The Alabama Paleontological Society

Trace Fossils of the Steven C. Minkin Paleozoic Footprint Site, Walker County, Alabama

How to use the Interactive Website

Prepared and maintained by:

Prof. Ronald J. Buta, Department of Physics & Astronomy, University of Alabama
Dr. Deborah A. Crocker, Office of Information Technology, University of Alabama

In 2000, the late Steven C. Minkin (1947-2004), a member of the Birmingham Paleontological Society, organized the first of a series of unusual meetings that came to be known as "track meets," where collectors would bring the fossil tracks and traces they found at the Union Chapel Mine for inspection by professional trace fossil specialists ("ichnologists") and for documentary photography. Eventually, six of these meetings would be held, leading to more than 4000 photographs of more than 2300 specimens. This database is large enough that a single individual would have a hard time examining it all in a reasonable amount of time. Although ideally, anyone interested in truly studying these trace fossils would want to see and measure the actual specimens themselves, this may not be practical. The next best thing, then, is to examine all the photographs. Here are some questions that could be answered just from doing this:
- which tetrapod trackways are more abundant at the site: amphibian or amniote? Amphibians lay their eggs in water, amniotes lay their eggs on land. The earliest amniotes were reptilian. Today's amniotes also include birds and mammals.
- what types of traces are found on the same slabs? Are there cases where an amphibian trackway and an amniote trackway are found on the same horizon of the same slab?
- how large are the footprints? How big is the forefoot (manus) compared to the hindfoot (pes)? What is the distribution of foot sizes? Which traces show shallow undertracks and which show deeper undertracks? Which show tail or body impressions dragging in the mud? Which are real surface tracks?
- how fast was an animal walking? What were its stride and pace? Did it walk around or avoid something as it moved?
- what were the properties of the substrate (material the animal moved in)? Was it mud formed from very fine sediment, or from coarser sediment? Was the water slow-moving, or fast-moving?

All of these questions can be answered at least approximately by examining the photographs in detail. The website facilitates this by allowing navigation through the database and the recording of information with minimal effort. Information is saved to files by making button selections or to typing comments or rough measurements in various small boxes. When one first goes to the interactive website, you can start at UCM 0001 or select another specimen from a dropdown list. If more than one picture of the same specimen is in the database, all the pictures will automatically come up in a slideshow mode. This can be started or stopped and done manually if desired. Many of the first 200 or so specimens have only one photograph, so no slide show of them will appear.

To the right of the displayed images, a series of dropdown selection boxes allow the classifier to make judgments about what the pictures show. If only a single trackway of a single ichnotype is seen on a slab, then only one box needs to be checked under "SELECT ICHNOTYPE." If one is not sure what a given ichnotype looks like, you can click on the ichnotype name and see some selected pictures of specimens of that type. The box next to each ichnotype asks for the number of trackways of that type on the slab. Many slabs have only one, but some slabs have many trackways of the same ichnotype.

Under SPECIMEN PROPERTIES, one can make some judgments about the nature of the trace. Negative epirelief is where the tracks are depressions in the rock, while positive hyporelief is where the tracks are elevated instead. Negative epirelief means the slab is right-side up, while positive hyporelief means the slab is upside-down. Determining whether tracks are surface tracks, shallow undertracks, or deeper undertracks is not straightforward and would require practice. In general, however, Minkin site tracks are undertracks, meaning they come from layers below the actual surface that were distorted when an animal walked over an area. Undertracks preserve less information on foot morphology than surface (or primary) tracks, the more so the deeper the undertracks. Loss of digits, or even manus or pes, are often what we see in undertracks. The problem is that surface tracks are more vulnerable to being washed away, that is, have less preservation potential than undertracks.

Under VERTEBRATE FOOTPRINT PROPERTIES, there are buttons for recording information on footprint characteristics. Most of it is self-explanatory. In principle, one can use the centimeter scale bars on each image to measure the lengths of footprints, paces, strides, trackway widths, and trackway lengths, to some level of accuracy. But if one does not wish to do this, buttons also allow eyeball measurements. Similar information is asked of invertebrate trackways in INVERTEBRATE FOOTPRINT PROPERTIES.

CIRCULAR IMPRESSIONS refers to the circular features on many slabs that have been mainly attributed to gas bubble impressions (Rindsberg 2005).

PLANTS refers to plant fossils occasionally found on track-bearing slabs. These can be identified by referring to two papers that can be viewed by clicking on the name of any plant type.

ADDITIONAL COMMENTS allows the classifier to provide information on things that may not be covered by the other buttons and small boxes. For example, a slab may show a previously unrecognized insect body fossil. Also, although many impression/counter-impression pairs are already recognized, some may have been missed and need to be noted to prevent statistical bias (counting some specimens twice). Impression/counter-impression pairs for UCM numbers greater than 2459 especially need to be recognized.

Name of Classifier: This needs to be typed in only once, at the beginning of a session. If the name of the classifier is in this box, it will be automatically written to the output file for a given specimen. An example of an output file is UCM0001.

Saving data: once all selections have been made for a given UCM specimen, the user clicks on the "Save Current Data" button. This writes to a pre-existing output file that saves the date and time as well as the name of the classifier. The classifier can then view the contents of the saved file but cannot edit it. If changes must be made, correct the box selections and do another "Save Current Data." The new data will be appended to the previously saved data. A statement in ADDITIONAL COMMENTS can point to ignore the previous data or to use corrected information.

Once "Save Current Data" is pressed, the webpage automatically brings up the slide show of the next specimen. If you have to go back to the previous specimen, or skip the displayed specimen, click the buttons above the image.

If you want to view the contents of the pre-existing data file for a given specimen, you can click on "View Previous Data" before pressing "Save Current Data."

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