Ontogeny of the proetoid trilobite Stenoblepharum, and relationships of a new species from the Upper Ordovician of Argentina

Silicified material from the Early Caradoc part of the Las Aguaditas Formation in San Juan Province, Argentina, includes a nearly complete growth series for a new species of the tropidocoryphid Stenoblepharum Owens, 1973. Cladistic analysis of Stenoblepharum species indicates that S. astinii new species is most closely allied to the Early Caradoc S. strasburgense (Cooper, 1953) from Virginia. Chinese species of Stenoblepharum are sister group to a Baltic/Laurentian clade. A single adult-like protaspid stage occurs in the life cycle or S. astinii, closely resembling the protaspis of Decoroproetus. It is preceded by a non-adult-like first protaspid instar that appears to be characteristic of Proetoidea in general but contrasts markedly with the early larval stages of other taxa in Proetida