A new trace fossil from the Middle Cambrian of the Grand Canyon, Arizona, USA

An unusual trace fossil from the Middle Cambrian Bright Angel Shale Formation of the Grand Canyon, Arizona, consisting of two rows of biserially opposed circular or oval depressions, with alternating symmetry, is described as Bicavichnites martini ichnogen. et ichnosp. nov. While specimens of this trace may represent the surface expression of a complex treptichnid-like burrow system, it is more likely that they are the walking traces of a bilaterally symmetrical benthic animal. The large variation in external width within the trackways is inconsistent with an arthropod producer. The trackway morphology and presence of limb spur marks suggest that the trace maker may have been a lobopodian, a Cambrian relative of modern onychophorans.