In situ ~2.0 Ma trees discovered as fossil rooted stumps, lowermost Bed I, Olduvai Gorge, Tanzania J € org M. Habermann a, * , Ian G. Stanistreet b, c , Harald Stollhofen a , Rosa M. Albert d, e , Marion K. Bamford e , Michael C. Pante f , Jackson K. Njau g , Fidelis T. Masao h a GeoZentrum Nordbayern, Friedrich-Alexander-Universit€ at (FAU) Erlangen-Nürnberg, Schlossgarten 5, 91054 Erlangen, Germany b Dept. of Earth, Ocean and Ecological Sciences, University of Liverpool, Brownlow Street, Liverpool L69 3GP, UK c The Stone Age Institute, Bloomington, IN 47407-5097, USA d Catalan Institution for Research and Advanced Studies (ICREA)/Research Group for Archaeometry and Archaeology (ERAAUB), Department of Prehistory, Ancient History and Archaeology, Universitat de Barcelona, c/Montalegre, 6e8, 08001 Barcelona, Spain e Evolutionary Studies Institute and School of Geosciences, University of the Witwatersrand, P Bag 3, WITS 2050, South Africa f Department of Anthropology, Colorado State University, Fort Collins, CO 80523, USA g Department of Geological Sciences, Indiana University,1001 East 10th Street, Bloomington, IN 47405-1405, USA h Archaeology Unit, Department of History, University of Dar es Salaam, Tanzania article info Article history: Received 4 March 2015 Accepted 15 September 2015 Available online xxx Keywords: Pleistocene landscape Ngorongoro fan apron Paleoecology Phytoliths Oldowan abstract The discovery of fossil rooted tree stumps in lowermost Lower Bed I from the western Olduvai Basin, Tanzania, age-bracketed by the Naabi Ignimbrite (2.038 ± 0.005 Ma) and Tuff IA (1.88 ± 0.05 Ma), provides the first direct, in situ, and to date oldest evidence of living trees at Olduvai Gorge. The tree relicts occur in an interval dominated by low-viscosity mass flow and braided fluvial sediments, deposited at the toe of a largely Ngorongoro Volcano-sourced volcaniclastic fan apron that comprised a widely spaced network of ephemeral braided streams draining northward into the Olduvai Basin. Preservation of the trees occurred through their engulfment by mass flows, post-mortem mold formation resulting from differential decay of woody tissues, and subsequent fluvially-related sediment infill, calcite precipitation, and cast formation. Rhizolith preservation was triggered by the interaction of root- induced organic and inorganic processes to form rhizocretionary calcareous root casts. Phytolith analyses were carried out to complete the paleoenvironmental reconstruction. They imply a pronounced sea- sonality and indicate a wooded landscape with grasses, shrubs, and sedges growing nearby, comparable to the low, open riverine woodland (unit 4c) along the Garusi River and tributaries in the Laetoli area. Among the tree stump cluster were found outsized lithic clasts and those consisting of quartzite were identified as Oldowan stone tool artifacts. In the context of hominin activity, the identification of wooded grassland in association with nearby freshwater drainages and Oldowan artifacts significantly extends our paleoenvironmental purview on the basal parts of Lower Bed I, and highlights the hitherto under- rated role of the yet poorly explored western Olduvai Gorge area as a potential ecologically attractive setting and habitat for early hominins. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Olduvai tree evidence Despite fairly systematic paleontological surveys, archaeological trenching, and geological exploration of Olduvai Gorge (Fig. 1) since the early 20th century (Reck, 1914; Leakey, 1959; Leakey et al., 1964; Leakey, 1971; Hay, 1976), followed by OLAPP (1989-present), TOPPP (2006-present), and OGAP (2009-present) initiatives, there has been no report of any evidence of in situ trees and their preserved root systems from Pleistocene Beds I to IV. This is despite the fact that considerable indirect evidence of the presence of trees has been presented from the essentially fluvio-lacustrine Olduvai Basin-fill. Uprooting of a tree on the Zinjanthropus land surface was postulated to have caused a pile of detritus on the so-called “living floor” at Bed I sub-Tuff IC level (Fig. 2; Leakey, 1971). Fossil wood * Corresponding author. E-mail address: joerg.habermann@fau.de (J.M. Habermann). Contents lists available at ScienceDirect Journal of Human Evolution journal homepage: www.elsevier.com/locate/jhevol http://dx.doi.org/10.1016/j.jhevol.2015.09.011 0047-2484/© 2015 Elsevier Ltd. All rights reserved. Journal of Human Evolution 90 (2016) 74e87