First occurrence of the Paleocene gastropod Ravniella Rosenkrantz, 1970 (Heterobranchia: Acteonidae) in North America

摘要

A new species of the acteonid heterobranch gastropod, Ravniella lipmanorum Squires, is described h-om upper lower Paleocene (upper Danian) strata in southern California. This is first record of genus Ravniella Rosenkrantz, 1970 in North America. This small-sized genus, which has a broad callus pad bearing two columellar plaits and one parietal plait, is known elsewhere only in Paleocene strata in Denmark, Poland, Austria, and western Greenland. The new species is found mainly at a single locality in the lower part of the Santa Susana Formation, north side of Simi Talley, Ventura County. At this locality, specimens are associated with abundant shallow-marine mollusks, which underwent relatively short-distance, post-mortem transport, probably by turbidity currents emanating from shallower marine depths. The new species is found rarely in the lower part of the San Francisquito Formation, Warm Springs Mountain area, Los Angeles County. Ravniella occurs questionably in Upper Cretaceous strata of northern Spain (Campanian). The senior author, Squires, is the sole author of the new species.