Fossil leaves: Click to enlarge
Fossil leaves fresh from the quarry

Who cares about fossil plants? Paleobotanists do, and for good reason. Venture out into the wild and count how many animals you see. Now count the plants. Notice the difference? Plants are everywhere. Plants are relatively common as fossils so when paleobotanists are reconstructing past environments, they have plenty of samples to examine.

Plants are also excellent indicators of the climate in which they live. Leaves in a rainforest are often big, with smooth margins and drip tips (long skinny extensions to drain off excess water). Leaves in temperate forests are usually smaller, with toothed margins and no drip tips. Leaves in arid areas are typically very small. By looking at characteristics of fossil leaves, paleobotanists can get a good feel for what the climate was like when those leaves were originally buried.

Prospecting for plant fossils is a little like prospecting for vertebrate fossils: it all starts with knowing where and how to look.

  • Millions of years after their burial, fossil plants are most easily found in badlands, arid areas with rocky outcrops. Badlands don't support much vegetation, and this means they expose plenty of bare rock that might be rich with fossils.
  • There are three basic kinds of rocks: igneous, formed from melting rock; sedimentary, eroded by wind or water and later redeposited; and metamorphic, changed by extreme heat or pressure. Almost all fossils are found in sedimentary rocks.
  • An area that has produced good fossils in the past is worth visiting again, so paleobotanists pay attention to finds recorded by other paleontologists and by the general public.

Wrong way: Click to enlarge
The wrong way to look for fossil leaves
Before collecting any fossils, paleontologists must pay careful attention to who owns the land and seek the proper permission from the landowner or governing agency.

Sample stratigraphic section
Sample stratigraphic column of rock layers in a quarry
Fossils are scientifically useless without supporting data. Supporting data include exact latitude/longitude coordinates (marked on a map), pictures and a sketch of the fossil locality, and possibly a measured section. To make a measured section, a paleontologist or geologist starts at the bottom of the quarry. Moving from bottom to top, he or she notes how the rock changes in color, grain size, relative softness or hardness, etc. Every significant change in the rock marks a new layer, and the thickness and characteristics of each layer are recorded. Quarry rocks aren't always deposited in perfect horizontal planes; they sometimes rest at an angle, which must also be taken into consideration when describing the quarry. The completed measured section can later be used to make a stratigraphic column: a diagram showing the different layers of rock stacked vertically in the quarry. Then the level that produces the fossils can be identified in the section.

Also crucial to the Museum's records is the field locality number. The locality number includes the initials of the curator, the year of the dig, and the site number for that year. For instance, KJ9520 would be the twentieth site excavated in 1995 by the DMNS paleobotany curator Dr. Kirk Johnson. If the same site is visited the next year, it gets a new locality number. This number is recorded in a field notebook and on a field map.

Prospecting: Click to enlarge
The right way to look for fossil leaves
Vertebrate paleontologists look for fossils by doing just that — looking. Sometimes that also works for plants, but usually plant prospecting is a little more physically taxing. Fossil bones erode out of the rock, but fossil leaves erode with the rock and rarely occur at the surface. This means that most of the time, finding a plant locality means digging a hole. While vertebrate paleontologists comb the dirt with scratch awls and toothbrushes, paleobotanists pound the rocks with pickaxes until they hit paydirt (literally). It is typical to dig hundreds of small holes a day in search of fossil leaves. The good news is that once you find one leaf, you've usually found a layer full of leaves.

Fossil leaves are often densely deposited in specific thin layers, so once the leaf layer is found (and it can take a lot of holes in the ground to get there), the real digging starts.


© 2000 DMNS. All rights reserved.