A dinosaur named Sue, and the way science really works

In 1990, a fossil-hunting team working in the South Dakota badlands made a dramatic discovery: their truck had a flat tire. While most of the team took the truck into town to get patched, Sue Hedrickson stayed behind to pick around some exposed sandstone bluffs nearby. What she found, and what now bears her first name, is the largest, most complete skeleton of a Tyrannosaurus rex ever found.

Sue is amazingly well-preserved. Sixty-seven million years in the South Dakota soil seems to have done little damage to her six hundred-pound skull. Even the delicate bones of her inner ear, once attached to her eardrum, were there. The bones of her seven-ton body have kept all their original texture, allowing scientists to learn much about the hardships of her life (paleontologists believe she suffered from spinal arthritis, as well as broken ribs that had healed somewhat messily).

I was personally very excited when I learned that the Field Museum in Chicago had, with the help of generous corporate and private donations, purchased Sue for their permanent dinosaur collection. Growing up in southeastern Wisconsin, the city of Chicago was close enough for "special occasion" weekend trips. Especially around the holidays, my family would head down I-94 to spend a day or two touring around the Windy City, staring at impossibly high skyscrapers, window shopping along the Magnificent Mile, and most importantly, visiting the excellent Chicago museums.

Some of my favorite memories from childhood involve planetarium shows at the Adler, walking through the giant human heart at the Museum of Science and Industry (a little scary), or slapping my hands on the cold iron surface of a meteorite at the Field Museum as my dad told me how this very rock beneath my hands used to drift between the planets in the cold reaches of space. There was so much magic in those museum halls, so much drama and awe.

Sue would, I knew, fit perfectly in that old great hall. I couldn't wait to see her in person. This winter vacation, I made a special effort to get back to the Field Museum. After several years living in Southern California, it felt deliciously seasonal to run in from the frigid, windy parking lot into the impressive main atrium, a soaring Roman temple dedicated to the power of wonder and the nobility of science. It was wonderful to stand exactly where I had stood as a child, and feel very much the same emotions. It was in these halls that I had vowed to become a scientist. There was so much knowledge here, so many new facts to learn.

The overwhelming impression I got from the museums was how much scientists knew about tbe universe. When I was a child, twenty five years ago, that was exactly the impression of science the museums were aiming for. But things have changed since then, and what the Field Museum did with Sue turned out to be a wonderful example of how our view of science has subtly shifted in the last generation.

Instead of a dimly-lit, dusty old hall, I found Sue under full lights in the main atrium. Sue didn't need any special lighting to be dramatic. Her skeleton had been arranged on a steel frame that allowed her to assume an active, life-like position, as if she was trotting along the old stream bed in South Dakota where she was found. One thing I noticed right away was that some bones looked very different from the others. A friendly docent explained that although Sue was the most complete tyrannosaur known, some bones had been missing and needed to be re-created.

The museum had made sure those bones looked smooth and somewhat fake, so as not to confuse people about which bones were real. Her skull had been too heavy for the steel mount, so a cast was made and put on the skeleton for display, while her real skull rested in a nearby case. Sue's real skull was displayed at eye-level, allowing people to peer inside. Captions pointed out details on her enormous teeth.

Seeing the detailed skull so close up, not lost in the atmospheric gloom of a dark hall was an epiphany. It seemed like I was being invited to investigate and explore, not just gape in awe. Another case held a jumbled collection of bones that hadn't been mounted with the skeleton. A caption explained that the scientists weren't quite sure exactly where these bones should be positioned on the skeleton. Since they didn't know (didn't know?!), they were keeping them aside until further research would reveal more clues to their correct location.

Now I was hooked. My husband and I stood there looking at the odd bones, trying to mentally piece them on to the skeleton. What purpose would they have served? Were there any other skeletons that had similar bones that might give us a hint as to their location? We were looking at the other skeletons in the collection with a fresh eye, trying to find patterns and reason things through.

A series of kiosks around Sue pushed the inquiry even farther. Instead of presenting authoritative knowledge about what dinosaurs were really like, the displays asked questions, and highlighted all the things we don't know about them yet. I had no idea that only seven Tyrannosaurus rex skeletons that were more than half complete had ever been found. Tyrannosaurus rexes seemed such archetypal examples of large dinosaurs. I had assumed we had many skeletons to study.

Another display pointed out the structure of her small forearms, and sent us on another hunt for ideas and theories. The forearms are really quite a mystery, it seems. Sue's arms were way too short to reach her mouth, so she couldn't have fed herself with them. They wouldn't have been any use for grabbing prey, and even ripping open dead prey would have been a challenge for the tiny arms. Still, Sue's forearm bones were thick and strong, with sturdy muscle attachments. She must have used them for something.

Illustrations showed several ideas about how Sue might have used her arms, from shredding meat into smaller bits, to grooming a friend (maybe a mate), to carrying a baby tyrannosaur. The last idea may be unlikely, but it's not impossible. The display emphasized just how little we know about Tyrannosaurus rex behavior. They very well may have raised their young, similar to modern large reptiles like crocodiles, which tenderly carry their young between their power jaws. Far from being a mindless hunting machine, tyrannosaurs might very well have had social behaviors and mating rituals. We just don't know. We're not even sure what sort of prey they hunted.

One display showed a famous old diorama that featured a frenzied Tyrannosaurus rex tearing into an unfortunate triceratops. Now the caption pointed out that the only holes we've ever found in a triceratops skeleton were made by the sharp frontal horn of another triceratops, not the knife-life teeth of a tyrannosaur. We really have no idea exactly what and how Sue would have hunted.

The extent of our ignorance was really brought home to me when another display explained that we can't quite figure out how Tyrannosaurs slept. With her massive frame and tiny forearms, it would have been difficult for Sue to lie down to sleep, and be able to get up again quickly if threatened. Did she sleep on one leg like a bird? Did she lean against something or just crouch down?

As I walked out of the Field Museum that day, I heard people talking about Sue, wondering about her forearms, laughing as their kids tried to mimic how a Tyrannosaurus Rex might settle down for a nap. And whether they knew it or not, they were taking home a very different impression about science that I had learned as a child. Science doesn't lose any of its drama or wonder when we admit that we aren't sure what the facts really are. Questions are much more important. Anyone can come up with a new idea, formulate a new theory. That's the way science really works. And as I said goodbye to Sue that day, I was sure that she hadn't taught us her last lesson yet. See you around the Field Museum, Sue.

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