WALKING TRAILS OF THE GIANT TERRESTRIAL ARTHROPOD ARTHROPLEURA FROM THE UPPER CARBONIFEROUS OF KENTUCKY

Large arthropod trackways interpreted as trails of the giant terrestrial millipede Arthopleura have been found in strata of the Mid-Late Pennsylvanian Conemaugh Formation in eastern Kentucky. The trails represent the ichnogenus Diplichnites and are preserved as convex hyporeliefs on three slabs of fine to very fine, micaceous sandstone. The slabs are 4-14 cm thick and were derived from a 1.5 m thick, interbedded sandstone and shale facies of early Stephanian age. Associated features include parallel lamination, ripple cross-lamination, current ripple bedding, graded bedding, mudcracks, root traces, and rare leaves of Cordaites and amphibian footprint casts. The facies is interpreted to have been deposited during repeated river flooding which produced alternating crevasse splay sands and muds.

The largest trackway is 30 cm wide and consists of two parallel series of tracks comprised of prominent ridges. In the widest trackway, these ridges are 4 cm long, with a maximum width of 6 mm at the distal end which is rounded. The width and relief of the larger ridges decreases toward the midline, generally ending as a sharp point. The ridges are regularly spaced at 3 to 4 cm intervals. Most ridges are inclined at a steep angle to the trackway midline. Shorter, lower relief ridges are also present and may represent tracks from shorter legs and/or narrower pleura near the anterior or posterior ends of the animal. Length/width ratios of known Arthropleurids suggest that the millipede had a length in excess of 1 meter.

The smallest trackway is 18 cm wide and the morphology of the tracks is similar to the largest example. Differences include smaller ridge length (1.5-2 cm) and width (0.5-1.0 cm), and track orientation perpendicular to the trackway midline.

Arthropleura is the largest known terrestrial arthropod to have ever lived, reaching up to 2 m in length. Body and trace fossils are known from Visean to lowest Permian. Body fossils have been reported from Ohio, Pennsylvania, and Illinois. This is the first definite occurrence of Arthropleura trackways from the Appalachian basin. The only other known occurrences in North America are from Canada, Kansas, and New Mexico.