what was once a meandering river on the edge of a tropical sea that once covered much of North America. He was thought to be a young adult, about 13 years old, when he died. The typical T. rex lived about 30 years, and research may tell us why Thomas died so early. He could have been the victim of another dinosaur. Evidence on his skull suggests he may have had a tumor, which also could have killed him.

Luis Chiappe says the study of dinosaurs like Thomas is important.

"Very important because they're an outstanding example of evolution, an outstanding example of how life has changed and adapted," he said. "Collectively, dinosaurs ruled every land ecosystem essentially for 160 million years."

Dinosaurs suffered a massive extinction 65 million years ago, possibly by an asteroid striking the earth and disrupting weather systems.

Many scientists say they did not really die out, but survive today as birds, modern-day descendants of dinosaurs.