Most people think of fossils as neatly mounted skeletons displayed in cool, clean museums with nicely printed labels at their feet.
That’s pretty much the way I think of them at the moment, since I’m writing this in the lunch room of the Royal Tyrrell Museum in Drumheller, Alberta.
Unfortunately they don’t occur that way in nature–though it would certainly be easier if they did!
First, fossil-hunters look for exposed bedrock in places where rivers or glaciers have carved up the land, such as the Badlands surrounding Drumheller. They might look for bedrock of a certain age if they’re searching for a particular kind of specimen.
After a while, a paleontologist builds up an image-bank in his head of what certain bones look like, which makes it easier to recognize one if he sees it poking out of the rock. And luck plays an important role, too: the sun might be at just the right angle, or the fossil-seeker might come across a hillside just when erosion has exposed a skeleton.
Typically one piece of a fossil is found on a hillside and other pieces at the hill’s base, because the same erosion that exposes fossils also destroys them. The first task is to dig carefully around the bone to see if there’s more inside the hill. If there is, then the next step is to remove the hill.
That could just be a matter of stripping away a metre of soil–or removing tonnes of shale with pick and shovel, or even jackhammers and dynamite.
Once the “overburden” is stripped down to within 30 centimetres or so of the fossil, hand tools are used to follow the bone into the rock. When the fossil’s extent is known, a trench is cut around it, and then it’s cut into smaller blocks.
Paleontologists try to avoid cutting through bones, but sometimes have to for the simple reason that they often have to lug the fossils out on foot.
The blocks are coated with about seven layers of burlap and plaster of Paris, with some two-by-fours between the third and fourth layers for stability. The top is covered first, then the block is flipped over and the bottom is covered.
Everything is photographed and thoroughly mapped, and the rock is sectioned to help date the fossil and determine its ancient environment.
The plaster-covered blocks (big ones can weigh a tonne) are then taken to the museum, where workers use very fine tools to free the fossil from the rock.
They work from the bottom up because the top, having been exposed, is already partially “prepared.” That preparation consists of coating the bone, as it is freed, with a shellac-like glue (thinned so it will penetrate the bone better). The glue helps minimize fractures, particularly in small bones.
Once it is free of the rock, the fossil is carefully catalogued and then studied. Paleontologists want to know what it is, what its environment was, and most of all, “What does it mean?” in terms of the history of that species and life in general.
Some fossils, after the initial study, are simply stored; others, destined for display, are replicated: latex rubber is painted over the bone to form a mold, and fibreglass or foam casts are made.
The fossil of a typical duck-billed dinosaur takes three weeks to collect, a year and a half to prepare, two months to replicate and a month to mount, with up to a year of research added in.
Yet for paleontologists the rewards are worth the backbreaking work in the field and the painstaking work in the lab.
One of our great attributes as a species is that we’re always asking “why?” That basic curiosity drives every paleontologist…and also drives visitors to places like the Royal Tyrrell Museum.
Well, that and the really cool gift shop.