Soil and plant phytoliths from theAcacia-Commiphoramosaics at Oldupai Gorge (Tanzania)

Abstract

This article studies soil and plant phytoliths from the Eastern Serengeti Plains, specifically the Acacia-Commiphora mosaics from Oldupai Gorge, Tanzania, as present-day analogue for the environment that was contemporaneous with the emergence of the genus Homo. We investigate whether phytolith assemblages from recent soil surfaces reflect plant community structure and composition with fidelity. The materials included 35 topsoil samples and 29 plant species (20 genera, 15 families). Phytoliths were extracted from both soil and botanical samples. Quantification aimed at discovering relationships amongst the soil and plant phytoliths relative distributions through Chi–square independence tests, establishing the statistical significance of the relationship between categorical variables within the two populations. Soil assemblages form a spectrum, or cohort of co-ocurring phytolith classes, that will allow identifying environments similar to those in the Acacia-Commiphora ecozone in the fossil record.

Phytolith Palaeoenvironments at Mumba Rock Shelter

“…The parameters for comparison from these two regional spectra are as follows: Mesic woodlands (Mercader et al, 2011) are characterized by dicot globular phytoliths (>50%) in cohort with Poaceae short cells, mostly in the Panicoid subfamily and led by short bilobates with convex ends. In contrast, the dry woodland/grassland mosaics of the Somalia -Masai ecozone (Mercader et al, 2019) are characterized by tabular and blocky phytoliths (>50%) with much scarcer globulars and lobates. Short cell assemblages are co-dominated by rondels, short saddles, and small bilobates with concave ends; with a total grass percent oscillating from about 25% in the Acacia -Commiphora woodland (Mercader et al, 2019) to about 65% in the wooded Serengeti grassland (Albert et al, 2015a).…”

“…In contrast, the dry woodland/grassland mosaics of the Somalia -Masai ecozone (Mercader et al, 2019) are characterized by tabular and blocky phytoliths (>50%) with much scarcer globulars and lobates. Short cell assemblages are co-dominated by rondels, short saddles, and small bilobates with concave ends; with a total grass percent oscillating from about 25% in the Acacia -Commiphora woodland (Mercader et al, 2019) to about 65% in the wooded Serengeti grassland (Albert et al, 2015a).…”

“…In order of abundance, the mean for the tabular class from woody dicot (cf. Mercader et al, 2009Mercader et al, , 2019) is 8.48% (range = 2.5%-52.92%). Mean percent for blocky phytoliths is 7.81% (range: 2.78%-41.02%).…”

“…To compare archaeological distributions with analogous baselines, we grouped all phytolith morphotypes per class. Two of the modern soil phytolith distributions came from large referential collections, and thus were bootstrapped (n = 1000) to retrieve a mean value for the 35 samples representing Acacia -Commiphora mosaics (Mercader et al, 2019) and the 25 samples indicative of Zambezian woodlands (Mercader et al, 2011).…”

“…Cylindroids from woody dicots (cf. Mercader et al, 2009Mercader et al, , 2019) have a mean of 3.43% (range = 1.11%-7.58%). The least abundant class is the rondel, with mean of 2.11% (range = 0.47%-7.76%).…”