Squires—Northeast Pacific Oniscidia
gastropods that originated in the OldWorld Tethys Sea region. These particular gastropods diversified during warm times, especially during the Paleocene (PETM), early Eocene (EECO), and middle Eocene (Squires, 1987), as well as the early Miocene and early middle Miocene (MMCO) (Fig. 4). As discussed earlier, it is likely that Oniscidia was not a shallow-marine nearshore dweller. It preferred to live in subtidal offshore depths, which would have inherently been slightly cooler. Although Oniscidia seems to have virtually ‘disappeared’ from the fossil record, or was diminished greatly during warm times, it was present, most likely, in adjacent, deeper waters. During cool-ocean times, therefore, Oniscidia diversified somewhat. As depicted in Figure 4, Oniscidia was moderately
widespread in the early Miocene, with occurrences in northern Europe, southwest India, New Zealand, the Caribbean Sea region, and Florida. The closure of the western Tethys seaway (TTE) in the middle Miocene severely curtailed the distribution of Oniscidia. Starting in the late Miocene and continuing into the Pliocene, Oniscidia became restricted to the Caribbean Sea region and Florida. In the Pleistocene, Oniscidia dispersed into the western Pacific and, to a lesser degree, into the central Pacific. Formation of the Panama Land Bridge at the end of the Pliocene (Leigh et al., 2013) would have impeded dispersal of Oniscidia from the Caribbean region into the west coast of North America. Intermittent marine connections between the Pacific and Atlantic sides of the land bridge probably continued between these two areas, however, during high sea levels in middle interglacial times (Beu, 2001). Oniscidia has about 30 living species, found mostly in the western Pacific (especially in Taiwan and the Philippine Islands) and, to a lesser degree, in the Caribbean Sea, western Atlantic, and South Africa and Madagascar regions (Dance and Poppe, 1999). The long distances involved for the dispersals of Oniscidia
801
South American Neogene mollusks. J. DeMouthe (CAS) and A. Hendy (LACMIP) facilitated loans. T.J. DeVries and L.T. Groves critically reviewed the manuscript and gave valuable comments.
References
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Acknowledgments
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