Why do paleontologists care about rocks? Rock formations house the secrets of the past! Let’s take a walk through time, starting with the oldest formation preserved at our field site, the Bearpaw Shale, and work our way forward through the Fox Hills Sandstone, to the Hell Creek and Tullock formations, the two formations that are the focus of our DIG research.

Bearpaw Shale

The lowest (and oldest) formation exposed near the DIG field camp is called the Bearpaw Shale (or Bearpaw Formation). This formation formed ~74-70 mya (million years ago) as a fine-grained layered mudstone (or shale) in a shallow sea, the Western Interior Seaway, that ran through the United States from the Gulf of Mexico to Canada. This formation was deposited just before the sea began to recede near the end of the Cretaceous Period. Can you believe there was once a sea cutting North America in half, and living in this seaway were sharks, giant marine reptiles like the long-necked plesiosaurs, and extinct molluscs called ammonites? All of these creatures (and others!) went extinct with the dinosaurs 66 mya.

Fox Hills Sandstone

As the Western Interior Seaway receded, eastern Montana went from being covered by a shallow sea to being near shore and beach, with the seaway still present but located further to the south and east. The sediments that preserve this ancient beach make up the Fox Hills Sandstone Formation, and were deposited 70-68 mya. These yellow/tan, plain sandstone beds are very thick and contain few fossils in our field area, so we most often use the resistant, ledge-forming sediments at the top of this formation as a “marker bed” to help identify the  overlying Hell Creek Formation. Scientists think the Fox Hills Sandstone would have been home to a community of dinosaurs, mammals, reptiles, and early birds that would have come down to the shores of the shallow sea to drink and feed.

Hell Creek Formation

The Hell Creek Formation overlies the Fox Hills Sandstone, and is one of the two focus formations for the DIG researchers. This is one of the more famous and widely exposed formations from the Mesozoic Era in the state of Montana. This formation was deposited 68-66 mya and is primarily composed of “drab” and “somber” colored beds of tan sandstones, gray siltstones, and purple mudstones, with little to no coal. These sediments were deposited by freshwater and brackish rivers flowing from the proto-Rocky Mountains into the Western Interior Seaway. Paleontologists have used these sediments to infer an environment that looked something like the picture below. During this time, the environment was composed of large rivers that had rocky shores. Fossils from many animals are found here including invertebrates (like clams and snails), fishes, amphibians, mammals, turtles, crocodiles and dinosaurs. In fact, the first T. rex skeleton, discovered in 1902 by Barnum Brown, was found in the exact region of the Hell Creek Formation that the DIG Field School takes place!

Tullock Formation

The second focus formation, and the highest we find at the DIG Field school preserves the first Paleogene sediments, and was formed just after the K/Pg mass extinction event. This earliest Paleogene formation was deposited 66-64 mya and is known as the Tullock Formation (also known as the Tullock Member of the Fort Union Formation in some areas). This formation consists of thinner, vibrant and colorful beds with yellow, orange, and tan sandstones, siltstones, and mudstones, and lots of large coal seams (low-grade coals known as “lignites”). These beds are so thin, that from far away the different sediments look like stripes on the outcrop, and they have been dubbed “pajama beds” by someone who must have had striped pj’s! During this Era, rivers carried sediment from the mountains to the inland sea causing a swampy vegetative environment. Here, we find remnants of the mammals, reptiles, amphibians, fish, and birds that succeeded the dinosaurs, some of whom survived, and others who immigrated to the area shortly after the mass extinction.

When you compare the deposits of the Hell Creek and Tullock formations, they look totally different, as do the inferred landscapes they represent! Can you differentiate the drab, somber, mudstones of the Hell Creek Formation from the more finely striped beds of the coal-bearing Tullock Formation in the photo below? Knowing where you are in time when you’re standing on the outcrop is a critical paleontological skill.

Next week we DIG into the fossils we will find during the DIG Field School!

Meet the rest of the distinguished 2015 DIG Field School Instructors! And if you missed last week’s post, keep reading below!

Corinna Casey

Hi there, my name is Corinna. I am a recent graduate of UCLA with a degree in paleobiology-geology, and an interest in pursuing vertebrate paleontology. I belong to a great research lab at UCLA, and have been working on a project examining the distribution of fossil Canidae (this family includes dogs, wolves, foxes) over their 40 million year history across North America. I’m a southern California native, in my spare time I enjoy going to the beach, gardening, pressing flowers, and backpacking. I am fascinated by natural history and love to identify birds, feathers, fossils, trees, flowers, and rocks and discover the world around me. This will be my fourth year at the Hell Creek field camp and my second year as a DIG staff member. I really enjoy being involved in science outreach, am so excited to be a part of the Dig Field School, and I can’t wait to meet you all!

Alex Brannick just finished up her first year as a graduate student in Dr. Greg Wilson’s lab at UW, and is excited to join the DIG Field School as a staff member! Alex received her B.S. in Geology from Lafayette College in 2012 and her M.S. in Biological Sciences from Marshall University in 2014, where she focused on jaw shape evolution in dire wolves at the Rancho La Brea tar pits. Her current research focuses on identifying and describing Cretaceous metatherian (marsupial) specimens from Egg Mountain (also located in Montana), as well as looking at aspects of their paleobiology. She can hardly wait to meet you all!

Luke Weaver was born and raised in Colorado, and is a recent graduate of Colorado State University. While an undergraduate, he studied early Eocene (~55-53 mya) mammals from the Bighorn Basin of Wyoming. He is interested in the evolution of mammalian dentition and in sedimentary geology. He will join the Wilson lab as a graduate student at UW in the fall of 2015. He’s ready to get the summer started!

Dave Grossnickle

After getting a BA degree in biology from DePauw University, I taught high school biology in Indiana for four years. I then returned to college, completing a MS degree in paleontology at Indiana University. I’m now finishing my second year as a PhD student at the University of Chicago, studying early mammal evolution and vertebrate paleontology. My long-term goal is to teach as a professor at a liberal arts college. This is my third summer of fieldwork in Montana, and my second year of helping with the DIG school. I love all aspects of the fieldwork, and I think the DIG Field School is an amazing program that can have a huge impact on teachers and their students–so I can’t wait to help out again this summer. Besides research and teaching, my other hobbies include basketball, volleyball, hoppy beers, malty beers, and traveling.

Courtney Sprain

I grew up in Stillwater, Minnesota. In 2012, I graduated from the University of Minnesota with a Bachelors of Science in both Geology and Geophysics, and a minor in History.  I am currently a Ph.D. candidate in Earth and Planetary Science at the University of California, Berkeley. My thesis encompasses work attempting to refine the timing of events around the Cretaceous-Paleogene boundary using both 40Ar/39Ar geochronology and paleomagnetism. This work includes collaborations with Greg Wilson and his students in the Hell Creek region to refine the timing of mammalian faunal decline and recovery around the mass extinction. I am also working in India to obtain high-precision dates for the Deccan Traps, a potential player in the Cretaceous-Paleogene mass extinction. In October I will be getting married in Minnesota.

 

The sixth annual DIG Field School is quickly approaching and we are working around the clock to prepare for an exciting week in the field with an excellent group of educators! Before everyone heads out to Montana, we wanted to give our teachers a chance to get to know more about the field instructors that will be guiding them through their DIG experience. We’ll introduce the first half of the instructors this week, and stay tuned for the second half next week!

Greg Wilson is the Executive Director and Co-Founder of the DIG Field School. At the University of Washington, he is an Associate Professor in the Department of Biology, Adjunct Curator of Vertebrate Paleontology at the Burke Museum, and Adjunct Assistant Professor in the Department of Earth and Space Sciences. He is also a Research Associate at the University of California Museum of Paleontology, and was formerly the Curator of Vertebrate Paleontology at the Denver Museum of Nature & Science. His research has been published in a number of prestigious scientific journals including Nature, Science, Geological Society of America Special Papers, Paleobiology, Journal of Vertebrate Paleontology, and Scientific Reports and has appeared in on-line reporting for the Huffington Post for his work in Hell Creek, Montana as well as Nature Podcasts and Science Daily. His work has been funded by a number of organizations including the National Geographic Society, National Science Foundation, Paleontological Society, and American Philosophical Society. Greg attended Stanford University, received his PhD in Integrative Biology from the University of California, Berkeley in 2004, and was a National Science Foundation Postdoctoral Fellow at the University of Helsinki in 2005.

In addition to his research and work with the DIG Field School, Greg is also a scientific expert consultant for “A New Prehistory” — a documentary trilogy focused on key events in the evolutionary history of different life forms. Greg can’t wait to get another exciting field season rolling!

 

Brody Hovatter returns for his second year as a DIG Field School instructor. Brody graduated from the University of Washington in 2014 and is currently the Wilson Lab’s manager. His research focuses on mammals from the early Paleocene in northeastern Montana, particularly a group of early primates called Plesiadapiformes. Brody loves working in the field and getting his hands dirty looking for bones. He can’t wait for another awesome summer in Montana and is looking forward to meeting all of you!

Dave DeMar joins the DIG Field school for his fourth year as a field instructor. He is a graduate student in Dr. Greg Wilson’s lab at the University of Washington and his research primarily focuses on amphibian, lizard, and snake extinction and recovery across the K/Pg boundary. Dave has described and identified several new species of amphibians and lizards from the Late Cretaceous Period based on fossils from the Hell Creek area and the slightly older Two Medicine Formation of northwestern Montana. The opportunity to step back in time and learn about animals that no longer exist today is one of the many things Dave loves about paleontology. He has been working in the Hell Creek area with Greg since 2007 and also has spent time collecting fossils in Wyoming during his undergraduate degree at the University of Wyoming in Laramie, WY. Dave is a military veteran and served his country in the US ARMY as a tank crewman for three years. Fun Fact: Prior to pursuing a career in paleontology Dave aspired to either be a professional bass fisherman or a member of a heavy metal band!

Stephanie Smith has just completed her third year as a graduate student in the Wilson lab and she loves mammals! She is especially interested in mammal teeth, which is handy because there are lots of fossil teeth in the Hell Creek area for her to study! She usually takes measurements on 3D models of teeth to try and understand how they process food, but she is hoping to soon learn how to use computer models to simulate feeding stress on Paleogene mammals’ teeth. This will be Stephanie’s fourth year at the DIG Field School and she can’t wait for another great year!

 

See below for our second DinoByte Wednesday re-post. Today, we’ll discuss the geologic time scale as it relates to our field site. Enjoy!

The Earth is 4.6 BILLION years old, and the geologic time scale breaks this long amount of time into smaller units. These units, arranged from longest to shortest, are eons, eras, periods, epochs, and stages. The divisions between units are based upon major geological and paleontological events. At our field site in Hell Creek, Montana, the fossils indicate dinosaurs lived there during the Phanerozoic Eon, of the Mesozoic Era, during the Maastrichtian Stage of the Cretaceous Period.

The Mesozoic Era is the “Age of Dinosaurs,” and the dinosaur fossils we find in the field are 68 million to 66 million years old! We will find dinosaurs during the DIG Field School (as well as turtles, crocodiles, fish, mammals), but one of the things that makes our field site so special is that in this area there are rocks that preserve the last two million years that non-avian dinosaurs inhabited the earth, the layer that shows dinosaur extinction, AND the first one million years of the Paleogene Period.

The Paleogene Period (and the Paleocene Epoch) marks the start of the Cenozoic Era, the “Age of Mammals.” At our field site, in addition to Cretaceous dinosaurs, we find fossils of the mammals and other animals that survived the Cretaceous-Paleogene Mass Extinction that killed the dinosaurs (except birds). That makes this area one of the best places in the world to study dinosaur extinction AND the subsequent recovery of mammals.

Most of the geologic layers in Montana that contain dinosaurs lay at the surface. Next week, we’ll DIG further into rock formations and uncover why these fossils sit at the surface when they are up to 60+ million years old.

P.S. Are you wondering how we can determine the age of the fossils found in the Hell Creek area? These are much too old to use carbon dating, so we can use nearby rocks as clues, particularly layers of ash and coal. Stay tuned for more on dating fossils in a future DinoByte post!

(Most of this information came from the excellent book Dinosaurs Under the Big Sky by Jack Horner)