Horseshoe crab trace fossils Arborichnus Romano et Meléndez, 1985 from the Bashkirian (Carboniferous) of the Donets Basin, Ukraine

This paper describes resting traces of horseshoe crabs Arborichnus repetitus Romano et Meléndez, 1985 from marine deposits of the Dyakove Group (Viséan–Bashkirian) and the Bashkirian coal-bearing rocks of the Mandrykyne and Mospyne formations in the Donets Basin, eastern Ukraine. The presence of Arborichnus repetitus indicates the widespread distribution of horseshoe crabs in the coastal paleobiocenoses of the Dyakove Paleobasin, located in the central part of the Donets Basin. The horseshoe crab resting traces Arborichnus repetitus from the Bashkirian strata of the Donets Basin are typical of deltaic and prodeltaic rocks, usually represented by sandstones and siltstones. Horseshoe crabs are the most likely trace-makers of Arborichnus Romano et Meléndez, 1985, but some other arthropods, e.g., aglaspidids, could also have produce these trace fossils. The discovery of the presumably horseshoe crab thoracetron on the same sandstone bedding plane as the traces Arborichnus indirectly confirms that xiphosurans were the trace-makers of these ichnofossils.