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

The species composition of the Recent Southwestern Atlantic (SWA) moiluscan biota (Argentine andMagallanic Provinces) has its roots mostly in post-Late Mlocene times. Among the more than 1300 speciesthat form the modern regional assemblage, only 37 are survivor specles and 25 are long-term survivorsgoing back to Miocene times: Leionucula puelcha, Nucula semiornata, Adrana electa, Crassosírearízhophorae, Felaniella villardeboaena, Tivela isabelleana, Amiantis purpurata, Mactra isabelleana,M.janeiroensis, Tellina gibber, Cyrtopleura lanceolata, Caryocorbula pulchella, C.cañbaea, Tegulapatagónica and Halystilus columna. An additional 13 species have closely related congeneric counterparts ofthat age: Lamellinucula semiornata, Glycymeris longior, Psychrochlamys patagónica, Aequipectentehuelchus, Trachycardium muricatum, Anomalocardia brasiliana, Pitar rostrata, Ameghinomya antiqua,Retrotapes exalbida, Tagelus plebeius, Trophon geversianus, Adelomelon beckii and Pachycymbiolabrasiliana. However, when upper levéis of the taxonomic hierarchy are considered, Tertiary Patagonianfaunas appear to have played an important role in the génesis, composition and biogeography of the livingregional faunas. Almost 80% of the Tertiary families and 42% of the genera survived in the SWA. Yet, in spiteof the high percentage of surviving families, generic diversity declined considerably in many of them, as isexemplified 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 theEocene, 29% in the Oligocene- Middle Miocene, and 30% in the Late Miocene. Endemic taxa such asTrophon, Miomelon, Adelomelon, Odontocymbiola and Zygochlamys, have been present in the área sinceEocene times, and Pachycymbiola, Retrotapes and Ameghinomya since the early Miocene.