An Archaeobotanist Blooms from the Classroom to the Field
On the ground floor of the University of Pennsylvania Museum of Archaeology and Anthropology sits a lab full of skulls while another is lined with ceramic sherds. There’s a lead-lined room housing X-ray equipment.
And then there are the seeds in miniature glass vials, neatly lined up along a lab’s windowsill, with hand-written identifiers to avoid confusion about the contents. Other seeds in clear plastic bags tucked into a corner of the room are sorted and studied under a state-of-the-art microscope by Alexandria Mitchem, a senior Anthropology major.
Mitchem, a Richmond, Va., native who transferred to Penn as a sophomore, spends hours in these labs at the Center for the Analysis of Archaeological Materials (CAAM), amassing data for her senior thesis. A class offered through CAAM inspired her to spend four weeks this past summer at a mound site in Mississippi with archaeologist Megan Kassabaum, an assistant professor of anthropology, one of the Center’s instructors, and the Weingarten Assistant Curator for the Penn Museum’s American Section.
CAAM, a joint initiative between the Penn Museum and the School of Arts & Sciences, has been around for a little more than a year, offering Penn undergraduates and graduate students unique opportunities for practical learning using real artifacts from an extensive museum collection.
The program’s full curriculum includes instruction in plant, animal, and human remains, as well as inorganic materials like ceramics and metals. Courses range from introductory classes like one called “Food and Fire: Archaeology in the Laboratory” to high-level expert lessons on ceramic petrography and archaeobotany.
During the spring or her junior year, Mitchem took one of those classes, “Living World in Archaeological Science,” with Kassabaum; Adjunct Professor Janet Monge, associate curator-in-charge and keeper of physical anthropology; and Katherine Moore, Mainwaring teaching specialist for zooarchaeology. It solidified Mitchem’s career trajectory.
“That course is how I found out about the fieldwork opportunity,” she says.
It was the second field season at the Smith Creek site, in the Lower Mississippi River Valley, close to the Mississippi-Louisiana border.
“It was hot, really muggy because it was Mississippi, and the bugs were relentless,” Mitchem says. “We all probably ate a gnat or two. They just fly into your mouth.”
There, the team excavated three areas, including two of the mounds (A and C) and the southern end of the plaza, expecting to uncover items associated with a culture called Cole’s Creek, dating from about A.D. 700 to 1000 and a later culture called Plaquemine, dating from about A.D. 1100 to 1400, just before Europeans first arrived.
They unearthed a good deal they expected to find—pieces of pottery, corn, and nutshell—but surprisingly, they also recovered sweetgum seeds in greater quantities than had previously been reported in the area. Though these dried-out orbs, which resemble spiky brown spheres the size of ping-pong balls, blanket the ground just about anywhere there’s a sweetgum tree, their appearance here intrigued the excavators.
“We found a pit full of burnt ones,” Mitchem says. “We kept turning up more and more of these to the point where we had so many, we had more sweetgum than anything else.” They couldn’t simply write it off as an unusual contaminant.
So Mitchem and Kassabaum brought back samples to campus and sent them off, with a few other items, for dating.
“Anything that was once living, you can radiocarbon date,” Kassabaum says. “We did pieces of nutshell, as well as pieces of corn and a piece of sweetgum.”
As expected, the nutshells, one from each mound, came from A.D. 800 to 900. The corn from the plaza dated to A.D. 1300, results the researchers also anticipated. But the fourth sample, also from the plaza, proved different.
“The sweetgum had a date that was identical—and I don’t say that lightly because no dates are ever identical—but it was actually identical to the dates from Mound A and Mound C,” Kassabaum says. That means the researchers need to reassess their interpretations of the places they dug.
Mitchem explains further: “Typically if you find a pit, that’s going to be newer material because the ground surface gets laid down first. If you go back into it you’re usually doing that at a later date. To have the sweetgum [dating] earlier means there was something else going on there.”
Perhaps it involved a ritual use for the plant, or something else entirely. Either requires more digging, but likely not by Mitchem, who is in the process of writing her thesis and waiting to hear about graduate school. This spring she’s also taking another CAAM course, a graduate-level archaeobotany class taught by new faculty member Chantel White, a teaching specialist.
This fluidity from classroom and lab to field and back to lab exemplifies the vision for the Center, Boileau says.
“Before CAAM, in our lectures, we would talk about what we can do in the field. It was good but it wasn’t hands-on. Here, the students really get to do the hands-on work themselves” and incorporate what they learn into fieldwork.
They’re using techniques beyond their years of experience, Boileau adds.
“We expect this type of research by graduates, but to be able to do something like this at the undergraduate level? Wow.”
As for Mitchem, if you ask Kassabaum, her student is well on her way to a long and exciting career.
“To me, the field is always the test. That’s where you get students who you clearly know are going to go on and do this forever,” she says. “Ally has really stuck with it and she’s shined, both in the field and in the lab.”
On the day Kassabaum tells Mitchem the news about the sweetgum dating, in the lab where they’ve spent innumerable hours staring at miniscule particles magnified by a microscope, they look giddy, as though they’ve made the discovery of a lifetime. Though few others will feel that same enthusiasm over sweetgum, it’s a moment the two will forever share, facilitated by CAAM and the opportunities it affords the students at Penn.