Biometric Analysis of Olenellid Trilobites from the Pioche Formation (Lower Cambrian), Nevada

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The Ohio State University

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Eight species of olenellid trilobites are present in the Lower Cambrian C-shale member of the Pioche Formation in east-central Nevada. The three most abundant of them, Olenellus (Olenellus) gilberti, Olenellus (Paedeumias) chiefensis, and Nephrolenellus geniculatus, were used for biometric analysis. The three species can be differentiated quantitatively, as indicated by the graphs created in this project. The graphs indicate the differences among the three species based on the relative length of the glabella, width of the cephalon, shape of the glabella, and size of the eye ridges relative to the total cephalic length. According to the graphs, 0. (0.) gilberti has a long glabella relative to the total cephalic length, and has large eye ridges. Most of the graphs of 0. (P.) chiefensis show low slopes on regression lines compared to the other two species. The cephalic width of 0. (P.) chiefensis is narrow relative to the total cephalic length and glabella, and the lateral glabellar segments are also narrow. The preglabellar filed is wide. On the other hand, N. geniculatus has a wide cephalic length relative to the total cephalic length and glabella, and all lateral glabellar segments are wide relative to the size of the glabella. The eye ridges of N. geniculatus are considerably shorter than that of the other two species.