Soil and plant phytoliths from the Acacia-Commiphora mosaics at Oldupai Gorge (Tanzania).

Julio Mercader,Jamie Inwood,Siobhán Clarke,Laura Tucker,Aloyce Mwambwiga,Fergus Larter,María Soto,Julien Favreau,Neduvoto Mollel,Robert Patalano,Dale Walde,Makarius Itambu,Patrick Lee,Garnet Lewiski-Mcquaid,Mariam Bundala

doi:10.7717/peerj.8211

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.

Highlights

Multiple proxies indicate that during the last two million years the East African climate changed, triggering a shift in its plant landscape from forested ecosystems to open woodland/grassland mosaics
Characteristic Somalia-Masai taxa analysed here comprise the dominant members of the canopy (Acacia mellifera, A. nilotica), emergents (Boscia angustifolia), bushes (Barleria eranthemoides, Maerua triphylla), the herbaceous layer (Hypoestes forskaolii, Ocimum spp.), succulents (Sansevieria robusta, Aloe secundiflora), and the grasses (Sporobolus consimilis, Cynodon dactylon -Chloridoideae, Aristida adoensis - Aristidoideae)
We provide a phytolith analog for Acacia-Commiphora mosaics that may represent the trend for more open landscapes recorded in East Africa since the early Pleistocene

Summary

Introduction

Multiple proxies indicate that during the last two million years the East African climate changed, triggering a shift in its plant landscape from forested ecosystems to open woodland/grassland mosaics These proxies include paleosol carbonates (Cerling, Bowman & O’Neil, 1988; Levin et al, 2004; Quinn et al, 2007; Levin et al, 2011), vertebrates (Bibi & Kiessling, 2015; Bibi et al, 2018; Prassack et al, 2018), palaeobotanical remains (Bonnefille, 1984; Bonnefille, 1995), and stable isotopes (Magill, Ashley & Freeman, 2013a; Magill, Ashley & Freeman, 2013b; Uno, Polissar & Jackson, 2016; Lupien et al, 2018). Over the last few decades, different investigations have attempted to identify modern ecosystems as referential correlates for Pleistocene East African vegetation communities within the Somalia-Masai floristic region; a center of endemism that extends over 2 million km in parts of Ethiopia, Sudan, Uganda, Kenya, and Tanzania Lakes such as Manyara and Makat are often considered correlates for paleo-Lake Oldupai as they have vegetation types not in equilibrium with the regional climate (Barboni, 2014; Copeland, 2007). Copeland (2007) examined habitats in northern Lake Manyara, Ngorongoro, and the Serengeti Plain as baseline to understand the paleolandscape inhabited by early Homo in terms of climate, land forms, and soil types

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