Shelf Life 10: The Dinosaurs of Ghost Ranch
STERLING NESBITT (Research Associate, Division of Paleontology): Ghost Ranch is kind of the idealistic Old Western set. There are these beautiful red cliffs that are surrounding the ranch itself. But down in the basin, just below Ghost Ranch, you get red, and purple, and green, and white Badlands. And those are the places that are really good to find fossils. It’s definitely the best place to find early carnivorous dinosaurs in the world.
I’m Sterling Nesbitt. I am a research associate of the American Museum.
[SHELF LIFE TITLE SEQUENCE]
NESBITT: So, starting in 1881, there’ve been a number of paleontologists that have searched these beds.
MARK NORRELL (Macauley Curator, Division of Paleontology): It really wasn’t until the 1940s, right after World War II that one of my predecessors, Ned Colbert, began excavating at Ghost Ranch. When Ned Colbert, his assistant George Whitaker first discovered the quarry they thought it was probably just one or two little dinosaurs sticking out of the side of the cliff. But it is one of the world’s great deposits of dinosaurs of any kind.
My name’s Mark Norell and I’m the Macauley Curator of Paleontology at the American Museum of Natural History.
It’s really unusual to find mass assemblages of dinosaurs. Occasionally we find things called bone beds, where we find lots of different species and we find single individual bones, but the thing that makes Ghost Ranch so special is so many of the entire skeletons are there – just piled on top of one another.
NESBITT: Most of what Colbert saw were these delicate bones of a carnivorous dinosaur named Coelophysis bauri.
When dinosaurs first appear, they weren’t the big animals on the block yet. They didn’t dominate ecosystems anywhere in the world. They were all pretty small. And when people think of dinosaurs, they usually think of T. rex or giant sauropods like Apatosaurus, but this is what probably all early dinosaurs looked like. And then later they grew into the gigantic monsters in movies and in dinosaur halls.
DANNY BARTA (PhD Student, Richard Gilder Graduate School): Ghost Ranch preserves our most detailed picture of late Triassic, that is about 200 million years ago, ecosystems in North America. Having all the Coelophysis specimens together in one bone bed like this, it’s the closest we as paleontologists can ever come to really, truly finding an equivalent of a living population.
I’m Danny Barta. I’m a PhD student in the Richard Gilder Graduate School at the American Museum of Natural History.
I’m interested in the growth and development of dinosaurs, particularly Coelophysis because Coelophysis sort of set the standard for this body plan that we saw later carried to extremes in Tyrannosaurus and then Velociraptor. And this is the group that gave rise to birds.
NESBITT: We have an okay handle on the anatomy, but we don’t know lots of details. So, even though thousands of skeletons may have been preserved, only a few dozen really are prepared and out of those, only a few are really prepared well.
These bones are really delicate, and once you expose some of these bones in the field, or you have uncontrolled conditions, they just break. And you can’t get the pieces back together.
So, instead of taking each bone out individually, Colbert took out these big blocks of rock and bone and everything else, wrapped them in plaster, and brought them here.
NORRELL: One of the things I think people don’t understand about collecting fossils is we go out on an expedition, it’s hard work, but what really takes the time is the preparation that we have to do to be able to expose these things.
So, when you look around a room like this, you look around the rooms that we have with the unopened blocks – these are really just libraries of objects. And it’s like if someone goes to the Vatican archives and they find, you know, something that was either penned by Leonardo or a Mozart manuscript.
That’s what we have here, and while it might take a while for it to be discovered at least it’s safe here and it’s amenable to using new technology on, and it allows a whole future generation of scientists to be able to look at these things almost in their original contexts.
BARTA: So, with the specimens here, I will be making very thin sections of the long bones of Coelophysis, usually about 50 or 30 microns. We have to be able to pass light through them. When we look at them under a microscope, we often see growth rings, analogous to tree rings. And so, we can count, you know, essentially one growth ring for every year. And this gives us an idea of how old all of the individuals in a population were when they died.
Coelophysis is really in some ways kind of a model dinosaur for understanding dinosaur growth. By studying, you know, what Coelophysis growth rate and metabolism may have been like, this will give us more detailed insight into how some of the evolutionary innovations we typically think of as occurring in birds—you know, high metabolism, warm-bloodedness—when exactly all of those things evolved.
These historic collections that were collected almost 70 years ago have so much to teach us. By applying, you know, techniques that have really only been developed in the last 30 years or so, like CT scanning and bone histology, we’re able to gather a lot more data than we would have ever thought possible back when Coelophysis was first discovered.
NORRELL: One of the real interesting things about Ghost Ranch is that it’s come back into a real place of prominence in paleontology right now.
NESBITT: This is our tenth field season out there. And we’re working in the formation just below where the Coelophysis quarry was found. So, it’s a bit older. We don’t know how much older— maybe five to seven million years older— but what we have are relatives of dinosaurs. And we have some earlier carnivorous dinosaurs that are unlike anything else found anywhere else in the world.
NORRELL: It’s not just the place where dinosaurs were found 75 years ago. It’s the place where dinosaurs are found today.
"What really takes the time is the preparation that we have to do to be able to expose these things."
-Mark Norell, Macaulay Curator of Paleontology
The Fossil Finessers
In the course of more than a century of fossil collecting, Museum paleontologists have unearthed fossils from every corner of the globe. But there are some sites so fruitful in fossils that they are visited again and again by the Museum’s fossil hunters, with each generation turning up new and unexpected finds.
One of those sites is New Mexico’s Ghost Ranch, home to four quarries that paleontologists from the Museum have excavated for decades. The remains of animals from the Triassic era, including dinosaurs, reptiles, and fishes, have all been discovered here, often preserved in exquisite condition. “These animals lived in a very different environment,” says Sterling Nesbitt, a research associate at the Museum who has spent 10 field seasons at the site. “About 212 to 200 million years ago it was marshy. There were big rivers going through this part of the United States. Think Mississippi Delta."
Paleontology began in earnest at Ghost Ranch in 1928, when the fossilized remains of crocodile-like reptiles including phytosaurs and aetosaurs were discovered by researchers from the University of California. The Museum’s work at Ghost Ranch began two decades later, in 1947, when curator Edwin H. Colbert and his team came upon a veritable graveyard of Coelophysis bauri in what is now called Whitaker Quarry. These early dinosaurs were small, fast, bipedal predators that likely chased down prey while looking much like a tiny T. rex.
The specimens Colbert found were remarkably well-preserved, complete, and in many cases articulated. The fossil discovery was also one of the most notable in the history of the state, and led to Coelophysis bauri being named the official state fossil of New Mexico in 1981.
But just discovering a specimen doesn’t make it useful to science. Despite enduring for millions of years, fossils of even the most awesome ancient animal can be fragile things. They must be excavated and prepared for study with painstaking care.
Preparing a fossil begins before the specimen even arrives in the Museum. In the field, a fossil find deemed worthy of bringing back for study is first encased in plaster, specifically plaster bandages—just like the ones that go into making a cast for a broken limb. They serve the same purpose, immobilizing and protecting a specimen for shipment back to the Museum from far-flung regions like Ghost Ranch, the Gobi Desert, or the Museum’s other dig sites around the world.
“Plaster bandages are a good choice because they dry faster than regular plaster,” says Senior Principal Preparator Ana Balcarcel. “They also use less water, which is important when you’re in the field, where water can be at a premium.”
Once protected in plaster, these specimens are moved from the dig site and annotated with a series of field notes. These record for posterity where, when, and by whom a fossil was excavated, indicate estimates of how many fossils are in a given block, and offer preliminary identification of the remains. Once these notes are made, the specimen is placed in a crate and shipped to the Museum.
For some fossils, that’s where the story takes a very long pause. Preparing a fossil takes a very long time, and the work has to be done by hand with the utmost care. That means that, in a world-class collection like the one housed in the Museum's Division of Paleontology, there are more fossils in the collection than time or experts to prepare them.
Preparators’ schedules are also determined by current research projects, and newly excavated items can take precedence. But maintaining all these crated fossils, says Ruth O’Leary, director of collections, archives, and preparation in the Division of Paleontology, is key to maintaining a healthy collection.
“A minority of the fossils we collect remain in crates for a variety of reasons. They are packed well and protected in the crates and don’t get moved around much. They take up less room than specimens in cabinets, which can be important when storage is at a premium. And we know what’s in the crates so they are accessible to researchers when they become a priority for study,” O’Leary says.
When a request to study a fossil lands at the top of a preparator’s to-do list, whether the specimen is fresh from the field or swaddled in shredded newspaper from the 1930s, the process is largely the same. It begins with a round of research, since preparators have to be anatomy experts to navigate a fragile fossilized specimen.
Before any work is done to remove the fossil, they hit the published literature to bone up on the specimen they’re about to begin extracting, or similar related creatures if an identification hasn’t been made. That’s when the real work of removing fossils from rock starts.
“Our basic function is to remove the specimen from the matrix, the stone it’s enclosed in, or if it’s too unstable for that, to expose the specimen within the rock,” says Balcarcel. “We want to salvage everything.”
Tools of the trade range from needle-like chisels to tiny jackhammers. For stable specimens, much of the extraction work is done using handheld pneumatic jackhammers capable of pulverizing rock. Powered by jets of pressurized air, these machines chip away at the stone bit by bit, revealing the fossil.
For more delicate work on unstable fossils, or finishing touches made closer to the bone, preparators use needles, brushes, and sharp sculpting tools to remove the final vestiges of rock from a fossil.
While today this work is done with the assistance of high-powered microscopes, the process of finishing a fossil in this way would look very familiar to a preparator from a century ago—and the tempo hasn’t changed a bit, either. Some things, it turns out, you just can’t rush.
Once a fossil is extracted, or as exposed as it can safely be, preparators often back up their hard work, making a silicon mold that can be used to create casts of the fossil. These casts, most often made from a polyester resin, are key to paleontological research. In addition to serving as a just-in-case reminder of the fossil’s exact dimensions and features, they also make it easier to study the specimen without handling it, reducing the likelihood that it will be damaged. Casts can also be made and sent to researchers around the world while the original stays safe in the collection. They can even improve researchers' understanding of the real fossil.
“The grey coloration of the cast helps detailed textures show up and prevents you from being distracted by multiple colors that could be found in the fossil,” Balcarcel says. “Sometimes, a cast can be more informative than the original.”
And while most of the work is still done with traditional tools, new technology is slowly beginning to change the field. Computed tomography (CT) scans of fossils, for instance, can provide scads of information about what’s contained inside.
“Sometimes a scan can guide prep work, revealing the structure of the specimen within the matrix, making the process a little easier,” says O’Leary. “In other situations it may preclude the need to prepare a specimen, particularly one that may be too delicate for manual preparation. But for many specimens, you will never take away the need for manual prep work.”
CT scans are a welcome development to fossil finessers like Balcarcel, whose work can be physically grueling, straining eyes and posture while the preparator prunes tiny particles of rock away from fossils for hours on end. Still, Balcarcel says nothing compares with the thrill of uncovering a fossil.
“Seeing something for the first time in millions of years, and sometimes a species that no one has ever seen before, is a really amazing feeling,” she says.