Abstract Detail

Paleobotanical Section

Stromberg, Caroline [1], Dunn, Regan [2], Kohn, Matthew [3], Madden, Richard [4], Carlini, Alfredo [1].

Did South America herald Earth's earliest grasslands?: New plant silica records from Gran Barranca, Argentina.

Based on the study of faunas from Patagonia, South America,it has long been assumed that savanna grasslands spread in the Middle Eocene(40-45 Ma) in southern South America, ~20 million years earlier than on other continents. Paleobotanical lines of evidence are contradictory, with plant silica (phytolith) assemblages supporting the idea of open, grassy habitats bythe Late Eocene, whereas macrofossils and palynofloras from Patagonia indicate closed forests during the Eocene and Oligocene. To test the South American early grassland hypothesis we conducted a high-resolution study of phytolith assemblages in the Sarmiento Formation at Gran Barranca, Chubut Province,Argentina. This section, which is known to produce well-preserved phytoliths,spans 42-18.5 Ma and is the most complete and important record of South American faunas. Phytolith analysis shows that a variety of forest indicators,including palms and woody dicotyledons, dominated phytolith assemblages throughout the section, with palms being particularly abundant during the Eocene and Oligocene. Grasses are present throughout the section, but initially consisted primarily of grasses likely related to bamboos. Phytoliths typical of open-habitat grasses (pooids, PACMADs) do occur by at least 38 Ma, marking the earliest appearance of these two clades, but are quite rare (typically <5%).By the Late Oligocene/Early Miocene, pooid open-habitat forms dominate grass phytolith assemblages, and increase in frequency to ≤30% of assemblages overall.This expansion of grasses coincided with markedly lower palm phytolith abundances, possibly suggesting drier or colder climates. This record is consistent with previous interpretations of macrofossil and palynological data and rejects the notion that open, grass-dominated habitats spread in southern South America before at least the late Early Miocene (18.5 Ma).

Broader Impacts:

1 - Museo de La Plata, Paleontología de Vertebrados, Paseo del Bosque s/n, La Plata, B1900 FWA, Argentina
2 - University of Washington, Biology, 24 Kincaid Hall, Box 351800, Seattle, WA, 98195-1800, USA
3 - Boise State University, Geosciences, 1910 University Drive, Boise, ID, 83725-1535, USA
4 - Duke University, Evolutionary Anthropology, 07 Bio. Sci. Bldg. Biological Sciences Building, Campus Box 3170 Med Ctr, Durham, NC, 27708-0680, USA

Keywords:
phytoliths
grasslands
Cenozoic
South America
Argentina
paleoecology.

Presentation Type: Oral Paper:Papers for Sections
Session: 46
Location: Forsyth Room/Chase Park Plaza
Date: Wednesday, July 13th, 2011
Time: 11:45 AM
Number: 46007
Abstract ID:607