SYSTEMATICS OF SHUMARDIIDAE (TRILOBITA), WITH NEW SPECIES FROM THE ORDOVICIAN OF ARGENTINA

New shumardiid trilobites from Arenig to Early Caradoc deposits of the Argentine Precordillera include species of a revised Kweichowilla (K. salasae, K. sterrenae, and K. piojensis) and the new genus Changchowilla (C. sanjuanina and C. gracielae, and C.? carrerai). Conophrys fabiani new species occurs in the Early Tremadoc of the western Puna region, northwestern Argentina. Leoforteyia new genus is based on L. hintzei new species from the Ibexian of Utah. Published taxa recognized as new species are Conophrys rushtoni, Conophrys wrighti, Leoforteyia ludvigseni and Shumardia whittingtoni. Phylogenetic analysis suggests the differentiation of Shumardia Billings, 1862; KweichowillaChang, 1964; Changchowilla new genus; and Leoforteyia new genus as separate taxa and indicates that Conophrys Callaway, 1877, is a grade group. Silicified material provides a nearly complete growth series for Kweichowilla salasae, including the first protaspides known with confidence for the Shumardiidae. Additionally, ontogenetic material for K. sterrenae, C. sanjuanina, C. riojana (Benedetto and Cañas) and C.? carrerai is described. Leoforteyia is restricted to the Ibexian-Whiterockian of western Laurentia; species of Shumardia are widespread in the Arenig to Early Ashgill of western Europe, Australia, Laurentia, China and Russia. Changchowilla is recorded in the mid-Late Arenig-Llanvirn of the Precordillera and in the Llanvirn-middle Caradoc of China. Argentine species of Kweichowilla are closely allied to Australian species, suggesting biogeographic affinities of the Precordillera to the eastern margin of Gondwana by the Llanvirn and Caradoc. Functional morphology, occurrence in fine grained sediments, and association mainly with atheloptic and pelagic trilobites suggest that shumardiids were deposit-feeders that inhabited low light levels in low energy settings, with a limited ability to burrow in soft sediments.