Digging the Fossil Record: Paleobiology at the Smithsonian

From the Field: Tracking the Last American Dinosaurs through Time #2

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.

Dean Pearson (left) and Tyler Lyson (right) are relocating old fossil sites, some found long ago, that need to be visited and mapped with the greater precision afforded by modern GPS systems.  Click photo to zoom.

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.

 

Triceratops is a big dinosaur. Get face to face with one at the Last American Dinosaurs exhibit at the Smithsonian. Click photo to zoom.

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."

The author with the partly-exposed skull of a Triceratops that was found in the side of a small hill.

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.

Mike Getty, chief fossil preparator at the Denver Museum of Nature and Science, uses a gas-powered saw to cut through some hard concretion to free a field jacket. Click photo to zoom.

 

Like a rugby melee, everyone join forces to tip a field jacket containing a Triceratops skull and flip it upside down. Click photo to zoom.

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.

No rodeo is complete without roping. The heavy jacket is brought downhill on a metal sled. Click photo to zoom.

 

Davie Wang, a local rancher, came with heavy equipment to help Tyler Lyson haul the heavy jackets from the outcrop to the closest road. Way to go! Click photo to zoom.

 

Strapped tightly onto the trailer, all the jackets are now ready for their trip down the road, straight to the Denver Museum of Nature and Science where they will be prepared. Click photo to zoom.

 

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).

One of the Triceratops skulls was found lying on a litter of Metasequoia twigs and cones (right), which look very similar to those of the modern dawn redwood (left, photo from Wikimedia Commons). Click photo to zoom.

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!

We camped on the outcrop for part of the summer to save gas and precious commuting time.  Being so close to our sites allowed us to work early in the morning and late in the afternoon when the light is best for finding fossils and conditions are a lot cooler than in the pounding noon sun. The trade-off was having to experience lots of bad weather, including one fierce hail storm that triggered tornado warnings in town. Left: Fury from the sky. Photo by John Hankla.  Right: Between storms, the valley offered us some of the most amazing sunsets. Click photos to zoom.

 

 

 

 

Our great helper Kitty Cat was back this summer for more bone digging! The bones of modern animals such as mule deer and are plentiful in the badlands, and she was good at finding them.

Click here to learn more about the different types of fossils recovered in the Hell Creek Formation during last year’s field season and here to learn more about the GPS mapping project.

Photos by Antoine Bercovici unless noted otherwise.

From the Field: Hunting Cretaceous Plants

Antoine Bercovici is a Peter Buck postdoctoral fellow in the Department of Paleobiology at the National Museum of Natural History. He spent most of July and August in the field in North Dakota and Montana. This is his first post about the trip.

This summer I continued working with a large multidisciplinary team on a major endeavor begun last year: 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 micro vertebrates (small fossils representing crocodiles, turtles, lizards, salamanders, snakes, birds, fishes, and mammals); Kirk Johnson, Director of the Smithsonian’s National Museum of Natural History and a paleobotanist, 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 of our work together is Erica Evans, our GPS mapping wizard.  Many students and volunteers are assisting us in the field.

Much of the rock in this area is part of the Hell Creek Formation, made up of sediments deposited during the end of the Cretaceous and earliest Paleogene.  It is extremely fossiliferous, and as erosion and weathering carve the soft sediments, bones are left exposed on the ground.  If you know what to look for, a walk in the badlands usually yields numerous fossil discoveries. 

In the early 1980’s, a scientific breakthrough that would spark a new level of interest in the Hell Creek Formation was published in Science by geophysicists Walter Alvarez and his father, Luis. They discovered an anomalously high concentration of iridium at the Cretaceous–Paleogene boundary. Because iridium is an element very rare in the Earth’s crust and relatively abundant in extraterrestrial bodies such as asteroids, they proposed that the demise of the non-avian dinosaurs at the end of the Cretaceous was linked to a large meteorite impact. Testing this hypothesis required good fossiliferous rocks spanning the Cretaceous–Paleogene boundary, like the Hell Creek Formation, to document how animal life responded to the impact. At that time, it was still a mystery as to how plants responded to the Cretaceous–Paleogene mass extinction event, but the Alvarez publication pushed a then-aspiring PhD student from Yale, Kirk Johnson, to go to North Dakota to test the extinction hypothesis from the plant point of view.

Fossil leaves are different than fossil bones. They are two dimensional objects that preserve as fine carbon imprints within sedimentary rock strata, while bones are three dimensional and harden in the fossilization process due to mineral replacement. Erosion and weathering destroy leaf fossils, so prospecting for leaf sites cannot be done by casually looking for fossils exposed on the ground. Because of this, the Hell Creek Formation, which had been prospected since the 19th Century starting with vertebrate paleontology pioneers such as Edward Cope, Othniel Marsh and Barnum Brown, had only sporadically yielded the remains of fossil plants and leaves.

Kirk Johnson's approach to finding plant sites was to use geology to identify the right sedimentary rock with the potential to preserve fossil leaves and then wield a pick axe and rock hammer to excavate and split large slabs of rocks to reveal the leaves trapped within.

Left: A good knowledge of geology and sedimentology, combined with a sprinkle of luck, helps in determining which rocks will split open to reveal fossil leaves. Kirk Johnson points at a first split that looks promising.  Right:  Fossil leaf bonanza, numerous stacked compressions of « Dryophyllum » subfalcatum and several other species were encased in this block of sandstone.

Left: Using a chisel-tip rock hammer, Kirk Johnson follows the bedding planes in this sandstone block in order to split it open.  Right: Breaking large block with a pick axe is an art form in itself: the larger the bloc, the more chance of finding lots of large, entire leaves. Tyler Lyson goes to the gym all year long to be ready for this very moment! Clock photos to zoom.

Pick axe prospecting allowed him to find hundreds of fossil plant localities in the Hell Creek Formation. Slowly building up a large dataset, he was able to observe changes in floral composition and diversity throughout the Hell Creek Formation associated with changes in climate.  But most importantly, he saw an abrupt and drastic change at the Cretaceous–Paleogene boundary. From a diversity of over 100 species in many Cretaceous plant sites, most of the earliest Paleocene sites yield no more than 4-5 species.  Plants are essential in supporting terrestrial ecosystems, forming the bases of food chains and providing shelter for many animals.  The sudden and drastic reduction in plant diversity observed in association with the asteroid impact shows that the essential foundations of the food chain were affected.  A chain reaction affecting all animal life depending on it must have followed.

Incidentally, finding numerous leaves opened a window onto another group of animals that is poorly know due to poor preservation potential: insects. Insects interact with leaves in various ways including feeding, galling, laying eggs, and drilling mines, and evidence of these behaviors can be found in fossil leaves.  Using this evidence, Conrad Labandeira from the Smithsonian Institution was able to draft a detailed pattern of insect diversity in the Hell Creek Formation and throughout the Cretaceous–Paleogene boundary.  The fossil leaf shown at left, from the Pioneer Trails Regional Museum collection in Bowman, North Dakota, has holes left by an insect that fed on it when the leaf was alive.

 

 

Paleobotanists consume an unusual amount of toilet paper. Erica Evans and myself are wrapping leaves in these small mummies for safe transportation to the laboratory at the museum. Clock photo to zoom.

Sometimes, parts of plants can also be fossilized as three dimensional objects. It is the case for seeds, pine cones, and petrified wood.

Left: A hand full of fossils preserved as three-dimensional casts in ironstone. On the top are unidentified seeds and nuts, on the bottom are two specimens of Metasequoia dakotensis pine cones, a typical fossil of the Hell Creek Formation.  Right: An encounter with some tree-hugging paleobotanists, Ian Miller and myself are proudly posing with this amazing petrified conifer stump found in the earliest Paleocene. Clock photos to zoom.

To collect fossils for my research, I also dig into the ground to expose and collect unweathered rock, but the preserved pollen is microscopic and will not become visible until the rock is processed back in the lab.  Analyzing the samples will occupy me through the coming winter. Learn more about collecting fossil pollen from this video interview recorded this summer at one of my excavation sites.

 

Click here to learn more about the different types of fossils recovered in the Hell Creek Formation during last year’s field season.

All photos by Antoine Bercovici except the panorama, which was photographed by John Hankla.

From the Field: The Data are in the Strata

Antoine Bercovici is a Peter Buck postdoctoral fellow in the Department of Paleobiology at the National Museum of Natural History. He spent most of the past summer in the field. This is his third post about his work in North Dakota on the Late Cretaceous rocks and fossils of the Hell Creek Formation.

Time-travel 66 million years back in time to explore the Late Cretaceous Hell Creek ecosystem, and you might be surprised to see a world that looks somewhat familiar: you walk across a landscape of wetlands and meandering rivers, making your way among palm trees, pines, cypress, redwoods, and other deciduous trees and flowering plants with tropical-looking leaves. The ground is not covered by grass (grasses will only evolve to form vast prairies 35 million years later). Instead, you walk on a carpet of mosses and ferns. You hear insects buzzing around your ears as you move around, frogs, and occasional bird calls. Near a pond, a lizard sunbathes peacefully on the bark of a dead tree while a salamander paddles its way across lilies and water ferns. At a distance, a crocodile watches your intrusion into its territory, eyes and nostrils raised just above the surface of the water. Then, if you are lucky (or unlucky, depending on which species!) you might encounter a dinosaur.

An artist’s reconstitution of a Hell Creek landscape. This is a detail from the mural on display in the Last American Dinosaurs Exhibit at the National Museum of Natural History. Artwork by Mary Parish. Click to zoom.

 

How do we know the Hell Creek was like this?  Reconstructing an entire extinct ecosystem is no easy task for paleontologists.  Fossils, trapped in rocks and sediments like time capsules, provide direct evidence of past animal and plant life, but there are a lot of other data to be assembled. The rocks and sediments, themselves, provide evidence about the environment, as does the condition of the fossils and their distribution in the modern landscape. Our group working in the Hell Creek Formation this past summer was part of a long-standing collaboration between scientists working in several disciplines within paleontology and geology.

While finding large fossils is always a thrill, the smaller ones can be more relevant when it comes to environment reconstruction: smaller animals like frogs and salamanders, are climate sensitive and tied to specific environments. After their death, the small remains of these animals may be transported by water and accumulate on river floodplains or in other places within a river system where the water slows enough for them to settle to the bottom. These ancient accumulations of small remains form what we call a microsite. Spending several hours collecting small fossils from microsites can rapidly give an image of animal diversity.

At a microsite, the team carefully scans the surface of the ground in search of small fossils. Click to zoom.

A collection of small fossil remains from a Hell Creek microsite. From left to right and top to bottom: Lepisosteus (gar fish) scale, small, curved T. rex tooth, a Turtle neural plate, a tooth of Brachychamspa (alligator) with a peg-like root and black crown, two angled teeth of Myledaphus (ray), another alligator tooth, missing the root, another small T. rex tooth, and a gar fish tooth, colored blue during fossilization. The red ant gives a sense of the size of these fossils. Click to zoom.

Left. Embedded in the sediment, this beautiful crocodile tooth waits to be picked up. Right. These small teeth are from little "raptor-like" theropod dinosaurs.  The largest one is just 1cm (less than half an inch) long. Click photos to zoom.

Left. Our holy grail of fossil finds in the Hell Creek Formation: this rare fragment of a mammal jaw still has three molars embedded in the tooth sockets. The asteroid impact at the end of the Cretaceous ended the reign of the dinosaurs, but some mammals survived, including an ancestor of all primates, including humans. This jaw fragment is barely 1cm long. Right. These little white nodules are fossilized poop (called coprolites). They are common finds in the Hell Creek Formation. Click photos to zoom.

 

Sedimentology is the science that studies how and where sedimentary rocks are formed.  It provides information about the existence of rivers, lakes, floodplains and soils.  Taphonomy, the science of how animal and plants remains were accumulated and buried after death and how they became fossils, gives even more insight into the ancient landscapes where the fossils formed.

This outcrop of the Hell Creek Formation shows many horizontal and colorful bands of sediment, alternating from dark grey, to pink, purple, green, and blue. They represent a sequence of floodplains and paleosols (ancient soils evidenced by roots) that supported the growth of a lush tropical forest during the very end of the Cretaceous. Click to zoom.

Another outcrop shows different types of sediment. The lower part of the outcrop is made of light and coarse sandstone deposits that are clearly angled. These rocks were not tilted, but deposited by a large meandering river system. As the river turned, sediments were deposited at an angle on the edge of the meander, forming a point bar in a process called lateral accretion. Later, the river channel either moved or dried up, and the pointbar was topped by a sequence of floodplain and paleosol sediments deposited in the horizontal layers, visible above the black line. Click to zoom.

 

Left. Sediments deposited by river systems show many structures that help us understand the conditions under which they were deposited. Here, this "pipe" of cemented sandstone shows angled bedding which indicate the direction in which the river was flowing. Right. Water is a force of nature, and rivers can carry large objects in their streams. Here, this large log, petrified in ironstone, is still embedded in the river sandstone deposits. Click photos to zoom.

Sedimentological analysis requires the excavation of a stratigraphical section, in order to expose fresh and unweathered rock. The exposed layers of sediment can then be described as to type, their thickness can be measured, and samples can be collected for geochemical analysis or for the study of the pollen and spore content.  Click to zoom.

A sample of Hell Creek floodplain sediment was dissolved in a series of strong acids, revealing some of the tiniest fossils that can be studied. Among various debris of wood and organic matter, this Aquilapollenites pollen grain is barely 50µm long. Pollen grains and spores can be recovered by millions and provide precious information on the composition of ecosystems and the evolution of plants. Click to zoom.

 

The animals living in this part of North Dakota today are adapted to a dry environment. They wouldn't begin to recognize the lush conditions that existed here 66 million years ago.

A rattlesnake, left, and horned lizard, right, were some of the many living animals we encountered during our weeks in the field.  Click photos to zoom.

 

As paleontologists traveling the modern landscape in search of clues about the ancient one, we get to experience both. Visitors to the Last American Dinosaurs exhibit at the National Museum of Natural History can experience both environments, as well, through fossils, artists' reconstructions, and photos from other recent expeditions to the Hell Creek Formation.

 

Photos by Antoine Bercovici.

 

Read earlier posts about collecting fossils in the Hell Creek Formation.

From the Field: Tracking the Last American Dinosaurs through Time

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.

 

The GPS technology, developed and maintained by the US Army, is capable of incredible accuracy. In military use, it measures positions down to the nearest centimeter (cm). The system available to civilians, however, has a degraded resolution, with elevations typically measured only to within 10 meters (m), which is too much uncertainty to be useful for our project. (The Hell Creek Formation is about 100 m thick, so a 10 m error represents a 10% uncertainty in the position of a fossil site.) To get the accuracy needed for our project, we are using a technique called differential GPS, where we compare the readings of two GPS units to reduce the error. Every day, we set up a fixed GPS base station that records position and drift for several hours. We then map our sites using a mobile GPS unit that we carry with us. In the evening, the data recorded from both GPS units are downloaded to a computer, where dedicated software computes a correction, bringing the error at each site down to about 10 cm.

 

 

 
(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.

Getting Ready for the Last American Dinosaurs: Preparing the Fossils

Preparations for the new exhibition, Last American Dinosaurs: Discovering a Lost World, continue on many fronts, with staff from the Departments of Paleobiology, Exhibits, and Education & Outreach busily readying fossils, exhibitry, and interpretive programming for the opening on November 25th. In Paleobiology, we have searched our collections for representative animal and plant fossils from latest Cretaceous fossil sites in the American West, collected new specimens, obtained casts (exact replicas) of important fossils collected by others, figured out how to exhibit the fossils safely, and assembled Stan, our cast of a skeleton of Tyrannosaurus rex, in the new exhibit hall.  Some photos from behind the scenes and summer fieldwork are below.

This Polyglyphanodon sternbergi, a lizard distantly related to present-day tegus, was collected in the 1930s and described by Charles W. Gilmore. It needed to be conserved and cleaned before it could be exhibited.  Matthew Miller is shown finishing the job.

This specimen, newly-acquired for the exhibit, is a cast (an exact replica) of Stangerochampsa sp., an extinct alligator that lived during the Late Cretaceous. The original fossil was collected by the Burpee Museum of Natural History in Rockford, Illinois.

Former National Museum of Natural History post-doctoral fellow Tyler Lyson with the limb bone of a hadrosaur, a type of dinosaur, discovered last summer in Montana.

Opening the field jacket that encased the bone during its trip to the Museum.  This specimen will be shown in the "Fresh from the Field" section of the new exhibit.

Last summer we also excavated a block of rock containing layers of material blasted into the atmosphere by the asteroid that hit the Earth 66 million years ago, ending the age of dinosaurs. Paleobiology Curator of Planktic Foraminifera and Chairman, Brian Huber, is on the left.

Back in the Museum, Michelle Pinsdorf is preparing a slice of the block for the exhibit. In it, visitors will be able to see layers of rock that mark the boundary between the end of the Cretaceous and the beginning of the Paleogene Period, including the orange-brown layer in the center of the block.

Scientists, including Curator of Vertebrate Paleontology Hans-Dieter Sues, shown holding a turtle shell, and Exhibits staff, including Chief of Design Michael Lawrence, foreground, planned how each specimen will be exhibited.

Custom-made brackets will hold most of the specimens in position for viewing.  The largest specimens require sturdy brackets made from metal bars. Here, Bill Keyser welds bracketing for the cast skull of a juvenile Triceratops.

The largest dinosaur in the exhibit will be our cast skeleton of Tyrannosaurus rex. It was moved from the now-closed Fossil Halls in pieces and has been reassembled.  The large and heavy sacrum required tall ladders and four sets of hands to lift it into place.

Attaching the ribs.  The Tyrannosaurus dwarfs anyone working nearby.  It looked big in the Dinosaur Hall, but in the new exhibit, where its head reaches almost to the ceiling, it is even more impressive!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To read earlier posts about our work in the field and in the Museum to get ready for the exhibit, click here.  Read more about the Cretaceous/Paleogene boundary layer in this post on the Museum's blog, Natural History Unearthed.

Getting Ready for the Last American Dinosaurs: Report from the Field

Members of the Departments of Paleobiology, Exhibits and Education and Outreach traveled to North Dakota and Montana this past July as part of our preparations for the Last American Dinosaurs exhibition.  We had visited the same area the previous summer to collect fossils of plants and animals that lived during the Cretaceous Period, shortly before the asteroid impact 66 million years ago that wiped out many plant and animal species, including dinosaurs.  This time, we expanded our search to include the fossils of species that survived the catastrophe and thrived during the years that followed, in the early part of the Paleogene Period.

 

At this eroded badlands site, we collected post-impact, Paleogene fossils in the younger rock layers on the hillside to the right, and then strolled down into the canyons on the left to find fossils of dinosaurs and other Cretaceous species in the older, deeper layers of rock. Click to zoom.

Our first order of business was to collect the fossils of small animals, so we spent a lot of time searching the ground at sites where the sediments are rich in small bones, teeth and other "microvertebrate" fossils.  The tiny fossils become visible on the surface as the sediment erodes away, but finding them requires sharp eyes, concentration, and a lot of stooping and crawling to see exposed rock surfaces up close.  We also collected bulk sediment at one of the sites -- material that volunteers in FossiLab, the fossil preparation lab anchoring the Last American Dinosaurs exhibit, will examine carefully under microscopes in search of more and smaller fossils.  Before we packed the bulk sediment for shipping to the Museum, we ran it through sieves made from screens that were coarse enough to let fine grains of sand and clay pass through, but fine enough to retain the smallest fossils.  Concentrating the fossils in this way means easier fossil hunting in the lab, and fewer heavy buckets to ship. 

 

Buckets of fossil-rich sediment, and the screens used for concentrating the fossils.

 

Concentrating small fossils by dry screening requires lots of back and forth shaking to coax fine sediment through the screen. What's left behind in the screen will be picked through in FossiLab, using a microscope to make the small fossils easier to see. Photo by Amy Bolton.

In wet screening, the sediment is soaked in water to loosen and break apart larger chunks of sediment. This takes a lot longer than dry screening, but more of the sediment is washed away, making it easier to find the fossils.

 

 

 

 

 

 

 

 

 

 

 

 

 

We also collected several larger fossils for educational programming in the exhibit.  The excavation of a turtle specimen is shown in the photo series below.

 

Fragments of a fossil turtle shell can be seen partly eroded out of the ground.  We can't tell how much more of the turtle has been preserved without removing all the sediment.  But that work is better done in the lab, so we decided to encase the fossil and surrounding sediment in a protective "field jacket" and bring it back to the Museum for preparation.

Curator Hans-Dieter Sues takes a GPS reading, allowing preparator Michelle Pinsdorf to record the precise location of the fossil.  Having this information will allow us to return to the site in the future if we need to.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Michelle Pinsdorf pours hardener over the exposed parts of the fossil to stabilize it during excavation, construction of the field jacket, and the trip back to the Museum.

Digging a trench around the fossil leaves it perched on a pedestal of sediment. Pedestals are dug just large and deep enough to make it likely they will contain the rest of the specimen. Make them too small, and you risk cutting into the parts you can't see as you dig the trench downward. Make them too big, and the field jacket becomes too heavy to carry!

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The fossil and its pedestal are covered with many layers of plaster bandages.  Once hardened, plaster field jacket holds everything together during transport.

Finally, the pedestal is broken free of the sediment below, and the jacket is lifted away. The jacket is turned upside-down so the bottom can also be covered with plaster bandages, forming a complete protective shell around the sediment block.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Paleontologists are very resourceful when it comes to figuring out how to carry heavy field jackets back to their vehicles.  For the turtle, we repurposed a sediment sieve as stretcher.

We visited many other sites during our time in the field, and we collected enough sediment and specimens in field jackets to fill a large shipping crate.  Typical of such short trips, our goal was to collect as much material and information as possible, leaving the delicate work of fossil cleaning, stabilization, and identification to be done in FossiLab and our behind-the-scenes preparation lab. The fossils found this season will be keeping our volunteers and staff busy for many months to come.

 

The Last American Dinosaurs Exhibition will open on November 25th.

Read earlier posts about our 2013 collecting trip and the work we do in FossiLab to isolate micro vertebrate fossils from sediment.

 

Photos by Abby Telfer unless labeled otherwise.

Getting Ready for the Last American Dinosaurs: Microvertebrate Fossils

Museum scientists and staff made a fossil collecting expedition to North Dakota and Montana last summer to gather specimens for a new exhibit, The Last American Dinosaurs: Discovering a Lost World, which will highlight a complex ecosystem shared by dinosaurs and many other organisms just before the end of the Cretaceous.  The exhibit is scheduled to open in November, 2014, and we've been processing the new fossils in FossiLab ever since they arrived at the Museum last August.  The biggest job, by far, is a continuing search through bags full of loose rock for the fossils of small animals that lived alongside the dinosaurs.  

 

We collected the rock at sites where small fossils had been found before.  After picking up every fossil we could see on the surface of the ground, we dug up chunks of the soft rock and filled our packs until we couldn't carry any more.  Curator Kay Behrensmeyer is shown below, left, digging at one of the sites.  One of the many bags of rock we carried over rough terrain to our field vehicle is on the right.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In the lab, we soak the chunks of rock in warm water to break them apart (below, left) and pour the resulting mud onto a stack of sieves which lets fine sediment, but not the fossils, pass through.  If the rock hasn't completely broken down at this point (below, right), we put the sieves into our sediment washing machine.

 

 

 

 

 

 

 

 

 

 

 

 

The sediment washer, shown on the left, is nicknamed "Duncan."   It sits by the sink slowly dunking two stacks of sieves, over and over again, into buckets of water.  We let it run until all the clumps have broken down and the sediment has washed away.

The photo below shows what was left in a set of sieves once all the fine sediment was gone -- mostly pebbles and pieces of charcoal, with a few fossils hidden among them.  Each sieve in the set has a different mesh size (2mm, 1mm and 0.425 mm) because it is easier to find the very smallest fossils when they've been separated from the larger material.

 

 

 

The photo on the left shows pairs of fossils trapped in the different sieves in a set.  The two fossils on the left, a broken piece of turtle shell (top) and a scale from a gar fish (bottom) were too large to pass through the 2mm mesh and stayed in the top sieve.  The fossils in the middle, a fish vertebra (top) and a fish tooth (bottom) washed through the 2mm mesh but were caught in the 1mm mesh of the middle sieve.  On the right, the tiny fragment of a fish jaw (top) and a small fish tooth (bottom) passed through the larger sieves, but were trapped by the fine mesh of the bottom sieve.

 

 

 

 

Below is the entire collection of teeth found in five bags of rock from one site after many hours of washing, sieving, and searching for fossil under the FossiLab microscopes.  The teeth are from several types of fishes and crocodilians.  We didn't find any teeth of small dinosaurs or mammals in these bags, but we expect to discover some as we search through rock collected at the other sites.  Sometimes we have to screen large quantities of rock to find such fossils.

 

 

 

Photos by Abby Telfer.

Our sediment washer was designed and build by Ken Moffett at Macalester College.

Follow this link to read an earlier post about how we collected the fossil-rich matrix we are processing in FossiLab.

 

Getting Ready for The Last American Dinosaurs: Fossil Leaves

 

Museum Director Kirk Johnson (r) and Hans Sues, the lead curator for the Last American Dinosaurs exhibit, examine blocks of rock containing Late Cretaceous fossil leaves collected last summer in North Dakota.   Photo by Siobhan Starrs.

The planning for The Last American Dinosaurs: Discovering a Lost World, an exhibit scheduled to open in November, 2014, is in high gear in the Departments of Paleobiology and Exhibits.  This exhibit will highlight a complex ecosystem shared by dinosaurs and many other organisms just before the end of the Cretaceous.  Visitors also will be able to explore what we know about the mass extinction and subsequent rebuilding of ecosystems that followed an asteroid impact 66 million years ago, and consider how this information relates to extinctions in the present and future. 

 

Some of the fossils we will display were collected just last summer by Museum scientists and staff on a fossil hunting expedition to North Dakota and Montana.  There will be dozens of fossil leaves, including many collected on the large rock slabs shown on the right.  FossiLab volunteers are working to ready these fossils for exhibit by removing the rock that partly obscures the leaves.  The results are stunning. 

 

 

 

 

The blocks are prepared for exhibit by using needles and air scribes to remove rock covering the leaves. Air scribes, like the one shown here, function like miniature jackhammers; the impact of the tip on the rock breaks it away in small pieces.  Preparators use a microscope or magnifying lens when working on fossil leaves.  This helps them see where to position the air scribe's tip so that it will strike the rock but not penetrate the delicate fossils.

 

 

Before preparation, nearly all the leaves on this block are partly obscured by rock.  Click to zoom.

 

The same block after prep, viewed from a similar angle. More leaves have been uncovered, and more of each leaf is visible.  Click to zoom.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Read more about how these leaves were collected and about using an air scribe in fossil preparation.

 

Photos by Abby Telfer unless labeled otherwise.

From the Field: The Last American Dinosaurs #5

 

A team from the National Museum of Natural History is in the North Dakota badlands collecting fossils for a new exhibit about the Late Cretaceous, called "The Last American Dinosaurs: Discovering a Lost World," that will open in November, 2014.   We are looking for small vertebrates, mollusks, plants and, of course, dinosaurs.

 

Leaf collecting mission accomplished! 

 

Department of Paleobiology staff members Skip Lyles and curator Scott Wing haul a rock slab covered with fossil leaves from the quarry.

 

One of the goals of this trip was to quarry large blocks of rock containing fossil leaves for the new exhibit, The Last American Dinosaurs.  Part of our crew did just that over the course of a very long day at one of National Museum of Natural History Director Kirk Johnson’s research sites.  Kirk has identified dozens of different kinds of plants among the thousands of fossils he’s collected here as part of his study of species turnover at the end of the Cretaceous.  The diversity of the plants and the beauty of the fossils made us want to quarry here rather than at other sites; the fossils will give visitors a good sense of the vegetation that formed the base of the food chain that led all the way up to Tyrannosaurus rex, the top carnivore during the latest Cretaceous.

Finding small blocks with one or two leaves on them is relatively easy, but with more effort it is possible to find large blocks that hold many leaves.   The crew began quarrying and splitting rock at 9:30 in the morning and quickly “hit pay dirt,” pulling out large slabs of rock with multiple fossil leaves on them.  All afternoon, excited whoops came from the quarry as rocks were split open to reveal one gorgeous leaf-covered slab after another.

 

Curator Scott wing uses a rock hammer to split open a large slab.

When the crack spreads far enough around the slab, the two pieces are eased apart.

 

 

 

 

 

 

 

 

 

Eureka! This large slab contains many fossil leaves.  Most are only partly visible, so volunteer fossil preparators in FossiLab will work carefully to remove enough of the rock covering them to expose the hidden parts.

 

 

Wrapping a large slab in toilet paper and bandages in hopes that it won't break during the trip back to the car.

Dozens of small blocks and five large ones, including an 80 pound behemoth, were wrapped tightly in toilet paper and medical tape for protection and then, as the light began to fade, hauled back to the cars in backpacks and on a stretcher.  

The weary and hungry crew rolled back into town at 8:45PM, most definitely having earned their dinner.

 

 

 

 

 

Photos by Diana Marsh.

To learn more about how we prepare fossils in FossiLab, visit the Projects and Fossil Preparation pages of the FossiLab website.

Read earlier posts in this series, From the Field: The Last American Dinosaurs.

From the Field: The Last American Dinosaurs #4

 

A team from the National Museum of Natural History is in the North Dakota badlands collecting fossils for a new exhibit about the Late Cretaceous, called "The Last American Dinosaurs: Discovering a Lost World," that will open in November, 2014.   We are looking for small vertebrates, mollusks, plants and, of course, dinosaurs. 

“Crawl it!”  Our group received these instructions many times during our trip to the badlands of Montana and North Dakota.  Whether visiting known “microsites” where small vertebrate fossils are eroding out of the latest Cretaceous rocks of the Hell Creek Formation, or assessing the richness of a newly discovered site, the first method of gathering fossils was always to crawl systematically across the hard, pebble-studded ground, picking up every fossil we saw. 

 

Curator Hans Sues, left, and Abby Telfer, right, collect tiny fossils at two different microsites. Step 1: Collect everything you can see.  Step 2: Crawl forward.  Step 3:  Repeat steps 1 and 2 until you stop finding fossils, then find a new starting position and do it again. Photo on right by Skip Lyles.

 

Many of the microsites contain sediments deposited in special environments, such as ponds or low spots in river floodplains, where animal remains tend to accumulate and become buried rapidly.  The most common fossil finds were turtle shell fragments, leading our group to joke that the Cretaceous really ought to be called the “age of turtles,” rather than the “age of dinosaurs,” at least in the Hell Creek Formation.  Other frequent finds were teeth of early crocodylians and scales of a variety of fish, especially gars.  In addition to these, however, were much rarer fossils from dozens of other types of animals, including dinosaurs, amphibians, birds and mammals. 

 

A tiny tooth from an early crocodylian sits on the knife point. Fortunately, spotting the fossils among the bits of rock gets easier with practice!

After we collected everything we could see on the ground at the richest microsite, we bagged samples of eroding surface rock and dug out blocks of unweathered rock from beneath the surface.   These will be excavated carefully back in FossiLab where, with the aid of binocular microscopes, we will search for fossils that are too small to be seen by hot people crawling uncomfortably over hard ground in bright sunlight, or too delicate to survive the process of screen-washing the fossil-bearing rock. 

 

Blocks of unweathered rock were dug from one of the microsites and then wrapped carefully to protect them as they were carried out in our backpacks and shipped to FossiLab.

We also looked for both large and small fossils away from the hotspots.  Curator Kay Behrensmeyer conducted a biostratigraphic survey, a.k.a. a “bone walk,”  in the area around the dinosaur excavation site.  She chose a single layer in the stacked sequence of different-colored sediments to survey, which limited the sample to organisms that lived at about the same time (the period when the one layer of sediment was accumulating).    By following the one rock layer from outcrop to outcrop, collecting every visible fossil and recording its exact position, she can learn about the distribution of animals across the ancient landscape. 

 

Curator Kay Behrensmeyer organizes and inventories fossils collected during a bone walk.

Siobhan Starrs prospects for fossils. The arrow points to the dinosaur site on the light gray outcrop and the field vehicles parked beyond it.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Some of the tiny fossils we collected will be displayed alongside the large dinosaurs that will anchor the Last Americah Dinosaurs exhibit.  Together with the plant fossils we collect, they will demonstrate the high diversity of species that lived in the Hell Creek ecosystem just prior to the end of the Cretaceous.

 

All photos by Abby Telfer unless otherwise noted.

 

To learn more about how we process microvertebrate fossils in FossiLab, visit the Projects page of the FossiLab website.

Read earlier posts in this series, From the Field: The Last American Dinosaurs.