Fossil pollen grains of Asteraceae from the Miocene of Patagonia: Barnadesioideae affinity

PALAZZESI, L.; BARREDA, V.; TELLERÍA, M.C.

REVIEW OF PALAEOBOTANY AND PALYNOLOGY

Elsevier

Año: 2009 vol. 155 p. 83 - 88

0034-6667

 New fossil pollen grains were recovered from marine Miocene deposits from eastern Patagonia (southern South America). Sculpture and structure exine features indicate a close relationship with modern Barnadesioideae, a basal lineage within Asteraceae. Barnadesioideae is confined to South America and is represented mainly by shrubs, herbs and some trees occurring in different habitats under a wide range of climatic conditions. It has recently attracted a great deal of attention as it was considered the sister-group to the remaining members of the family based on molecular data. Barnadesioideae has not previously been described in the fossil record. One new genus and three species are erected in Quillembaypollis gamerroi, Q. tayuoides and Q. stuessyi to assemble distinct pollen types clearly similar to those produced today by extant Chuquiraga, Dasyphyllum and Schlechtendalia, respectively. These are the first fossil records of these genera, taking them back 23-20 Ma (Dasyphyllum and Chuquiraga types) and 11-9 Ma (Schlechtendalia type). The new morphotaxon is clearly distinguishable by being microechinate, and by having a thick sexine formed by one (Q. tayuoides), two (Q. gamerroi) or three (Q. stuessyi) layers, as the most prominent features. Their closest living relatives today grow far from the studied site (eastern Patagonia), with the exception of Chuquiraga which is the sole surviving genus in the region. Pollen and spore assemblages of Early Miocene age (23-20 Ma) from southern South America indicate that the climate was sub-humid and temperate to warm temperate. This climatic trend may have allowed Dasyphyllum species to radiate in eastern Patagonian forests, while Chuquiraga probably occupied more open areas along the coast. Late Miocene (11-9 Ma) palynological assemblages suggest warm conditions but seasonally dry, in which Schlechtendalia developed probably in the hinterland vegetation joined with low trees, and halophytic/xerophytic shrubs and herbs.