The ontogeny of Failleana and the origin of the Bumastinae (Trilobita)

Abstract

SummaryThe metaprotaspid of the bumastine Failleana calva is similar to protaspids of scutelluids, whilst late meraspids and early holaspids of F. calva are similar to fully mature styginids. This suggests that the bumastines were derived from the styginids in the Early Ordovician and that the bumastines later gave rise to the scutelluids. Bumastus and similar Silurian trilobites are phyletic derivatives of Ordovician bumastines and not effaced scutelluids as claimed recently by Lane & Thomas. Revised diagnoses of Illaeninae and Bumastinae are presented.