First fossil record of Vivianiaceae (Geraniales), Miocene of North-eastern Patagonia (Puerto Madryn Formation): pollen evidence

PALAZZESI, L.; WEIGEND, M.

Panamá

Congreso; 40th American Associatioin of Stratigraphic Plalynologists; 2007

Smithsonian Tropical Research Institute

Some million years ago Vivianiaceae (or Ledocarpaceae) had a different geographical range (Miocene) from today. Most members of this shrubby family are today restricted to seasonally dry habitats in the Andes of South America, with a single species in southern Brazil. Fossil metareticulate pollen grains collected from the Puerto Madryn Formation (northeastern Patagonia) indicate the presence of some Viviania species along the Atlantic coastline in north-eastern Patagonia during the Late Miocene. Morphological patterns of the fossil specimens suggest a close relationship with extant V. marifolia, V. ovata, and V. rosea. They all are spheroidal, pantoporate pollen grains which show a highly distinct metareticulum with a single row of columellae as the crucial character visible on pollen of both the extant species and the fossil specimens. Other Viviania speices have differentiating characters such as supratectal spines (e.g. V. albiflora) or more than one row of columellae (e.g. V. elegans), so that a close and possibly exclusive affinity of the fossil pollen to the three species named above appears plausible. Both V. ovata and V. rosea are nowadays restricted to the western Andean slopes of Chile, V. marifolia is relatively widespread in Chile but is also found on the eastern slope of the Andes in the Provinces San Juan and Neuquén in Argentina. The subsequent extinction of the family in the non-Andean regions of Patagonia is likely related to the development of an unfavourable cold and arid climate in this region in the Late Neogene. The fossils here documented indicate that the present-day populations of Viviania marifolia in Argentina may not be the result of recent (man-mediated?) dispersal across the Andes, but may rather be more correctly interpreted as relict populations of a once much wider geographical range of this species group. Molecular studies investigating the degree of divergence of these populations from those of the western Andean slope would be clearly necessary to confirm their relictual nature.