Micromammals Tell a Mega-Story

Most research in archaeology happens in a lab. Despite the images of sweaty excavators and big hats that come to mind when “archaeology” is mentioned, the bulk of archaeology happens when the digging is done. It’s a truism among project directors that you plan three days in the lab for every one day in the field, but the essential work that goes on behind the scenes is largely invisible to the public.

I’m a zooarchaeologist – an archaeologist who studies animal remains – and I do most of my work in labs. Right now, I’m working at the Muséum national d’Histoire naturelle in Paris, where I study the bones of micromammals like mice and voles. These tiny remains were excavated from Bronze and Iron Age sites on the island of Sardinia (c. 1700-300 BCE), and despite their small size, they help me answer big questions about the cultures I study. Micromammals are sensitive to the environments around them. Different species have particular preferences for habitats and living conditions, which means that identifying the micromammals at a site is a way to reconstruct the site’s environment. And reconstructing the ancient environment is fundamental to understanding everything from past economies to climate change.

I use a microscope to examine bones for evidence of digestion by predators

A typical day of zooarchaeology includes multiple projects. Today, I’m working on three. I begin the day by tackling a taphonomic analysis of the micromammal remains. Taphonomy is the study of how ancient bones are incorporated into archaeological sites, and it includes everything that happens to the bones after the animals die. You can imagine why taphonomy would be important for interpreting ancient bones. Let’s say, for example, that the ancient environment was swampy, so the local micromammals were adapted to wet terrain. But if there were grasslands nearby, an ancient owl could nest in the swamp but hunt in the grasslands, scattering bones of grassland species around its nest. A case like this will give you a confusing mixture of grassland and wetland species showing up together – so what was the ancient environment really like? A careful taphonomic analysis can sort out which species died at the site and which were brought there by predators, helping differentiate the immediate local conditions from the wider surroundings.

Special software lets me capture detailed images of the micromammal teeth

After a morning in front of the microscope recording taphonomic clues, I’m ready to move to my second project. This project uses geometric morphometrics – a kind of spatial statistics – to analyze the shape of micromammal teeth. The shape of the teeth shows genetic plasticity, meaning that it changes depending on which groups of micromammals bred with each other. Looking at the shape of ancient teeth is therefore a way of tracing population dynamics, and when the only way new micromammals get to an island is by sneaking onto ships, ancient micromammal interactions become a proxy for ancient human interactions.

Drawers full of tiny reference skeletons at the Muséum national d’Histoire naturelle

I spend several hours taking images of the micromammal teeth. When I’ve captured images of all of the teeth, I’ll use specially developed software to compare the teeth with each other and with teeth from archaeological sites around the Mediterranean. Capturing the images takes up the major part of my day, but it’s only the beginning. Outlining each tooth so I can compare their shapes will take days. It’s a slow process, and I’ll work on it a little at a time after I return to the states.



I have just about an hour left in my day, so I decide to spend it studying. My third, long-term project is to do an environmental reconstruction for my site in Sardinia – Sa Conca Sa Cresia – which I excavated with my colleague Mauro Perra in 2009-2011. Even though we completed the excavations a while ago, I’ve only recently finished sorting the heavy fraction to remove the tiny micromammal bones. To prepare to do a complete environmental study, I first consult The Atlas of European Mammals to see which species are currently known to exist on the island. Then I visit the Muséum’s reference collections to familiarize myself with the characteristics of these species’ bones – and especially their highly diagnostic teeth.

The number and shape of the cusps make teeth “diagnostic,” meaning they can usually be assigned to a species

By the end of the day, my brain is fried. I cover the microscopes, turn off the lights, and make my way to the metro line 7, then transfer to the 6. I’m in a bit of a daze, but it’s a good kind of exhaustion – similar to how muscles feel after a trip to the gym. It’s an exhaustion that lets me know I deserve to take the night off. And there’s no better place for a night off than Paris. 


Magnifiers, Mouse Teeth, and Hope

Archaeologists love their equipment. Most of us can tell you when and where we got our first trowel, when and where we got our last trowel, whether we prefer a leaf blade or a pointing blade or a margin blade, why we buy Marshalltown or WHS or Battiferro. And it isn’t just our trowels. We’re obsessed with our hand picks, our Leatherman tools, our GPS units, our water bottles, our boots, and – perhaps the one realistic thing in the Indiana Jones movies – our hats.

It doesn’t stop with field archaeology. Lab archaeologists are just as intense about their microscopes and stereo macroscopes, their sonic cleaners and deionized water, their bags and bottles and pipettes. I’m as bad as the next archaeologist when it comes to equipment, so when a magnifying lamp I ordered finally arrived on Wednesday, I was stoked.

My lab in Sardinia is still being set up. I buy a few new pieces of equipment each time I return, and this year’s addition of a magnifying lamp is a significant upgrade. It enables me to take some time for a second zooarchaeological project that has been on the back burner for a year now. That project is looking for mouse teeth.

Yes, mouse teeth. Mouse teeth may sound insignificant, but these adorable, tiny fragments of ancient Rodentia are actually quite meaningful. Rodents are sensitive indicators of their local environments, and some species have particular relationships with humans that archaeologists use to understand how ancient people lived. In an ongoing research project that I’m pursuing in collaboration with the workgroup Mousetrack, run by Dr. Thomas Cucchi at the Muséum national d’Histoire naturelle, I’m using different mouse species to understand when exchange relationships developed between Sardinia and the cultures of the East Mediterranean. This is an important question because archaeologists debate whether the prehistoric cultures of Sardinia were more isolated or more connected to other Mediterranean groups.

Sorting for mouse teeth with my new magnifying lamp

I took my new lamp to the lab first thing on Thursday morning and set it up at a specially reserved desk. This desk is now my mouse study desk, where I do the painstaking work of sifting through what archaeologists call “heavy fraction.”

When archaeologists dig, they collect a sample of sediment from every important stratigraphic layer. This sample of sediment is then mixed with water and agitated in a process called “flotation.” Flotation can be done by hand in a bucket or with a variety of more or less sophisticated pump-and-barrel mechanisms, but the point is to get carbonized plant remains to rise to the surface. The floating material – which sometimes also includes fish scales and tiny bones – is called the “light fraction.” We collect it using an extremely fine mesh like chiffon and dry it carefully, preferably out of direct sunlight (if carbonized seeds dry too quickly, the difference between the dry surface and the wet interior can make them break).

The stuff that doesn’t float during the flotation process is also collected, usually in a slightly larger mesh with holes about 1 mm2. This is the heavy fraction, and it’s where we find lots of tiny animal bones as well as pottery, chipped stone, metal, glass – any heavy material that breaks into small pieces. The tiny artifacts that show up in heavy fraction can be fascinating. Beads and jewelry, nails, pins, and fragments of carved bone are all common. Food waste is also common, and evidence for small foods like eggs, fish, and sea urchins is often recovered only in the heavy fraction.

The heavy fraction I’m sorting comes from my excavation of the early Nuragic site Sa Conca Sa Cresia, located on the small plateau near Siddi, Sardinia, that also includes Sa Fogaia. I co-directed the excavation of Sa Conca Sa Cresia with Sardinian archaeologist Dr. Mauro Perra between 2009-2011. The excavation was very successful and our analysis of the resulting artifacts is ongoing – a good rule of thumb is that archaeologists expect to spend three days in the lab for every one day of excavation.

At first, sorting heavy fraction feels like doing excavation in miniature. It’s exciting to notice the shiny flakes of obsidian, the broken pottery, the piglet toes and lizard jaws and frog legs as they emerge from the tiny rocks that make up 99% of the heavy fraction. After a while, though, I start to get nervous. Where are the mouse teeth? Why haven’t I found one? Will I end up finding any at all, or will I just spend hours of precious research time looking for something that isn’t there? The problem, of course, is that there’s only one way to answer these questions, and that is to get in there and sort.

Got one!

Realistically, I was rewarded pretty quickly with my first mouse tooth. And not just any tooth, a first molar of the mandible: the specific tooth that is most useful for my study. My heart leapt a little as I recognized the characteristic shape, and I picked it up gingerly and transferred it to a plastic specimen tray. I couldn’t say immediately what species the tooth belonged to – that requires careful cleaning and more powerful magnification – but the tooth was the right size to be one of the species I’m interested in.

It was an exciting find, and it re-energized me for a while. But after a couple of hours, the frustration crept back in. Then the concern. Obsessively, I sorted on.

When you’re invested in the outcome, sorting heavy fraction feels like playing a weird archaeological slot machine. I use flexible tweezers to spread out a small pile of sediment, then examine it minutely with the magnifying lamp. “C’mon, mouse tooth!” I say to myself as I flick past the ribs and toes and vertebrae that aren’t relevant for my study. There’s lots of what I don’t want, but is there anything I do want? No, nothing. I push this pile of sediment to the other side of my tray and start a new pile: “C’mon, mouse tooth…”

The hope is addictive. The possibility that each little pile of sediment might hold the tooth I’m looking for. The possibility that the tooth might belong to a significant species. The possibility that enough significant teeth will add up to a significant find, a meaningful advance in what we as humans know about our past. Students sorting heavy fraction for the first time usually put down their tweezers after fifteen minutes. “You do this all day?” they ask in disbelief. “Don’t you get bored???”

Yes, I get bored. But I stay hopeful.

After non-stop sorting for three days, I’m almost finished. I currently have eight new teeth, an average of less than one tooth for every liter of sediment. I’m hoping to find one more, but the sediment I’m working on now includes very little cultural material of any kind. There are only the rarest fragments of pottery, obsidian, or bone. Still, you never know. I always have hope.

Four mouse teeth – a full day’s work