Abstract: Evidence of fossil horseshoe crabs from Joggins, Nova Scotia: Paleoichnology and paleonvironmental implications

The existence of horseshoe crab activity within the Upper Carboniferous section at Joggins, Nova Scotia is well known, however it remains a poorly studied part of this Coal Age ecosystem. We present an overview of the paleoichnology of limulids from Joggins and their implications for a possible brackish coastal paleoenvironment. Limulids at Joggins are primarily represented by the trackway Koupichnium, which is characterized by two rows of multiple foot impressions including a Y-shaped impression from the limulid “pusher” foot and a tail drag. By contrast, the arthropod ichnogenus Diplichnites currently includes traces of myriapods, such as the colossal two metre long Arthropleura. Diplichnites is defined as two parallel rows of footprints and it lacks tail drags or Y-shaped foot impressions. The large specimens of Diplichnites at Joggins are interpreted as terrestrial. At smaller sizes undertracks of Koupichnium bear a striking resemblance to small Diplichnites, leading to potential confusion between the two ichnotaxa. Furthermore, intergradations along the length of the trackway between Diplichnites and Koupichnium ichnofossils have also been observed. These discoveries explain the close proximity of both Koupichnium (aquatic limulid) and small Diplichnites (supposed terrestrial myriapod) trackways within the same paleoenvironment at Joggins, which is otherwise a seemingly unlikely association. The taxonomic problems and paleoenviromental interpretations of these two traces are reviewed and possible solutions proposed.