Antoine Bercovici is a Peter Buck postdoctoral fellow in the Department of Paleobiology at the National Museum of Natural History. He has been in the field since early July, and sent this post from North Dakota.
During the past two summers, members of the Department of Paleobiology conducted fieldwork in the badlands of North Dakota and Montana. They were collecting fossils for the Last American Dinosaurs Exhibit and contributing to decades of research aimed at unlocking the secrets of an ancient ecosystem. This ecosystem, known as the Hell Creek after the fossil-rich rock formation that formed here at the very end of the Cretaceous period, saw the iconic battle of the mighty Tyrannosaurus rex and Triceratops. But it was not just dinosaurs that lived there: many smaller animals thrived in this ecosystem, including crocodiles, turtles, lizards, salamanders, snakes, birds, fishes, and small mammals. They were living in a very lush world, comparable to today's Everglades, as indicated by the very diverse plant fossils also found in the rocks. This world came to an end 66.043 million years ago, as a giant asteroid hit the Earth in what is now the Yucatan Peninsula. The environmental disaster that followed caused many of the Hell Creek species to go extinct — most notably, the non-avian dinosaurs.
The North Dakota badlands show different layers of colored rocks. A major change in deposition can be seen here, indicated by the arrow: below are grey and monotonous sediments of the Hell Creek Formation, and above are the multi-colored sediments of the Fort Union Formation. Click to zoom.
This summer, our team is collecting new data that will tell us how stable the Hell Creek ecosystem was prior to the asteroid impact. We want to know how abundant the last dinosaurs inhabiting this part of North America were, and how their populations were changing over time. In order to answer these questions, we need to be able to place the fossils discovered here on an extremely accurate timeline. In geology, time is represented by the deposition of layers of sediments that accumulate on top of each other like a stack of pancakes: the deeper you go, the older the sediments and the fossils they contain. We are building our timeline by recording the elevations of Hell Creek fossil discoveries relative to the top of the Hell Creek Formation (the top of the pancake stack).
The mapping team is composed of Kirk Johnson, Sant Director of the National Museum of Natural History; Tyler Lyson, Curator of vertebrate Paleontology at the Denver Museum of Nature and Science; Gabi Rossetto, also from the Denver Museum of Nature and Science; Erica Evans of Colorado College; Dean Pearson of the Pioneer Trails Regional Museum in Bowman North Dakota; and myself. This mission involved a trip down memory lane as we pulled out old field notebooks to re-locate close to a thousand fossil sites that were discovered during the past thirty years of work in the Hell Creek of North Dakota. Walking back to every single site, we are marking their geographical positions with a Global Positioning System (GPS) unit and, more importantly, measuring their precise elevations.
Erica Evans (top), Tyler Lyson (right) and I point at a very distinctive white layer of sediment just above the Hell Creek - Fort Union formation contact. This layer marks the end of the Cretaceous and the demise of the non-avian dinosaurs; it is composed of material ejected from the crater that formed as an asteroid struck the Earth about 66 million years ago. We are using the GPS unit that Erica holds to measure the elevations of all our fossil sites relative to this layer. Click to zoom.
(Left) Erica Evans and Tyler Lyson setting up the GPS base station, nicknamed "The Brain,” early in the day. It will record the drift of the GPS position for a fixed point during several hours, allowing us to increase the accuracy of our field measurements. (Right) Erica Evans recording the position of a hadrosaur (duckbill dinosaur) rib that is eroding out of the hill. Click to zoom.
Our timeline fills with more and more fossil sites with each passing day of fieldwork. As we get a better idea of the distribution of our sites in time, we see gaps that we were not aware of before. Fortunately, the data also direct us to areas where we should prospect for new fossils that will fill the timeline gaps! Ultimately, we will have a very good understanding of how the fossils of dinosaurs and other animals are spread out in the 100 m thick Hell Creek Formation, and how ecosystems may have changed in the 1.3 last million years of the Cretaceous, before the asteroid impact.
So much ground to cover. Where should we go next? So far, we have visited about 300 fossil sites in an area of approximately 1000 square kilometers. Click to zoom.
Photos by Antoine Bercovici.
View earlier posts about Department of Paleobiology fieldwork in the Hell Creek Formation in 2013 and 2014.