GSA Annual Meeting in Indianapolis, Indiana, USA - 2018

Paper No. 115-5
Presentation Time: 9:00 AM-6:30 PM


NG, Reuben Y., Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, IA 52242 and ADRAIN, Jonathan M., Department of Earth and Environmental Sciences, University of Iowa, 115 Trowbridge Hall, Iowa City, IA 52242

The Laurentian trilobite genus Clelandia Cossman, 1902, presently contains 12 formally named species ranging from the late Cambrian (Furongian; Jiangshanian; Sunwaptan) to the Early Ordovician (early Tremadocian; Skullrockian). The genus as a whole has rarely been subject to detailed study and most of the species are inadequately known. Clelandia has never been subject to phylogenetic analysis, and even its phylogenetic affinity and familial assignment is unclear. In addition, much of the published work on the genus is in need of revision, especially the published images which are few in number and of poor resolution.

Undescribed material from the Great Basin of North America represents four new species of Clelandia from the Skullrockian Stage of the Early Ordovician. The secondarily silicified nature of this material allows for detailed study of trilobite sclerites free of matrix and in three dimensions, following acid digestion. Species are represented by multiple examples of sclerites which often document different growth stages.

The new Skullrockian species of Clelandia are each characterized by several diagnostic features of the cranidium. None of the new species appear to have the extended glabellar-occipital spine structure found in C. bispina or C. wilsoni, nor do they exhibit glabellar furrows as are seen in C. parabola, C. briscoensis, C. typicalis, C. texana, or C. albertensis. Two of the new species entirely lack an occipital spine, a condition rarely found in other species. These two species also have a dramatic reduction in furrow definition, especially of the occipital and posterior border furrows which are almost completely effaced.

Phylogenetic analysis shows a subclade dominated by species with glabellar furrows, well-expressed axial furrows, and a curved preglabellar furrow. A second component consists of species with a unique glabellar-occipital spine. The most effaced species of Clelandia, with disjunct axial, posterior, and occipital furrows and limited or absent occipital spines, are resolved as a third subclade.

Based on distinctive morphology of the cranidium, the species Desmetia annectans Walcott, 1925 is reassigned to Clelandia, and Desmetia is considered a junior synonym.