A New Trace Fossil from the Cambrian Bright Angel Shale, Grand Canyon, Arizona

Angulichnus alternipes n. ichnogen. and n. ichnosp. is a distinctive epichnial trail from the heterolithic facies of the Middle Cambrian Bright Angel Shale at Horn Creek, Grand Canyon, Arizona. It consists of a central zig-zag furrow bordered by biserially opposed alternating tracks. Though clearly formed by a benthonic arthropod, the trail cannot be attributed to a trilobite and is therefore important as an indicator of the presence of nontrilobite arthropods in the Bright Angel Shale. It is suggested that an arthropod similar to Habelia optata from the Burgess Shale would be a convincing trail-former. Sedimentologic analysis indicates that the heterolithic facies represents storm-induced deposition of sand, followed by a low-energy period during which traces were formed as mud settled to the bottom.