PaleoBios

This checklist is a sequel to the one published by A. Myra Keen and Herdis Bentson in 1944 and is an alphabetical listing of California marine Paleogene–Neogene mollusk species or subspecies described and/or figured in the published literature spanning the interval of 1944 through 2020. The original data are given for each species and subspecies of bivalves, gastropods, chitons (polyplacophorans), scaphopods, and cephalopods. Where detected, formation names, ages, taxonomy, systematics, and specimen disposition were corrected. A total of 559 genera and 1,698 species/subspecies were tabulated, with the bivalves and gastropods being the most abundant taxa. Bivalve and gastropod diversity steadily built up during the Paleocene, nearly doubled during the Eocene warm time, declined greatly during the cool time of the Oligocene, rebounded to its highest peak in the Miocene and then declined slightly during the Pliocene. The other classes represented only minor faunal components. Chitons were only reported from the Pliocene, and cephalopods had their highest diversity during the Paleocene and Eocene. Bivalve genera having the highest diversity are: Glycymeris, Macoma, Mactromeris, Nuculana, and Tellina. Gastropod genera having the highest diversity are Cancellaria and Turritella. It is very likely that the Turritella species/subspecies complex has been significantly overnamed. The high point of research productivity of published reports on California Paleogene-Neogene mollusks was in 1990–1994, and a significant decline occurred in 1995–1996, following the closure of the Menlo Park USGS Paleontology and Stratigraphy facility. An overall decline in productivity has continued, with noticeable upticks in 2003 and in recent years.