Redescription of the genus Modiomytilus Griffin, 1990 (Bivalvia: Mytilidae) from Southern Patagonia with remarks on the paleobiogeography of the genus

摘要

Modiomytilus Griffin, 1990, was based on composite molds collected from Cenozoic rocks in southern Patagonia. The type species comes from the early Miocene Centinela For-mation, exposed along the southern shore of Lake Argentino An additional species is known from the Eocene Rio Turbio Formation, which outcrops only at the southwestern corner of Santa Cruz Province. New material preserved as original shell was collected recently in beds referred to the Centinela Formation exposed in the same area as the Rio Turbio For-mation, about 150 km south of Lake Argentine. Enough detail is preserved in collected the shells to warrant an emended diagnosis and a new and more complete descrip-tion of the genus, as they provide a set of characters not recorded in the currently known material of any of the spe-cies described. The shells clearly belong to the type species, i.e., Modiomytilus urgentinensis Griffin, 1990. These charac-ters, among which are included the ligament, adductor mus-cle scar, pallial line, and byssal retractor muscle scar allow a reinterpretation of this genus and confirm its validity. At the same time these new morphological characters may be potentially useful for further phylogenetic analyses and a new interpretation of the currently available material, a pre-requisite for understanding the palaeobiogeographic history of this genus.