Graptolites from the Wheeler and Marjum Formations (Cambrian, Series 3) of Utah

Abstract

Specimens from the Wheeler and Marjum Formations of Utah comprising an elongate stipe with freely projecting conical thecae are described as dithecoid graptolites, the first reported from these units. The Wheeler Shale specimens, assigned to Archaeolafoea monegettae (Chapman, 1919), provide the first record of Archaeolafoea Chapman, 1919 from the Cambrian of Laurentia and show clear fusellar structure in backscattered electron images, confirming a graptolite affinity for this taxon. Mastigograptus sp., described on the basis of a single well-preserved specimen from the Marjum Formation, shows for the first time in a Cambrian mastigograptid an arrangement of thecae similar to that known for Ordovician representatives of the genus.