There's an element of mystery in much of the work that Marilyn Fox does at the Peabody Museum of Natural History, and there are even times when her heart pounds from fright.

As a museum preparator, Fox is the person who chisels fossils out of rock and sediment so they can be studied by researchers. Sometimes, she has no idea what kind of creature is embedded in the stone. While looking under a microscope that magnifies her subject up to 70 times its actual size, Fox uses fine needles and other tools to chip away the rock surrounding the fossilized bones. A piece of flying debris can provoke a lot of anxiety.

"Something that to the naked eye might look like a tiny fleck can look pretty big under the microscope," says Fox. "So scraping away at little pieces of rock seems more like moving boulders to me. Seeing something go flying from my field of vision -- and not knowing whether it's just debris or a piece of the fossil that has broken off -- can be terribly frightening."

For some, the precise, painstaking work might make the job of museum preparator seem tedious, but Fox loves what she does, despite those anxious moments.

"When I'm looking in the microscope, I'm looking at another world," comments Fox. "There's always a sense of discovery, and it's exciting when you see the end product. Besides, I think the bones are beautiful."

One of her most exciting jobs since she came to the Peabody Museum in 1997 was to prepare some of the fossils from a major dinosaur find: the embryonic remains of titanosaurs discovered in Patagonia, in southern Argentina. Fox, who worked as a preparator at the American Museum of Natural History for seven years before coming to Yale, had been invited to travel to Patagonia with a team of researchers co-led by Luis M. Chiappe, a research associate and her former colleague at the New York museum. The team stumbled upon the unhatched embryos in November of 1997 and announced the find a year later after researching the specimens.

The discovery received worldwide attention because the embryos were the first ever found belonging to sauropods, which were giant plant-eating dinosaurs. They also are the first embryos to show fossilized skin, and are the first ever found in the southern hemisphere. They were discovered in a square-mile nesting site that is approximately 70 to 90 million years old.

The team came upon the embryos on the second day of prospecting, according to Fox. "We were planning on walking out further, near some hills, when all of a sudden we came upon thousands of eggs," she recalls. There were so many that team members were literally walking on eggshells, though they made every effort not to step on them.

Fox says her first reaction was disbelief. "I just remember standing there and thinking 'Wow!'" she remembers. Her talents as a museum preparator were put to use immediately; over the next two weeks, Fox dug up some of the eggs and their embryonic remains. She then put them in a "field jacket," an encasement of plaster and burlap that ensures their safe travel. About four of the baby dinosaur fossils were sent to the Peabody Museum, where Fox spent several months preparing them.

"My job, essentially, is to expose the information that's in a fossil," says the museum preparator. "I'm basically delineating it for scientists to see and study." Hundreds of scientists visit the Peabody yearly to research items in its fossil collections, notes Fox.

Though her work is science-related, Fox actually started out as a printmaker. A graduate of the Pratt Institute in New York City, she learned how to make molds and casts of fossils while at the American Museum of Natural History, where she also gained knowledge of paleontology and anatomy. For her, the worlds of art and museum preparation are not so far apart.

"Both printmaking and my current work are similar in that they are both very detail-oriented," she explains. "And a certain amount of patience is required."

In addition to preparing fossils, Fox also makes molds and casts of items in the Peabody collections for use by researchers both at Yale and outside the University. A recent project, for example, involved making a cast of a hand of the carnivorous dinosaur Deinonychus for a museum in Paris. She also has begun a two-year project to restore all of the dinosaurs in the Peabody's Marsh Collection, a vast array of fossils collected by 19th-century Yale paleontologist Othniel C. Marsh. This job involves using a conservation-strength glue to join together bones which have become unfastened or loose due to deterioration of the old glue.

Fox's work is not limited to dinosaurs, however. She has also prepared numerous fossils of lizards, birds and other vertebrates, and is an experienced preparator of mammal fossils. In her fossil-filled laboratory in the basement of the Peabody, she is assisted by volunteers Brian Roach, Anne Johnson, Mary Weigand, Nancy Wellek and Melissa Gibbons, who share Fox's interest in preserving Yale's collections. The staff is overseen by Jacques Gauthier, professor of geology and geophysics and curator of vertebrate paleontology at the Peabody Museum.

Recently, Fox's skill with delicate objects was put to use in the Peabody Museum's Great Hall of Dinosaurs, where she cleaned the large dinosaurs in preparation for the influx of visitors to the recently opened exhibit "China's Feathered Dinosaurs." She is currently gearing up for the annual "Dinosaur Days," a five-day series of events related to the museum's dinosaur collection, which will take place Monday-Friday, Feb. 15-19. (See related story, below.) Each day during "Dino Days," Fox will describe the various facets of her work as a museum preparator 1-3 p.m. in the Great Hall of Dinosaurs, where she also will demonstrate some of the techniques she uses to prepare fossils and safeguard them for study by future generations. During her demonstration, she will "unbury" the bones of an unknown creature collected in South America in 1892.

"There are still a few things [at the museum] that haven't been prepared," Fox says. "This one from South America is a mystery. It could be a bird ... we'll soon find out for sure."

Fox admits that she occasionally develops a certain affection for the specimens she has prepared. "I sometimes want to pat them because they are quite lovely," she says. But seeing others enjoy or make use of them in their research gives the museum preparator the most satisfaction. "It's nice to know that they are used," she says, "so I do like to see them go on from my lab and have a 'life.'"

-- By Susan Gonzalez

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