70-10 New Mid-Cambrian Agnostoid Arthropods of the Lincoln Peak Formation, Eastern Nevada

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns (Posters)

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Abstract:

Known from the early Cambrian through the Late Ordovician, agnostoid arthropods are an extinct cosmopolitan group of blind, benthic arthropods. Although the subject of longstanding disagreements over their phylogenetic affinity with trilobites and position on the arthropod tree, agnostoid arthropods are among the most common Cambrian fossils and have widespread use as biostratigraphic indices.

While there are decades of research on Great Basin silicified trilobite faunas, comparatively little work has been conducted on the silicified agnostoid arthropods found alongside them. As a result, these Great Basin silicified agnostoids provide a rich, largely undescribed source of well-preserved juvenile and adult material that will aid in better resolving the higher-level phylogeny within Agnostida as well as offering potential insight regarding the evolutionary affinities of the group.

The material described was collected from the Marjuman (Cambrian; Miaolingian; Guzhangian) Lincoln Peak Formation—a succession of thin-bedded limestones, shales, and siltstones representing a deep subtidal environment with silicified faunas of the Cedaria and Crepicephalus zones—from a locality near Cleve Creek, northwest Schell Creek Range, White Pine County, eastern Nevada. Secondarily silicified specimens were freed from their host limestone using hydrochloric acid digestion and are mostly disarticulated, although there are some articulated (enrolled) specimens. Here, five new species are assigned to Kormagnostus, three new species are assigned to Proagnostus, two new species are assigned to Lejopyge, and new species are assigned to the genera Acmarhachis, Aspidagnostus, Biciragnostus, Clavagnostus, Connagnostus, Oedorhachis, Pseudagnostina, and Pseudagnostus.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9375

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