Tertiary roots in the Recent Molluscan faunas of the Southwestern Atlantic Ocean

DEL RIO, CLAUDIA JULIA; MARTINEZ SERGIO,; ORENSANZ, JOSE

lONDRES

Congreso; 3° International Paleontological Congress; 2010

International Palaeontological Association

The species composition of the Recent Southwestern Atlantic (SWA) molluscan biota (Argentine and Magallanic Provinces) has its roots mostly in post-Late Mlocene times. Among the more than 1300 species that form the modern regional assemblage, only 37 are survivor specles and 25 are long-term survivors going back to Miocene times: Leionucula puelcha, Nucula semiornata, Adrana electa, Crassostrea rízhophorae, Felaniella villardeboaena, Tivela isabelleana, Amiantis purpurata, Mactra isabelleana, M.janeiroensis, Tellina gibber, Cyrtopleura lanceolata, Caryocorbula pulchella, C.caribaea, Tegula patagónica and Halystilus columna. An additional 13 species have closely related congeneric counterparts of that age: Lamellinucula semiornata, Glycymeris longior, Psychrochlamys patagónica, Aequipecten tehuelchus, Trachycardium muricatum, Anomalocardia brasiliana, Pitar rostrata, Ameghinomya antiqua, Retrotapes exalbida, Tagelus plebeius, Trophon geversianus, Adelomelon beckii and Pachycymbiola brasiliana. However, when upper levéis of the taxonomic hierarchy are considered, Tertiary Patagonian faunas appear to have played an important role in the genesis, composition and biogeography of the living regional faunas. Almost 80% of the Tertiary families and 42% of the genera survived in the SWA. Yet, in spite of the high percentage of surviving families, generic diversity declined considerably in many of them, as is exemplified specially by the Struthiolariidae, Muricidae, Buccinidae, Veneridae, Ostreidae and Pectinidae. Among all surviving Tertiary genera, 10% were already present in the área in Paleocene times, 31% in the Eocene, 29% in the Oligocene- Middle Miocene, and 30% in the Late Miocene. Endemic taxa such as Trophon, Miomelon, Adelomelon, Odontocymbiola and Zygochlamys, have been present in the área since Eocene times, and Pachycymbiola, Retrotapes and Ameghinomya since the early Miocene.