Arthropod ichnofossils from the Ordovician Stairway Sandstone of central Australia

Strata from the Darriwilian stage of the Middle Ordovician in central Australia yield a number of ichnofossils that are usually considered to have been produced by arthropods, mainly those of Cruziana, Diplichnites, Monomorphichnus and Rusophycus. Three new ichnospecies are identified, described and illustrated, along with eight previously described and one indeterminate ichnospecies. The three new ichnospecies are: Cruziana penicillata, Diplichnites arboreus and Monomorphichnus sinus. The arthropod traces occur with other biogenic sedimentary structures in a fine to medium grained sandstone with minor mudstone interbeds of the Stairway Sandstone. The substrate composition and ichnological evidence places the trace-rich unit (upper part of the Stairway Sandstone) in the Cruziana ichnofacies.