Abstract

Cladistic revision of supergeneric taxa of Trilobita has revealed that taxonomic turnover between Cambrian and Ordovician systems is less than was implied by traditional gradistic classifications Taking the late Cambrian "Ptychaspid Biomere" as an exemplar of biomere diversification, taxonomic artifacts (nonmonophyletic groups) have contributed to spurious extinction patterns: cladistic relationships predict ages of origination (sensu Hennig) that may predate biomere boundaries. Calibrating a cladogram for the suborder Asaphina with stratigraphic first appearances, ghost lineages (range extensions inferred from earlier appearance of a sister group) are a substantial component of Cambrian taxon duration Characters from protaspid (larval) morphology afford resolution of the enigmatic relationships of several highly autapomorphic trilobite orders that diversified in the Early Ordovician: the order Phacopida provides a case study. A high degree of taxonomic congruence is afforded between cladograms based on larval and adult characters for phacopide families.