Preposterous Universe

 
Dinosaur report II

Continuing the story from yesterday, let's say you're an enthusiastic amateur about to go out in the field (led by one of the world's experts) and dig up some dinosaur fossils. Your first question would of course be: what do I wear? You'll want good hiking boots, sturdy but not too heavy. It's beastly hot, so you'll be tempted to wear shorts, but don't; you'll be tromping through cactus and sagebrush, and then spending hours kneeling on rocks and dirt, so jeans are definitely called for. Hat and sunglasses are mandatory. Some of us wore lightweight long-sleeved shirts, although I did fine with T-shirts and heavy doses of sunscreen; despite the relentless Wyoming sun, I managed to keep my healthy pale complexion largely intact.

Besides clothes, the only necessary items we were personally responsible for were our water canteens. Bug spray is a good idea, and cameras or binoculars are useful, but not required. The serious equipment was provided for us by the Project Exploration folks: GPS units, walkie-talkies, brushes, awls, hammers, gloves, shovels, pickaxe, hardener, glue, tinfoil, burlap, plaster, measuring tape. Nothing very high-tech, other than the GPS. The physicist in me was sure that there must be some X-ray-like technique to probe into the soil to distinguish fossils from the surrounding rock; but nobody knows of any good way to do it, and I didn't have any useful ideas. (I'm a cosmologist, okay?)

Suitably equipped, we head out to the site. Let me just mention that none of the skills one develops by spending one's days doing theoretical physics and one's evenings at jazz clubs really come in handy out in the field. The work involves serious physical labor and tremendous patience; the good news is that, although it requires years of training and practice to be really good at it, essentially anyone can be productive after a short tutorial. It helps that Paul seems to have an endless (or at least substantial) supply of patience and confidence in his motley crew of city folks; in his shoes, I would be scared to death of what these klutzes were likely to do to my fossils, and would simply ask them to watch from a respectful distance while I did the work myself.

Our group was about fifteen people, of whom two (Paul and Bob Masek, a fossil preparator at the University of Chicago) really knew what they were doing. Of the rest of us, about half had been along the year before, and the newcomers would occasionally (in their naivete) look to us for guidance. We took two vans from the ranch where we were staying out to the site, or at least as close to the site as we could get in the vans. From there we have to lug the aforementioned equipment to the actual fossils, at which point the excitement starts.

The main fossil Paul and his students had found was a vertebra from the tail of what is likely to be a Camarasaurus, a large sauropod common in the Jurassic. (Yes I know the link says that Camarasaurus was "much smaller" than other sauropods, but when you're 60 feet long and weigh 20 tons, you're large in my book.) Sauropods are the hulking big four-legged herbivorous dinosaurs with long necks, like Brachiosaurus and Diplodocus; other major categories are the mostly-carnivorous theropods such as raptors and T. Rex, and ornithischians or bird-hipped dinosaurs, including most of the funky armor-plated species like Triceratops and Ankylosaurus. Just to add an element of confusion, actual birds evolved from the lizard-hipped theropods, not from the bird-hipped ornithischians.

What you typically find, of course, is a single bone sticking out of the rock. In this case, Paul had found a vertebra from the tail. The question then is, if you follow the trail into the rock, do you just find the tip of the tail, or most of the dinosaur? In other words, in which direction is the tail pointing? You just have to dig and find out.

This is where the patience and determination come in. You basically poke gingerly at the area around the fossil with an awl, then remove the dirt and stones with a brush. (Try not to use your fingers, or let the stones fall onto the fossil; a brush is gentlest.) The awl and brush are your most common tools. From the variations in texture and color, you should be able to tell the bone from the surrounding rock if you are careful, although sometimes it's tricky even for the experts. (The experts, by the way, refer to the rock in which the fossil is embedded as "matrix," thus adding to the science-fictiony feel of the whole enterprise.) At first you have to move extremely carefully and tentatively, as you don't know where the rest of the bones are. Every time you uncover a little bit of bone, you pour hardener over it to help protect it from being scratched or shattered. As often as not, the bones are not "articulated" -- arrayed in a nice dinosaur shape -- but rather are jumbled together. But after you make a little bit of progress, you can begin to get a feeling for the way in which the skeleton is arrayed in the rock. At that point, you might decide that the three feet of rock above your fossil can be removed more rapidly than awls and brushes allow; that's where the pickaxe and shovels come in, or even jackhammers or heavy machinery in extreme cases.


Here's a picture of Paul hugging the part of the tail we have uncovered. He's feeling protective because we had very good news: the fossil seems to be pretty much articulated, and even better the vertebrae are growing as we move into the rock! Which means there is an excellent chance of finding a substantial portion of Camarasaurus skeleton lying in there, undisturbed for the last 150 million years.

Our rate of progress wasn't nearly enough to imagine actually excavating the thing; the picture here basically shows the end result of a day and a half of work. Further trips will be required before the entire fossil can be shipped to Chicago. To protect what we have uncovered, we first cover the bones with tinfoil, then with strips of burlap dipped in plaster. The plaster will not only protect the bones once we cover them with dirt again, it also will make it much easier to eventually bring the fossil home. In fact you don't nearly dig away all the rock from the bone; you intentionally leave an inch or two of matrix surrounding the bottom half of bones, dig out from the bottom, and then plaster around the entire collection, which gets shipped back to the lab. (A ton or two of shipped materials is common.) There a real expert, working in decent conditions (presumably involving air-conditioning), can remove the rest of the matrix. Then you take appropriate pictures and measurements, and possibly think about mounting the specimen for display. If (as Paul often does) you went to Niger or Mongolia or Argentina to collect the fossils in the first place, the original country will typically want it back; you get the science out of it, and it ultimately returns home. For our Wyoming fossils, we hope to build up a collection at the University; the previous collection was short-sightedly given away.

This is the second year I've gone on one of these trips with PE. The first year was great fun but I was exhausted by the end; this year I wanted to stay out there and keep digging. It's an exhilarating experience, and utterly different from being a theoretical physicist. On the other hand, dinosaurs and cosmology are two topics that readily engage the public imagination, and the folks at PE hope to extend their reach into other areas of science, so I hope I can be some help. At the end of a long day in the field I gave an informal lecture on black holes -- amazingly, despite myriad other distractions and every reason to be tired (the lecture began at 9:30 p.m.), everyone on the expedition attended and asked great questions about the curvature of spacetime. Just one more reminder, as if any were needed, that most people are intrinsically fascinated by science, and it's our duty to do a better job of sharing the excitement that professional scientists get to feel all the time.

~ posted by Sean Carroll at 11:06 AM ~ link ~ ~ ~