Come with us on a trip back through time.
It is 150 million years ago -- a steamy Jurassic afternoon in a part of the world that will eventually come to be known as Utah.
A meat-eating allosaurus is looking for food, and spies a baby apatosaurus, cowering beneath its mother.
"So he wants to come in and knock off the baby," said Matt Lamanna, a paleontologist helping to set the scene for us. "Naturally, the mother isn't too excited about that, so she's swinging her tail at the allosaurus, hoping to knock him off his feet."
Lamanna is a curator at the Carnegie Museum of Natural History in Pittsburgh, which has one of the largest collections of dinosaur fossils in the world. He and his colleagues have now spent three years and $36 million rethinking their entire dinosaur hall.
The problem is that even though the last dinosaurs died 65 million years ago, scientists' understanding of them has been racing along, changing with each new find.
Our image of dinosaurs is mostly what one finds in old sci-fi films -- big, lumbering creatures, dragging their tails on the ground. In recent years, scientists have decided they were probably much more energetic and agile -- and the way most fossils were displayed was wrong.
No Instruction Manual
"These things are tens of millions of years old. Don't we have this down yet?" we asked.
"Unfortunately, they don't come with instruction manuals," said Lamanna, smiling.
The Carnegie Museum dismantled its great skeletons, and shipped them off to a studio in Paterson, N.J., where a gentle dinosaur lover named Phillip Fraley oversees a small army of painters, sculptors, welders and former museum staffers. They rebuilt the fossils under the scientists' watchful eyes.
"These bones begin to dictate to you the way that they want to be put back together again," said Fraley, "the way they want to be lifted up or held."
A Mix of Art and Science
Fraley, a long-time exhibit designer at New York's American Museum of Natural History, oversaw the rebuilding of the dinosaur collection there. He and his wife went into business for themselves, painstakingly assembling skeletons for museums from Chicago to Singapore.
"In mounting fossils you really see a process that began a hundred, a hundred and fifty years ago," he said.
The scientists back then certainly had the best of intentions but not the best information. Very few of the fossil skeletons they dug up were complete, so they made educated guesses, sometimes based on other species.
"If you look at some of those old mounts," said Lamanna, "there are actually huge spaces between the vertebrae where they actually had to kind of 'disarticulate' them, in other words, throw their backs out of joint, to get them to fit together the way that they thought they went."
Tail in the Air
Since then, they've found that a Tyrannosaurus rex probably had a tail a few feet shorter than most museums show -- and that many dinosaurs held their tails up in the air for balance.
By way of proof, Lamanna points out that the footprints of dinosaurs are fairly common. But if the dinosaurs really dragged their tails on the ground, there would probably be evidence of ruts behind the footprints. Scientists have searched, and found places where a tail may have swished back and forth, but it appears a T-rex did not drag its tail.
The fossils have now been shipped, crate by crate, back to Pittsburgh, where the Carnegie staff is putting the finishing touches on its new dinosaur wing. The hall, called Dinosaurs in Their Time, opens Nov. 21.
Instead of mounting the skeletons on pedestals, the Carnegie is posing them the way science now believes they would have looked eons ago. Visitors will see dinosaurs gathered in herds. Small mammals -- which survived whatever killed the dinosaurs -- hide underfoot.
Even the foliage is based on fossil findings -- gingko trees and ferns, little changed since the Jurassic.
It's a dramatic scene compared to what one saw in the old hall. Is it realistic?
"Absolutely," said Lamanna. "And I think, given the immensity of time, it's quite likely that something like this did happen from time to time."
And years from now, as the scientists learn more, they said they'll probably have to change the exhibits all over again.