Quantitative palaeobiogeographical analysis of South American Neogene Chioninae (Bivalvia: Veneridae)

Abstract

Chionine bivalves are one of the most important components of Neogene and Recent molluscan faunas in southern South America, but it was not until recently that their phylogenetic relationships has been explored quantitatively. Based on this robust framework, we analyzed the palaeobiogeographical history of the group. The geographic areas used in this analysis were discretized using a multivariate K-means cluster analysis based on the palaeocoordinates of chionine-bearing localities. Statistical comparison of quantitative, event-based biogeography models using likelihood suggests that our data best fits models that include long-distance jump dispersal (+J), with a slight preference for a model that also gives increased weight to vicariance. The ‘Chione’ clade (including the genera Chione, Anomalocardia, and Chionopsis) is mainly a Caribbean and central Eastern Pacific lineage with expansions to California and the southern Western Atlantic coast. The ‘Protothaca’ clade (including Protothaca, Nioche, Austrovenus, and Chionista) is mainly an Eastern Pacific lineage–with a proposed southern South American origin–with occasional dispersals to the western Pacific (Oceania and East Asia). A new alternative dispersal route is proposed across the North Pacific from California and the north Eastern Pacific to East Asia and Oceania, as shown by Austrovenus stutchburyi, Tuangia crassicosta, and Protocallithaca adamsii. The ‘Ameghinomya’ clade (including all Ameghinomya species) is a southern South American lineage–south Eastern Pacific origin–that subsequently dispersed into the southern Western Atlantic. The ‘Protothaca’ and ‘Ameghinomya’ clades show opposite histories, the former being mainly Pacific and the latter mainly Atlantic. The distribution of both clades on both sides of South America may have been allowed by the opening of the Drake Passage Gateway around the Oligocene-Miocene boundary.