The otarionine trilobite cyphaspis, with new species from the silurian of northwestern Canada

Abstract

The genus Cyphaspis Burmeister, 1843, is first known from the northern Laurentian Sheinwoodian. By the late Homerian, the genus had appeared in England and Baltica, and from the Ludlow through the Lower and Middle Devonian it had an essentially cosmopolitan distribution. The Mississippian Dixiphopyge Brezinski, 1988, may represent a relict distribution of Cyphaspis, and if so should be considered a junior subjective synonym. Cyphaspis is considered the sister taxon of Otarion Zenker, 1833. The oldest, Sheinwoodian, species of either genus are very similar, but the clades evolved to the point of gross morphological disparity in the Devonian. New species from the Wenlock and probably Ludlow of northwestern Canada are Cyphaspis lowei, C. munii, C. buchbergeri, and C. mactavishi. New ontogenetic material of the Zlichovian C. dabrowni (Chatterton, 1971) further demonstrates the pervasiveness of the basic juvenile morphology of the tribe Otarionini.