Lower Devonian aulacopleuroidean trilobites from Oklahoma

Abstract

New aulacopleuroidean trilobites from the Lochkovian of Oklahoma include the otarionine Cyphaspis carrolli new species from the Haragan Formation, and the brachymetopid Cordania wessmani new species from the overlying Bois d'Arc Formation. Cyphaspis carrolli is the first record of the genus from the North American Devonian. It is a highly plesiomorphic species, dissimilar to contemporaries from Europe, but closely related to Silurian species from Northern Laurentia and England. Cordania wessmani had previously been interpreted as a possible sexual dimorph of Cordania falcata Whittington, 1960, but new material and information shows that the forms occur separately with no stratigraphic overlap. New information on trilobite occurrence in the Haragan and Bois d'Arc Formations does not support previous hypotheses of trilobite sexual dimorphism, but rather indicates the presence of distinct, stratigraphically successive faunas.