The Bones in the Bog

An early fascination for fossils

When I was growing up in the Midwest, I remember looking forward to the day every year when a pile of limestone gravel would be delivered and spread on the drive-way at my grand-parent’s home. I would sit for hours in the heat and humidity sifting through the rocks for fossils. They were evidence of something fantastic: the rolling hills of my home were once covered with seawater. The crinoids and clam shells trapped in the rock were once aquatic, residing in an inland sea maybe 250-500 million years ago.

Discovering Oregon fossils

My new home in Oregon has a much different geological history. The fossils I have found here along the Pacific coast (Astoria formation) and inland near Vernonia (Keasey formation) are estimated to be much younger, between 5-25 million years old.

Most likely dolphin vertebra and ribs from the Astoria Formation. Collected on Moolack Beach near Newport, OR

Many fossils and bones have also been found here dated to the Ice Age (10,000-15,000 years old). Mammoth bones have been found in the town of Tualatin and along the Yamhill River. Just last year, mammoth, camel, and bison bones were unearthed during an expansion of the football stadium at Oregon State University in Corvallis.

The bones in the bog

I recently participated in my first, official paleontological survey in Woodburn, a small, rural town about 15 miles as the crow flies from my home. In 1987, bones were discovered along Mill Creek, a small, muddy stream running through town, during placement of a sewer line. Since then, several professional groups have researched multiple areas along Mill Creek, including a site right next to the high school, and discovered bones from giant sloths, bison, squirrels, frogs, turtles, and birds. These species and stratigraphic evidence point to the area once being covered with a muddy bog surrounded by grassland approximately 10,000-15,000 years ago.

Every year, city workers use a backhoe to dig 15-20 foot trenches at designated spots near the high school. Volunteers from different organizations, such as Oregon Archeological Society (OAS) and North American Research Group (NARG), meticulously sift through the soils by hand looking for bones. As a member of NARG, I was invited to participate this year.

About 20 volunteers were on site when I arrived, all sitting on upturned plastic buckets in front of 3 feet high piles of dark soil and clay. I found that the official process for sifting through the material is surprisingly simple: pick up a large clod of earth and thinly slice through it with a triangular putty knife. If you find a bone (a rarity on this day), place it in a plastic bag containing some water. It is important to keep the bone wet until it can be dried slowly, preventing the bone from splitting. As you are sifting, collect all the broken up soil in a large bucket. Repeat until the bucket is full. Once your bucket is full of soil sifted through once by hand, spread the dirt over screens and spray with water. This can sometimes reveal bits of bones you missed by hand excavation.

Volunteers from several organizations at the Woodburn Ice Age bog site
Tools of the trade: bucket and triangular putty knife
Dirt is washed away over sifting screens, revealing bone and wood from the bog

Is this what a gambling addiction feels like?

After spending 6 hours on site, I found three bones: a frog femur and pelvis, and a spine from a stickleback fish. These were tiny and a bit underwhelming for any common observer, but I felt like I had won the jackpot!

Three small bone from the Ice Age bog: frog femur (top), stickleback fish spine (bottom left) and frog pelvis (right). Bootle cap added for reference size.
Close-up of the serrated stickleback spine

In fact, I found the whole experience much like a day at the casino. A gambler chooses a specific slot machine hoping it will be lucky, just as I had chosen the dirt pile I hoped would be holding precious bones. As a gambler doesn’t want to sit next to a “cooler,” or loser, I looked for another digger who was “winning.” In this case, Doug was finding bones like crazy. I wanted some of his luck to rub off on me. While gambling, if the slot machine doesn’t pay off, you move to another one, even though you know that the next pull on the lever might be a winner. I found myself moving from one pile to another hoping that the next dirt clod might have that prize bison or giant sloth bone. And finally, after hours of finding nothing and thinking about going home, when I discovered a bone, even a small, fragile frog femur, I was re-energized and committed to staying for another round. It’s that addiction-reward system that keeps you going looking meticulously one layer at a time through the dark wet earth.

At the end of four days of hand excavations by the team, we had found approximately 200 bones, all of which could fit inside a small plastic baggy. We were inordinately pleased with ourselves to have made some discoveries for science. I am looking forward to next year when I can get back and gamble for my Ice Age bone fix!



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