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Paleontological
Expeditions (a.k.a. Fieldwork)
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When I tell people I'm a
paleontologist and that I go out on "digs," they usually think I spend
most of the
trip literally "digging" in one place for fossils. This
does happen on occasion, but it really isn't typical. Most of my time
is spent looking, and relatively little is actually spent collecting.
In fact, when we're exploring new sites, we may go for days and never
even find a scrap of bone.
Sometimes paleontologists do excavate fossils in one area for an extended period of time and when they do, it is known as "quarrying." I don't do much quarrying in our fossil mammal sites, mainly due to the types of rocks we're working in and the way the fossils were preserved. Quarrying is much more common when collecting the remains of large animals such as dinosaurs, in which a single individual can be spread over a large area. It is also used to excavate highly concentrated fossil deposits. Good examples would be the La Brea Tar Pits in California or Agate Fossil Beds in Nebraska. The tar pits were a trap for animals and slowly accumulated the remains of many individuals over hundreds to thousands of years. Agate Fossil Beds is a mass death site in which many individuals died in a small area during a drought of probably only several years. Instead of quarrying, the majority of my time in the field is spent walking around looking for fossils, a type of collecting generally known as "prospecting." Most of these fossils I find can picked up off the ground or can be excavated by a single person in a matter of minutes or hours, depending on the size and fragility of the specimen and the hardness of the encasing rock. It's an especially common method of looking for fossils in new areas when you're not exactly sure where fossils will be found. It's a lot like going on a nature hike, except that you're looking for fossils in addition to enjoying the scenery. A third category of fossil hunting (besides quarrying and prospecting) might be called "crawling": when a site is so rich with fossils that you have to get on your hands and knees to examine every square inch of ground for bones and teeth. This doesn't occur very often, but in spots where small fossils are concentrated by weathering, which can remove the fine sediments while leaving the fossils, this is one of the best ways to collect specimens. I have worked some sites like this both in dinosaur-age rocks out west and in mammal-bearing rocks in South America. It differs from quarrying in that you're mostly just picking things up off the surface rather than actually digging down into the sediments. Sometimes areas can be screen washed after being crawled. Screen washing is sort of a variation of quarrying, except that the goal is to collect very small specimens that typically aren't big enough to see easily with the naked eye. The way it works is that lots of sediment is collected using by shovel (usually hundreds or thousands of pounds) and then the dirt and other fine particles are washed away using water and fine screens or mesh bags. The remaining material, known as "concentrate," is then examined piece by piece, often under a dissecting microscope. This allows the small teeth and fossil bones to be separated from the sand, small rocks, and other debris. A couple weeks looking for fossil mammals typically will involve lots of prospecting and collecting isolated specimens, some crawling, and little (if any) quarrying. During my career, I've participated in a variety of different collecting trips, sometimes looking for things besides fossil mammals. Depending on where you are, what types of rocks you're investigating, and what you're looking for, you can spend widely varying amounts of time in each of these activities. Below are links to pages with some representative photos and notes from some of these expeditions. |
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Bolivia May 2007 |
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This
page was last updated on March 7, 2010.
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