Journal of Paleontology, 92(5), 2018, p. 794–803 Copyright © 2018, The Paleontological Society 0022-3360/18/0088-0906 doi: 10.1017/jpa.2018.13
First report of Oniscidia Mörch, 1852 (Neogastropoda, Harpidae) in the northeast Pacific fossil record and paleobiogeographic review of the genus
Richard L. Squires
Department of Geological Sciences, California State University Northridge, California, 91330-8266, USA; and Research Associate, Invertebrate Paleontology, Natural History Museumof Los Angeles County, 900 Exposition Boulevard, Los Angeles, California, 90007, USA ⟨richard.squires@
csun.edu⟩
Abstract.—The harpid neogastropod genus Oniscidia Mörch, 1852, which has not been recognized before in the northeast Pacific fossil record, is represented there by rare specimens of Oniscidia plectata (Waring, 1917) n. comb., of late early Paleocene age, in a region extending from southern California, USA to Baja California, Mexico. This species is the earliest unequivocal record of Oniscidia and its only known Paleocene record. It apparently lived in silty, inner- to middle-shelf depths, which were inherently cooler than adjacent shallower marine depths. Its habitat was subject to the influx of shallow-marine shells, especially turritellas, contained in turbidity currents emanating from nearshore depths. The global paleogeography of Oniscidia, which is presented here for the first time, has been overlooked previously
because this genus has a long and complicated history of taxonomic confusion with the harpid genus Morum Röding, 1798. Oniscidia questionably originated during the Late Cretaceous (Campanian) in southern India and apparently dispersed westward through the Tethys Seaway into the New World. Paleocene and early Eocene occurrences of this genus are rare, and middle Eocene occurrences are uncommon. During the cool times of the Oligocene and into the early Miocene, it was most widespread. Its range became restricted during the middle Miocene and continued to be so during the Pliocene, Pleistocene, and modern day, with occurrences only in the Caribbean Sea region, Florida, and the western Pacific. Its distribution through warm and cool times was most likely controlled by its habitat preference for relatively deep cool waters.
Introduction
Waring (1917), in his study of ‘Martinez lower Eocene’ mollusks from the Simi Hills in Ventura County, southern California, named Ficus plectatus, based on only the imperfect holotype. He assigned this gastropod an early Eocene age, but this pre-dated modern biostratigraphic information. Since 1917, no worker had reported finding this rare species anywhere else in the northeast Pacific. In recent years, however, a few addi- tional specimens of Waring’s species were collected from upper lower Paleocene (upper Danian Stage) strata in southern California and Baja California, Mexico. These new specimens have good to excellent preservation and can be identified with certainty as the harpid neogastropod Oniscidia Mörch, 1852, an extant genus. Placement of Waring’s species in Oniscidia is significant because it is the earliest unequivocal harpid. In addition to taxonomically updating Waring’s species,
this paper better describes and illustrates it, and provides upda- ted information concerning its geologic age, depositional environment, and habitat preference. This paper also presents the first inventory of the known fossil representatives of Oniscidia and includes their geologic ranges and geographic occurrences. This inventory provided the basis for determining the paleobiogeography of Oniscidia and correlating its dis- tribution with global paleoclimate events.
Stratigraphic information
Oniscidia plectata (Waring, 1917) is known from three areas: Simi Valley, Simi Hills, and Mesa San Carlos (Fig. 1.1–1.4). Geospatial coordinates of these localities are given in the Appendix.
Simi Valley.—Oniscidia plectata is from LACMIP loc. 41691 in the lower part of the Santa Susana Formation, Simi Valley, Ventura County, southern California (Fig. 1.1, 1.2). This specimen is from a thin, poorly exposed Turritella-rich storm bed consisting of mollusks, arthropods, and bivalve-bored petrified wood that all underwent relatively short-distance, post-mortem transport, probably by turbidity currents emanat- ing from inner-shelf depths. The immediately underlying and overlying strata consist of gray siltstone. This locality contains abundant specimens of Turritella peninsularis qualeyi Saul, 1983 and Turritella peninsularis Anderson and Hanna, 1935. Turritella reversa Waring, 1917 is also present, along with a moderately diverse molluscan fauna. Based on known concurrent molluscan-stage ranges, this fauna is of late early Paleocene (late Danian) age (Squires et al., 2017).
Simi Hills.—The holotype of Oniscidia plectata (Waring) is from CAS loc. 61667 in the Simi Hills, Ventura County,
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