Shelf Life 10: The Dinosaurs of Ghost Ranch
"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.