The earliest seed plants from Gondwana: paleobiogeographical and evolutionary implications based on Tournaisian (Mississippian) records from Argentina

PRESTIANNI, C; RUSTÁN, J.J.; BALSEIRO D.; VACCARI, N.E; STERREN, A. F.; STEEMANS, P; RUBINSTEIN, CLAUDIA V.; ASTINI, R. A.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

CCT CONICET Mendoza - International Palaeontological Association

One of the oldest known seed occurrences on Gondwana have been recognized in a new stratigraphic section located in Sierra de Las Minitas, La Rioja Province, western Argentina (Precordillera Basin). New palynological evidences indicate an early Mississippian (probably early Tournaisian) age for this new succession, instead of Late Devonian as previously reported. The two identified early seeds, Pseudosporogonites cf. hallei and Warsteinia were up to now considered to be restricted to the Devonian of Laurussia. This finding suggests a dispersal of earliest spermatophytes from Laurussia to Gondwana during Devonian/Tournaisian times, accounting for the Rheic Ocean (the sea-extension separating these two main landmasses) as a surmountable biogeographic barrier for continental biotas. This new information supports a weak impact of the Devonian/Carboniferous biotic crisis on earliest seed plant diversity. Alternative, contrasting biogeographic hypotheses dealing with the diachronic occurrence of early seed plants and the occurrence of Devonian-like herbaceous communities in cool high latitudinal regions, are being explored for explaining the recognized paleobiogeographical pattern. Based on preliminary evidences of niches differentiation and ecological dynamics probably affected by wildfires, Tournaisian Gondwanan plant communities from high latitudes are interpreted as being more complex than previously thought, and thus ecologically more similar to those reported from Laurussia. In addition, their discovery in a sedimentary environment associated with glacigenic deposits, shows that this new record might be linked to the coeval glacial age widely recorded elsewhere in Gondwana