A NEW CAMBROCLAVE (METAZOA INCERTAE SEDIS) FROM THE MID-CAMBRIAN PIOCHE FORMATION, SOUTHEASTERN NEVADA

So-called small shelly fossils are a polyphyletic assemblage of shells and sclerites typically preserved by secondary phosphatization and widespread in carbonates from the lower part of the Cambrian. They are one of our major records of the early animal radiation, documenting the earliest widespread occurrence of animal biomineralization. Recent work has helped clarify the affinities of several previously mysterious groups of small shelly fossils, but others remain problematic. Noteworthy among these are the cambroclaves, whose skeletons are composed of multiple elements, each usually consisting of a long spine borne atop a flat, plate-like base. It’s widely considered that these represent sclerites from an armor densely shingling the outer surface of some animal, but the identity and biology of this creature are not known. During an effort to document the previously little-studied small shelly fossils of the Basin and Range Province, we recently discovered cambroclave sclerites from the Delamaran (“Middle” Cambrian) Susan Duster Member of the Pioche Formation of the Pioche–Caliente region of southeastern Nevada. Their morphologies are unusual for cambroclave sclerites in that they have only a very short spine and an inflated, almost cylindrical base. These are the first definitive record of cambroclaves from Laurentia, a noteworthy paleogeographic range extension for a group previously considered to be restricted to the peri-Gondwanan region.