Plant remains from the Devonian of San Juan, Argentina.

COTUREL, ELIANA P.; ARNOL, JONATAN

Paris

Congreso; 5th International Paleontological Congress; 2018

Throughout the Devonian occurred the most important stages of plant propagation onland and their subsequent evolution, yet the extent of this process is far from being completelyunderstood, mainly by the scarcity of the register. The fossiliferous localities of the Devonianof Precordillera, in Argentina, have provided sterile or poorly preserved remains of fossilplants and, very rarely, palynomorphs. Associations of low diversity have been described,composed of primitive vascular plants and herbaceous lycophytes. Here we present newsamples from the Punta Negra Formation, collected from the Precordillera of San Juanprovince. Punta Negra Formation lays over the marine sediments of the Lower DevonianTalacasto Formation with a transitional limit and reaches 1000 m thick. The lower limit ofthe Punta Negra Formation is diachronic, being older in the southern localities. Plants comefrom four localities. Sandstones from the Ro San Juan locality yielded a compression ofstem with petiolate, divided microphylls, assignable to Haskinsia Grierson and Banks 1983.It is noteworthy that this is the rst record of a lycopsid with preserved leaves from this unit.Southern, nearby Puesto Bachongo fossil remains were found comparable with the bryophyteSporogonites Halle 1916. These samples consist in an ovoid-globose capsule which showslongitudinal costae in the middle sector, which resembles Sporogonites excellens Frenguelli1951. Sterile lycophyte stems were found in both localities. Plant debris, consisting insmooth and ridged sterile axes, putative sporangia and isotomous bifurcated stems, was alsofound. The association is in general consistent with the previously described for the unit, andthe discovery of better preserved taxa allow us a more detailed comparison to elucidate theage of the deposits. Sporogonites was found in the Lower Devonian of Argentina, Australia,Belgium, and Brazil, and younger strata from Spain. The lycophyte Haskinsia, on theother hand, was widespread in the Middle Devonian, with a species also found in Sierrade la Ventana (Buenos Aires Province, Argentina). The presence of both taxa is coherentwith the age given to Punta Negra Formation and the diachronic nature of its base, couldhelp in the stratigraphic correlation between localities. Lastly, the nding of these newmaterial encourages us to continue the research in this large unit, which could lead to abetter understanding of the expansion of the early land plants.