Revision of Eocene warm-water cassid gastropods from coastal southwestern North America: implications for paleobiogeographic distribution and faunal-turnover

Abstract

The warm-water (thermophilic) Eocene cassid gastropods reported previously from coastal southwestern North America (CSWNA), a region extending from the Olympic Peninsula, Washington to Baja California Sur, Mexico, are revised in terms of taxonomy, description, geographic distribution, and biostratigraphy. Five species of the cassine Galeodea and a single species of the phaliine Echinophoria are recognized. Galeodea meganosensis, G. sutterensis, G. louella, G. californica and G. tuberculiformis are predominantly found in California and, collectively, range in age from early to middle Eocene. Echinophoria trituberculata of middle Eocene age in southern California and of earliest late Eocene age in southwestern Washington, is the earliest known record of this genus. Several poorly known supposed cassids are discussed. The pre-Oligocene global record of Galeodea is compiled for the first time. The first arrival of Galeodea in the CSWNA region occurred in the early Eocene just after the warmest peak and highest sea level of the Cenozoic. Some of the CSWNA Galeodea species are very similar morphologically to some found in the Tethys Realm of Western Europe, especially in England and France, and to some found in the Gulf Coast and Mexico (Nuevo León and Chiapas). These similar species are indicative that the migratory route of Galeodea into the CSWNA region was via a current system that emanated from the Old World, passed near southern Western Europe, the Gulf Coast of the United States, northern and southern Mexico, and eventually influenced the CSWNA region. Thermophilic CSWNA cassids radiated during the early Eocene but declined by the end of the middle Eocene, and, because of global cooling, disappeared near the beginning of the Oligocene.