Etch stop

Abstract

Why does the Proterozoic shelly fossil Qinella occur in a Cambrian limestone? Qinella’s unique shell morphology, thin walls separated by fluid–filled spaces (etch stop defense), served as an effective deterrent to Cambrian shell–boring predators. Family Cloudinidae was likely driven to extinction by first boring, and later crushing, predators. Qinella provides an excellent example of the predator–prey escalation that took place during the Early Cambrian.