The bones aren’t stuck to each other. Instead, they’re assembled around a steel armature that provides support for the whole specimen—a metal skeleton for the actual skeleton. For the Diplodocus, two vertical columns will run up between each pair of legs, while a sinuous horizontal bar will hold up the neck, spine, and whiplike tail. So far, six vertebrae from the tail are in place. Four men from the dinosaur-mounting company Research Casting International (RCI) are getting ready to attach the seventh. Their shirts say SKELETON CREW on the back, under pictures of skeletal cowboys riding rodeo on dinosaurs.

The fossilized tail bone looks like a stony leg of ham, and weighs around 70 pounds. It sits on its own custom-made steel bracket, which has been locked into a lifting harness. The bone is both heavy and irreplaceable, so the men spend a long time testing it to make sure that it’s secure. Once they’re confident, they winch it up and carefully maneuver it into place. They bolt the bracket to the armature, and remove the harness. Seven down, dozens to go. A Diplodocus tail has around 80 bones in it, and each will take around 40 minutes to assemble.

The feet go on last, so for most of their construction the skeletons look like they’re levitating just off the ground. “When you’re walking around, [the feet] get in your way,” says Matt Fair, a production manager at RCI.

Fair, like many of the people at RCI, possesses an unusual blend of fine-arts expertise, trade skills, and paleontological knowledge. He has an intuitive sense for fossils and how strong or fragile they are, given the species they come from, their anatomical location, and the conditions in which they were created. “I’ve dealt with some stuff where if you breathe on it, it cracks,” he says. “And ribs are very fragile. I don’t have my hard hat on now because I was just up inside that ribcage.”

The ribcage he’s referring to belongs to a Camarasaurus, another giant sauropod that’s standing opposite the Diplodocus on the other side of the tree. In the old hall, it was lying on the floor in a death pose, and visitors frequently overlooked it. They’ll have a hard time doing so now, as the animal rears up dramatically on its hind legs, with its neck stretching from 20 to 25 feet into the air.

Re-posing a dinosaur is difficult work. In the Camarasaurus’s previous position, most of the Camarasaurus’s bones were still encased in exceptionally hard rock, and had to be liberated—a common problem for many of the museum’s old fossils. Some of the vertebrae had become warped and contorted over geological time, which meant that the neck had to arch in a specific way. I suggest that it’s a bit like ordering IKEA furniture, finding that the pieces don’t quite fit, and having to jimmy them into place.

“It’s a little more complicated than IKEA furniture,” Fair says, bristling slightly.