Fossil pollen grains of Asteraceae (Nassauviinae) from the Miocene of Patagonia, southern South America

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

Panamá

Congreso; 40 th American Association of Stratigraphic Palynologists; 2007

American Association of Stratigraphic Palynologists

Fossil pollen grains with morphological features unique in the tribe Nassauviinae (subfamily Mutisioideae, Asteraceae) occur in Miocene marine deposits of eastern Patagonia, southern South America. They are characterized by having a complex bi-layered exine structure with delicate columellae, separated by an internal tectum. Two major morphotypes were identified by their shape and exine types. Fossil subprolate specimens with Trixis exine type (ectosexine thinner than endosexine, straight internal tectum) are similar to pollen of extant Acourtia, Holocheilus, Jungia, and Proustia. Suboblate specimens with Oxyphyllum exine type (ectosexine and endosexine equally thick, zigzag internal tectum) are similar to pollen of extant Triptilion. The spore pollen suites in which Nassauvinae pollen types occur suggest a wide range of vegetation types varying from forest dominated during the Early Miocene (Chenque Formation) to virtually xerophytic ones during the Late Miocene (Puerto Madryn Formation). The tribe Nassauviinae comprises 25 genera and ca. 320 species of vines, shrubs and low trees endemic to America with a wide range of ecological preferences; the nearest living relatives of the fossil types being mostly confined to humid landscapes. The unusual persistence of these groups during the arid characterized Late Miocene time could be attributed to the complex interplay of the mountain uplift and global circulation patterns. These forcing factors would have created a mosaic of different habitats with both patches of forest and dry-adapted species developing in relatively small regions. This is the first fossil record of Nassauviinae and confirms that this tribe of Asteraceae was differentiated by the Miocene.