Holocene paleoagrostological impressions from the eastern Chaco region (Argentina)

Abstract

Although no data are available on the paleoflora of the Chaco plain, plant fossil impressions are found in the banks of the low Bermejo River, which flows along the Eastern Chaco phytogeographic region. Here, we analyze paleoagrostological impressions recovered from two fossiliferous localities in order to provide insights into the environmental history of the Chaco region. Sixty complete Poaceae spikelet impressions were studied morphologically and compared with extant Chaco grass species. For each fossil spikelet, 11 morphological characters were described and statistically analyzed. All spikelets were found to belong to the Panicoideae subfamily, and some have consistent morphological features with this subfamily; hence, we assign them to the extant genera Cenchrus, Echinochloa, Hymenachne, and Paspalum. These impressions are the first floral remains found in the Eastern Chaco and collectively suggest that environmental and climatic conditions from these sediments corresponded to a subtropical humid climate and that vegetation was similar to the extant Eastern Chaco flora.