Abstract
AbstractExceptionally preserved specimens of the Cambrian stem-group brachiopodMickwitzia occidensWalcott, 1908 are described in detail from the Indian Springs Lagerstätte in Nevada, USA. Shell structure and preserved mantle setae from these specimens reveal a variable diagenetic (taphonomic) history and provide insight into the phylogenetic position of mickwitziids. Morphologic and morphometric comparison toM. monilifera(Linnarsson, 1869) from Sweden andM. muralensisWalcott, 1913 from British Columbia, Canada reveals clear species-level distinctions. Scanning electron microscopic analysis allows revision of the generic diagnosis. TheMickwitziashell is characterized by the presence of inwardly pointing phosphatic cones and tangential setae-bearing tubes. The inwardly pointing cone structures are not consistent with setal bearing structures as previously thought, but rather represent endopunctae-like structures. Acrotretid-like shell structures and shell-penetrating setae inM. occidensstrengthen the previously proposed close relationship between stem-group brachiopods and tommotiids, a group of small shelly fossils.
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