Taxonomic position and phylogenetic relationships of the bivalve Goniophorina Isberg, 1934, and related genera from the early Ordovician of northwestern Argentina

on the basis of collections from tremadoc and arenig successions of northwestern argentina, the affinities of goniophorina isberg, 1934, are reassessed. studied material includes ucumariids, lipanellids, goniophorina , and other specimens for which the new genus lossella is proposed with the new species l . juancruzi sp. nov. as type species. goniophorina and lossella are grouped in the new family goniophorinidae. synapomorphies of goniophorinids, ucumariids, and lipanellids lead to the conclusion that goniophorina integrates a major group of edentulous bivalves, a lineage of which -the ucumariidsprobably gave rise to anomalodesmata. this fauna represents a rapid, local diversification event that is part of the west-gondwanan bivalve radiation during the early ordovician.