TAXONOMIC REVIEW AND EVOLUTIONARY TRENDS OF LEVIPUSTULINI AND ABSENTICOSTINI (BRACHIOPODA) FROM ARGENTINA: PALAEOBIOGEOGRAPHIC AND PALAEOCLIMATIC IMPLICATIONS

TABOADA, ARTURO CÉSAR; SHI GUANG R.

Melbourne

Congreso; 6th International Brachiopod Congress; 2010

Deakin University

The tribe Levipustulini has been recorded abundantly in Argentina and a great number of genera are represented, including Bulahdelia, Levipustula, Lanipustula, Verchojania, Jakutoproductus and Piatnitzkya. A review of some key genera and species has allowed the recognition of Levipustula levis Maxwell and a new species of the Absenticostini Absenticosta Lazarev in western Argentina, as well as confirming the presence of Lanipustula patagoniensis Simanauskas and a new species of Lanipustula in Patagonia. Levipustulini commonly exhibits antitropical distribution but some of the genera from this tribe are shared only between Siberia and Patagonia. Lanipustula, Verchojania and Jakutoproductus, with Absenticosta interpreted as their common ancestor, together constitute a phylogenetic lineage, which we consider as having undertaken parallel evolution in the high latitudes of both hemispheres during the Late Palaeozoic. If this scenario is accepted, the parallel evolution must have commenced during the late Viséan at a time when the Earth was experiencing a global cooling phase allowing the trans-oceanic and global dispersal of some cool-water tolerant brachiopod genera (e.g. Absenticosta) from lower to higher latitudes. At this time, Patagonia would have been separated from western Argentina and was progressively drifting toward southern higher latitudes. Thus, the isolation of Patagonia, coupled with its southward drift toward a colder climate, could have triggered the parallel evolution of the Levipustulini lineage between Patagonia in southwestern Gondwana and Angaraland in Northeast Asia. Since Bashkirian times, warm ocean currents invaded western Argentina, and these currents were warm enough to build a thermal barrier between Patagonia and western Argentina, effectively restricting biotic interchanges between them and also between Gondwana and Eurasia. Under such a palaeogeograhically and palaeobiogeographically isolated setting, Patagonia progressively became a sanctuary for the development of a highly endemic but locally abundant marine fauna, which persisted until the earliest Cisuralian. The weak glacial record since Bashkirian times in western Argentina contrasts sharply with widespread evidence in Australia indicative of several main episodes of glaciation extending from late Mississippian till late Permian. The asymmetrical climatic pattern between Argentina and Australia reflects the clockwise rotation of Gondwana resulting in the consequent migration of western Argentina to lower latitudes and the drift of eastern Australia toward the South Pole. Patagonia, located in an intermediate palaeogeographic position between these two regions, was also rotated and displaced across latitudes, but must have been shifted to lower latitudes later and more slowly than western Argentina. A thalassocratic regime during the late Asselian-Sakmarian and a global climatic amelioration since late Sakmarian could explain the fast recovery of migration pathways for the biotic interchange between Patagonia and other Gondwanic regions, including Western Australia and the Cimmerian regions now stretching from the Middle East to Southeast Asia.