Experiment of the month

Natural History, Sept, 2003 by Stephan Reebs

It isn't easy being an archaeologist. The ancient artifacts you work with are often battered and fragmentary, and you have to base a lot of your interpretations on the stratum where you find the artifacts. Given the many species of burrowing animals--which seem pretty cavalier about the effects of their excavations on scientific evidence--it seems perilous indeed to put much stock in the discovery stratum. Animals might have displaced your crucial artifacts many times before you unearthed them.

Knowing what a burrower the armadillo is--and how little attention had been paid to it--the Brazilian archaeologists Astolfo G. Mello Araujo of the University of Sao Paulo and Jose Carlos Marcelino of Sao Paulo's Department of Historical Patrimony decided to study the animal's effects on an experimental "dig" at the Sao Paulo Zoo. They spray-painted four groups of ersatz artifacts (actually ceramic shards and stone flakes) in four distinct colors and sprinkled them into four separate layers in the ground. The result was a two-foot-deep "layer cake," whose top layer of artifacts was open to the air and whose other layers were separated from one another by eight inches of earth.

Then a lone female armadillo was turned loose at the site for almost two months, after which the archaeologists surveyed the thoroughly mucked-up earth. The effects were easy to see: blue objects pushed many inches up to the yellow ones, yellows pushed down among the blues, big and small items both dislodged. Fortunately, though, the concentration of objects from a given stratum still peaked near their original level.

One possible benefit of this kind of "noise" in the archaeological signal is that by bringing artifacts to the surface, armadillos can help archaeologists locate promising sites for their own, more systematic digging. ("The role of armadillos in the movement of archaeological materials: An experimental approach," Geoarchaeology 18:433-60, 2003)

Stephan Reebs is a professor of Biology at the University of Moncton in New Brunswick, Canada, and the author of Fish Behavior in the Aquarium and in the Wild (Cornell University Press).