Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin

Transcription

1 Evolutionary Anthropology 20: (2011) ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin RENÉ BOBE Although best known for its fossil hominins, the Omo-Turkana Basin of Kenya and Ethiopia is the source of one of the best records of vertebrate evolution from the Late Cenozoic of Africa. Located near the heart of the East African Rift Valley, the basin serves as an important frame of reference for the continent. The fossil record from this region plays a key role in our efforts to understand the environmental and ecological context of human evolution in Africa. The Omo-Turkana faunal data shed light on key questions of human evolution: What kinds of environments did early humans inhabit? How did these environments change over time? What is the relationship between faunal change in East Africa and broader patterns of climatic change? The author is Associate Professor of Anthropology at George Washington University. His research focuses on fossil mammals providing long-term records of the ecological and environmental context of human evolution in Africa. He has active field projects in the Dikika area of Ethiopia and the Omo-Turkana Basin of Ethiopia and Kenya. bobe@gwu.edu Key words: paleoecology; faunal analysis; Late Miocene; Pliocene; Early Pleistocene VC 2011 Wiley Periodicals, Inc. DOI /evan20330 Published online in Wiley Online Library (wileyonlinelibrary.com). Lake Turkana is located in northern Kenya, but the Turkana Basin is part of the broader geological context that includes the lower Omo Valley of Ethiopia (Fig. 1). The main fossiliferous sediments exposed in the lower Omo Valley are the Mursi, Usno, and Shungura formations. The Koobi Fora Formation is exposed on the east side of Lake Turkana. The Nachukui Formation is exposed on the west side of the lake. The Nawata Formation is exposed at Lothagam, southwest of the lake, and the Kanapoi Formation occurs near the southwestern tip of the basin. In this review, I refer to the Turkana Basin to include the fossiliferous sediments east and west of Lake Turkana in Kenya, and to the Omo-Turkana Basin to include also the fossiliferous deposits from the lower Omo Valley of Ethiopia. In this contribution, I review the Late Miocene through Early Pleistocene paleontological record from the Omo- Turkana Basin, with an emphasis on fossil mammals. The geological and chronostratigraphic settings of the Omo-Turkana Basin are described in this issue by Feibel 1 and Brown and McDougall. 2 The large-scale ( km 2 ) geological and sedimentological context of the basin 3 5 is complemented by detailed stratigraphic analyses of geographically well-constrained localities. 6 8 These studies provide a framework for the study of hominin paleoenvironments and paleoecology in eastern Africa. TAXONOMIC FRAMEWORK AND THE TURKANA DATABASE The taxonomic framework of the fossil vertebrate fauna has been relatively well established. Paleontological work during the 1960s and early 1970s on the east and west sides of the lake, as well as the lower Omo Valley, was published in the volume Earliest Man and Environments in the Lake Rudolf Basin. 9 (Lake Rudolf was the former, colonial name for the lake). This volume provided initial descriptions of fossil vertebrates, but more detailed descriptions followed in a series of Koobi Fora monographs and volumes devoted to the Nachukui, Kanapoi, and Nawata formations All fossil mammals described or listed in these publications are documented in the Turkana Database, currently having about 13,500 records (Box 1). Several field projects continue to operate in the Lake Turkana region and the record of fossil vertebrates continues to grow at a rapid pace. The record of fossil mammals from the Omo Shungura, Usno, and Mursi formations has appeared in several publications The Omo fossil record, which includes about 45,000 vertebrates, is accessible through the French and American Omo databases at the National Museum of Ethiopia. 24,25 This record provides key evidence of the analysis of past environments and the ecological context of early humans PALEOECOLOGICAL FRAMEWORK Initial studies of hominin paleoecology in the Turkana Basin were carried out by A. K. Behrensmeyer in the 1960s and 1970s. Her groundbreaking studies were based on thoughtful consideration of sedimentology, taphonomy, and issues of geographical scale. 30 In this early work, Behrensmeyer found that patterns of faunal and sedimentological associations indicated habitat differences between the two Early Pleistocene hominin genera, Paranthropus

2 ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 255 Figure 1. Schematic map of the Omo-Turkana Basin including Lake Turkana and the lower Omo Valley. Gray shading indicates geological formations discussed in the text. Inset shows the basin in the context of eastern Africa. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] and Homo. Behrensmeyer suggested that Paranthropus was associated with fluvial environments, but that Paranthropus and Homo occurred in similar numbers in lake margin environments. 31 Beyond the conclusions, a key aspect of this work was the documentation of different environments across the Koobi Fora landscapes and the recognition that, to assess this environmental variation, it is critical to obtain comparable paleontological samples across diverse paleolandscapes. 32 Important studies of hominin paleoenvironments were also carried out, with data from the lower Omo Valley documenting trends toward more open environments from the Pliocene into the Pleistocene. 26,33 Further work on the lower Omo Valley fossil Bovidae (antelopes, in a broad sense) has shown important shifts in relative abundances at 2.8 Ma and after 2 Ma coinciding with increasing aridity in the region. 29,34 Fossil bovids have played an important role in paleoenvironmental research in eastern Africa because they are typically abundant and provide information about diet, locomotion, and substrate, and thus, indirectly, about vegetation (Fig. 2). Bovids of the tribe Tragelaphini (for example, kudus, bongo, and eland) typically occur in woodlands, although eland are found in open grassland environments. Aepycerotini (impala) are broadly distributed along ecotonal zones at the edge of woodlands and grasslands. Reduncini (for example, waterbuck) and Bovini (for example, buffalo) are grazers in habitats close to water. The Alcelaphini (for example, wildebeest and topi) are primarily 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 Neotragini, are less common in the fossil record and are not discussed in this review. Analysis of stable isotopes from dental enamel and ecomorphology provide much-needed data for the ecological characterization of extinct animals, including bovids Geochemical analyses of stable isotopes from paleosols have provided additional information about past vegetation and temperatures. These studies indicate that significant increases in the extent of C 4 vegetation occurred in the Late Miocene, about 7 Ma, 44 and in the Early Pleistocene, about 1.8 Ma. 45 Although vegetation and faunas in the region clearly changed during the Late Cenozoic, recent results indicate that temperatures were consistently high during the last 4 Myr 46 and that tropical savannas consisting of significant proportions of grassland have characterized hominin environments for the last 6 Myr. 47 But it is also apparent from the geochemical data that there was significant geographic variation in vegetation across different parts of the region during the Plio-Pleistocene. 48,49 Thus, multiple lines of evidence indicate that the Omo-Turkana Basin was characterized by a complex and dynamic suite of environments from the Late Miocene through the Pleistocene. With a wealth of information from many different sources, this region has become one of the preeminent places to study the environmental and ecological context of human evolution. LATE MIOCENE Vertebrates from the Late Miocene of the Turkana Basin derive from fluvial sediments of the Nawata Formation at Lothagam, with most specimens dated between about 7.5 Ma and 6.5 Ma. 18,50 The first paleontological expeditions to the Lothagam area were carried out in 1967 by Bryan Patterson of Harvard University, fol-

3 256 René Bobe ARTICLES BOX 1: The Turkana Database: An Archive Of Vertebrate Evolution In East Africa After more than four decades of paleontological and geological research, the Turkana Basin has become one of the preeminent places to study the ecological and environmental context of early human evolution. To strengthen and enhance continuing research on human origins, it is important that the wealth of paleobiological information from the Turkana Basin be readily available to the scientific community and tothepublicatlarge,beyondpublications in specialized journals and comprehensive monographs. Publicly available databases have become standard tools in scientific research in many areas of study, including, for example, the field of genomics, and paleoanthropology is no exception. In a partnership between the National Museums of Kenya and the Smithsonian Institution, we have established a living faunal database that can serve as a powerful and sustainable tool in the analysis of paleoecological patterns and faunal change in the context of human evolution. The Turkana Database is a specimen-based compilation of fossil vertebrates from the Turkana Basin of Kenya. This contrasts with other database structures that provide lists of taxa by locality or collection (for example, species occurrences), such as the Paleobiology Database (PBDB, the Eurasian NOW Database ( and the Smithsonian s Human Origins Program Database. The Paleobiology Database includes taxonomic occurrence records for the East African Mio-Pleistocene fauna originally captured by the Evolution of Terrestrial Ecosystems (ETE) database. 100,103 The Turkana Database contains searchable information about all published specimens from Lothagam (Nawata and Nachukui formations), Kanapoi (Kanapoi Formation), West Turkana (Nachukui Formation), and East Turkana (Koobi Fora Formation). The specimens date from the Late Miocene to the Early Pleistocene; that is, from about 7.5 million years ago to about 1.4 million years ago. The fossils and the information they contain represent tens of thousands of hours devoted to searching, collecting, cataloguing, and conserving by hundreds of researchers and skilled technicians since the mid-1960s. Currently, the public version of the database has more than 13,500 records from 28 mammalian families. It will continue to grow as new publications appear. There are 34 fields in the public database, with each field providing, along with other contextual information, basic information about a fossil specimen: museum accession number, associated specimens, geographical location of the site, stratigraphic information, taxonomic designation, skeletal part, and degree of completeness. The parent Turkana Database contains both published and unpublished specimens, currently totaling about 17,000 records; access to unpublished information requires permission from the Palaeontology Division at the National Museums of Kenya. The Turkana Database was designed as a research tool, and it has been used for this purpose in peer-reviewed publications as well as dissertations and student projects. It has also become a valuable tool for curators at the National Museums of Kenya (NMK) and for researchers visiting the vast vertebrate paleontology collections at the museum. Scholars who conduct research at NMK can easily locate specimens of interest and find appropriate comparative collections. Scholars who are planning to visit NMK can get exact numbers and locations of specimens they wish to study before they travel, and thus can plan their work ahead of time. The public database can be accessed through the National Museums of Kenya, Earth Sciences Department (Palaeontology Division), and the Smithsonian Institution s Evolution of Terrestrial Ecosystems web pages: and Turkana.html. There are several aspects of the current database and data quality that we plan to improve in the near future. First, some of the specimens were originally collected with relatively broad stratigraphic provenience data (at the level of geological members), even though the geographic origin of the specimens is known with meter-level accuracy and precision. We plan to reassign specimens with well-known geographic provenience records to updated geological subunits within known geological members. Second, some of the taxonomic identifications of Turkana Basin fossils have not been revised or updated since they were first published two or three decades ago. The recent publication of a volume on African mammal evolution provides renewed impetus to update these records and bring them into the current taxonomic framework for African paleofaunas. 104 Third, some of the nonmammalian taxa have not been well studied and require thorough reevaluation, although there are some notable exceptions, such as the fossil fishes from Kanapoi and Lothagam. In future versions of the database, we plan to include all vertebrate fossils, not just mammals. With refined stratigraphic provenience, updated taxonomy, and inclusion of all fossil vertebrates, we also will include in the database a range of new ecomorphological and paleoecological data derived from the fossils. Currently there is no single source of paleoecological information of Turkana Basin fossils. These data can be easily incorporated into the structure of the Turkana Database (fields for measurements and interpretations, such as grazer, browser, mixed feeder). The database will continue to be maintained by the National Museums of Kenya and the Smithsonian Institution. René Bobe Anna K. Behrensmeyer Meave G. Leakey Emma Mbua

4 ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 257 Figure 2. Fossil Bovidae play an important role in paleoenvironmental research in eastern Africa. Artist s reconstruction of Tragelaphus from the lower Omo Valley of Ethiopia. Inset: Tragelaphus specimen L861-1 from the lower Omo Valley. Artwork by Christina Moon. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] Parapapio, and the equid Eurygnathohippus. In this review, I follow Boisserie s (2005) revision of hippopotamid taxonomy in referring Lothagam specimens previously published as Hexaprotodon to the genus Archaeopotamus. 59 The two most abundant genera from Lothagam, Nyanzachoerus and Archaeopotamus, had diets that shifted over time (between the Lower and Upper Nawata Formation) from C 3 to a mix of C 3 and C 4 vegetation. The bovid Aepyceros from Lothagam had a C 3 diet, although later impala had a mixed diet. 53 Among equids there was a rapid transition in the early part of the Nawata Formation, at about 7 Ma, from a mix of C 3 and C 4 vegetation to a pure C 4 diet. 53 Boselaphin bovids of the genus Tragoportax (browsers) were also abundant at Lothagam, but essentially disappear from later African fossil samples. Today, boselaphins (nilgai and fourhorned antelope) are found only in Asia. Among carnivores, amphicyonids are present in the Late Miocene lowed by work under the leadership of Vincent Maglio in Subsequent field research led by Meave Leakey and colleagues contributed to a collection of more than 2,000 fossil vertebrates. The Nawata Formation provides evidence of mammal turnover in the Late Miocene in relation to earlier sites in eastern Africa. 51 This turnover follows the global shift in climate that resulted in the first widespread expansion of C 4 grasslands. 52 Some of the Lothagam mammals show evidence of a grazing diet. 53 The most abundant families of mammals from the Nawata Formation are the Bovidae (antelopes), Suidae (pigs, warthogs, and their extinct ancestors), Hippopotamidae (hippos), Cercopithecidae (monkeys), and Equidae (horses), in that order These families constitute 81% of the described mammals. At the genus level, the most common taxa are the suid Nyanzachoerus, the hippopotamid Archaeopotamus, the bovid Aepyceros, the cercopithecid Figure 3. A. Relative abundance of Alcelaphini plus Antilopini as a percentage of all Bovidae in the Late Cenozoic of the Omo-Turkana Basin. These bovids are considered to be indicative of open grassland and bush habitats. B. Fisher s alpha, a measure of taxonomic diversity relative to sample size, for Bovidae from the Omo-Turkana Basin (all areas combined). Data from Bobe and coworkers 78 and Bobe and Leakey. 79 [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

5 258 René Bobe ARTICLES at Lothagam, but not in later samples from the region. 60 Among rhinos, the genus Brachypotherium, an extinct browser, is more common than the ancestors of the modern Diceros (black rhino) and Ceratotherium (white rhino). 61 Fossil fishes are also abundant at Lothagam and provide important paleoecological information regarding the major bodies of water in the region. 62 Overall, the Lothagam fossil vertebrates indicate the presence of heterogeneous environments, including forest, woodland and grassland in proximity to a broad river during the latest Miocene, but with conditions becoming more open (more grasslands) in the transition from the Lower to the Upper Member of the Nawata Formation about 6.5 Ma (Fig. 3A). How do hominins fit into this picture? Turkana hominins from this time are noteworthy for their rarity. There are only three fossil hominins from the Mio-Pliocene of Lothagam, an upper third molar, a lower incisor, and the better known hominin mandible LT 329. The two isolated teeth derive from the Upper Member of the Nawata Formation and date to between 6.5 and 5 Ma, although they are probably closer to the later date; the hominin mandible derives from the Early Pliocene Apak Member of the Nachukui Formation. 50,63 These hominins, then, derive from the later intervals of the Nawata sequence and early part of the Nachukui Formation. Thus, although most of the Lothagam fauna is of Late Miocene age, the hominins are best considered part of the earliest Pliocene or very close to the Miocene/Pliocene boundary. The Lothagam mammals indicate shifting environmental conditions toward more open environments in the Late Miocene, but their relationship to the hominins is not clear. The rarity of hominin fossils in the Late Miocene of the Turkana Basin may reflect low hominin abundance in the paleolandscape or, perhaps, factors such as prolonged life history, which would have lowered the number of individuals available for fossilization, or hominin avoidance of the environments that led to fossilization in this part of East Africa. Other primates that may be considered taphonomically equivalent to hominins, such as Parapapio, are much more common (107 specimens of Parapapio in a sample of 1,050 mammals). Establishing the reasons for the rarity of hominin fossils during this time remains an intriguing area for future research. PLIOCENE The Pliocene ( Ma) is represented at Lothagam (Apak and Kaiyumung members of the Nachukui Formation), Kanapoi (Kanapoi Formation), West Turkana (Kataboi and Lomekwi members of the Nachukui Formation), East Turkana Although most of the Lothagam fauna is of Late Miocene age, the hominins are best considered part of the earliest Pliocene or very close to the Miocene/ Pliocene boundary. (Lonyumun, Moiti, Lokochot, and Tulu Bor members of the Koobi Fora Formation), and the lower Omo Valley (Mursi and Usno formations, and Shungura Basal Member through Member C). Abundant faunal samples derive from Kanapoi, where the hominin Australopithecus anamensis appears in the record at about 4.2 Ma. 64,65 The Kanapoi locality was first described by Patterson in the 1960s. Further work by Meave Leakey and colleagues in resulted in the well-documented earliest record of the genus Australopithecus. 66,67 In contrast to their sparse record at Lothagam, hominins are relatively common at Kanapoi, represented by about 50 specimens, which constitute almost 9% of the 583 described mammals. Most of the Kanapoi fossils derive from tightly dated horizons between 4.17 and 4.12 Ma. Australopithecus appears at Kanapoi in a context that has very different fauna from that of the earlier deposits at Lothagam. The Kanapoi mammalian fauna lacks several taxa that were abundant in earlier Lothagam deposits. The amphicyonid carnivorans, the elephantids Stegotetrabelodon and Primelephas, the rhinocerotid Brachypotherium, the giraffid Paleotragus, and the previously abundant boselaphin bovids such as Tragoportax are all gone from the record. Kanapoi provides evidence of the first radiation of endemic African carnivorans during the Pliocene, including taxa such as Parahyaena, Dinofelis, Homotherium, and Felis. 68 At Kanapoi, grazing taxa such as Nyanzachoerus, Notochoerus, Eurygnathohippus, Loxodonta, Elephas, and Anancus outnumber browsing taxa (for example, Aepyceros, Deinotherium, andgiraffa). However, in terms of numbers of specimens, browsers are more abundant among the identified specimens than are grazers. 65 Kanapoi has also yielded a noteworthy record of micromammals, particularly useful indicators of paleoenvironments. 67,70 The rodent fauna is dominated by species of the gerbil Tatera and murines, and resembles the younger fauna from the lower Omo Valley. 69,70 Interestingly, at the generic level, the Kanapoi fossil rodents are similar to the modern rodent fauna from the south Turkana region, and suggest a degree of taxonomic stability in rodents from the Pliocene to the present. Harris and Leakey interpret the Kanapoi fossil mammals associated with Australopithecus anamensis as indicating a mixture of woodlands and grasslands, but with a predominance of wooded habitats. 17 Wynn s study of paleosol stable isotopes also paints a complex mosaic of paleoenvironments at Kanapoi, but places the hominins in closer association to the low tree-shrub savanna vegetation in the area. 71 Rodents associated with the holotype of Australopithecus anamensis support interpretations of relatively dry and open paleoenvironments.

6 ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 259 Most of the fossil mammals at Kanapoi, including the hominins, derive from fluvial deposits separated by a lacustrine interval. This lacustrine phase, which represents the southern extent of the Pliocene Lonyumun Lake, includes more than 2,800 specimens of fossil fishes, with most species being piscivorous and molluscivorous rather than herbivorous. 72,73 The taxonomic composition of the fossil fishes suggests a well-oxygenated and nonsaline fresh- water lake. Specimens of A. anamensis were also recovered at the Area excavation in Allia Bay on the east side of Lake Turkana. 64 These fossils, mainly consisting of isolated teeth, derive from high-energy fluvial deposits near the base of the Moiti Tuff, dated to 3.97 Ma. 2 The Allia Bay hominins were collected with a large sample of fossil vertebrates, but thus far only the hominins and other primates have been described in detail. From the Allia Bay locality there are about 30 hominin specimens and 320 cercopithecids. 14,74 Cercopithecines outnumber colobines by nearly 3 to 1, which is about the same ratio of these primate subfamilies at Kanapoi. Both at Allia Bay and Kanapoi, the most abundant cercopithecid genus is Parapapio. This suggests similarities between the Australopithecus paleoenvironments at Kanapoi and Allia Bay, but the Allia Bay fauna remains to be analyzed in detail. It is noteworthy that hominins were relatively abundant in the Pliocene landscapes of Kanapoi and Allia Bay, in contrast to their sparse representation in the Late Miocene site of Lothagam. Younger Pliocene hominin specimens have also been recovered from the Kataboi and Lomekwi members of the Nachukui Formation, on the west side of Lake Turkana. These specimens include the well-known Kenyanthropus platyops cranium (KNM-WT 40000), along with maxillary and mandibular fragments and about 34 isolated hominin teeth. 75 These specimens are well constrained in age between 3.6 and 3.3 Ma, and are associated with fauna that includes Theropithecus brumpti, Kolpochoerus limnetes, Tragelaphus nakuae, and Aepyceros shungurae. These taxa suggest woodlands with patches of grassland. Other Pliocene sites on the east side of Lake Turkana have also yielded hominins and other vertebrates, but hominins are not very common. Systematic surveys to document faunal abundances on surface collections above the Tulu Bor Tuff, dated to 3.44 Ma, have shown that the most abundant families of mammals are bovids, hippos, suids, monkeys, and elephants, in that order, and that hominins make up about 0.5% of the mammalian fauna in this context. 76 The earliest artifacts in the Omo-Turkana Basin occur at about 2.4 Ma in the Shungura and Nachukui formations, and broadly coincide with the earliest specimens attributed to the genus Homo in the region. The Mursi Formation, underlying a basalt dated to about 4 Ma, has a record of about 300 fossil vertebrates, but not a single primate. 77 The Usno and Shungura formations have a total of 249 hominins from the Pliocene and Pleistocene, but most of these specimens are isolated teeth and jaw fragments. 74 Among these specimens, we have the earliest record of Paranthropus, at about 2.7 Ma from Shungura Member C. The environments available to hominins in the Pliocene Omo-Turkana Basin varied from one part of the basin to another. The lower Omo Valley remained distinct from other parts of the basin from 4 to 2 Ma, with consistently higher proportions of Tragelaphini and Aepycerotini, bovids that are associated with woodlands or ecotonal environments at the edge of woodlands and grasslands and, to some extent, Reduncini and Bovini, grazers in environments close to water. The geological formations from the east and west sides of Lake Turkana had consistently higher proportions of Alcelaphini and Antilopini than did the Omo (Fig. 3A), indicating that the lower Omo Valley was characterized by more forested and stable environments than those in other parts of the basin. The Omo paleoenvironments did change over time, but were more consistently wooded than those represented by the Koobi Fora and Nachukui formations. 78,79 It also appears that Nachukui paleoenvironments were drier than contemporaneous Koobi Fora paleoenvironments, given the higher proportions of Alcelaphini and Antilopini on the west side of the rift basin. 80 Thus, Pliocene localities in the Turkana Basin present a picture of dynamic and spatially variable environments associated with early hominins. Although grasslands were clearly an important part of the Pliocene landscape, none of the localities discussed here represents a grassland environment without the presence of nearby woodlands or forest. Likewise, none of these localities can be said to represent a closed, strictly C 3 forest ecosystem without the presence of grasses and open habitats in the vicinity. EARLY PLEISTOCENE The Pleistocene Epoch, as recently redefined, begins at about 2.6 Ma. 81 It marks the first appearance of the genus Homo and the evolution of Paranthropus in eastern Africa. The earliest artifacts in the Omo-Turkana Basin occur at about 2.4 Ma in the Shungura and Nachukui formations, and broadly coincide with the earliest specimens attributed to the genus Homo in the region. 23,82 84 In the Shungura Formation, earliest Homo and lithic artifacts occur with an increase in the abundance of grazing bovids and faunal instability at about 2.4 Ma. 85 Faunal assemblages from the Kalochoro Member of the Nachukui Formation, including

7 260 René Bobe ARTICLES Figure 4. A. Plant biomarker data from the Gulf of Aden (site 231) showing an increase in C 4 vegetation at about 3.2 Ma followed by a further shift after 2 Ma. 92 B. East African paleosol carbonate data showing an increase in C 4 biomass beginning about 2 Ma. 93 C. Relative abundance of mammals indicative of seasonally arid grasslands in the lower Omo Valley showing an increase in abundance after about 2 Ma. 34 [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] the earliest archeological localities, have abundant Antilopini, Alcelaphini, and Reduncini, all bovids indicative of grassland environments. 86 The Koobi Fora Formation has a particularly abundant fossil record in the Upper Burgi, KBS, and Okote members spanning from about 2 to 1.4 Ma. Hominins from this interval included a number of contemporaneous species: Paranthropus boisei, Homo habilis, Homo rudolfensis, and Homo erectus (or ergaster). This diversity among hominins is matched by an overall increase in mammalian diversity in the interval between 2 Ma and 1.4 Ma (Fig. 3B). Several species of grazing bovids appeared shortly after 2 Ma: Beatragus antiquus, Connochaetes gentryi, Damaliscus eppsi, Megalotragus isaaci, Pelorovis oldowayensis, Pelorovis turkanensis, and Hippotragus gigas. 87,88 Among suids, at least three species of Metridiochoerus appeared or became more abundant in the basin after 2 Ma. 89 Among monkeys, the common Theropithecus brumpti of the Lokochot and Tulu Bor members ( Ma) was replaced by T. oswaldi, a more terrestrial species of the genus. Large colobines that were common in earlier intervals of the Koobi Fora Formation disappeared by the Okote Member, about 1.6 Ma. 90 Deinotherium, the only browsing proboscidean at this time, disappeared from the Turkana record before deposition of the Okote Member at 1.6 Ma. 91 These faunal changes during the Early Pleistocene correlate with broader indications of grassland expansion. Stable isotope data from biomarkers in the Gulf of Aden and paleosol carbonates from East African localities show patterns of increasing dominance of C 4 grasslands in parallel with the increasing abundance of Alcelaphini and Antilopini in the lower Omo Valley (Fig. 4). 92,93 Increases in East African wind-transported dust found in ocean cores suggest that the time between 2 Ma and 1.5 Ma may have been an important climatic transition. 94 Thus, fossils mammals from the Early Pleistocene appear to reflect significant changes in the Omo-Turkana Basin landscape toward more open conditions than prevailed in earlier times, with extensive grasslands, including edaphic grasslands, and persistent gallery forests. The fluctuating lake that is extensively represented in the Upper Burgi and KBS members undoubtedly added environmental heterogeneity to the basin during the Plio-Pleistocene. 1 Early Pleistocene hominins, including Homo erectus, Homo habilis, Homo rudolfensis, and Paranthropus boisei, had a diverse and dynamic suite of environments available to them in the Omo-Turkana Basin. There are intriguing indications that Homo and Paranthropus may have preferred different habitats within

8 ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 261 the range of those available in the basin, but further work is needed to test this and related hypotheses regarding hominin habitat preferences. 31,34 There is also evidence that hominins expanded the range of environments they occupied during the early part of the Pleistocene. 95 PATTERNS OF FAUNAL CHANGE Much debate has focused on the question of climate as a driver of human evolution, and several hypotheses have been proposed to explore such links. Among these, Vrba s turnover pulse hypothesis 96,97 and Potts variability selection hypothesis 98,99 have generated considerable discussion and research. The Omo-Turkana Basin, with its rich record of well-dated fossil mammals, has provided critical evidence to test hypotheses linking climate change to human evolution. Behrensmeyer and colleagues 100 analyzed the entire record of Pliocene and Pleistocene mammals from the Omo-Turkana Basin and found patterns of prolonged change and turnover rather than any single pulse of speciation and extinction. A reanalysis of the larger mammals from the Omo-Turkana Basin between 4 and 1 Ma documented significant changes in the relative abundances of mammalian families, as well as peaks of turnover at about 3.3, 2.7, and 1.7 Ma. 34 Although there are parallels among patterns of faunal change, human evolution, and paleoclimate records, possible connections remain tentative and much work remains to be done. 94,101,102 FUTURE RESEARCH In Africa, one of the best sources of paleoecological information is the abundant record of fossil mammals associated with relatively scarce hominin fossils. Because of more than four decades of intensive research on the geological context, stratigraphy, dating, and taxonomy of fossil vertebrates, the Omo-Turkana Basin has become one of the best places in Africa to study the ecological and environmental context of early human evolution. But the full paleoecological potential of this region has yet to be fully realized. In this regard, it is important to develop criteria to widely share data from diverse research projects working in the basin. A database of published fossil mammals already exists and is freely available (Box 1), but data sharing among different projects working in the basin remains limited. It is important to improve the chronostratigraphic provenience data of many specimens. Further work in ecomorphology, as well as integrating ecomorphology with studies of stable isotopes, would provide alternative ways to assess the evolution of faunas associated with fossil hominins. The faunal findings discussed here have provided valuable insights into the biotic history of East African mammals and the environments associated with early humans, but major questions remain to be fully answered. What is the relative importance of global climate change as opposed to local environmental shifts in driving mammalian evolution? What role has regional volcanism played in shaping floral and faunal communities? Did hominin taxa such as Homo and Paranthropus occupy different habitats within the broader context of Plio-Pleistocene environments? How did different biotic and abiotic variables, such as interspecific competition, vegetation, climate, volcanism, and hydrology interact to shape paleocommunity associations of hominins and other mammals? Although much work into these questions has been done, more comprehensive integration of paleobiological, geological, and climatic data at different temporal and geographical scales remains a challenging goal for future research. ACKNOWLEDGMENTS I thank John Fleagle and Meave Leakey for inviting me to submit this contribution. John Fleagle, Meave Leakey, Kay Behrensmeyer, David Patterson, Victor Iminjili, Norman Thomson, and three anonymous reviewers provided useful comments on an earlier version of this paper. I am most thankful to the staff at the National Museums of Kenya for their kindness and generosity during more than a decade of my research in the Turkana Basin and at the National Museums of Kenya. REFERENCES 1 Feibel C A geological history of the Turkana Basin. Evol Anthropol 20(6):xx xx. 2 Brown FH, McDougall I Geochronology of the Turkana Depression. Evol Anthropol 20(6):xx xx. 3 Brown FH, Feibel CS Stratigraphy, depositional environments and palaeogeography of the Koobi Fora Formation. In: Harris JM, editor. Koobi Fora Research Project, vol 3. The fossil ungulates: geology, fossil artiodactyls, and paleoenvironments. Oxford: Clarendon Press. p Feibel CS, Harris JM, Brown FH Palaeoenvironmental context for the late Neogene of the Turkana Basin. In: Harris JM, editor. Koobi Fora Research Project, vol 3. The fossil ungulates: geology, fossil artiodactyls, and paleoenvironments. Oxford: Clarendon Press. p de Heinzelin J, editor The Omo Group. Tervuren: Musée Royale de l Afrique Central. 6 Behrensmeyer AK, Isaac GL Geological context and paleoenvironments. In: Isaac GL, editor. Koobi Fora Research Project, vol 5. Plio- Pleistocene archaeology. Oxford: Clarendon Press. p Stern N, Porch N, McDougall I FxJj43: a window into a 1.5 million-year-old palaeolandscape in the Okote Member of the Koobi Fora Formation, Northern Kenya. Geoarchaeology 17: Lepre CJ, Quinn RL, Joordens JCA, Swisher CC, Feibel CS Plio-Pleistocene facies environments from the KBS Member, Koobi Fora Formation: implications for climate controls on the development of lake-margin hominin habitats in the northeast Turkana Basin (northwest Kenya). J Hum Evol 53: Coppens Y, Howell FC, Isaac GL, Leakey RE, editors Earliest man and environments in the Lake Rudolf Basin: stratigraphy, paleoecology, and evolution. Chicago: University of Chicago Press. 10 Leakey MG, Leakey RE, editors Koobi Fora Research Project, vol 1. The fossil hominids and an introduction to their context, Oxford: Clarendon Press. 11 Harris JM, editor Koobi Fora Research Project, vol 2. The fossil ungulates: Proboscidea, Perissodactyla, and Suidae. Oxford: Clarendon Press. 12 Harris JM, editor Koobi Fora Research Project, vol 3. The fossil ungulates: geology, fossil artiodactyls, and paleoenvironments. Oxford: Clarendon Press. 13 Wood BA Koobi Fora Research Project, vol 4. Hominid cranial remains. Oxford: Clarendon Press. 14 Jablonski NG, Leakey MG, editors Koobi Fora Research Project, vol 6. The fossil monkeys. San Francisco: California Academy of Sciences. 15 Black CC, Krishtalka L Rodents, bats, and insectivores from the Plio-Pleistocene sediments to the east of Lake Turkana, Kenya. Contrib Sci 372: Harris JM, Brown FH, Leakey MG Stratigraphy and paleontology of Pliocene and

9 262 René Bobe ARTICLES Pleistocene localities west of Lake Turkana, Kenya. Los Angeles: Natural History Museum of Los Angeles County. 17 Harris JM, Leakey MG, editors Geology and vertebrate paleontology of the early Pliocene site of Kanapoi, northern Kenya. Los Angeles: Natural History Museum of Los Angeles County. 18 Leakey MG, Harris JM, editors Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. 678 p. 19 Howell FC, Coppens Y An overview of Hominidae from the Omo succession, Ethiopia. In: Coppens Y, Howell FC, Isaac GL, Leakey RE, editors. Earliest man and environments in the Lake Rudolf Basin. Chicago: University of Chicago Press. p Wesselman HB The Omo micromammals: systematics and paleoecology of early man sites from Ethiopia. Contrib Vertebrate Evol 7: Coppens Y, Howell FC, editors Les Faunes Plio-Pléistocène de la Basse Vallée de l Omo (Ethiopie): les Périssodactyles, les Artiodactyles. Paris: CNRS. 22 Eck GG, Jablonski NG, Leakey MG, editors Les faunes Plio-Pléistocène de la basse vallée de l Omo (Éthiopie). Tome 3: Cercopithecidae de la Formation de Shungura. Paris: CNRS. 23 Suwa G, White TD, Howell FC Mandibular postcanine dentition from the Shungura Formation, Ethiopia: crown morphology, taxonomic allocations, and Plio-Pleistocene hominid evolution. Am J Phys Anthropol 101: Alemseged Z, Bobe R, Geraads D Comparability of fossil data and its significance for the interpretation of hominin environments: a case study in the lower Omo valley, Ethiopia. In: Bobe R, Alemseged Z, Behrensmeyer AK, editors. Hominin environments in the East African Pliocene: an assessment of the faunal evidence. Dordrecht: Springer. p Eck GG The effects of collection strategy and effort on faunal recovery: a case study of the American and French collections from the Shungura Formation, Ethiopia. In: Bobe R, Alemseged Z, Behrensmeyer AK, editors. Hominin environments in the East African Pliocene: an assessment of the faunal evidence. Dordrecht: Springer. p Boaz NT Paleoecology of early Hominidae in Africa. Kroeber Anthropol Soc Pap 50: Geraads D, Coppens Y Évolution des faunes de mammifères dans le Plio-Pléistocène de la basse vallée de l Omo (Éthiopie): apports de l analyse factorielle. C R Acad Sci Paris, série IIa 320: Alemseged Z An integrated approach to taphonomy and faunal change in Shungura Formation (Ethiopia) and its implication for hominid evolution. J Hum Evol 44: Bobe R, Eck GG Responses of African bovids to Pliocene climatic change. Paleobiol Mem Paleobiol 27(suppl): Behrensmeyer AK The taphonomy and paleoecology of Plio-Pleistocene vertebrate assemblages East of Lake Rudolf, Kenya. Bull Museum Comp Zool 146: Behrensmeyer AK The habitat of Plio-Pleistocene hominids in East Africa: taphonomic and microstratigraphic evidence. In: Jolly CJ, editor. Early hominids of Africa. London: Duckworth. p Behrensmeyer AK Taphonomy and the paleoecologic reconstruction of hominid habitats in the Koobi Fora Formation. In: Coppens Y, editor. L Environnement des Hominidés au Plio- Pléistocène. Paris: Masson. p Wesselman HB Of mice and almostmen: regional paleoecology and human evolution in the Turkana Basin. In: Vrba ES, Denton GH, Partridge TC, Burckle LH, editors. Paleoclimate and evolution with emphasis on human origins. New Haven: Yale University Press. p Bobe R, Behrensmeyer AK The expansion of grassland ecosystems in Africa in relation to mammalian evolution and the origin of the genus Homo. Palaeogeogr Palaeoclimatol Palaeoecol 207: Vrba ES The significance of bovid remains as indicators of environment and predation patterns. In: Behrensmeyer AK, Hill A, editors. Fossils in the making: vertebrate taphonomy and paleoecology. Chicago: University of Chicago Press. p Greenacre MJ, Vrba ES Graphical display and interpretation of antelope census data in African wildlife areas, using correspondence analysis. Ecology 65: Harris JM, Cerling TE Isotopic changes in the diet of African proboscideans. J Vertebrate Paleontol 16: Harris JM, Cerling TE Dietary adaptations of extant and Neogene African suids. J Zool 256: Sponheimer M, Reed KE, Lee-Thorp JA Combining isotopic and ecomorphological data to refine bovid paleodietary reconstruction: a case study from the Makapansgat Limeworks hominin locality. J Hum Evol 36: Sponheimer M, Lee-Thorp JA, DeRuyter DJ, Smith JM, van der Merwe NJ, Reed K, Grant CC, Ayliffe LK, Robinson TF, Heidelberger C Diets of southern African Bovidae: stable isotope evidence. J Mammal 84: Lee-Thorp JA, Sponheimer M, Luyt J Tracking changing environments using stable carbon isotopes in fossil tooth enamel: an example from the South African hominin sites. J Hum Evol 53: Kappelman J, Plummer T, Bishop L, Duncan A, Appleton S Bovids as indicators of Plio-Pleistocene paleoenvironments in East Africa. J Hum Evol 32: Spencer LM Dietary adaptations of Plio-Pleistocene Bovidae: implications for hominid habitat use. J Hum Evol 32: Cerling TE, Wang Y, Quade J Expansion of C4 ecosystems as an indicator of global ecological change in the Late Miocene. Nature 361: Cerling TE, Bowman JR, O Neil JR An isotopic study of a fluvial-lacustrine sequence: the Plio-Pleistocene Koobi Fora sequence, East Africa. Palaeogeogr Palaeoclimatol Palaeoecol 63: Passey BH, Levin NE, Cerling TE, Brown FH, Eiler JM High-temperature environments of human evolution in East Africa based on bond ordering in paleosol carbonates. Proc Natl Acad Sci USA 107: Cerling TE, Wynn JG, Andanje SA, Bird MI, Korir DK, Levin NE, Mace W, Macharia AN, Quade J, Remien CH Woody cover and hominin environments in the past 6 million years. Nature 476: Quinn RL, Lepre CJ, Wright JD, Feibel CS Paleogeographic variations of pedogenic carbonate d13c values from Koobi Fora, Kenya: implications for floral compositions of Plio- Pleistocene hominin environments. J Hum Evol 53: Levin NE, Brown FH, Behrensmeyer AK, Bobe R, Cerling TE Paleosol carbonates from the Omo Group: isotopic records of local and regional environmental change in East Africa. Palaeogeogr Palaeoclimatol Palaeoecol 307: McDougall I, Feibel CS Numerical age control for the Miocene-Pliocene succession at Lothagam, a hominoid-bearing sequence in the northern Kenya Rift. J Geol Soc London 156: Leakey MG, Harris JM Lothagam: its significance and contributions. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Cerling TE, Harris JM, MacFadden BJ, Leakey MG, Quade J, Eisenmann V, Ehleringer JR Global vegetation change through the Miocene/Pliocene boundary. Nature 389: Cerling TE, Harris JM, Leakey MG Isotope paleoecology of the Nawata and Nachukui Formations at Lothagam, Turkana Basin, Kenya. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Harris JM Bovidae from the Lothagam succession. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Harris JM, Leakey MG Lothagam Suidae. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Weston EM Fossil Hippopotamidae from Lothagam. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Leakey MG, Teaford MF, Ward CV Cercopithecidae from Lothagam. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Bernor RL, Harris JM Systematics and evolutionary biology of the late Miocene and early Pliocene hipparionine equids from Lothagam, Kenya. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Boisserie J-R The phylogeny and taxonomy of Hippopotamidae (Mammalia: Artiodactyla): a review based on morphology and cladistic analysis. Zool J Linnean Soc 143: Werdelin L Mio-Pliocene Carnivora from Lothagam, Kenya. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Harris JM, Leakey MG Lothagam Rhinocerotidae. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Stewart K Fossil fish remains from Mio-Pliocene deposits at Lothagam, Kenya. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p Leakey MG, Walker AC The Lothagam hominids. In: Leakey MG, Harris JM, editors. Lothagam: the dawn of humanity in eastern Africa. New York: Columbia University Press. p

10 ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin Leakey MG, Feibel CS, McDougall I, Walker A New four-million-year-old hominid species from Kanapoi and Allia Bay, Kenya. Nature 376: Harris JM, Leakey MG, Cerling TE, Winkler AJ Early Pliocene tetrapod remains from Kanapoi, Lake Turkana Basin, Kenya. In: Harris JM, Leakey MG, editors. Geology and vertebrate paleontology of the early Pliocene site of Kanapoi, northern Kenya. Los Angeles: Natural History Museum of Los Angeles County. p Patterson B A new locality for early Pleistocene fossils in north-western Kenya. Nature 212: Leakey MG, Feibel CS, McDougall I, Ward CV, Walker A New specimens and confirmation of an early age for Australopithecus anamensis. Nature 393: Werdelin L Carnivora from the Kanapoi hominid site, Turkana Basin, northern Kenya. In: Harris JM, Leakey MG, editors. Geology and vertebrate paleontology of the early Pliocene site of Kanapoi, northern Kenya. Los Angeles: Natural History Museum of Los Angeles County. p Winkler AJ Preliminary assessment of the Kanapoi micromammals. In: Harris JM, Leakey MG, editors. Geology and vertebrate paleontology of the early Pliocene site of Kanapoi, northern Kenya. Los Angeles: Natural History Museum of Los Angeles County. p Manthi FK The taphonomy of the Pliocene microfauna from Kanapoi, north-western Kenya. J Taphonomy 6: Wynn JG Paleosols, stable carbon isotopes, and paleoenvironmental interpretation of Kanapoi, Northern Kenya. J Hum Evol 39: Feibel CS Stratigraphy and depositional setting of the Pliocene Kanapoi Formation, lower Kerio valley, Kenya. In: Harris JM, Leakey MG, editors. Geology and vertebrate paleontology of the early Pliocene site of Kanapoi, northern Kenya. Los Angeles: Natural History Museum of Los Angeles County. p Stewart K Fossil fish remains from the Pliocene Kanapoi site, Kenya. In: Harris JM, Leakey MG, editors. Geology and vertebrate paleontology of the early Pliocene site of Kanapoi, northern Kenya. Los Angeles: Natural History Museum of Los Angeles County. p Wood B, Leakey MG The Turkana Basin fossil hominins and their contribution to our understanding of human evolution. Evol Anthropol 20(6):xx xx. 75 Leakey MG, Spoor F, Brown FH, Gathogo PN, Kiarie C, Leakey LN, McDougall I New hominin genus from eastern Africa shows diverse middle Pliocene lineages. Nature 410: Behrensmeyer AK, Bobe R, Campisano CJ, Levin N High resolution taphonomy and paleoecology of the Plio-Pleistocene Koobi Fora Formation, northern Kenya, with comparisons to the Hadar Formation, Ethiopia. J Vertebrate Paleontol 24(suppl):38A. 77 Drapeau M, Bobe R Renewed work in the Mursi Formation. Am J Phys Anthropol 50(suppl): Bobe R, Behrensmeyer AK, Eck GG, Harris JM Patterns of abundance and diversity in late Cenozoic bovids from the Turkana and Hadar Basins, Kenya and Ethiopia. In: Bobe R, Alemseged Z, Behrensmeyer AK, editors. Hominin environments in the East African Pliocene: an assessment of the faunal evidence. Dordrecht: Springer. p Bobe R, Leakey MG Ecology of Plio-Pleistocene mammals in the Omo-Turkana Basin and the emergence of Homo. In: Grine FE, Fleagle JG, Leakey RE, editors. The first humans: origins of the genus Homo. Dordrecht: Springer. p Harris JM, Leakey MG The faunal context. In: Walker A, Leakey RE, editors. The Nariokotome Homo erectus skeleton. Cambridge: Harvard University Press. p Ogg JG, Pillans B Establishing the Quaternary as a formal international period/ system. Episodes 31(2): Merrick HV, De Heinzelin J, Haesaerts P, Howell FC Archaeological occurrences of Early Pleistocene age from the Shungura Formation, Lower Omo Valley, Ethiopia. Nature 242: Roche H, Delagnes A, Brugal JP, Feibel C, Kibunjia M, Mourre V, Texier PJ Early hominid stone tool production and technical skill 2.34 Myr ago in West Turkana, Kenya. Nature 399: Prat S, Brugal J-P, Tiercelin J-J, Barrat J-A, Bohn M, Delagnes A, Harmand S, Kimeu K, Kibunjia M, Texier P-J, Roche H First occurrence of early Homo in the Nachukui Formation (West Turkana, Kenya) at Myr. J Hum Evol 49: Bobe R, Behrensmeyer AK, Chapman RE Faunal change, environmental variability and late Pliocene hominin evolution. J Hum Evol 42: Brugal J-P, Roche H, Kibunjia M Faunes et paléoenvironnements des principaux sites archéologiques plio-pléistocènes de la formation de Nachukui (Ouest-Turkana, Kenya). Comptes Rendus Palevol 2: Harris JM Family Bovidae. In: Harris JM, editor. Koobi Fora Research Project, vol 3. The fossil ungulates: geology, fossil artiodactyls, and paleoenvironments. Oxford: Clarendon Press. p Bobe R The evolution of arid ecosystems in eastern Africa. J Arid Env 66: Harris JM Family Suidae. In: Harris JM, editor. Koobi Fora Research Project, vol 2. The fossil ungulates: Proboscidea, Perissodactyla, and Suidae. Oxford: Clarendon Press. p Jablonski NG, Leakey MG The importance of the Cercopithecoidea from the Koobi Fora Formation in the context of primate and mammalian evolution. In: Jablonski NG, Leakey MG, editors. Koobi Fora Research Project, vol 6. The fossil monkeys. San Francisco: California Academy of Sciences. p Harris JM Family Deinotheriidae. In: Harris JM, editor. Koobi Fora Research Project, vol 2. The fossil ungulates: Proboscidea, Perissodactyla, and Suidae. Oxford: Clarendon Press. p Feakins SJ, demenocal PB, Eglinton TI Biomarker records of late Neogene changes in northeast African vegetation. Geology 33: Wynn JG Influence of Plio-Pleistocene aridification on human evolution: evidence from paleosols of the Turkana Basin, Kenya. Am J Phys Anthropol 123: demenocal PB Climate and human evolution. Science 331: Rogers MJ, Harris JWK, Feibel CS Changing patterns of land use by Plio-Pleistocene hominids in the Lake Turkana Basin. J Hum Evol 27: Vrba ES Ecological and adaptive changes associated with early hominid evolution. In: Delson E, editor. Ancestors: the hard evidence. New York: Alan R. p Vrba ES The fossil record of African antelopes (Mammalia: Bovidae) in relation to human evolution and paleoclimate. In: Vrba ES, Denton GH, Partridge TC, Burckle LH, editors. Paleoclimate and evolution with emphasis on human origins. New Haven: Yale University Press. p Potts R Evolution and climate variability. Science 273: Potts R Variability selection in hominid evolution. Evol Anthropol 7: Behrensmeyer AK, Todd NE, Potts R, Mcbrinn GE Late Pliocene faunal turnover in the Turkana Basin, Kenya and Ethiopia. Science 278: Behrensmeyer AK Climate change and human evolution. Science 311: NRC Understanding climate s influence on human evolution. Washington DC: National Academies. 103 Damuth J The ETE database manual. Washington: Evolution of Terrestrial Ecosystems Consortium, Smithsonian Institution. 104 Werdelin L, Sanders WJ, editors Cenozoic mammals of Africa: University of California Press. VC 2011 Wiley Periodicals, Inc.