Fossil invertebrate and vertebrate tracks, which are abundantly represented in the Pottsville Formation (Lower Pennsylvanian) from the Union Chapel Mine (UCM) site in Walker County, Alabama, constitute one of the most important Carboniferous tracksites in the world. Originally described by Aldrich and Jones (1930), awareness of the significance of these tracks increased through the recovery of hundreds of new specimens by the Birmingham Paleontological Society. This amateur group and scientists from the Geological Survey of Alabama, Alabama Museum of Natural History, and Emory University catalogued these specimens cooperatively. The trace fossil assemblage of the Union Chapel Mine site includes amphibian tracks (Cincosaurus cobbi), fish trails (Undichna), horseshoe-crab traces (Planolites, Kouphicnium), millepede tracks, and other invertebrate burrows (Diplocraterion, Protovirgularia, Treptichnus).
Although the UCM site also contains large and small plant debris and one body fossil of a dragonfly, the importance of the UCM site can be discerrned in the breadth and quality of its vertebrate and invertebrate tracks. Both amphibian tracks and horseshoe crab traces show size ranges suggesting an ontogeny of juveniles to adults trackmakers, potentially providing a means to estimate ancient population size and structure. Literature searches indicate that very few places elsewhere in the world, if any, demonstrate such a profusion of specimens like the UCM tracksite, where specimen numbers for both individual invertebrate and vertebrate tracks are in the hundreds. Furthermore, amphibian tracks from the Carboniferous of the excellent quality of the UCM specimens are exceedingly rare. Although Paleozoic tetrapod footprints have been characterized as ^Óprimitive and nondescript^Ô (Schult and Farlow, 1992), the UCM tetrapod tracks exhibit a clear and distinct front- and back-foot morphology that confirms the amphibian identity of the trackmaker. Other Carboniferous track sites in the world include sites in Nova Scotia, Scotland, the Czech Republic, but these sites do not demonstrate a similar quantity or quality of the UCM vertebrate or invertebrate ichnofossils. Thus, the Union Chapel Mine is a truly exceptional Carboniferous tracksite on a world-wide scale.