DinoByte Wednesday: Field Update Part I – Collecting Microvertebrate Fossils

We are now one week into fieldwork with undergraduates and the Hell Creek III Research Project. Our camp is pretty large, with 24 people total from UW, UC Berkeley, Montana State and the Museum of the Rockies, undergraduate students (from University of Oregon, University of Michigan, Smith College, and Western Washington University), and many volunteers! Meals are hectic, evening campfires are entertaining, and the fossil-finding thus far is very successful – we’ve found a half dozen dinosaur localities and over one dozen mammal teeth.

You might be wondering what we do all day in the field, if so, read on! In this first field update, we’ll talk about the process of collecting microvertebrates in the field.

Collecting Microvertebrates

Step 1: Surface collecting for microvertebrates

Microvertebrates are small! So small, that to find the really tiny elements (like mammal teeth), we wear knee pads and “cheaters” (magnifying lenses attached to a visor). When we find a fossil, we use an awl to free it from the surrounding sediment, and we put it in a film canister for safe keeping.

Tools used to collect surface microfossils include ‘cheaters’ (magnifying lenses), awls, film canisters, and knee pads (left). Students are crawling on their hands and knees (good thing they have knee pads!) wearing their magnifying ‘cheaters’ to find fossils they can free with their awl and place in a film cannister for safe keeping (right). Photo credit: Lauren DeBey.
Tools used to collect surface microfossils include ‘cheaters’ (magnifying lenses), awls, film canisters, and knee pads (left). Students are crawling on their hands and knees (good thing they have knee pads!) wearing their magnifying ‘cheaters’ to find fossils they can free with their awl and place in a film canister for safe keeping (right). Photo credit: Lauren DeBey.

Step 2: Find the ‘productive layer’ and collect fossiliferous sediment

After we’ve scoured the outcrop for all the surface fossils we can find, we want to identify exactly where the fossils are coming from in the hill. We trace the surface material to its highest point, and at that level we dig into the hillside and crack open rocks until we find a fossil ‘in situ’ or encased in fresh rock. If we find something, we’ve hit on the ‘productive layer’ and it’s time to collect bags of sediment!

To collect sediment we use geopicks and rock hammers to free in situ rock from the deposit, and a shovel and bag to collect the fossiliferous sediment. Then we pack the material out in frame packs, and we return to camp victorious!

Geopicks, rock hammers, frame packs, and notebooks (left) are important tools for collecting fossiliferous sediment. DIG Assistant Director, Lauren DeBey, excavates rock from the productive layer using a geopick (center). Students sit on the outcrop and break apart rocks from the productive layer searching for encased in situ fossils (right). Photo credit: Lauren DeBey.
Geopicks, rock hammers, frame packs, and notebooks (left) are important tools for collecting fossiliferous sediment. DIG Assistant Director, Lauren DeBey, excavates rock from the productive layer using a geopick (center). Students sit on the outcrop and break apart rocks from the productive layer searching for encased in situ fossils (right). Photo credit: Lauren DeBey.

Step 3: Describe the lithology

Identifying rock types and inferring depositional environment remains a big part of what we do during our paleontology fieldwork. Each time we find a productive layer, we describe its rock type and contents in our field notes. Now, after decades of fieldwork, we have a sense for the rock layers most likely to produce fossiliferous material. We’re most often looking for sediments that represent the base of stream channels, because it’s here that materials were dropped from the moving water and fossils, mud balls (‘mud rip-up clasts’), rocks, lignite, and organic material (wood, plants) were deposited. This often produces a ‘dirty’ fossiliferous productive layer, and hopefully it’s highly concentrated with fossils! But we won’t know for sure until we get back to camp.

The geopick marks a rock unit we hope is the productive layer of sediment producing fossils (top). This ‘junky’ layer (bottom) contains black lignite (coal), wood debris, mud balls, and hopefully it is also full of fossils! Photo credit: Lauren DeBey.
The geopick marks a rock unit we hope is the productive layer of sediment producing fossils (top). This ‘junky’ layer (bottom) contains black lignite (coal), wood debris, mud balls, and hopefully it is also full of fossils! Photo credit: Lauren DeBey.

Step 4: Screenwash collected sediment

We return to camp with bags of sediment, and to reduce the total weight we bring back to Seattle, we first screenwash collected material in the lake. Each day we put our collected sediment into wooden boxes with window screen on the bottom and let these soak overnight in the Fort Peck Reservoir. The gentle wave motion of the lake breaks up hard rocks, and the smaller particles of sand, silt, and clay will fall through the window screen, leaving the larger items (including fossils and larger rock particles) in the boxes. We pull boxes from the water each morning and let them dry during the hot Montana days, bag the sediment each night, and repeat the process with the next material collected.

Students place wooden boxes full of collected sediment into the Fort Peck Reservoir to allow the natural movement of the water to screenwash the sediment (top). The next day the boxes are placed in the sun to dry (middle), and fossils and larger rocks remain trapped in the screen box (bottom). Photo credit: Lauren DeBey.
Students place wooden boxes full of collected sediment into the Fort Peck Reservoir to allow the natural movement of the water to screenwash the sediment (top). The next day the boxes are placed in the sun to dry (middle), and fossils and larger rocks remain trapped in the screen box (bottom). Photo credit: Lauren DeBey.

At the end of this microvertebrate collection process we have a diversity of fossils from different animal groups including mammals, dinosaurs, reptiles, amphibians, and fish! These freshly collected fossils help us reconstruct the paleoenvironment pre- and post- K/Pg extinction.

Want more from the field? Check back for next week’s update and follow our Facebook page to see more photos!

 

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