| The world's oldest trilobite. Two cephalons (head shields) of Repinaella--the oldest genus of trilobite yet described in the scientific literature--from the Andrews Mountain Member of the lower Cambrian Campito Formation, Esmeralda County, Nevada. Repinaella appears simultaneously in the geologic record in Siberia and Esmeralda County, Nevada. Photograph courtesy J. Stewart Hollingsworth. |