The presence of Tawera gayi (Hupé in Gay, 1854) (Veneridae, Bivalvia) in southern South America: Did Tawera achieve a Late Cenozoic circumpolar traverse?

Abstract

Cenozoic Tawera Marwick, 1927 from the Southern Hemisphere exhibits a pattern of disjunt distribution around the southern oceans. A single species, Tawera gayi (Hupé in [Gay, C. (1854). Historia Física y Política de Chile, Zoología 8. Paris.]) is confined to southern South America. Taking into account the occurrence of Tawera in the fossil record, taxonomy based on shell morphology, and available information on extant species of Tawera, it is plausible that the genus appeared first in southern Australia during the Early Miocene, and then expanded and radiated to New Zealand. It also appears that Tawera first crossed from Australasia to South America during the Early Pleistocene. This picture can be better explained if Tawera was able to achieve circumglobal range by means of the Antarctic Circumpolar Current. Thus, different potential factors of dispersal (i.e., larval dispersal, drifting, kelp rafting and Pleistocene cooling) are considered and discussed. Shell morphology and overall appearance of Tawera gayi is very similar to Tawera philomela (Smith, 1885) from South Africa and Tawera mawsoni (Hedley, 1916) from Macquarie Island, suggesting these taxa have a close relationship. One postulated explanation, which should be confirmed by means of a phylogenetic study, is a subsequent migration of Tawera from South America arriving first to the Southern African Region (via the West Wind Drift Islands Province), and then probably coming back again to Australasia. It could have been mediated via the same current during the Late Pleistocene and much later during the Holocene.