In November 1986, geologists with the West
Virginia Geological and Economic Survey's Coal Resources Section
had the opportunity to examine the fossilized footprints of an ancient
amphibian, a rare fossil find in West Virginia. The trails of footprints,
called trackways, were uncovered during the removal of overburden
in a surface coal mine on the west side of Piney Swamp Run, Elk
District, Mineral County (Figures 1 and 2).
|Figure 1. Trackway (boxed area) left
in siltstone by an amphibian about 300 million years ago, and
recently unearthed at a surface mine in Mineral County. Camera
lens cap, center, shows scale. (All photos by the author)
This discovery was similar to the fossilized
amphibian trackway investigated by Survey geologists in Tucker County
in 1982 (see the article "300 Million Year Old Footprints Found
in Tucker County" in the 1982 issue of Mountain State Geology).
Both of these finds are important because there are few well-documented
examples of fossilized animal tracks within the State's boundaries.
Upon arrival at the site, the geologists' primary
task was to identify and date the rock units containing the trackways.
Dating the rocks also dates the animal that left the footprints.
Identifying the rock units gives an idea of the environment in which
the animal lived.
Two trackways were found, both in a dark gray siltstone.
Neither trackway was in its original place, having been disturbed
by the overburden removal. However, from observations made at the
site, it was concluded that the trackways must have come from the
interval of rocks between the roof of the Pittsburgh coal and the
base of the Sewickley coal. This puts the trackways in the Monongahela
Group (Late Pennsylvanian age) and means that they, like the 1982
Tucker County find, are almost 300 million years old. At that time,
this area of Mineral County was low-lying, wet, and swampy. Since
the trackways were in siltstone (laid down as a layer of sediment
carried in by meandering streams) and not coal, the environment
would not have been as lushly vegetated as was necessary for a
coal-forming peat swamp.
Figure 2. Closeup of an individual
footprint in siltstone. Lens cap shows scale.
What if the Specimen Can't Be Brought
Sometimes a geological specimen, such as a fossilized trackway,
can't be brought back for further study. It might be too big
(at least in relation to its value) or too delicate to transport.
Time may be too short to permit digging it out.
What can be done? At the very least, measurements and sketches
can be made, and detailed notes recorded in a field notebook.
Stereo photographs, which give the appearance of three dimensions,
are simple to make. (Perhaps in the future, making holograms
in the field will be routine, thus giving a true three-dimensional
image.) If a technical illustrator is available, technical
drawings can be made. Often they are more valuable than photographs.
Another useful technique is making a cast of the specimen.
Fiberglass, room temperature vulcanizing rubber, latex, and
plaster of Paris can be used to make the mold in which the
cast is made.
In the case of the Piney Swamp Run fossils, molds were made
using a gelatin-based compound used by dentists. This material
sets up rapidly, a big advantage when working in an awkward
spot. As long as the mold is kept moist, a number of plaster
casts can be made from it under more convenient conditions.
(If the mold dries out, it shrinks. The proportions are the
same but the true dimensions of the mold are lost.) After
making a mold in the field of the best individual footprint,
several plaster casts were made from it at the Survey's offices,
preserving something from the trackway for future study (Figure
In addition to the mold of the individual footprint, a rubbing
of the trackway was made using a pencil and a long piece of
blank newsprint. The technique is that used to make rubbings
of old gravestones. Although the results were only fair; they
were good enough to allow measurements to be rechecked in
How the Fossils Formed
Fossilized footprints such as these are formed under
a fairly narrow set of conditions. An animal heavy enough to form
an impression must walk slowly across sediments that are fine-grained,
cohesive, and moist. If the sediments are too coarse, the footprints
will lack detail. If the sediments are not cohesive, only a depression
and not a footprint will be left behind (like walking on the dry
part of a beach). If the sediments are cohesive but strong enough
to bear the weight of the animal, no impression will be made.
Moisture is usually the controlling factor. It may
give some cohesion to a material that is not otherwise cohesive.
For example, a detailed footprint can be made in the moist sand
at a beach, whereas wet or dry sand lacks cohesion and hence the
strength to retain the impression of the foot.
There is a similar moisture range in clayey soils
which have the right strength to take the impression of the foot
and hold it without distorting. Then, before the footprint is destroyed
by rain, erosion, or other forces, it must be filled in with a sediment
having a different texture so that, assuming the sediments lie undisturbed
until they harden, they will separate at the footprint. In a swamp,
such conditions are most likely to be found when high water has
receded at the end of a rainy season.
What the Fossils Revealand
What They Don't
|Figure 3. Hypothetical example of a trackway.
Measurements taken can give information on an animal's walking
behavior, size, and broad clues as to its type. (Illustration
by Ray Strawser)
Preservation was not very good on the Piney Swamp
Run trackways. One was so poorly preserved that there were no
details in the individual footprints. The better trackway had one
footprint which showed five toes and may have been the animal's
hind foot. (Modern salamanders have five toes on their hind feet.)
Due to the size of the specimens, the nature of the rock, and the
poor preservation of the footprints, the trackways were not collected.
However, photographs were taken, and notes and casts were made for
future study (see box).
The 1982 Tucker County footprints were associated
with mollusks, fern-like plants, and trace fossils other than the
footprints. Fossils of these types were not noted at the Mineral
County site. Thus, a less complete picture of the environment
the animal lived in can be reconstructed for the Piney Swamp Run
Mossman and Sarjeant (1983) have given a good overview
of fossil vertebrate footprints. They point out that to be scientifically
valuable, several measurements should be made on the trackway: stride,
pace, step angle, and trackway breadth (Figure 3). For quadrupeds
an additional useful measurement is the distance between the midpoint
of the line connecting two hindfoot prints with the midpoint of
the line connecting two forefoot prints. (This gives the animal's
trunk or body length.) Measurements on the Piney Swamp Run trackways
are shown in Figure 4. (Measurements of the 1982 Tucker County trackway are shown for comparison.)
Piney Swamp Run
Figure 4. Measurements taken from the Piney
Swamp Run trackways and the Tucker County trackway.
Compared with those found in Tucker County, the
individual tracks at Piney Swamp Run are larger. The best-preserved
footprint was about 41h inches at its longest and about 3¼
inches at its widest. A footprint from Tucker County measured only
about 21h inches at its longest and about 2¼ inches at its
widest. None of the Tucker County footprints had five toes showing
but at least one of the footprints from the Piney Swamp Run site
had five toes.
Figure 5. Making plaster casts of the Piney
Swamp Run footprints. Casts at left are from the 1982 Tucker
County find, and were used for comparison.
Were the trackways made by the same species of amphibian?
The footprints are of similar but not identical size. The animal
could have had four toes on the forefeet and five toes on the hind
feet, as do modern salamanders. The various measurements of walking
behavior are similar. Could the difference in footprint size be
due to a large individual or a different type of individual? Right
now there is not enough information to say. These footprints are
all we have as a record of the amphibian.
Still, each discovery like this adds to the evidence
of what West Virginia was like in prehistory, and the nature of
the ancient animals who lived here.
300 Million Year Old Footprints Found in
Tucker County: T. R. Jake and B. M. Blake, in 1982 Mountain State
Geology magazine, p. 23-25. Publication MSG-82, $1.00.
Mossman, D. J., and Sarjeant, W.A.S., January,
1983, The footprints of extinct animals: Scientific American,
vol. 248, no. 1, p. 75-85.
Thanks to being alerted by Mr. David Idleman
of the West Virginia Department of Energy, Survey geologists were
able to examine these fossil trackways, and thus share this unique
find with the people of West Virginia.
Article reprinted from the 1988 Mountain State