Phytoliths as indicators of Quaternary vegetation at the Paleolithic site of Attirampakkam, India

Abstract

The paleoecological context of hominin occupation in South Asia during the early and middle Pleistocene is virtually unknown. Attirampakkam, India, is an archeological site of global importance, with an early Acheulian occupation (age bracket of ~1.07–1.77 Ma) succeeded by Middle Paleolithic levels. Here we report on the recovery of phytoliths from artifact-bearing Quaternary deposits in excavated trenches. We focus on the reconstruction of past vegetation during hominin occupation of the site. The present study provides information on hominin microenvironments and local habitats in South Asia, situating them in a more tangible ecological context than so far achieved. Results show that this region was arid during the earlier stages of the early Pleistocene, and was occupied by hominins living in a landscape locally lacking woody plants. Herbaceous vegetation was dominated by C4 Chloridoid grasses. In the later phase of the early Pleistocene, the landscape was wooded and dominated by C4 Panicoid grasses, with a significant reduction of C4 Chloridoid grasses indicating a shift from a drier to a relatively more humid climate. A diverse husk and leaf phytolith assemblage of wild Oryza spp. (rice) occurring as natural annual or perennial components of the vegetation in the area, other herbaceous plants such as Cyperaceae (sedges), and the continuous presence of blackened phytoliths, suggest the establishment a grassland landscape with enclaves of wetland habitat affected by seasonal flooding and frequent fires. The transition from the early to the middle Pleistocene was marked by a moderately humid climate, with a shift toward aridity during the late Pleistocene, during which we note an environment dominated by C4 Chloridoid grasses, by a sharp reduction of C4 Panicoid grasses, and by a rise in woody taxa. During the middle to late Pleistocene, Middle Paleolithic populations would have witnessed water bodies near the site, as reflected by the presence of plants adapted to swampier conditions such as Cyperaceae and Oryza spp. The archeological record terminates in Layer 1, when human occupation decreased drastically, possibly because of increased aridity and/ or greater environmental variability. The phytolith fingerprint at ATM sheds light on the co-occurrence of, vegetation, fire and early prehistoric land occupation. An important aspect is the evidence of Oryza spp., suggesting that wild rice occurred in the environment frequented by these early hominins.