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The trilobite family Pliomeridae Raymond, 1913, is composed of 44 genera and some 190 species, with a global distribution through the Ordovician. Despite the common presence of pliomerids in paleotropical faunas, its phylogenetic structure is virtually unknown. Several pliomerid subfamilies are highly autapomorphic and clearly monophyletic, but the phylogenetic status of others is unclear at best. Higher level relationships within the family are unclear and untested, as are its inclusivity (i.e., what constitutes its basal node) and its relationship to other cheiruroidean groups such as the family Cheiruridae Hawle and Corda, 1857. A particular problem is lack of knowledge of stratigraphically early, potentially basal taxa. These taxa are particularly important because their morphology may critically inform the higher level phylogenetic problems.
Abundant, well preserved, stratigraphically early taxa are available in well known Lower Ordovician successions in the Great Basin of the western United States. Pliomerid species from these strata have been poorly described or entirely overlooked, even though they are some of the most completely known taxa ever discovered, due to their silicified preservation. The Pseudocybele-Group of trilobites is one such group of early, potentially well known pliomerids. It forms a plexus of 39 species belonging to the genera Hintzeia Harrington, 1957, Panisaspis n. gen., Protopliomerella Harrington, 1957, Lemureops McAdams and Adrain, 2009, and Pseudocybele Ross, 1951. Members of this clade occupied shallow subtidal habitats in western Laurentia (present-day Great Basin, western United States), and radiated through the Tulean and Blackhillsian stages of the Ibexian Series (Upper Tremadocian-Floian).
The goals of this project are 1) to revise and describe of all members of the Pseudocybele-Group from the Pogonip Group in western Utah and eastern Nevada and from the Garden City Formation in southeastern Idaho and northern Utah; 2) to reconstruct their phylogenetic relationships through species-level morphological parsimony analysis; and 3) to gain some insight into broader (subfamily-level) relationships within Pliomeridae using new knowledge from these species and their phylogenetic relationships.