| Stenothecoida from the Lower Cambrian Poleta Formation, Esmeralda County, Nevada. Stenothecoida is an extinct organism of unestablished zoological affinity; lived during early to middle Cambrian times, roughly 516.0 to 504.0 million years ago. Superficially resembles a brachiopod valve, but is tentatively assigned to an undetermined class of non-bivalve mollusk, based on rare internal shell preservations. Genus Stenothecoides. Image courtesy an anonymous individual. |