MACNBR   00242
MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The fossil cycads of Argentina: new taxa, evidences and relationships about their evolutionary history
Autor/es:
MARTÍNEZ, L.C.A.; ARTABE, A.E.
Lugar:
Mendoza
Reunión:
Congreso; 4° International Palaeontological Congress; 2014
Institución organizadora:
IPA
Resumen:
Cycads are an ancient and enigmatic group of seed plants, with a fossil record dating back to the Early Permian of China and reaching a great diversity in the Mesozoic. In spite of having a diverse and continuous fossil record, cycads do not grow as a native plant in Argentina. Stems, leaves, reproductive structures, pollen and seeds are known from the Triassic, with a peak in the Late Cretaceous, to decline and became extinct in the Paleogene. The goal of this research is to show the diversity attained by Cycadales in Argentina, to understand the diversification of some clades (e.g., Encephalarteae) across the Cretaceous of Patagonia, and to infer the causes of their extinction in southern South America. The phylogenetic relationships among extant and fossil Cycadales were tested by cladistic analysis. Taxa with close affinities with the Cydadales, e.g., Nilssonilaes (Baikalophyllun, Nissoniocladus), Lyginopteridales, Medullosales, and Bennettitales, were taken into account in our cladogram. Our analysis shows that the most of Cretaceous Patagonian Cycadales belongs to Encephalarteae and their diversity could be correlated with a humid to xeric subtropical climate, analogous to those developed in Africa today. The extinction of cycads in Patagonia could be influenced by abiotic and biotic factors. The Andean uplift (forming a topographic barrier), and the temperature diminution (drop of atmospheric CO2, inception of the Antarctic Circumpolar Current) caused a drastic climatic change (from humid and template to cold and dry). The extinction of animals (e.g., dinosaurs) produced alterations in seed dispersal strategies, limiting the migration of cycad to new areas. Furthermore, floristic changes involving the diversification of the Magnoliophyta, and the appearance of groups that compete by the same habitat (and even with a similar life-form as the palms), also constrained the cycad populations.