Of Fossil Mice and Man

Talk to people about fossils, and they think big — dinosaur big. But fossils, to the surprise of many, come in an immense array of sizes. William Korth, Ph.D., a visiting professor in Nazareth's chemistry department, concentrates on the little stuff, and he's one of the nation’s foremost experts in the petrified remains of rodents.

Wait — fossil mice?

"Mice, rats, squirrels, beavers, occasionally rabbits — anything that gnaws," explains Korth.

For fossilized rodents, Korth is the go-to guy. His field work since 1975 has yielded thousands of fossils for collections across the country. The site in northwestern Kansas at which he worked for more than a decade is too young for dinosaurs — between 9 million and 10 million years old — but is laden instead with fossils from prehistoric rhinos, elephants, and camels. More recently he's been doing field work in the Oligocene of South Dakota with a colleague from the Field Museum of Natural History (Chicago). Large animals may sound intriguing to the rest of us, but what Korth finds compelling is what's left behind once those large bones are removed. Dirt that's been dug through and discarded isn't actually thrown away, he explains, but is instead carefully screened for little bones.

And he means really, really little. The hardest bones, or those most likely to be preserved, are teeth, which means Korth collects fossils approximately the size of grains of sand. A mouse molar can rest on the head of a pin with ample room to spare.

So why focus on the small stuff? Turns out things move pretty fast in the world of fossil mice, biologically speaking. "An elephant gestates for two years, a mouse for 21 days," explains Korth. "Who's going to evolve quicker? There's much more diversity, adaptation, and reaction to the environment in rodents."

Fossil mice are also more easily accessible than the sought-after dinosaurs. "A lot of people love dinosaurs—they're big and scary and fancy," says Korth. "Even big mammals are fun and flashy. In graduate school, everyone wanted to work on the big stuff, but there are thousands and thousands of little tiny fossils available. You could go into a collection for 50 years and never come out. There are thousands to look at at any time, and there's always the chance of discovery."

Korth has discovered plenty during his career, naming 190 new species from all over North America. He has, in fact, his very own fossil mouse namesake: Willeumys korthi, christened in 2009 by Dr. John Wahlert of the American Museum of Natural History in acknowledgment of Korth's many contributions to the field.

One of those was fossil rodent #153 — which was serendipitously unearthed while conducting research on a completely different species at the Carnegie Museum of Natural History, where he is a research associate. Preserved in a small glass vial labeled simply "rodent," the fossils had lain untouched in the collection since 1937. Korth stumbled across them, put the bones under a microscope, and knew instantly he was looking at something dramatically new. "This was the earliest and most primitive species of this family of rodents," he says. "It predates the earliest previous record by about 10 million years."

That thrill of discovery is what has sustained Korth's interest in his tiny fossils.

"I could describe 152 species in the next year, and each would still be exciting," he says. "Every time is a new adventure."

William Korth

Dr. William Korth, chemistry professor, with a fossil mouse jawbone.

He includes Nazareth students in his research. In 2015, one student was the junior author for a Journal of Vertebrate Paleontology article, along with Korth and his colleague from the Smithsonian. In 2016-17, four students are working on projects with him.