Radiation of basal Asteraceae and allied families during the Oligocene and Miocene in the Gondwanan continents

BARREDA, V.; PALAZZESI, L.; TELLERÍA, M.C.; KATINAS, L.; CRISCI, J.V.

Mar del Plata

Simposio; XIV Simposio Argentino de Paleobotánica y Palinología; 2009

The evolutionary radiation of the Asteraceae and their closest relatives is one of the most important and yet unresolved questions in today's botanical research because unequivocal fossil evidence is scarce for the development of reliable hypotheses. This issue is now becoming progressively more realistic thanks to the increasing fossil findings from southern Africa, Australia, New Zealand, and southern South America (Patagonia). Unequivocally assigned morphotaxa from accurately dated sediments have permitted for the first time a comprehensive review of the past distribution of the most important core of the sunflower alliance of families (Menyanthaceae, Goodeniaceae, Calyceraceae and Asteraceae). Several taxa, which today are restricted to isolated geographic regions, were widespread in the Southern Hemisphere during Paleogene times. Menyanthaceae, Goodeniaceae and Mutisioideae (Asteraceae), for example, had a wider distribution in Gondwanan landmasses by the Oligocene and are now drastically reduced in their geographic range. This broad distribution pattern during the Oligocene supports previous assumptions of an Eocene origin of the clade. Early Neogene records, in contrast, suggest diversification and extinction events that progressively led to the present day configuration. In broad terms, the distribution of Miocene fossils assigned to this clade agrees with that of today (Barnadesioideae, Nassauvieae, Calyceraceae). Southern Hemisphere continents, and particularly Patagonia, are unique by having the highest diversity of sunflower-related fossils of any region. The major floristic turnovers coincided with the final isolation of Antarctica, leading to cooler, drier, and more seasonal climates that forced the evolution and distribution in space of all these Gondwanan elements.