Take a took at the latest DIG newsletter here!
Check out the latest DIG newsletter here!
The Cretaceous-Paleogene (K/Pg) extinction event wiped out up to 75% of ALL species on earth, including the non-avian dinosaurs! Why the “non-avian” distinction and what does it mean? The fossil record indicates that birds (avians) evolved from dinosaurs by the end of the Jurassic Period, meaning birds ARE dinosaurs. Birds obviously survived the K/Pg mass extinction, but what happened to the all of the “non-avian” dinosaurs? The K/Pg mass extinction was rapid, global, and severe. Evidence from 66 million-year-old rocks around the world support various theories and scientists today continue to debate whether the K/Pg mass extinction was due to a single cause, or to multiple causes. In fact, DIG teachers help scientists answer this very question during their time at the DIG Field School. Let’s examine each of these ideas and the evidence supporting them.
Single Cause Theory (or the Asteroid Impact Theory)
If you ask most people how the dinosaurs went extinct they would probably tell you it was from an asteroid impact. This idea was first proposed in 1980 by Luis and Walter Alvarez, a nobel-prize winning physicist father and geologist son team from UC Berkeley. In the 1970s Walter was a young professor doing fieldwork in Italy in sediment that straddles the Cretaceous-Paleogene boundary. In sediments older than 66 million years ago (mya), he discovered abundant marine microfossils (including various forms of plankton), above these was a distinct clay layer lacking any fossils, and in the layers above the clay, (younger than 66 mya), there were very few microfossils. Further investigation revealed that the clay layer contained extremely high concentrations of iridium (30x normal levels!), a rare earth element found in high concentrations in asteroids and comets. Walter’s father, Luis, suggested this “iridium anomaly” could be due to some sort of extraterrestrial impact, and the hunt was on for more evidence to support this theory for non-avian dinosaur extinction, or the “Alvarez Hypothesis.”
A few pieces of evidence to corroborate an extraterrestrial event were found in Italy and ultimately worldwide. Shocked quartz results from impact shock waves (extraterrestrial, nuclear bomb) penetrating quartz crystals with such force that the crystalline structure is disrupted. Produced at the site of K/Pg impact, shocked quartz would have floated into the atmosphere, and dispersed across the globe. Additionally, the impact would have been forceful enough to liquefy nearby rock and sand, creating tiny “glassy spherules” that would also have been dispersed globally.
It appeared the rocks were telling Walter the story of how the dinosaurs met their fate! At the site of the DIG Field School, rocks tell the same story. We find a clay layer at the K/Pg boundary, with shocked quartz, glassy spherules, and high levels of iridium, as well as a coal layer immediately above the clay that contains high levels of spores from ferns. This “fern spike” is a common indicator of “primary succession” following an ecological disturbance, and even today, as on Mount St. Helens, ferns are the first to colonize devastated areas. At the K/Pg boundary, the fern spike tells us plants were growing again and the environment was recovering after the mass extinction.
There was ample evidence to suggest an extraterrestrial impact, but where was the crater? Separately but at approximately the same time, geophysicists searching for oil off the coast of the Yucatan Peninsula region in the Gulf of Mexico found a 110-mile wide circular feature. Working with geologist Alan Hildebrand, they determined it was a crater that was the result of an asteroid impact, and they named it the Chicxulub Crater, after a nearby town.
Based on the size of the enormous crater, it is estimated that the asteroid was 6-miles wide! Such a large impact would have had approximately the energy of 100 trillion tons of TNT, or about 2 million times greater than the most powerful thermonuclear bomb ever tested. An impact of this size would have produced many cascading environmental effects in addition to distributing iridium, glassy spherules, and shocked quartz globally. First, the collision of the asteroid with the earth’s crust likely triggered earthquakes, tsunamis, and wildfires. In some places deposits from this time preserve giant trees that suggest these monster tsunamis from the Gulf of Mexico penetrated all the way to Texas and Brazil! Second, the impact would have ejected huge amounts of debris and rock into the atmosphere, which would have globally darkened the skies and cooled the planet for approximately a year, ultimately inhibiting photosynthesis and collapsing ecosystems dependent upon plants
Scientists generally agree that this enormous impact was a significant contributing cause to the K/Pg mass extinction. However, many scientists argue that evidence of environmental change and disturbance BEFORE the impact suggests the asteroid impact was not the ONLY cause, but was potentially one of MANY causes resulting in such a devastating extinction event.
Multiple Causes Theory
During the last few million years of the Cretaceous, and the last ~10 million years that non-avian dinosaurs were in existence, the earth was a very dynamic place. Volcanic activities in India, known as the Deccan Traps, were erupting 1.5 million square kilometers of lava (thats half the size of India!) and releasing huge amounts of dust and sulfurous gases into the atmosphere. These factors caused decreases in sunlight, as well as global cooling that would have affected plant-dependent food chains worldwide before the K/Pg mass extinction. Fossil evidence from our field sites suggests that during these Deccan Trap eruptions in India, ecosystems in the Hell Creek of northeastern Montana were stressed. Stressed ecosystems are analogous to the whole pile of straw on a camel before the last piece added (the asteroid) will break its back. Much of our work during the field season and during the DIG is designed to investigate which groups of animals were suffering decreased numbers before the asteroid impact (like dinosaurs and mammals), and which animals were thriving or doing just fine (like amphibians).
Another contributing factor was regression of the Western Interior Seaway (remember the Western Interior Seaway?) that we can trace in the changing rock formations in northeastern Montana. As the Western Interior Seaway regressed, or receded, areas that were once marine or near shore would have dried up and been replaced by more inland ecosystems and different species. Also during this time, global climate change was also occurring and the once warm, mild climate became more varied. So although the asteroid impact at ~66 mya would have had a major effect on the planet and its inhabitants, the geological and biological evidence suggests a much more complicated explanation for the end of the non-avian dinosaurs. Will YOU help us find more evidence to answer these questions?
Regardless of the exact cause, the K/Pg mass extinction wiped out three quarters of the species on earth and led to a major transition in floras and faunas. Not all groups were affected equally, but non-avian dinosaurs, pterosaurs, ammonites, and many mammals went completely extinct during this time. A loss of different species at various levels of the food chain can result in empty “ecological niches,” and with these previously occupied ecological niches now open, other groups can evolve to fill them. What followed the K/Pg mass extinction were a series of radiations (rapid diversification of organisms resulting from environmental change), with Cenozoic mammals ultimately replacing the niches left empty by the Mesozoic non-avian dinosaurs. We can even think of today’s tigers, cows, and rodents as the modern day version of the Mesozoic’s theropod carnivorous dinosaurs, Triceratops, and multituberculates, respectively. Most dinosaurs went extinct 66 mya, but a few survived and have been very successful. If you had chicken for dinner last night, you ate one!
*If you are interested in learning more about Walter Alvarez’s scientific journey and his process of science, the Understanding Science website has an excellent interactive narrative describing his discovery.
The May/June 2015 DIG Newsletter is out! Check it out here!
It is thrilling to find fossils and know you are the first to uncover those remains of an ancient world. Word of new, large fossil discoveries, like the recent uncovering of a sauropod dinosaur in Argentina, makes news headlines across the globe. However, much of the information paleontologists use to reconstruct paleoenvironments comes from the study of microfossils. Microfossils, as you might imagine, are very small, and therefore require a microscope to properly examine. The picture below will give you a better idea of the scale of fossils we find.
Many different animals are represented here, including dinosaurs, turtles, and fish. Let’s take a closer look at the type of animals we find fossilized during the DIG.
The mammal fossils found at the DIG field site are from three major groups: marsupials, placentals, and multituberculates (called the “rats of the Mesozoic,” see below). Due to the fragility of bones of these animals, we primarily find their teeth and jaw bones. The main focus of DIG Executive Director Dr. Greg Wilson’s lab is the evolution and ecology of early mammals in the context of major earth history events. Specifically, Greg investigates change across the K/Pg boundary by examining mammalian tooth shape and diet, and relative abundances of different species through time. Although teeth are by far the most commonly found elements, there are a few other bones of mammals we can find in Hell Creek. Lauren DeBey, a graduate student in the Wilson lab, and DIG Field School Assistant Director, studies the limb elements (e.g., femur, humerus) of these small mammals to assess changes in locomotion in relation to the K/Pg extinction event.
In the Hell Creek Formation, we find representatives of both major dinosaur groups, the Saurischians (“lizard-hipped” dinosaurs), and the Ornithischians (“bird-hipped” dinosaurs). As with mammals, the most common dinosaur microfossils we find are teeth because dinosaurs constantly shed their teeth, and teeth are the hardest substance in the body. Carnivorous saurischian dinosaurs from the Hell Creek Formation include the raptors Dromaeosaurus and Saurornitholestes, and the Tyrannosaurus rex. Ornithischian dinosaurs we find include the herbivorous Triceratops, which was so common on the Cretaceous landscape their nickname is the “cows of the Mesozoic.” We also find duck-billed ornthiscian dinosaur remains, often toe bones from Edmontosaurus.
In addition to dinosaurs, many other reptilian groups are preserved in the Hell Creek, including common finds like turtles, crocodiles, champsosaurs, and more rare finds like lizards, snakes, birds, and winged pterosaurs (related to Pterodactyls). Fossilized turtle shells are very common, and the majority come from soft-shelled aquatic species. Crocodile microfossils include teeth, vertebrae, and scutes (flat-plate-like bones embedded in the skin). Champosaurs were mostly aquatic, crocodile-like reptiles and we find mainly teeth and vertebrae from these creatures that went extinct over 50 million years ago (mya). Lizards and snakes are more rare finds in the Hell Creek, most often found as jaws and vertebrae.
We know of three groups of amphibians, two living and one now extinct, that inhabited the Hell Creek region. Of the groups still living today, we find the jaws and vertebrae of salamanders, and less commonly the jaws, skull parts, and hip bones from frogs. We also find jaws and vertebrae of extinct, salamander-like amphibians called albanerpetontids. A graduate student in the Wilson Lab at UW, Dave DeMar, studies the fate of amphibian groups across the K/Pg extinction boundary.
The Hell Creek region preserves fossils from both cartilaginous and bony fish. The two most abundant cartilaginous fishes found here are sharks and rays, (yes, sharks and rays are as old as the dinosaurs!). Since the skeletons of these fish are made of cartilage, we generally only find their teeth and placoid (or “tooth-like”) scales in the fossil record.
Remains of bony fish found in our field area include scales, vertebrae, jaws, teeth, and skull elements from primitive bony fish (some that are still alive today!) like the paddlefish, gar, and bowfin, and more derived teleost fish like Coriops. The most common fossil we find in the Hell Creek area is a gar fish scale, which are easily recognized by their (usually) black color, and flat, shiny surfaces.
In total, the vertebrate microfossils found at our field site represent over 125 different species! Because these microfossils are so abundant they provide a more complete picture of the vertebrate fauna. And, since they are from multiple fossil horizons spanning different geologic time periods they allow us to paint a detailed picture of the last two million years of the Cretaceous Period and first one million years of the Paleogene.
If there are fossils from 125+ species at the DIG field site, how will you know what you’ve found? Well, fossils can be distinguished based on characteristic shapes (circular, thin and flat, cone-shaped, flat with pegs) or textures (smooth, pitted, bumpy). By observing the shape and texture of the fossils, it quickly becomes easier to pinpoint what kind of fossil you have found.
Next week we will DIG deeper into the causes of the K/Pg mass extinction, and the evidence found in the Hell Creek for the end of the dinosaurs and some 75% of species on earth!
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.
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!
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!
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!
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.
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)
See below for a re-post of our first Wednesday DinoByte…and stay tuned for more every week!
What is a geologic formation? We can think of a formation as a unit of rock. Each unit is a package of sediments, such as sand, silt, and volcanic ash, that cover an area large enough to be mapped, and contain a particular group of fossils. As time passes, different sediments are packed on top of one another forming different geologic layers of rock. So, the top layer of rock should be the most recent formation and the deeper we dig down vertically, the older the rocks and corresponding fossils, right?
It’s a bit more complicated than that, as sometimes rocks exposed at the surface are older (or younger) than you would expect. Changes in the earth’s landscape are represented in the geology of the different rock layers. Then, movement of deep molten rock pushing upward to form mountains can rearrange different rock layers and can tip originally flat layers. Similarly, changes in the movement of different bodies of water like streams, lakes, and oceans cut through the rock layers, erasing younger sediments on the surface, and exposing older sediments in stream and road cuts. The Grand Canyon is a picturesque example of geologic change, with billions of years of exposed rock, tilted layers, and river channels cutting through layers.
Having trouble visualizing how this works? Watch this short video of paleontologist Kirk Johnson as he explains how rocks can change over time, using pancakes!
In Montana, many of the formations are from the Mesozoic Era, but the site of the DIG Field School contains formations from both the Mesozoic and Cenozoic Eras (remember last week’s post?). By looking at the different rock formations we are actually trying to piece together clues about how the environments differed during each of these geologic time periods. We use the rock formations to guide our interpretation of the landscape and environments experienced by the dinosaurs, mammals, crocodiles, turtles, amphibians, and fish when they were alive here, 68-65 mya (million years ago).
So what packages of rocks do we encounter during the DIG Field School? Next week we’ll discuss the specific formations found at our field site, namely the Hell Creek and Tullock formations.