Digging: Click to enlarge
Leaf Whackers digging away the overburden

Equipment: Click to enlarge
Sometimes the job is too big for a shovel.
Digging a hole in just the right spot turns up fossil leaves, but getting them out of the ground in good shape is no small job. Actually, it's the hardest part of leaf excavation. Since fossil leaves usually occupy a horizontal plane (anywhere from a few millimeters to a few meters thick), getting to them requires clearing the overburden. This can be accomplished with several tools: pickaxes, shovels, or — when the work gets too back-breaking — the occasional earth moving machine.

The size of a typical quarry for a fossil leaf dig is one by three meters. Once the rocks above that area are cleared away, it's time to get out the brooms and tidy up to ensure no overburden scraps mix with the quarry's yield. Why does this matter? Because collecting the leaves proceeds through the excavation of large blocks, and a clean quarry allows the paleobotanist to easily find natural structures that make for easier digging. It's also much easier to find a lost leaf fragment in a clean quarry. The DMNS curator of paleontology Dr. Kirk Johnson maintains that he's fussier about the cleanliness of his quarries than the cleanliness of his house. (In fact, that's not saying much, but his quarries are pretty clean.)

Discipline: Click to enlarge
Kirk Johnson directs his Leaf Whackers with a firm hand.
Swept quarry: Click to enlarge
Quarry sweepers take a break.
Next to cleanliness, Kirk believes discipline makes for a happy quarry. (Out of genuine happiness or bone-chilling fear, his workers generally act happy.) After sweeping the ground clean, Leaf Whackers (Museum volunteers specializing in fossil plants) take an assembly line approach to leaf excavation.

Big split result: Click to enlarge
Splitting a big slab and showing the results
The first part of the assembly line includes the Leaf Whackers who tease slabs of rock out of the quarry with pickaxes and crowbars. Fossil leaves come in all shapes and sizes, and this has important implications for how the first part of the assembly line must work. You can find a small leaf on a big rock, but you can't find a big leaf on a small rock, so Leaf Whackers on quarry duty make an extra effort to extract the largest possible blocks. This usually takes a team effort.

First split: Click to enlarge
Splitters show off their first find.
Once Leaf Whackers at the first part of the assembly line get the slabs out of the ground, they hand those slabs off to the next group: splitters. Depending on the type of rock in the quarry, Leaf Whackers assigned splitting duty use rock hammers, chisels, or even putty knives to split the slabs and look for leaves. Fossil leaf preservation varies from faint impressions that a leaf was once there to exceptional quality in which the leaf's smallest veins are still visible. Sometimes even the cuticle (the leaf's outer waxy coating) is preserved, after tens of millions of years. Good preservation is invaluable to paleobotanists because it helps them better identify the fossil species.

Leaf detail: Click to enlarge
Detail of a fossil leaf showing insect damage
Fossil leaves yield other clues to ancient landscapes. It makes sense that the best fossil leaves are the best looking, the ones that were buried under the sediment after fairly uneventful lives, right? In fact, the most instructive leaves are often the ones that emerge with battle scars, namely from the battles they lost. Look closely at a modern plant and you'll see that most leaves are far from perfect. Insects use leaves for nurseries, home improvement supply stores, and buffets. What's more, different kinds of insects leave different kinds of damage. These tiny trails of destruction are as useful to paleontologists studying fossil insects as recognizable vein patterns are to paleontologists studying fossil plants.

Trimming: Click to enlarge
Trimming fossils of excess rock

Fossils sit patiently in flats, awaiting wrapping.
All this evidence of what the ancient landscape was like is safely preserved under layers of sediment for millions of years, but once the fossil is unearthed, exposure to sun and wind can evaporate the evidence in hours or even minutes. Leaf Whackers move quickly to make sure the goods get safely back to the Museum. The first step is trimming excess rock off the fossil. A trimmed fossil consumes less space and leaves more room for other fossils. What's more, it's lighter and less likely to crush its neighbors.

Next, each fossil leaf is numbered with a magic marker. By recording the locality number on each fossil, Leaf Whackers prevent confusion when the fossils are later unwrapped at the Museum.

Dispensing TP: Click to enlarge Wrapping: Click to enlarge
Dispensing the supplies, and wrapping and packing fossils

Do fossils ever break in the excavation process? You bet they do! Leaf Whackers keep glue on hand to repair the damage. Vertebrate paleontologists often use vinyl acetate (better known as vinac) to strengthen the fossil bones, but what works well for bones is a big mistake with fossil plants. Vinac can destroy the vein patterns in the leaf, and this makes photographing and identifying the fossils difficult if not impossible. When the matrix is wet and the rock is soft, Leaf Whackers quickly wrap the fossils so they can dry slowly in the Museum, where the temperature and humidity can be better controlled.

Wrapped leaves: Click to enlarge
Piles of wrapped fossils look like so many little mummies.
Plant fossils are wrapped in the most pedestrian of materials: toilet paper. The best toilet paper is the restaurant grade (without perforations). Depending on the fragility of the fossils, toilet paper may be followed with newspaper and tape. Wrapped fossils are again numbered and packed in cardboard flats or boxes.

After everything has been packed, it's driven or shipped back to the Museum to be unwrapped and prepared in the fossil lab.


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