The Omo-Turkana Basin of southern Ethiopia and northern Kenya preserves a rich record of late Cenozoic fossil vertebrates and plays a central role in our understanding of early hominin evolution. In this chapter we focus on the northern area of the basin, the lower Omo Valley of Ethiopia. We provide a brief history of research in the area, present a review of previous studies focused on the paleoenvironments of the Shungura Formation (Figure 24.1), and offer a fresh perspective for the paleoecological context of hominin evolution in the lower Omo Valley with analyses of mammalian diversity and faunal similarity patterns from ~3.6 to 1 Ma.

The importance of the Turkana Basin (northern Kenya) and lower Omo Valley (southern Ethiopia) in our understanding of the environments in which early hominins lived, and on how climate changes may have influenced the emergence and disappearance of species, is undeniable (e.g., Bobe and Leakey, 2009; Levin et al., 2011). The majority of the Plio-Pleistocene sediments belong to the Omo Group, which consists of the Shungura, Usno, Nkalabong, and Mursi formations in Ethiopia and of the Nachukui and Koobi Fora formations in Kenya (e.g., Brown and McDougall, 2011). The Shungura, Nachukui, and Koobi Fora formations are well-studied (e.g., Howell and Coppens, 1976; de Heinzelin, 1983a, 1983b; Harris et al., 1988a, 1988b; Koobi Fora Research Project Volumes). The Mursi Formation of the lower Omo Valley, with a date of more than 4 million years, is among the oldest formations of the Omo Group in Ethiopia. However, it has been poorly documented despite its importance in informing us on the mid-Pliocene, a period in which the genus Australopithecus arose, but that is presently inadequately known. This chapter will present the formation with the history of the research in the area, including renewed fieldwork. It will be followed by a description of the geology and taphonomy and, finally, a preliminary analysis of the fauna found to date.

Early hominins were not limited to particular sites or localities in a paleontological or archeological sense, but lived and died in complex and dynamic landscapes and ecosystems of which we have partial, incomplete records. The fossil evidence of early hominin paleoenvironments is always limited, sometimes providing brief snapshots of small areas, other times affording very coarse chronological and spatial resolution over large distances. Taphonomic conditions typically vary within any one locality over time, and from one locality to another. And yet, it is these partial and biased records that we use to build an understanding of the forces that have shaped our evolution.

The Koobi Fora Fm (Formation) east of Lake Turkana in northern Kenya is one of the most important paleoanthropological rock units in the world (Figure 26.1). Nearly 250 hominin specimens are documented from East Turkana, representing the species Australopithecus anamensis, A. afarensis, Paranthropus boisei, Homo rudolfensis, H. habilis, and H. erectus (or ergaster) (M.G. Leakey, 1970; R.E. Leakey, 1973, 1976; Day et al., 1976; M.G. Leakey and R.E. Leakey, 1978; Kimbel, 1988; Wood, 1991; M.G. Leakey et al., 1995, 2012; Spoor et al., 2007; Wood and Leakey, 2011). Spanning from about 4.3 Ma (million years ago) to about 0.7 Ma, the abundant paleontological and sedimentological records of the Koobi Fora Fm offers a rich picture of hominin evolution and paleoenvironments during the Pliocene and early Pleistocene. In this contribution we present a synthesis of previous paleoecological work at East Turkana and add new paleontological analyses relevant to understanding the ecology of early hominins.

In a book on African paleoecology and human evolution, it is important to define several key themes, including biomes, vegetation formations and associations, as well as plant physiognomy. We first define these terms, before examining the sources of data employed in paleoenvironmental reconstructions. Finally, we provide an overview of the approaches used to understand past habitats, which underpin the chapters on the specific sites which make use of these approaches to refine our understanding of African paleoenvironments and the place of hominins within them.

In this chapter we review the evidence for hominid paleoenvironments in tropical Africa from the late Miocene to the early Pleistocene (Figure 15.1). Here we use the term hominid to refer to the family of the great apes and humans (family Hominidae, superfamily Hominoidea), and hominin (tribe Hominini) for the clade on the human side of the divergence from our last common ancestor with the genus Pan (Figure 15.2). This review is intended to complement the other regional reviews (northern African and southern African sites, see Chapters 6 and 36, respectively) and the overviews of Miocene to Holocene faunas (late Miocene and early Pliocene by Doman and Goble Early, this volume and Middle Pleistocene to Holocene by Faith, Chapter 5). The methods used in the reconstruction of past environments, e.g., stable isotopes, ecomorphology, community paleoecology, are summarized in Andrews and colleagues (Chapter 2).

The paleontological site of Dikika in the Afar Depression of Ethiopia (Figure 19.1) has been systematically studied since 1999, when a team led by one of us (ZA) launched the Dikika Research Project (DRP). This project set out to survey and document sedimentary exposures of the Hadar Formation south of the Awash River (Figures 19.2 and 19.3), and has produced important discoveries of fossil hominins and other mammals from the time between about 3.6 and 3.2 Ma. These discoveries include the earliest and most complete skeleton of an Australopithecus afarensis juvenile at locality DIK-1 (Alemseged et al., 2006); the earliest hominin from the Hadar Formation at locality DIK-2 (Alemseged et al., 2005); a new species of Canidae, Nyctereutes lockwoodi (Geraads et al., 2010b); a new species of gigantic otter, Enhydriodon dikikae (Geraads et al., 2011); and a new species similar to some modern otters, Lutra hearsti (Geraads et al., 2015b). Also, the earliest traces of stone-tool-modified bones were described from locality DIK-55 (McPherron et al., 2010). The study of these fossils and their paleoenvironmental context has offered new perspectives on the evolutionary forces that may have shaped early hominin adaptations (Wynn et al., 2006). The Dikika Research Project has therefore played a key role in deepening our understanding of A. afarensis paleobiology and its environmental context during the Pliocene.