TETRAPOD FOOTPRINT ASSEMBLAGE OF THE MISSISSIPPIAN MAUCH CHUNK FORMATION, SCHUYLKILL COUNTY, PENNSYLVANIA

In 1850, Isaac Lea reported vertebrate footprints from the Mississippian age Mauch Chunk Formation at Mount Carbon, Schuylkill County, Pennsylvania. Now referred to as Palaeosauropus primaevus, these are among the oldest known tetrapod tracks from the United States. A large number of Mauch Chunk footprints collected during the early 20th century, now housed at the Reading Public Museum, Pennsylvania, as well as recent collecting by the authors, establishes an extensive footprint assemblage from the Mauch Chunk Formation. These footprints, like Lea's original discovery, are from the middle member of the Mauch Chunk, occurring primarily on mud-draped surfaces of ripple-laminated sandstones. Extensive rain drop impressions, rare mudcracks and a low diversity invertebrate ichnofauna (principally two or three kinds of grazing/feeding trails) co-occur with the tetrapod tracks. Three tetrapod ichnogenera can be recognized: (1) tracks of Palaeosauropus dominate the ichnoassemblage and consist of two size grades, large (includes the holotype of P. primaevus), in which pes width is 8-10 cm, and small, in which pes width is 4-6 cm; these are plantigrade tracks with a median body/tail drag that have a pentadactyl pes, tetradactyl manus, are nearly overstepped, and have digits that are blunt tipped and often slightly curved; (2) much less common are lacertoid tracks of Hylopus, with curved, pointed digits in which digit IV is substantially longer than the other digits; and (3) a few trackways of Batrachichnus that are small (about 15 mm width x length), do not overstep and have a pentadactyl pes, tetradactyl manus and short, blunt digits. The sample size of P. primaevus is large and encompasses a wide variety of extramorphological variants that include large, thin scratch marks (swimming traces), rounded, digit-tip undertracks and a variety of tracks missing some digit impressions and/or sole marks, such as can be seen in the holotype specimen of P. primaevus. The Mauch Chunk tracks are primarily those of temnospondyls that encompass a wide range of body size, and also, rarely, of reptiles.