2009•Memoir ... of the Association of Australasian PalaeontologistsRequires access
The Late Cambrian (Furongian; Steptoean) Trilobite Genus 'Xenocheilos' Wilson, 1949: Systematics and Biostratigraphic Significance
Stephen R. Westrop, Jonathan M. Adrain
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Abstract
The affinities of the poorly known Laurentian trilobite genus Xenocheilos Wilson, 1949, have been the subject of much discussion in the literature. Here, we revise the genus through study of type material as well as new collections from Oklahoma and Utah. There are probably at least five distinct species but only two of these, X. minutum Wilson, the type species, and X. spineum Wilson, are named formally at present; 'X.' granulosum Palmer and 'X'. orthos Kurtz are assigned incorrectly to the genus. All species are limited to a narrow stratigraphic interval within the late Steptoean Elvinia Zone. Xenocheilos shares traits, including a very long frontal area, long, backwardly deflected posterolateral projections of the fixigenae, and bacculae opposite L1 glabellar lobes, with the Gondwanan family Nepeidae Whitehouse. Parsimony analysis provides support for a relationship between these taxa.