Bone By Bone: The Delicate Art of Fossil Preparation
Friday, July 23 4:20 pm
Fossil preparation requires an uncommon degree of adaptability and patience. (c) AMNH/D. Finnin
Two decades ago, a chunk of sand containing a nearly perfect 80-million-year-old lizard fossil — just pulled loose from the red desert floor and resting on the hood of a Jeep — exploded into dust when touched by a member of the Museum’s annual summer expedition to the Gobi desert. A preparator knows why: paleontology depends on glue.
“Some of the fossils from Ukhaa Tolgod, this massive dinosaur graveyard found in 1993, survive only because they are so tightly packed in sand,” says Amy Davidson, one of the Museum’s senior fossil preparators, who happened to be on that expedition. In a cavernous room perched over several stories of meticulously labeled fossils, she darts to a beautifully fragile and nearly complete dinosaur skull.
“This fossil was also turning into crumbs,” she continues. “We need to know our adhesives. I stabilized the porous bone and sandy matrix (any material in which fossils are embedded) with just the right strength and solubility to be able to sculpt out the fossil, just like a magician pulls a tablecloth from under the table setting.” Last year, this delicate carnivorous cousin toTyrannosaurus rex was described and named Alioramus altai.
Fossil preparation requires an uncommon degree of adaptability and patience. Museum preparators bring to the task diverse sets of skills from such backgrounds as art, paleontology, and archaeology. They generally learn their craft on the job, drawing from related fields such as object conservation to adapt modern glues, solvents, and other archival materials to stabilize fragile areas or repair damage.
But the basic approach remains the same. Davidson, for example, removes her frameless glasses to face a fossil through her microscope, resting her wrists on a black velvet sandbag, securing a fine needle between her thumb and index finger, and using her third and fourth fingers to lightly touch the specimen. She moves almost imperceptibly, for minutes on end, carefully excavating a jaw from the soft sand. At the ready, laid out on a cutting board, are her preferred tools of the trade: brushes and droppers for dispensing glue, needles of different sizes and shapes for excavating, an air pedal for removing scraps of matrix, and glass jars of carefully labeled adhesives.
In another part of the lab, the newest preparator, Justy Alicea, sits similarly immobile. A black curve of a tattoo peeks above his crew-neck shirt, and headphones help him block out the distraction of visitors and scientists shifting around him. Alicea’s workbench is lined with projects and paraphernalia—a detailed schematic plan for liberating a Velociraptor’s jumble of limb bones to reconstruct its skeleton, the upper jaw of a duck-billed dinosaur encased in mudstone that had been partially prepared in 1913, dental drills and glues, and an original scientific illustration from 1931 that came with his lab space. He points to his proudest achievement—a delicateProtoceratops skull with a frill the width of cardstock and internal flying buttresses built of excess matrix and glue. Although the matrix was “falling off the bone,” Alicea says he stabilized it to uncover detail like the new teeth awaiting eruption in the jaw’s resorption pits.
While some Museum paleontologists head to the Gobi each year, another group of scientists have been traversing the high Andes in search of mammals that evolved in isolation in South America’s ancient forests and on the world’s first grasslands. Now under Alicea’s microscope is what he calls “a whole class of difficult”—a Chilean mammal entombed in volcanic ash that has compacted into something that requires carbide needles on airscribes, or pneumatic drills, to remove. And while the volcanic layers make radiometric dating feasible, the removal of fossils is a painstaking process that Alicea is learning and one in which preparator Ana Balcarcel is already an expert. Under Balcarcel’s microscope is a row of high-cusped teeth no taller than a half centimeter. She is exposing the teeth out of a dark gray slab of rock where they have been entombed for more than 30 million years, working in short intervals because the amount of silica in the matrix’s dust requires removal with a steady vacuum that chills her nearly static hands. Her first step in preparing this fossil—the upper jaw of a notoungulate, or an extinct hoofed plant-eater native to South America—was to cut the excess matrix with a diamond-bladed rock saw. She estimates that she has spent about two months of often intense concentration using different pneumatic drills and other tools that withstand the pressure of volcanic rock.
“The tools vary,” says Balcarcel, sitting cross-legged and zipping her yin-yang pendant along its chain. “Each specimen is different, and you have to get to know each one—how soft, how well preserved.” Even so, the inevitable break occurs. Tooth enamel is often so thin and brittle that the needle’s pressure chips it. At that point, matrix removal stops so that she can repair the break, often gluing with compounds that don’t set immediately so that she can position the minute chip perfectly.
“I used to be very stressed preparing a fossil—it took a long time to get comfortable with breakage,” Balcarcel continues. “But part of our job is learning how to put things back together, and my time under the microscope has changed from stressful to almost zen-like relaxation.”
A version of this story originally appeared in the Summer issue of Rotunda, the magazine for Museum Members.
