Evolutionary Anthropology 20:254–263 (2011) ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin RENE´ BOBE Although best known for its fossil hominins, the Omo-Turkana Basin of Kenya EnvironmentsintheLakeRudolfBa- and Ethiopia is the source of one of the best records of vertebrate evolution sin.9 (Lake Rudolf was the former, co- from the Late Cenozoic of Africa. Located near the heart of the East African Rift lonial name for the lake). This volume Valley, the basin serves as an important frame of reference for the continent. provided initial descriptions of fossil The fossil record from this region plays a key role in our efforts to understand vertebrates, but more detailed descrip- the environmental and ecological context of human evolution in Africa. The tions followed in a series of Koobi Omo-Turkana faunal data shed light on key questions of human evolution: What Fora monographs10–15 and volumes kinds of environments did early humans inhabit? How did these environments devoted to the Nachukui, Kanapoi, change over time? What is the relationship between faunal change in East Africa and Nawata formations.16–18 All fossil and broader patterns of climatic change? mammals described or listed in these publications are documented in the Turkana Database, currently having Lake Turkana is located in northern erous sediments east and west of about 13,500 records (Box 1). Several Kenya, but the Turkana Basin is part Lake Turkana in Kenya, and to the field projects continue to operate in of the broader geological context that Omo-Turkana Basin to include also the Lake Turkana region and the re- includes the lower Omo Valley of the fossiliferous deposits from the cord of fossil vertebrates continues to Ethiopia (Fig. 1). The main fossilifer- lower Omo Valley of Ethiopia. In this grow at a rapid pace. The record of ous sediments exposed in the lower contribution, I review the Late fossil mammals from the Omo Shun- Omo Valley are the Mursi, Usno, and Miocene through Early Pleistocene gura, Usno, and Mursi formations has Shungura formations. The Koobi paleontological record from the Omo- appeared in several publications.19–23 Fora Formation is exposed on the east Turkana Basin, with an emphasis on The Omo fossil record, which side of Lake Turkana. The Nachukui fossil mammals. includes about 45,000 vertebrates, is Formation is exposed on the west side The geological and chronostrati- accessible through the ‘‘French’’ and of the lake. The Nawata Formation is graphic settings of the Omo-Turkana ‘‘American’’ Omo databases at the exposed at Lothagam, southwest of Basin are described in this issue by National Museum of Ethiopia.24,25 the lake, and the Kanapoi Formation Feibel1 and Brown and McDougall.2 This record provides key evidence of occurs near the southwestern tip of The large-scale (102–103 km2) geolo- the analysis of past environments and the basin. In this review, I refer to the gical and sedimentological context the ecological context of early Turkana Basin to include the fossilif- of the basin3–5 is complemented by humans.26–29 detailed stratigraphic analyses of geographically well-constrained local- PALEOECOLOGICAL 6–8 The author is Associate Professor of ities. These studies provide a frame- FRAMEWORK Anthropology at George Washington Uni- work for the study of hominin paleo- versity. His research focuses on fossil Initial studies of hominin paleo- mammals providing long-term records of environments and paleoecology in the ecological and environmental context eastern Africa. ecology in the Turkana Basin were of human evolution in Africa. He has active carried out by A. K. Behrensmeyer in field projects in the Dikika area of Ethiopia the 1960s and 1970s. Her ground- and the Omo-Turkana Basin of Ethiopia TAXONOMIC FRAMEWORK AND breaking studies were based on and Kenya. E-mail: [email protected] THE TURKANA DATABASE thoughtful consideration of sedimen- The taxonomic framework of the fos- tology, taphonomy, and issues of Key words: paleoecology; faunal analysis; Late sil vertebrate fauna has been relatively geographical scale.30 In this early Miocene; Pliocene; Early Pleistocene well established. Paleontological work work, Behrensmeyer found that pat- during the 1960s and early 1970s on terns of faunal and sedimentological VC 2011 Wiley Periodicals, Inc. the east and west sides of the lake, as associations indicated habitat differ- DOI 10.1002/evan20330 Published online in Wiley Online Library well as the lower Omo Valley, was pub- ences between the two Early Pleisto- (wileyonlinelibrary.com). lished in the volume Earliest Man and cene hominin genera, Paranthropus ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 255 example, waterbuck) and Bovini (for example, buffalo) are grazers in habi- tats close to water. The Alcelaphini (for example, wildebeest and topi) are pri- marily grazers in open environments, while Antilopini (gazelles) inhabit fairly arid environments where they may browse or graze.35,36 Other bovid tribes, such as Hippotragini and Neo- tragini, are less common in the fossil record and are not discussed in this review. Analysis of stable isotopes from dental enamel and ecomorphol- ogy provide much-needed data for the ecological characterization of extinct animals, including bovids.37–43 Geochemical analyses of stable iso- topes from paleosols have provided additional information about past vegetation and temperatures. These studies indicate that significant increases in the extent of C4 vegeta- tion occurred in the Late Miocene, about 7 Ma,44 and in the Early Pleis- tocene, about 1.8 Ma.45 Although vegetation and faunas in the region clearly changed during the Late Ceno- zoic, recent results indicate that temperatures were consistently high during the last 4 Myr46 and that tropi- cal savannas consisting of significant proportions of grassland have charac- terized hominin environments for the last 6 Myr.47 But it is also apparent from the geochemical data that there Figure 1. Schematic map of the Omo-Turkana Basin including Lake Turkana and the lower was significant geographic variation in Omo Valley. Gray shading indicates geological formations discussed in the text. Inset vegetation across different parts of the shows the basin in the context of eastern Africa. [Color figure can be viewed in the region during the Plio-Pleistocene.48,49 online issue, which is available at wileyonlinelibrary.com.] Thus, multiple lines of evidence indicate that the Omo-Turkana Basin and Homo. Behrensmeyer suggested ley fossil Bovidae (antelopes, in a was characterized by a complex and that Paranthropus was associated broad sense) has shown important dynamic suite of environments from with fluvial environments, but that shifts in relative abundances at 2.8 the Late Miocene through the Pleisto- Paranthropus and Homo occurred in Ma and after 2 Ma coinciding with cene. With a wealth of information from 29,34 similar numbers in lake margin envi- increasing aridity in the region. many different sources, this region has 31 ronments. Beyond the conclusions, Fossil bovids have played an impor- become one of the preeminent places to a key aspect of this work was the doc- tant role in paleoenvironmental study the environmental and ecological umentation of different environments research in eastern Africa because context of human evolution. across the Koobi Fora landscapes and they are typically abundant and pro- the recognition that, to assess this vide information about diet, locomo- environmental variation, it is critical to tion, and substrate, and thus, indi- LATE MIOCENE obtain comparable paleontological sam- rectly, about vegetation (Fig. 2). Vertebrates from the Late Miocene 32 ples across diverse paleolandscapes. Bovids of the tribe Tragelaphini (for of the Turkana Basin derive from Important studies of hominin example, kudus, bongo, and eland) fluvial sediments of the Nawata For- paleoenvironments were also carried typically occur in woodlands, mation at Lothagam, with most speci- out, with data from the lower Omo although eland are found in open mens dated between about 7.5 Ma Valley documenting trends toward grassland environments. Aepycerotini and 6.5 Ma.18,50 The first paleontologi- more open environments from the (impala) are broadly distributed along cal expeditions to the Lothagam area 26,33 Pliocene into the Pleistocene. ecotonal zones at the edge of wood- were carried out in 1967 by Bryan Further work on the lower Omo Val- lands and grasslands. Reduncini (for Patterson of Harvard University, fol- 256 Rene´ Bobe ARTICLES BOX 1: The Turkana Database: An Archive Of Vertebrate Evolution In East Africa After more than four decades cene; that is, from about 7.5 mil- www.mnh.si.edu/ete/ETE_Datasets_ of paleontological and geological lion years ago to about 1.4 million Turkana.html. research, the Turkana Basin has years ago. The fossils and the in- There are several aspects of the become one of the preeminent places formation they contain represent current database and data quality to study the ecological and environ- tens of thousands of hours devoted that we plan to improve in the near mental context of early human evolu- to searching, collecting, catalogu- future. First, some of the specimens tion. To strengthen and enhance ing, and conserving by hundreds were originally collected with rela- continuing research on human ori- of researchers and skilled techni- tively broad stratigraphic prove- gins, it is important that the wealth cians since the mid-1960s. Cur- nience data (at the level of geological of paleobiological information from rently, the public version of the members), even though the geo- the Turkana Basin be readily avail- database has more than 13,500 graphic origin of the specimens is able to the scientific community and records from 28 mammalian fami- known with meter-level accuracy tothepublicatlarge,beyondpubli- lies. It will continue to grow as and precision. We plan to reassign cations in specialized journals and new publications appear. There are specimens with well-known geo- comprehensive monographs.