Lower and Middle Devonian ostracods from South America: their palaeobiogeographical affinities

SALAS, MARIA JOSE

Mendoza

Congreso; 4th INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014

IPA- International Paleontological Association

The knowledge of Paleozoic ostracods from South America is scarce and patchy, and the most recent studies have been almost entirely focused on the Ordovician of Argentina. In turn, Devonian ostracod records are include in a series of isolated papers ranging from Lower to Middle Devonian mainly from Bolivia and Argentina, with only one mention in Brazil. A new ostracod association from the Lochkovian horizons of Argentine Precordillera, as well as, a review of the Devonian faunas of South America, are herein provided. In addition, palaeobiogeographical affinities of all known Devonian ostracods from South America will be evaluated in order to provide new insights into the recognition of the Malvinokaffric Realm. The new association was recorded from the Talacasto Formation (Lochkovian?Pragian). It is composed of endemic taxa like Keslingiella? teresae, Pircawayra n. sp., Lapazites n. sp., Petrisigmoopsis n. sp. and Gen. nov., with other of a wider distribution like Bollia n. sp., Ulrichia sp., Aechmina sp., and Thlipsurella sp. In the South American context the new association is the oldest Devonian fauna except for the Siluro-Devonian species described by Vannier and collaborators. Other known fauna comes from the upper Lower Devonian (Emsian) of Argentina (upper levels of Talacasto Formation, lower levels of Punta Negra Formation), Bolivia (Belen Formation) and only one species from Brazil (Ponta Grossa Formation), and from the Middle Devonian (Eifelian-Givetian) of Argentina (Punta Negra Formation) and Bolivia (Iquiri Formation). Although the Devonian of ostracod studies are still limited in number, some common features of the fauna can be recognized. The Devonian ostracods from South America show low diversity knowing until now 14 genera (dubious genera are not considered) and 35 species belonging to Palaeocopina, Platycopina, Metacopina and Podocopina suborders. This composition is kept throughout the Devonian, however the diversity decreases towards younger levels, reaching only 5 genera in the Eifelian-Givetian. Respect to the paleogeographical affinities, the Lower Devonian ostracod fauna is composed by a 50 % of endemic forms, and by laurentian and cosmopolitan genera. Middle Devonian, in contrast, is fully composed by endemic forms, that closely resemble coeval ostracods from South Africa. The two regions exhibit a remarkable endemism, not only at genus level, but also at species level. According to these preliminary evidences, the paleobiogeographic pattern shows the Lower Devonian as a mixed of affinities, while the Middle Devonian exhibits a typical Malvinokaffric association. Based on the ostracod faunas, the Malvinokaffric Realm is clearly recognizable only during the Middle Devonian.