Preposterous Universe

Monday, August 02, 2004
Dinosaur report I

Having returned from dinosaur hunting basically intact, I'd like to explain a little of the process that is actually involved. Also very interesting, of course, would be to talk about the dinosaurs themselves, and what we hope to learn by studying them. But that's another huge subject, which I am fairly unqualified to talk about, so you'd do better to hunt about on the web (or visit a museum). What I can try to do is give you an idea of what it is like to actually go out there and dig up some bones.

In particular, there are two questions I've always had about the nuts and bolts of paleontology: how do you actually find the fossils in the first place, and how to you dig them out once found? Answer in both cases: a little bit of know-how, and a huge amount of effort.

This is the second year I've gone to Wyoming with Project Exploration; last year I did manage to find a fossil myself, but this year we focused more on digging than on prospecting for new specimens. The prospecting was done ahead of time by Paul Sereno and some of his students. (Paul is the paleontologist half of the husband-and-wife team who founded PE; Gabrielle Lyon is the educator half.) The relevant know-how, as best I can make out, involves a combination of geological background and word of mouth. In fact, it seems from my outsiders perspective that there isn't much of a bright line separating the disciplines of geology and paleontology; each relies heavily on knowledge from the other field, and experts in one are typically well-versed in the other. For dinosaur-hunting purposes, the geology comes in once you realize that your prospecting efficiency is greatly enhanced if you spend your time peering at rocks that actually date from the Mesozoic (the dinosaur era, between 248 and 65 million years ago), rather than before or after. Not only that, but you would especially like to have a layer that has been uplifted by geological activity, so that exposed rock faces (out of which might be sticking dinosaur fossils) are plentiful. Formations of this sort are common in certain areas of the Rocky Mountains, which is one reason why this region has produced so many significant dinosaur finds. We were working in the Morrison Formation, a limestone bed dating from the Jurrasic. (The Mesozoic is divided into three periods: the Triassic [248-108 Mya], the Jurassic [208-146Mya], and the Cretaceous [146-65 Mya].) The Morrison has long been a prolific source of dinosaur fossils. Here is a picture of the layered topography through which we were poking around; click for a bigger view.

Word of mouth comes in for the simple reason that, once you find a dinosaur somewhere, the surrounding regions are (sensibly) thought to be more likely to contain fossils than other randomly-chosen regions of the countryside. Not only that, but much of the land in this region of Wyoming is owned by ranchers who know the terrain like the back of their hand, and have become adept at spotting fossils. So sometimes it's as simple as being told by a local rancher that there are some interesting-looking fossils at a certain site, or at least that a certain region seems promising.

In this particular case, Paul and some of his students had visited some formations around Shell, Wyoming (pop. approx. 50) a few weeks before we went for our expedition. They found some interesting fossils the old-fashioned way: waking up early in the morning and spending their days walking for miles, paying close attention to every rock that was part of the relevant geological layer. Fossils, of course, are bones (or other parts of an organism) that have been preserved in rock, and the process of fossilization typically involves much of the original organic material actually being replaced by rock. Which is to say, the fossils look awfully rock-like. So you have to know what you are doing, and long practice is at least as important as being told ahead of time what to look for. (Most common sentence heard at these digs, spoken by we amateurs to one of the people who knew what they were doing: "Is this a bone?") Once you've seen some examples, you begin to recognize the striations characteristic of fossilized bone marrow, in contrast with the relative smoothness or unstructured graininess of rock. Still, wandering through long stretches of hillside, you need to have an eagle eye to be effective at prospecting.

In addition to a few dinosaur fossils, they found the trunk of a tree from the Jurassic that was over five feet wide; if it continues into the rock in which it is embedded, it may very well be over forty feet long. Paul calculated that two semi trucks should be able to haul the thing back to Chicago, where it could be used as part of an exhibition for PE of dinosaurs in their native habitat. At the same time, by looking at the interior we could learn something about the climatological conditions at the time the tree was alive (over perhaps a century or two). Personally, I'm happy to spend my time doing the delicate work of digging out dinosaur bones, and not having to be responsible for a several-ton fossilized tree.

The areas in which one finds these specimens are what most of us would describe as the middle of nowhere. Once you've found an interesting site, you mark its location in the handheld GPS unit that you remembered to bring with you while prospecting, so that you can actually find the thing when you come back. (Don't ask me what they did before GPS.) There is also the worry that someone else comes along and digs up the fossil that you have found (expeditions like ours take place largely on government land, maintained by the Bureau of Land Management, so in principle anyone can come and dig them up, so long as they get a government permit to dig). So after finding a fossil and perhaps doing some preliminary digging to verify that it's worth a follow-up visit, you then take a shovel and cover it back up with dirt so that it's not obvious to future visitors. It's not even obvious to you when you come back some time later, so a certain amount of time is spent re-finding the sites that were found on a previous visit.

Tomorrow: we go out and actually dig up some bones.

Ideas on culture, science, politics.
Sean Carroll

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