Antoine Bercovici is a Peter Buck postdoctoral fellow in the Department of Paleobiology at the National Museum of Natural History. He was in the field in North Dakota and Montana for most of last summer. This is his second post about the fieldwork.
In the summer of 2015, a large multidisciplinary team started a major endeavor: mapping with great precision all known fossil sites in Southwestern North Dakota and Southeastern Montana relative to the Cretaceous-Tertiary boundary, the rock layer that holds residue from the asteroid impact that wiped out the land-dwelling dinosaurs and many other forms of life 66 million years ago. By assembling this map, we will be able to track the evolution of terrestrial ecosystems through the time of the last dinosaurs. Spearheading this project are four individuals, each providing a piece of the puzzle: Tyler Lyson, from the Denver Museum of Nature and Science, has found many dinosaur skeletons in the area; Dean Pearson, from the Pioneer Trails Regional Museum (Bowman ND), has numerous sites with small fossils representing crocodiles, turtles, lizards, salamanders, snakes, birds, fishes, and mammals; Kirk Johnson, Smithsonian Institution, has numerous fossil leaf localities; I provide data on fossil pollen and stratigraphy, which help us understand environmental conditions at each site and when the fossils formed. Tying all our work together, is Erica Evans, our GPS wizard.
|Erica Evans is mapping the contact between the Cretaceous Hell Creek Formation and the Tertiary Fort Union Formations with a differential GPS unit. In this video interview, she describes her work to John Hankla.|
This summer, we all returned to our home base for this work, Marmarth, North Dakota, to continue the mapping project for as much as eight weeks. We began our work in a place we call "Valley of the Last Dinosaurs," where numerous dinosaur skeletons have been found in the past. We mapped many more localities this year and, not surprisingly, during the course of our work we also made some spectacular new fossil finds. Finding fossil bones always is accompanied by excitement and a question: what animal did these belonged to? Because the only large animals that lived during the Late Cretaceous where dinosaurs, the answer is usually fairly obvious, but what species? Answering this question ultimately requires finding the right bones that allow for identification. Sometimes diagnostic bones are visible, but other times they won't be revealed without digging the fossils out of the ground. Either way, a statistically informed answer in this area would be "it’s a ceratopsian" (a horned dinosaur like Triceratops and Torosaurus). Hell Creek dinosaurs have been documented for more than a century and, by far, the most commonly found are ceratopsians. Paleontologist Jack Horner has even dubbed them "the cows of the Cretaceous."
It is thus no surprise that almost all dinosaur specimens that we managed to find in this summer are ceratopsian, in fact, we found more than twenty partial skeletons, some with complete skulls! The photo to the right shows me next to one of the last major finds of the season: a complete Triceratops skull encased in an ironstone concretion. Just peeking out of the rust-colored concretion are white colored bones: both brow-horns, the nasal horn, and the beak at the bottom.
Usually, finding a dinosaur is the easy part of the process. Getting it out of the ground and back at the museum is another story that involves a lot of labor and ingenuity to tackle the tons of rocks and bones -- a Cretaceous rodeo, for real. Delicate hand tools like rock hammers, chisels and brushes are used first to expose more of the bones, and sometime power tools like jack-hammers and rock saws must be used to remove excess rock from around the fossils and lighten the load. Before the bones can be removed from the site, they are wrapped in a plaster field jacket for protection during transport, a proven process that dates back to the early days of paleontology.
Safely wrapped in their plaster jackets, the fossils now have to be removed from the outcrop and transported back to the museum. Ideally a helicopter is called to take care of the job when the jackets are extremely heavy. The reality is however less glamorous. A lot of ingenious solutions have to be found to remove the plaster jackets from very remote areas with no practical roads. Some of our jackets this summer weighed over a ton.
During a dig, a lot of data are recorded: photos are taken, and bones are drawn and their positions reported on a bone map. Other evidences such as the rock type, sedimentary structures, and other fossils found in the quarry are recorded, since together they can provide precious information as to the events and processes that occurred after the death of the animal and during burial (a branch of paleontology called taphonomy).
While this summer brought us a lot of exciting fossil discoveries, nature also treated us to some exciting and fairly unusual weather: multiple thunderstorms pouring heavy rain and hail made life in the camp, on the road, and in Marmarth quite exciting at times!
Photos by Antoine Bercovici unless noted otherwise.