Arthropod trace fossils from the Permian De Chelly Sandstone, northeastern Arizona

Abstract

Four previously undescribed arthropod trackways from the Lower Permian De Chelly Sandstone of northeastern Arizona are assigned toPaleohelcuraandOctopodichnus, originally described from the Coconino Sandstone (Lower Permian) of northeastern Arizona. In addition toP. dunbariandO. minor, a new ichnospecies,O. raymondi, is described. Analysis of the De Chelly specimens, and comparison with similar tracks from the Coconino Sandstone and with experimental traces produced by modern arthropods, clarifies some problems in arthropod trace fossil analysis. The experiments support earlier hypotheses that spiders and scorpions were possible trail makers for the Coconino and De Chelly trackways, and show that features of these tracks can be used to determine direction of movement. These experiments also reaffirm that an animal can produce more than one morphology in a single trackway, patterns that would be classified as two distinct ichnogenera. In addition, the results of this research suggest that the tracks were made on slightly damp sand, and were preserved by being rapidly covered with dry sand.