We started the Ledi-Geraru Research Project in 2002 to look for sediments in the Afar region of Ethiopia that were the correct age to answer questions about the disappearance of Australopithecus afarensis and the appearance of the genus Homo and other hominin taxa. We found deposits that range in age from 2.88 million years ago (Ma) to ~1.0 Ma that also contain hominin fossils. Deposits such as this are rare in this region, and in Africa in general.
So far, we have found the earliest representative of the genus Homo — a left mandible fragment, as well as many isolated teeth of this Homo species that date to 2.82 Ma to ~2.4 Ma. In addition to focusing on finding early human ancestors, we are also investigating what might have caused the disappearance of Au. afarensis in the area, and what made it suitable for the genus Homo, such as changes in habitat and climate that might change the availability of food resources.
Our limited understanding of human biological and behavioral evolution between 2.95 and 2.5 Ma represents one of the most important gaps in our knowledge of the human lineage. Australopithecus afarensis — one of the best-understood Pliocene species — is unknown after 2.95 Ma in the Lower Awash Valley or Africa in general, and a subsequent, well-documented hominin species does not appear until ~2.5 Ma. There is evidence of hominin tool making during this interval; the only published evidence of such tools, to date, is from Gona in the lower Awash valley (Semaw et al., 1997). Because of limited outcrops in eastern Africa, the fossil record has provided scant actual biological or behavioral evidence of hominins in this time period.
During earlier field seasons, the Ledi-Geraru Research Project (LGRP) identified several regions (on the order of several km2) with good sedimentary exposures that encompass the time period from ~3.0–2.4 Ma (DiMaggio, 2013; see Fig. 1). Sedimentary rocks of this age are absent from other regions in the lower Awash, Afar, Ethiopia (such as Hadar, Dikika, Woranso-Mille and Gona; see Campisano and Feibel, 2008; Quade et al., 2004, 2008; Wynn et al., 2008, Deino et al., 2010). In our 2013 field season, we recovered a fossil hominin hemi-mandible within ~2.8 Ma strata (Villmoare et al., in prep.), and identified and began excavations on several archaeological sites that are also within this time period.
The lower Awash valley has provided important hominin discoveries over the past 40 years (e.g., Johanson et al., 1982; Kimbel et al., 1996; Semaw et al., 1997; Alemseged et al., 2006; Kimbel and Delezene, 2009, Haile-Selassie et al., 2010; McPherron et al., 2010), and we seek to add to this record by providing a link from the older Australopithecus localities of Hadar, Dikika, Woranso-Mille and southern Ledi-Geraru, to the younger record of hominin behavior at Gona. The last appearance datum (LAD) of A. afarensis at ~2.95 Ma (in Hadar), followed by the appearance of stone tools at ~2.58 Ma (in Gona) and Homo cf. H. habilis (in Hadar) at ~2.35 Ma (Kimbel et al., 1996), represent a dramatic niche shift of the hominin lineage (Roche et al., 2009) at the end of the Pliocene.
Building on prior work in the region, we seek to understand the context of hominin biological and behavioral evolution from a time period previously unknown in this region of the Afar and, in fact, represented by a paucity of material throughout all of Africa. Any information provided will add considerably to human evolutionary studies. We are:
- Investigating critical contextual details of early archaeological sites (e.g., available raw materials and ecological context) to provide a better understanding of the role of this very early technology-mediated resource extraction.
- Reconstructing past habitats at small spatial scales in the LGRP using both faunal and botanical indicators to better understand the context of the biological and behavioral changes in the hominin lineage that occurred during this time period.
- Determining the distribution of ecological communities throughout the broader lower Awash valley between 3.0–2.3 Ma by comparing LGRP fauna to that from Hadar, Dikika, Woranso-Mille and Gona, to develop a regional framework of mammalian species turnover and environmental change and to assess how hominins fit into that context.
- Comparing the paleoenvironmental and faunal results at LGRP with other paleoanthropological localities across Africa, to understand the regional and continental biogeographic movements of mammals, including hominins, during critical periods of climate change.
- Expanding and refining the geology, mapping and tephra collection in the eastern and western regions of LGRP.
- Kaye Reed, Arizona State University
- Christopher Campisano, Arizona State University
- J. Ramon Arrowsmith, Arizona State University
- David Feary, Arizona State University
- Brian Villmoare, University of Nevada, Las Vegas
- Lars Werdelin, Swedish Museum of Natural History
- Amy Rector, Virginia Commonwealth University
- David Braun, George Washington University
- Erin DiMaggio, Pennsylvania State University
- Faysal Bibi, Museum fur Naturkunde
- Alan Deino, Berkeley Geochronology Center
- Guillaume Dupont-Nivet, Potsdam University
- Eric Scott, California State University
- Pauline Coster, University of Kansas
- William Archer, Max Planck Institute
- Ignacio Lazagabaster, Haifa University
- John Rowan, University of Massachusetts, Amherst
- Chalachew Mesfin Seyoum, Student, Arizona State University
- Irene Smail, Student, Arizona State University
- Dominique Garello, Student, Arizona State University
- Tomas Getachew, Student, Arizona State University
- Niguss Gitaw Baraki, Student, Arizona State University
- Jacob Harris, Student, Arizona State University
- Nicole Mann, Student, Arizona State University
- Degsew Zerihun Mekonnen, Student, Arizona State University
- Nacashni Naidoo, Student, Arizona State University
- Jonathan Reeves, Student, Arizona State University
- Maryse Beirnat, Student, Arizona State University
National Science Foundation (2012 - 2015)
NSF BCS 1157351 Collaborative Research: Paleoanthropological Investigation of the Ledi-Geraru Hominin Site (Afar, Ethiopia) 4/15/12-3/31/15
National Science Foundation (2015 - 2019)
NSF BSC 1460493 Collaborative Research: Filling a Gap in Hominin Evolution 2/15/15-1/31/2019
Pending NSF Collaborative Research: Hominin diversity, paleobiology, and behavior at the terminal Pliocene from Ledi Geraru (Afar, Ethiopia)