West Antartica (WANT) Paleogene terrestrial biota: testing the biogeographical patterns of the final breakup of Gondwana

REGUERO, M.; ABELLO, M. A.; DUTRA, T; IGLESIAS, A; CANDELA, A. M.; MARENSSI, S

Punta Arenas

Simposio; III Simposio - Paleontología en Chile; 2012

The thickest Late Cretaceous to lowermost Paleogene (Campanian to Ypresian) sedimentary succession in the world is exposed on southern Seymour Island (65° South) in the James Ross Basin, Antarctic Peninsula Paleogene terrestrial vertebrate fauna from Seymour Island exhibits high levels of species endemism, i.e., marsupials and meridiungulates, yet, for certain groups, is relatively species-poor (MacPhee et al. 2008). This fauna is also taxonomically imbalanced in that it is not typically “South American” (Reguero and Marenssi 2010), as might be expected if most of its ancestors dispersed over a land bridge across the Antarctic Peninsula isthmus (Fig. 2) or used several intervening islands in a stepping-stone chain facilitated by past lower sea levels (Reguero et al. 2002). Although a few groups appear to be stranded relicts, resulting from West Antarctica’s shared plate tectonic history with other Gondwanan continents (Goin et al. 2006), for most clades current evidence indicates that the basal stocks arrived after the island, and the Antarctic Peninsula, were geographically isolated, thus refuting a vicariance model for these organisms. The close similarities and, in most cases, inferred sister-group relationships of a number of terrestrial vertebrate taxa recovered from Early Eocene deposits of Antarctic Peninsula and South America (marsupials and meridiungulates) suggest that the Weddellian land bridge between southern South America and West Antarctica may have been functional until the Thanetian (Late Paleocene) (Reguero et al. in press). The Paleogene floras from West Antarctica document the same pattern In order to resolve disputed biogeographical histories of terrestrial biota with Gondwanan continental distributions, and to assess the null hypothesis of vicariance, it is imperative that a robust geological time-frame be established. The discovery of Early Eocene terrestrial vertebrate taxa (gondwanatheres) on West Antarctica that have sister-taxon relationships to Campanian-Maastrichtian taxa of the Indian subcontinent, Madagascar, Africa, and South America has resulted in considerable controversy and the characterization and labeling of competing palaeobiogeographic hypotheses that have profound implications for the timing and sequence of Gondwanan fragmentation.