Trenching a Turtle—Saving a Fossil for Study

The museum’s dinosaur researcher, Dr. Jordan Mallon, led his first field expedition this June accompanied by collections technician Margaret Currie. Their three-week journey to southeastern Alberta was mainly a search for dinosaur remains, but along the way they found an ancient turtle. Read how they prepared it for our study.

Backpack and rock pick lie on ground by the turtle fossil.

The fossil as it was found in the field (shown next to rock pick). The location overlooks the South Saskatchewan River. Image: Jordan Mallon © Canadian Museum of Nature.

On June 21, the longest day of the year, Margaret and I were lucky enough to stumble across a fossil turtle shell in the badlands near Hilda, Alberta. We found the specimen in a grey sandstone that once formed the bank of an ancient river, dating nearly 75 million years old. Only the underbelly (plastron) of the turtle was exposed, but we were quickly able to recognize it based on the preserved texture and outline. The specimen measured about 20 cm long and more than half as wide.

On finding the turtle, we knew immediately that we would be interested in collecting it. We were quick to snap photos of the specimen in the ground and record the locality data using our GPS. We also bagged all loose fragments surrounding the specimen in the hopes that we could later glue them back into place in the lab.

A closeup of the turtle’s plastron embedded in the rock.

A close-up of the turtle’s plastron. The pen provides an idea of its size. Image: Jordan Mallon © Canadian Museum of Nature.

Next, we began using brushes and awls to expose the surface of the plastron so that we would have a better idea about the size of the specimen was and what was preserved. Once we were satisfied that we had exposed the outline of the turtle, we used picks and awls to trench into the rock around the specimen, paying careful attention to not accidentally cut into the fossil itself. We created a deep and wide trench around the turtle, eventually undercutting it so that it sat on a sort of rocky pedestal (we call this process, unsurprisingly, “pedestalling”).

Margaret Currie lies on ground around the exposed turtle specimen.

Technician Margaret Currie exposes the turtle specimen. Image: Jordan Mallon © Canadian Museum of Nature.

We then began preparations to create a “jacket” for the specimen, wrapping it in a plaster cast to transport it safely back to Ottawa. First, we covered the turtle in a layer of water-soaked toilet paper. This provides some cushioning for the specimen during transport and forms a protective layer between the fossil and the plaster. We then used a mixture of plaster and burlap to wrap the exposed surface of the fossil, and allowed the cast to harden overnight.

Jordan Mallon sits behind the plastered turtle shell.

Having plastered one side of the shell, Jordan Mallon prepares to plaster the other side. Image: Margaret Currie © Canadian Museum of Nature.

When we returned the next morning, we finished cutting the fossil from the rock and flipped it so that we could wrap the other side. We did this in much the same way as before and allowed the plaster to dry in the hot afternoon sun while we prospected elsewhere. On returning, we used a black marker to label the specimen with a field number and placed it in a heavy canvass sack to haul out of the badlands.

This, more than anything, was the hardest part of the job. We carried the fossil, weighing roughly 50 pounds, up and down the steep and craggy landscape of the badlands for close to a kilometre.

A person with back to the camera carries a sack containing the turtle specimen.

Hiking the heavy fossil out of the badlands at the end of the day. Image: Jordan Mallon © Canadian Museum of Nature.

Of course, the trip was much shorter as the crow flies, but clambering across the various buttes and coulees made for a much longer trip. We were greatly relieved once we reached our truck parked at the edge of the prairie. We loaded up the heavy fossil and drove back to camp for a well-deserved beer.

Read previous blogs about this fieldwork:

This entry was posted in Fieldwork, Fossils, Research and tagged , , . Bookmark the permalink.

2 Responses to Trenching a Turtle—Saving a Fossil for Study

  1. Pingback: Bonebeds and dinosaur remains—three weeks of prospecting in Alberta | Canadian Museum of Nature – Blog

  2. Pingback: From foothills to badlands—fossil discoveries in Alberta | Canadian Museum of Nature – Blog

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