Evolutionary Anthropology 20:254–263 (2011)

ARTICLES

Fossil and Paleoenvironments in the Omo-

RENE´ BOBE

Although best known for its hominins, the Omo-Turkana Basin of EnvironmentsintheLakeRudolfBa- and is the source of one of the best records of vertebrate sin.9 (Lake Rudolf was the former, co- from the Late of . Located near the heart of the East African 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 evolution in Africa. The tions followed in a series of Koobi Omo-Turkana faunal data shed light on key questions of : What Fora monographs10–15 and volumes kinds of environments did early inhabit? How did these environments devoted to the Nachukui, Kanapoi, change over time? What is the relationship between faunal change in 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 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 through Early 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 , 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, , and issues of Key words: paleoecology; faunal analysis; Late sil vertebrate fauna has been relatively geographical scale.30 In this early Miocene; ; 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, ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 255

example, ) and (for example, buffalo) are grazers in habi- tats close to water. The Alcelaphini (for example, and ) are pri- marily grazers in open environments, while () 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 , 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 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 . Behrensmeyer suggested ley fossil (, 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 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 (for of the Turkana Basin derive from Important studies of hominin example, , 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 () 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 , 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 years ago to about 1.4 million Turkana.html. research, the Turkana Basin has years ago. The 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. Publicly 34 fields in the public database, graphic provenience records to available databases have become with each field providing, along updated geological subunits within standard tools in scientific research with other contextual information, known geological members. Second, in many areas of study, including, basic information about a fossil some of the taxonomic identifica- for example, the field of genomics, specimen: museum accession num- tions of Turkana Basin fossils have and is no excep- ber, associated specimens, geo- not been revised or updated since tion. In a partnership between the graphical location of the site, strat- they were first published two or National Museums of Kenya and the igraphic information, taxonomic three decades ago. The recent publi- Smithsonian Institution, we have designation, skeletal part, and cation of a volume on African mam- established a ‘‘living’’ faunal database degree of completeness. The parent mal evolution provides renewed that can serve as a powerful and sus- Turkana Database contains both impetus to update these records and tainable tool in the analysis of paleo- published and unpublished speci- bring them into the current taxo- ecological patterns and faunal change mens, currently totaling about nomic framework for African paleo- in the context of human evolution. 17,000 records; access to unpub- faunas.104 Third, some of the non- The Turkana Database is a speci- lished information requires permis- mammalian taxa have not been well men-based compilation of fossil sion from the Palaeontology Division studied and require thorough vertebrates from the Turkana at the National Museums of Kenya. reevaluation, although there are Basin of Kenya. This contrasts The Turkana Database was some notable exceptions, such as with other database structures that designed as a research tool, and it the fossil fishes from Kanapoi and provide lists of taxa by locality or has been used for this purpose in Lothagam. In future versions of the collection (for example, species peer-reviewed publications as well database, we plan to include all verte- occurrences), such as the Paleobi- as dissertations and student proj- brate fossils, not just mammals. With ology Database (PBDB, http:// ects. It has also become a valuable refined stratigraphic provenience, www.paleodb.org/cgi-bin/bridge.pl), tool for curators at the National updated , and inclusion of the Eurasian NOW Database Museums of Kenya (NMK) and for all fossil vertebrates, we also will (http://www.helsinki.fi/science/now/), researchers visiting the vast verte- include in the database a range of and the Smithsonian’s Human brate paleontology collections at the new ecomorphological and paleoeco- Origins Program Database. The museum. Scholars who conduct logical data derived from the fossils. Paleobiology Database includes tax- research at NMK can easily locate Currently there is no single source of onomic occurrence records for the specimens of interest and find paleoecological information of Tur- East African Mio-Pleistocene fauna appropriate comparative collections. kana Basin fossils. These data can be originally captured by the Evolu- Scholars who are planning to visit easily incorporated into the structure tion of Terrestrial Ecosystems NMK can get exact numbers and of the Turkana Database (fields for (ETE) database.100,103 The Turkana locations of specimens they wish to measurements and interpretations, Database contains searchable infor- study before they travel, and thus such as grazer, browser, mixed mation about all published speci- can plan their work ahead of time. feeder). The database will continue to mens from Lothagam (Nawata and The public database can be accessed be maintained by the National Muse- Nachukui formations), Kanapoi through the National Museums of ums of Kenya and the Smithsonian (Kanapoi Formation), West Tur- Kenya, Earth Sciences Department Institution. kana (Nachukui Formation), and (Palaeontology Division), and the Rene´ Bobe East Turkana (Koobi Fora Forma- Smithsonian Institution’s Evolution of Anna K. Behrensmeyer tion). The specimens date from the Terrestrial Ecosystems web pages: Meave G. Leakey Late Miocene to the Early Pleisto- http://www.museums.or.ke/ and http:// Emma Mbua ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 257

Parapapio, and the equid Eurygnatho- hippus. In this review, I follow Boiss- erie’s (2005) revision of hippopota- mid taxonomy in referring Lothagam specimens previously published as Hexaprotodon to the Archaeo- potamus.59 The two most abundant genera from Lothagam, Nyanzachoe- rus and Archaeopotamus, had diets that shifted over time (between the Lower and Upper Nawata Forma- tion) from C3 to a mix of C3 and C4 vegetation. The bovid Aepyceros from Lothagam had a C3 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 C3 and C4 vegetation 53 to a pure C4 diet. Boselaphin bovids of the genus Tragoportax (browsers) were also abundant at Lothagam, but essentially disappear from later African fossil samples. Today, boselaphins ( and four- Figure 2. Fossil Bovidae play an important role in paleoenvironmental research in eastern horned ) are found only in Africa. Artist’s reconstruction of from the lower Omo Valley of Ethiopia. Inset: Asia. Among carnivores, amphicyo- Tragelaphus specimen L861-1 from the lower Omo Valley. Artwork by Christina Moon. [Color nids are present in the Late Miocene figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

lowed by work under the leadership of Vincent Maglio in 1972–1973. Subse- quent field research led by and colleagues contributed to a collection of more than 2,000 fossil vertebrates. The Nawata Formation provides evidence of turnover in the Late Miocene in relation to earlier sites in eastern Africa.51 This turn- over follows the global shift in climate that resulted in the first widespread expansion of C4 grass- lands.52 Some of the Lothagam mammals show evidence of a diet.53 The most abundant families of mammals from the Nawata For- mation are the Bovidae (antelopes), (, , and their extinct ancestors), (hippos), Cercopithecidae (monkeys), and Equidae (horses), in that order.54–58 These families constitute 81% of the described mammals. At Figure 3. A. Relative abundance of Alcelaphini plus Antilopini as a percentage of all the genus level, the most common 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 taxo- taxa are the suid , the nomic diversity relative to sample size, for Bovidae from the Omo-Turkana Basin (all areas hippopotamid Archaeopotamus, the combined). Data from Bobe and coworkers78 and Bobe and Leakey.79 [Color figure can bovid Aepyceros, the cercopithecid be viewed in the online issue, which is available at wileyonlinelibrary.com.] 258 Rene´ Bobe ARTICLES at Lothagam, but not in later sam- silization in this part of East Africa. appears at Kanapoi in a context that ples from the region.60 Among rhi- Other that may be consid- has very different fauna from that of nos, the genus Brachypotherium,an ered taphonomically equivalent to the earlier deposits at Lothagam. extinct browser, is more common hominins, such as Parapapio, are The Kanapoi mammalian fauna than the ancestors of the modern much more common (107 specimens lacks several taxa that were abun- Diceros (black rhino) and Ceratothe- of Parapapio in a sample of 1,050 dant in earlier Lothagam deposits. rium (white rhino).61 Fossil fishes mammals). Establishing the reasons The amphicyonid carnivorans, the are also abundant at Lothagam and for the rarity of hominin fossils dur- elephantids and provide important paleoecological in- ing this time remains an intriguing ,therhinocerotidBra- formation regarding the major area for future research. chypotherium,thegiraffidPaleotra- bodies of water in the region.62 gus,andthepreviouslyabundant Overall, the Lothagam fossil verte- boselaphin bovids such as Tragopor- brates indicate the presence of heter- PLIOCENE tax are all gone from the record. ogeneous environments, including Kanapoi provides evidence of the first The Pliocene (5.3-2.6 Ma) is repre- , woodland and grassland in radiation of endemic African carni- sented at Lothagam (Apak and proximity to a broad river during the vorans during the Pliocene, including Kaiyumung members of the Nachu- latest Miocene, but with conditions taxa such as Parahyaena, Dinofelis, kui Formation), Kanapoi (Kanapoi becoming more open (more grass- 68 Formation), West Turkana (Kataboi ,andFelis. At Kana- lands) in the transition from the and Lomekwi members of the poi, grazing taxa such as Nyanzachoe- Lower to the Upper Member of the Nachukui Formation), East Turkana rus, Notochoerus, Eurygnathohippus, Nawata Formation about 6.5 Ma Loxodonta, , and out- (Fig. 3A). number browsing taxa (for example, How do hominins fit into this pic- Although most of the Aepyceros, ,andGiraffa). ture? Turkana hominins from this However, in terms of numbers of time are noteworthy for their rarity. Lothagam fauna is of specimens, browsers are more abun- There are only three fossil hominins dant among the identified specimens from the Mio-Pliocene of Lothagam, Late Miocene age, the than are grazers.65 an upper third , a lower inci- hominins are best Kanapoi has also yielded a note- sor, and the better known hominin considered part of the worthy record of micromammals, mandible LT 329. The two isolated particularly useful indicators of teeth derive from the Upper Member earliest Pliocene or very paleoenvironments.67,70 The rodent of the Nawata Formation and date to close to the Miocene/ between 6.5 and 5 Ma, although they fauna is dominated by species of the are probably closer to the later date; Pliocene boundary. gerbil Tatera and murines, and the hominin mandible derives from resembles the younger fauna from 69,70 the Early Pliocene Apak Member the lower Omo Valley. Interest- of the Nachukui Formation.50,63 (Lonyumun, Moiti, Lokochot, and ingly, at the generic level, the Kana- These hominins, then, derive from Tulu Bor members of the Koobi Fora poi fossil rodents are similar to the the later intervals of the Nawata Formation), and the lower Omo Val- modern rodent fauna from the south sequence and early part of the ley (Mursi and Usno formations, and Turkana region, and suggest a Nachukui Formation. Thus, although Shungura Basal Member through degree of taxonomic stability in most of the Lothagam fauna is of Member C). Abundant faunal sam- rodents from the Pliocene to the Late Miocene age, the hominins are ples derive from Kanapoi, where the present. best considered part of the earliest hominin anamensis Harris and Leakey interpret the Pliocene or very close to the Mio- appears in the record at about Kanapoi fossil mammals associated cene/Pliocene boundary. 4.2 Ma.64,65 The Kanapoi locality was with Australopithecus anamensis as The Lothagam mammals indicate first described by Patterson in the indicating a mixture of woodlands shifting environmental conditions to- 1960s. Further work by Meave and grasslands, but with a predom- ward more open environments in the Leakey and colleagues in 1994–1997 inance of wooded habitats.17 Late Miocene, but their relationship resulted in the well-documented ear- Wynn’s study of paleosol stable to the hominins is not clear. liest record of the genus Australopi- isotopes also paints a complex The rarity of hominin fossils in the thecus.66,67 In contrast to their sparse mosaic of paleoenvironments at Late Miocene of the Turkana Basin record at Lothagam, hominins are Kanapoi, but places the hominins may reflect low hominin abundance relatively common at Kanapoi, repre- in closer association to the low in the paleolandscape or, perhaps, sented by about 50 specimens, which - vegetation in factors such as prolonged life his- constitute almost 9% of the 583 the area.71 Rodents associated with tory, which would have lowered the described mammals. the holotype of Australopithecus number of individuals available for Most of the Kanapoi fossils derive anamensis support interpretations fossilization, or hominin avoidance from tightly dated horizons between of relatively dry and open of the environments that led to fos- 4.17 and 4.12 Ma. Australopithecus paleoenvironments. ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 259

Most of the fossil mammals at with fauna that includes Theropi- woodlands or ecotonal environments Kanapoi, including the hominins, thecus brumpti, Kolpochoerus lim- at the edge of woodlands and grass- derive from fluvial deposits sepa- netes, Tragelaphus nakuae,andlands and, to some extent, Reduncini rated by a lacustrine interval. This Aepyceros shungurae.Thesetaxa and Bovini, grazers in environments lacustrine phase, which represents suggest woodlands with patches of close to water. The geological forma- the southern extent of the Plio- grassland. tions from the east and west sides of cene Lonyumun Lake, includes Other Pliocene sites on the east Lake Turkana had consistently more than 2,800 specimens of fos- side of Lake Turkana have also higher proportions of Alcelaphini sil fishes, with most species being yielded hominins and other verte- and Antilopini than did the Omo piscivorous and molluscivorous brates, but hominins are not very (Fig. 3A), indicating that the lower rather than herbivorous.72,73 The common. Systematic surveys to Omo Valley was characterized by taxonomic composition of the fos- document faunal abundances on sur- more forested and stable environ- sil fishes suggests a well-oxygen- face collections above the Tulu Bor ments than those in other parts of ated and nonsaline fresh- water , dated to 3.44 Ma, have shown the basin. The Omo paleoenviron- lake. that the most abundant families of ments did change over time, but Specimens of A. anamensis were mammals are bovids, hippos, suids, were more consistently wooded than also recovered at the Area 261-1 monkeys, and , in that those represented by the Koobi Fora excavation in on the east order, and that hominins make up and Nachukui formations.78,79 It also side of Lake Turkana.64 These fossils, about 0.5% of the mammalian fauna appears that Nachukui paleoenviron- mainly consisting of isolated teeth, in this context.76 ments were drier than contempora- derive from high-energy fluvial neous Koobi Fora paleoenviron- deposits near the base of the Moiti ments, given the higher proportions Tuff, dated to 3.97 Ma.2 The Allia The earliest artifacts in of Alcelaphini and Antilopini on the Bay hominins were collected with a west side of the rift basin.80 large sample of fossil vertebrates, but the Omo-Turkana Basin Thus, Pliocene localities in the thus far only the hominins and other occur at about 2.4 Ma in Turkana Basin present a picture of primates have been described in dynamic and spatially variable envi- detail. From the Allia Bay 261-1 lo- the Shungura and ronments associated with early homi- cality there are about 30 hominin Nachukui formations, nins. Although grasslands were clearly specimens and 320 cercopithe- animportantpartofthePliocene cids.14,74 Cercopithecines outnumber and broadly coincide landscape, none of the localities dis- colobines by nearly 3 to 1, which is with the earliest cussed here represents a grassland about the same ratio of these pri- specimens attributed to environment without the presence of mate subfamilies at Kanapoi. Both nearby woodlands or forest. Likewise, at Allia Bay and Kanapoi, the most the genus Homo in the none of these localities can be said to abundant cercopithecid genus is Par- region. represent a closed, strictly C3 forest apapio. This suggests similarities ecosystem without the presence of between the Australopithecus paleo- grasses and open habitats in the environments at Kanapoi and Allia vicinity. The Mursi Formation, underlying Bay, but the Allia Bay fauna remains a basalt dated to about 4 Ma, has a to be analyzed in detail. It is note- record of about 300 fossil verte- EARLY PLEISTOCENE worthy that hominins were relatively brates, but not a single .77 abundant in the Pliocene landscapes The Pleistocene Epoch, as recently The Usno and Shungura formations 81 of Kanapoi and Allia Bay, in con- redefined, begins at about 2.6 Ma. have a total of 249 hominins from trast to their sparse representation It marks the first appearance of the the Pliocene and Pleistocene, but in the Late Miocene site of Lotha- genus Homo and the evolution of most of these specimens are isolated gam. Paranthropus in eastern Africa. The teeth and jaw fragments.74 Among Younger Pliocene hominin speci- earliest artifacts in the Omo-Turkana these specimens, we have the earliest mens have also been recovered Basin occur at about 2.4 Ma in the record of Paranthropus, at about 2.7 from the Kataboi and Lomekwi Shungura and Nachukui formations, Ma from Shungura Member C. members of the Nachukui Forma- and broadly coincide with the ear- tion, on the west side of Lake Tur- The environments available to liest specimens attributed to the ge- 23,82–84 kana. These specimens include the hominins in the Pliocene Omo-Tur- nus Homo in the region. In well-known platyops kana Basin varied from one part of the , earliest cranium (KNM-WT 40000), along the basin to another. The lower Omo Homo and lithic artifacts occur with with maxillary and mandibular Valley remained distinct from other an increase in the abundance of fragments and about 34 isolated parts of the basin from 4 to 2 Ma, grazing bovids and faunal instability hominin teeth.75 These specimens with consistently higher proportions at about 2.4 Ma.85 Faunal assemb- are well constrained in age between of Tragelaphini and Aepycerotini, lages from the Kalochoro Member of 3.6 and 3.3 Ma, and are associated bovids that are associated with the Nachukui Formation, including 260 Rene´ Bobe ARTICLES

Figure 4. A. Plant biomarker data from the Gulf of Aden (site 231) showing an increase in C4 vegetation at about 3.2 Ma followed by a 92 93 further shift after 2 Ma. B. East African paleosol carbonate data showing an increase in C4 biomass beginning about 2 Ma. C. Rela- tive 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, after 2 Ma.89 Among monkeys, the wind-transported dust found in ocean have abundant Antilopini, Alcela- common brumpti of cores suggest that the time between 2 phini, and Reduncini, all bovids in- the Lokochot and Tulu Bor members Ma and 1.5 Ma may have been an dicative of grassland environments.86 (3.6 – 2.6 Ma) was replaced by important climatic transition.94 The Koobi Fora Formation has a T. oswaldi, a more terrestrial species Thus, fossils mammals from the particularly abundant fossil record in of the genus. Large colobines that Early Pleistocene appear to reflect the Upper Burgi, KBS, and Okote were common in earlier intervals of significant changes in the Omo-Tur- members spanning from about 2 to the Koobi Fora Formation disap- kana Basin landscape toward more 1.4 Ma. Hominins from this interval peared by the Okote Member, about open conditions than prevailed in included a number of contemporane- 1.6 Ma.90 Deinotherium, the only earlier times, with extensive grass- ous species: Paranthropus boisei, browsing proboscidean at this time, lands, including edaphic grasslands, , , and disappeared from the Turkana re- and persistent gallery . The (or ergaster). This di- cord before deposition of the Okote fluctuating lake that is extensively versity among hominins is matched Member at 1.6 Ma.91 represented in the Upper Burgi and by an overall increase in mammalian These faunal changes during the KBS members undoubtedly added diversity in the interval between 2 Early Pleistocene correlate with environmental heterogeneity to the Ma and 1.4 Ma (Fig. 3B). Several broader indications of grassland basin during the Plio-Pleistocene.1 species of grazing bovids appeared expansion. Stable isotope data from Early Pleistocene hominins, includ- shortly after 2 Ma: Beatragus anti- biomarkers in the Gulf of Aden and ing Homo erectus, Homo habilis, quus, Connochaetes gentryi, Damalis- paleosol carbonates from East Afri- Homo rudolfensis, and Paranthropus cus eppsi, Megalotragus isaaci, Peloro- can localities show patterns of boisei, had a diverse and dynamic vis oldowayensis, Pelorovis turkanen- increasing dominance of C4 grass- suite of environments available to sis, and gigas.87,88 lands in parallel with the increasing them in the Omo-Turkana Basin. Among suids, at least three species abundance of Alcelaphini and Antilo- There are intriguing indications that of appeared or pini in the lower Omo Valley Homo and Paranthropus may have became more abundant in the basin (Fig. 4).92,93 Increases in East African preferred different habitats within ARTICLES Fossil Mammals and Paleoenvironments in the Omo-Turkana Basin 261 the range of those available in the cological potential of this region has kindness and generosity during more basin, but further work is needed to yet to be fully realized. In this regard, than a decade of my research in the test this and related hypotheses it is important to develop criteria to Turkana Basin and at the National regarding hominin habitat preferen- widely share data from diverse Museums of Kenya. ces.31,34 There is also evidence that research projects working in the ba- hominins expanded the range of sin. 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