Diversity of Atlantic Coastal Plain Mollusks Since the Pliocene

Abstract

About 70 percent of tropical western Atlantic mollusk species have become extinct since the Pliocene, which has led to perceptions of a corresponding decline in diversity. However, a compilation of gastropod species from Plio-Pleistocene faunas of the United States Atlantic coastal plain and from Recent western Atlantic faunas indicates that regional diversity has not changed since the Pliocene. Gastropod diversity in the Pliocene Pinecrest Beds in Florida approximates that seen today on either coast of Florida. Gastropod diversity is not demonstrably different in the Recent tropical western Atlantic than in the Recent tropical eastern Pacific. High extinction rates must have been balanced by high origination rates.

The Great American Schism: Divergence of Marine Organisms After the Rise of the Central American Isthmus

“…Gastropods and bivalves suffered a pulse of extinction in the Pleistocene (about 2 Mya) that was apparently more severe in the WA than in the EP (Stanley 1986, Todd et al 2002, Vermeij 1978. However, extinction was balanced by species origination (Allmon et al 1993;Jackson et al 1993Jackson et al , 1996b. Scleractinian corals have also been undergoing major faunal turnovers on both sides of the Isthmus since the Pliocene (Budd 2000.…”

“…It has been pointed out that the severe extinctions of molluscs in the Pleistocene may account for the rarity of recent geminate pairs in this phylum (Marko 2002, Williams & Reid 2004). However, given that mollusc extinctions were balanced with species originations in the Pleistocene (Allmon et al 1993, Jackson et al 1993 were split at some point during the long period of geological upheavals associated with the rising Isthmus. Thus, dates that have been obtained from molecular transisthmian comparisons should be viewed as hypotheses to be further tested with more data and with statistical techniques that allow the calculation of the degree of variation expected in substitution rates.…”

Evidence for Nearby Supernova Explosions

“…Two hypotheses have been advanced to explain this phenomenon: the emergence of the Panama isthmus [40,41] and cooling due to the onset of Northern Hemisphere glaciations [42,43,44]. However, this extinction episode was too rapid to be due to the Panama isthmus closure [43,44] and a detailed analysis of the extinction patterns seems to rule out cooling as the cause [35,40]. A simultaneous, although slower, episode of extinction affected corals [44], which are known to be highly susceptible to UV-B radiation [33].…”

Marine latitudinal diversity gradients: Tests of causal hypotheses

“…In the tropical western Atlantic, however, the cooling of the marine climate with the onset of glacial cycles appears to have brought intense biotic turnover, perhaps because species were trapped within the Caribbean region (27). Early Pleistocene extinction rates in the western Atlantic were about twice those in the eastern Pacific (27)(28)(29); however, originations must also have accelerated, as western Atlantic diversity now appears to be similar to the preglaciation levels (28), and even exceeds eastern Pacific values. Thus the marine data show (i) that the latitudinal diversity gradient is not a simple consequence of recent geologic history, because the two oceans had different histories yet exhibit similar diversity trends today; and (ii) that the western Atlantic diversity gradient was resilient to an intense turnover episode, thereby suggesting an evolutionary dynamic underlying the latitudinal patterns, such that speciation compensated for heightened extinction rates.…”