OVERVIEW OF LATE CRETACEOUS MARINE GASTROPODS FROM THE CHATSWORTH FORMATION, SIMI HILLS, SOUTHERN CALIFORNIA

The marine Chatsworth Formation (upper mid-Campanian to lower Maastrichtian) crops out in the Simi Hills of Los Angeles and Ventura Counties, southern California. Most of the exposed formation consists of non-fossiliferous mid-deep-sea fan deposits, but some consists of fossiliferous slope facies. Although known and collected for almost 100 years, the Chatsworth's molluscan fauna has not been studied in detail until now. This study of the gastropods is based on specimens for the Los Angeles County Natural History Museum's Invertebrate Paleontology Collection and is currently ongoing.

Fossil localities are most numerous in canyons near the bottom of the exposed section in the southeastern Simi Hills, and in an area near the top of the section in the western Simi Hills. Fossils are not found in living positions but have been concentrated in beds by storms, currents or other flows. Preservation is typically moderate to poor, and many specimens are broken. About 20 gastropod families, 45 genera and 50 species are represented in the collecitons. In addition, there are several undescribed new species and possibly new genera.

The most common taxa are: the ringiculid Biplica; naticids Gyrodes and Euspira; the trocid Atira; aporrhaids Anchura and Lispodesthes; the turritellid Turritella; and the perissityid Perissitys. These genera are represented by different species at stratigraphically lower (more eastern) and higher (western) localities. A number of epitoniid-like specimens have yet to be identified, but they are fairly common.

Less common are at least two forms of volutes, some buccinids and possible rissoids. New taxa may include fusiform specimens that resemble the fasciolariid Graphidula and a large (> 18 cm long) specimen that may be a very large epitoniid.