After returning from the field and getting some much needed rest we are eager to share more about what we do in Montana. While the Wilson lab is primarily focused on the ‘microvertebrate‘ animals that lived alongside the dinosaurs (and survived the K/Pg mass extinction), we aren’t only here for the small things – we’re digging for dinosaurs too! This week we’ll share how those dinos you see in a museum got there.
Step 1: Prospecting
To collect a dinosaur, you must first find a dinosaur! We use a combination of maps and old field notes on exposed rock formations to pick where we will ‘prospect,’ or look for specimens, and we are always respectful of land ownership and carry appropriate permits. Ultimately, it’s about eyes on the outcrop and boots on the ground to locate a dinosaur skeleton, and much of our time this summer has been spent hiking the hills.
Finding a dinosaur is always exciting, but not all skeletons are created equal in the eyes of scientists and preparators. We are fortunate to find pieces of dinosaurs all over the badlands, in fact, Triceratops bones are so abundant that they are almost a dime a dozen. These are the “cows of the Mesozoic” and you wouldn’t want to collect every piece of cow you found, would you? So then what makes a fossil worthy of excavation? We are of course looking for really beautiful Triceratops specimens, but we are also focused on a few other species of herbivorous dinosaurs like the duck-billed hadrosaurs and dome-headed pachycephalosaurs, and we’d love to find a skeleton of a carnivorous dinosaur (think T. rex!). Nicely preserved specimens get our attention, as do any specimens where it appears there are multiple bones or a skull preserved. It’s a lot of work to excavate a dinosaur, and with so much out there and so little time during the summer, we have to be picky.
In fact, we often walk past dinosaur skeletons without collecting them. Why? Because by the time we find them, they have turned from potentially lovely, museum-quality specimens, into what we affectionately call “Explodo-saurus.” We find many Explodo-saurus skeletons in the field (and DIG teachers will too!), and that makes the excellent specimens all the more valuable to collect.
Step 2: Excavation and Data Collection
Once an excavation-worthy specimen has been located, it’s time to begin! One of the most important things to remember when excavating a dinosaur is that you don’t get a second chance to collect data, so we make a conscious effort to collect data early and often. Depending on how the animal is preserved in the rock, we may be able to infer the environment where it lived and died, how its skeleton ended up there, and maybe even how it died. These pieces of information make skeletons infinitely more valuable to scientists studying their ecology. We make quarry maps that put all the bones on a grid, collect latitude, longitude, and elevation data, describe the rock in which the specimens are found, and take tons of photos. You never know what data could be critical to another scientist in 10+ years.
For the actual excavation, we use different tools based on the ‘matrix,’ or the rocks surrounding the fossil. Some siltstones and claystones will crack away from the bone so easily that you can simply use an awl to uncover the specimen, while some sandstones can be so hard you need a jackhammer – we see specimens like these and everything in between! We generally bring a variety of tools to a quarry: awls, chisels, rock hammers, whisk brooms, soft brushes, foil, paper towel, and vinac (polyvinyl acetate, or plastic beads dissolved in alcohol.) Vinac is used as a consolidant or glue in the field because it’s reversible (adding more alcohol dissolves the plastic again), and can be mixed in different viscosities to meet your gluing needs, spanning from a thin veneer to coat freshly-uncovered bone, to re-attaching broken pieces.
To free up loose rock, we alternate between chisel and awl, then sweep away the debris with brushes. It’s critical to be able to see where you are working and to recognize bone that has just been uncovered (which looks a lot like rock). “A clean quarry is a happy quarry!” When working in a quarry where fossil bone looks just like rock, we gently tap on rocks with our awl, since rock and bone sound slightly different!
Step 3: Protect and Preserve the Fossil
Field excavations are necessary to free fossils from the ground, but the curation and preparation of fossils really happens back in the lab where professional preparators have access to optimal tools and adequate light. In the field, we are trying to determine the size and extent of the elements (bones), and then quickly cover them with protective materials for a safe trip back to the lab.
After exposing the element, and ‘opening up the quarry’ to determine its size and extent, we leave a few inches of rock around each edge and begin to dig down to form a pedestal or platform. Then we cover the surface with strips of burlap dipped in plaster of paris to make a cast for the fossils, similar to what a doctor does for a broken arm or leg. This ‘top jacket’ protects the surface of the bone and rock as we dig deeper and can also be left as a ‘winter jacket’ if we can’t finish the excavation in a single summer.
If we do plan to take the fossil out, we continue to pedestal until we have a tall platform and it would be easy and safe to flip the jacket and fossil inside without losing any material. This step in the process is the most nerve-wracking – you’ve been cautiously excavating a tiny bit of rock at a time up to this point and now you will risk everything you’ve been working on to quickly flip hundreds of pounds of rock upside-down! If you’ve done everything right, the jacket will safely flip and you can plaster the now exposed underside of the fossil cradle.
Step 4: Pack it out!
Before you can celebrate a successful excavation, you have to get the fossil in its jacket to the vehicle. We are diligent about strong jackets to protect the fossil in transit, but it’s important to remember that rocks are heavy, and rocks coated with plaster of paris are even heavier! Sometimes a Triceratops rib that is a few feet long but only a few inches thick will end up being hundreds of pounds to carry in its jacket. It is not until fossils are safely in the museum that an excavator breathes a sigh of relief.
Remember all the steps that go into a fossil you see at a museum, and try to imagine yourself excavating, recording data, jacketing, and packing out fossils. There is a LOT of effort that goes into every single specimen in collections or on display, but beautiful specimens are more than worth the effort.
If you want to learn more about this process, visit the Burke Museum of Natural History website or the Burke Blog to learn about the excavation and preservation of the mammoth tusk found at a residential development site in Seattle this spring!