SURVIVING THE CAMBRIAN EXPLOSION: QINELLA FROM DEATH VALLEY, CALIFORNIA

The small shelly fossil Qinella occurs in an oolite sample from the Lower Cambrian Wood Canyon Formation, Echo Canyon, Death Valley, California. Until now, Qinella has been reported exclusively from upper Proterozoic strata. The Death Valley specimens reach 3.5 mm diameter, and are preserved in limestone matrix that hosts ooids, trilobites, and archaeocyaths with lumpy, cerebroid coatings. Although reworked, the Qinella specimens are not derived from Proterozoic deposits, as one specimen has a trilobite fragment lodged deeply in its interior.

The fossils were collected under permit from an elevated desert pavement surface during a Mount Holyoke College expedition to Death Valley. The oolite sample suite was initially thought to belong to the Proterozoic Johnnie Formation. Thin sections, however, revealed the presence of juvenile ethmophylloid archaeocyaths occurring as coated grain nuclei alongside the Qinella. Cerebroid ooids characterize the lower oolite of the upper Wood Canyon Formation. Under cathodoluminescence, the small shelly fossils reveal characteristic Qinella wall structure, manifest as nested, loosely‑spaced cylindrical walls of variable thickness. Walls may thin and pinch out against adjacent walls, as seen in both transverse and longitudinal section.

Qinella, also known from the Proterozoic La Ciénega Formation of Sonora, México, is one of very few genera known to survive the Cambrian explosion. Qinella's wall structure evidently provided a formidable defense against boring micropredators. The enhanced protection afforded by its multilamellate shell allowed Qinella to survive well into the Cambrian.