UNRAVELING THE IMPACT OF A PLIO-PLESITOCENE EXTINCTION ON THE SPECIES LEVEL; A PHYLOGENETIC ANALYSIS OF THE MURICID GASTROPOD GENUS UROSALPINX

The molluscan fauna of Florida underwent several pulses of extinction near the end of the Pliocene. Despite estimates that species extinctions were severe (roughly 70% for mollusks), diversity for the fauna remained high due to invasion, diversification of survivors, or widespread pseudoextinctions. In order to further our understanding of the affects and nature of the extinction event, this study tests the three models through a species-level phylogenetic analysis of extinct and extant taxa. Our analysis focuses on the muricid gastropod genus Urosalpinx of Florida. This genus underwent 100% turnover making it an ideal test of the pseudo-extinction hypothesis.

The data matrix, constructed with MacClade (4.08) and analyzed in PAUP (4.0), included 29 ingroup taxa and 10 outgroup taxa coded with 45, mostly binary, characters describing shell features of the adult teleoconch and larval protoconch. We included all described species of Urosalpinx and representatives of similar ocenebrine genera in the analysis to maximize coverage of possible ancestor-descendent pairs and instances of invasion and rapid diversification of survivors. An Eocene ocenebrine muricid, Ocenebra dubuissoni, was selected as an outgroup. Pseudoextinctions were identified on the phylogeny as instances where two taxa share a common node in the cladogram but one is restricted to a lower stratigraphic interval and the other one to a higher interval.

A heuristic tree search resulted in two most parsimonious trees, the consensus of which had almost perfect bifurcating resolution. Of the six mid-Pliocene Pinecrest Beds and Jackson Bluff Formation taxa that became extinct, half were pseudoextinctions with lineages continuing on into the latest Pliocene Caloosahatchee Formation. Of the five species appearing in the Caloosahatchee Formation, two apparently descended from ghost lineages not represented by any known mid-Pliocene taxa, and three descended from pseudoextinct taxa. Three of the five Caloosahatchee species (60%) became truly extinct at the Plio-Pleistocene boundary, with only two (40%) lineages surviving into the Pleistocene as different species. These data suggest that, at least for Urosalpinx , there were at least two separate extinction events in the late Neogene, and that the proportion of pseudo-extinctions for both was relatively high.