Chancelloriid sclerites from the Dyeran–Delamaran (lower–middle Cambrian) boundary interval of the Pioche–Caliente region, Nevada, USA

Chancelloriids are a poorly understood group of phylogenetically problematic Cambrian metazoans; complete specimens show they were sessile, radially symmetric, club-shaped organisms covered with sclerites in the form of rosettes of spines. While isolated sclerites are common components of Cambrian shelly assemblages, they have been relatively little studied. We describe chancelloriid sclerites from a series of nine sections spanning the upper Dyeran (uppermost traditional ‘lower’ Cambrian of Laurentia) to lower Delamaran (lowermost traditional ‘middle’ Cambrian) stages from the Pioche–Caliente region of east-central Nevada, USA. Samples were collected from the Combined Metals, Comet Shale, and Susan Duster Limestone members of the Pioche Formation on a bed-by-bed basis; acid maceration yielded more than 2000 sclerites. Based on careful examination of these sclerites and statistical analyses of co-occurring sclerite types, we distinguish six species, five of them new, and each with a res...