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FaunalChangeintheTurkanaBasinduringtheLateOligoceneandMiocene

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MeaveGLeakey

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AryehGrossman

MidwesternUniversity

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MercedesGutiérrez

TuftsUniversity

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JohnFleagle

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Faunal Change in the Turkana Basin During theLate Oligocene and MioceneMEAVE LEAKEY, ARI GROSSMAN, MERCEDES GUTIERREZ, AND JOHN G. FLEAGLE

Faunal evolution over the last 65 million years of earth’s history was dominatedby mammalian radiations, but much of this era is poorly represented in Africa.Mammals first appeared early in the Mesozoic, living alongside dinosaurs for mil-lions of years, but it was not until the extinction of dinosaurs 65 myr ago that thefirst major explosion of mammalian taxa took place. The Cenozoic (65 Ma toRecent) witnessed repeated and dynamic events involving the radiation, evolution,and extinction of mammalian faunas. Two of these events, each marking theextinction of one diverse fauna and subsequent establishment of another equallydiverse fauna, both involving advanced catarrhine primates, are recorded in sitesin the Turkana Basin, despite the poorly represented record of Cenozoic faunaselsewhere in sub-Saharan Africa. The first of these events occurred at the Oligo-cene-Miocene transition and the other at the Miocene-Pliocene transition.

Just before the Oligocene-Mioceneboundary (23 Ma), the African con-tinent, which was previously isolated,geologically contacted Eurasia. Thelate Oligocene of Africa is character-

ized by established endemic lineages,including proboscideans, empritho-pods, hyraxes, and sengis (elephantshrews). Faunas during this time werethus dominated by mammals that had

evolved on an isolated African conti-nent (Afrotheria),1–3 as well as a fewnon-Afrotherian groups such asanthracothere artiodactyls,4 primates,5

and rodents.6 After Africa joined Eura-sia, however, many of the taxacommon in the late Oligocene disap-peared and the early Miocene faunasbecame dominated by northern Eura-sian immigrants. Until recently, littlewas known about this transition dueto the paucity of sites. Thus the lateOligocene Turkana Basin sites are thuscritically important for revealing thetiming of faunal replacements thattook place as Orders of mammalsentered Africa from Eurasia inrepeated episodes that lasted fromapproximately the latest Oligocene tothe middle Miocene.Several sites in the Turkana Basin

date to the late early Miocene. Theseare important because they provide acomparison with the well-knownsites of this age from western Kenya,such as Songhor and Koru, wherediverse faunas, including numerousspecies of primates, have been recov-ered. Sites of this age are also knownin the geographically proximal areaof eastern Uganda.7 The TurkanaBasin early Miocene sites provideevidence of faunas in drier, morewooded habitats than the forestedsites that dominate western Kenya.8

The middle Miocene is importantfor the information it provides of atime when many taxa, among themKenyapithecus and Giraffokeryx, beganto take on recognizable modern char-acteristics, just prior to major faunalchanges in the late Miocene. Sites inthe Kenyan middle Miocene includeFort Ternan, Nakali, and localities inthe Tugen Hills, Baringo Basin. Themiddle and, especially, the late Mio-cene saw the increasing spread of C4

ARTICLE

Meave Leakey is a research professor in the Department of Anthropology, Stony BrookUniversity, New York. She has carried out field work in the Turkana Basin over the past fourdecades and currently co-leads the Koobi Fora Research Project with her daughter Louise.She is an Explorer-in-Residence of the National Geographic Society, which has funded fieldwork in East Africa for many decades and currently largely funds the KFRP field research atTurkana. Meave’s research interests include the evolution of cercopithecids and hominids andthe study of past faunal assemblages as proxies for reconstructing paleohabitats and pastenvironmental changes. Together with Richard and Louise Leakey and in collaboration withStony Brook University, Meave is developing the Turkana Basin Institute with two researchfacilities to the east and west of Lake Turkana. E-mail: Meave.leakey@stonybrook.eduAri Grossman is a paleontologist interested in the ecological context of mammalian evolu-

tion. He received his Ph.D. in Physical Anthropology at Stony Brook University, where his dis-sertation focused on the primates and other mammals from Miocene sites in West Turkana.His current work focuses on the ecological and morphological diversity of primates and othermammals from the Miocene of Africa and the Middle East, with particular emphasis on recon-structing habitats and climate at the local and regional scales. He is currently Assistant Profes-sor of Anatomy at Midwestern University in Glendale, Arizona. E-mail: agross@midwestern.eduMercedes Gutierrez is a physical anthropologist interested in understanding the Oligocene-

Miocene faunal transition in Africa and how it affected the evolution of catarrhine primates.She received her Ph.D. from Washington University in St. Louis, and currently holds a lec-turer position in the Medical School at Tufts University. E-mail: mercedes.gutierrez@tufts.eduJohn Fleagle is Distinguished Professor of Anatomical Sciences at Stony Brook University. In

1990 and 1992, he conducted paleontological field work at Fejej in southern Ethiopia; in 1995-1996, he conducted field work in Oligocene and Miocene deposits in northern Kenya. He is theauthor of Primate Adaptation and Evolution (1999, Elsevier). E-mail: John.Fleagle@stonybrook.edu

Key words: mammals; primates; fossil; Kenya; Ethiopia

VVC 2011 Wiley Periodicals, Inc.DOI 10.1002/evan.20338Published online in Wiley Online Library (wileyonlinelibrary.com).

Evolutionary Anthropology 20:238–253 (2011)

grasses, which spurred the evolutionof diverse grazing herbivores.9,10 Thiswas the interval during which the im-mediate ancestors of modern mam-malian species appeared.11

Although better known for itsPliocene and Pleistocene fauna, theTurkana Basin also has a significantlate Oligocene and Miocene fossil re-cord. Oligocene and Miocene fossilsites in the Turkana Basin12 (Fig. 1)were first described by Arambourgin 1933.13 However, the importanceof these faunas was not fully appre-ciated until discoveries in the 1980syielded new early Miocene primatetaxa.14–18 These discoveries providednew insight into this time interval,

previously largely known from sitesin western Kenya. More recentlyrenewed interest in late Oligoceneand Miocene sites in the TurkanaBasin has yielded important faunas.Here we discuss the Turkana Basinsites and their associated faunas inchronological order with emphasison their primate components.

LATE OLIGOCENE

Late Oligocene Sites

Three late Oligocene sites, all to thewest of Lake Turkana, are known inthe Turkana Basin (Fig. 1). Lokone isthe earliest. Situated in the LokicharBasin at 028 220N and 358 570E, this

site was initially discovered in the1980s by the Koobi Fora Research Pro-ject (KFRP) during a brief survey ofKanapoi just to the south. Prospectingat Lokone in 1989 by the KFRPresulted in the collection of severalcemented sandstone blocks containinglate Oligocene fossil vertebrates.19 Fivelocalities containing vertebrate fossils(LOK 1, 2, 10, 12, and 13) were identi-fied in 2007 during further surveys ofthe site by the Lokone Palaeontologi-cal Research Project (LPRP).19

Although not well dated, biostrati-graphic correlation of the Lokonefauna suggests an early-late Oligo-cene or late Oligocene age for theLokone fossiliferous strata.19 AfricanOligocene faunas that appear to datefrom slightly earlier are known fromChilga, Ethiopia, dated at 28-27Ma2,20,21 and Dogali, Eritrea, datedto a little older than 26 Ma.22 Thus,this site fills a poorly known timeinterval in the late Oligocene ofAfrica. The Lokichar Basin is one ofthe oldest sedimentary basins on thewestern side of Lake Turkana.The second late Oligocene site, Loso-

dok (also known as Lothidok), islocated at 038 210N and 358 470E. Thissite was discovered in 1948 by teamsfrom the University of California,Berkeley,23 who recovered an impor-tant fauna, including two primatespecimens, representing a new speciesof possible hominoid affinity.24,25 In1987, the KFRP prospected in the areaand found a sparse fauna that includedmore of the same higher primate.26

Losodok is situated in the Lothi-dok Range, a series of low-lying hillsrunning north-south to the west ofKalakol (Fig. 1). The geology of theLothidok Range was investigated byBoschetto and colleagues,27 who pro-posed a formal stratigraphic nomen-clature for the fossil-bearing strataexposed in 1,540 m of sedimentaryand volcanic rocks. Although no con-tinuous section was found that exposesthe entire sequence of strata, four mainunits were recognized: the KalakolBasalts, the Lothidok Formation, theLoperi Basalts, and the Turkwell Beds.Only the lowermost unit, the Kalakolbasalts, date to the late Oligocene; theremaining units are dated to the earlyand middle Miocene.The Kalakol basalts are 785 m thick

and are the principle componentexposed in the Lothidok Range.27 At

Figure 1. Map of Oligocene and Miocene localities in the Omo-Turkana Basin. [Color fig-ure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]

ARTICLE Faunal Change in the Turkana Basin 239

least 600 m below the top of the Kala-kol basalts, a fossiliferous sedimentaryunit with a thickness of approximately37-50 m, named the Eragaleit Beds,crops out along the Eragaleit andNathuraa Rivers close to the easternand southeastern slopes of LosodokHill. Near the top of the Eragaleit Bedsis a dark red conglomerate-sandstone-siltstone sequence from which the ma-jority of the Losodok fossils derive. Ba-salt horizons below and above the Era-geleit Beds have been dated, establish-ing a maximum age of 27.5 Ma and aminimum age of 24.2 Ma, respec-tively.27 Until the discovery of Lokone,the fossil taxa from the Eragaleit Bedsat Losodok represented the only knownlate Oligocene East African fauna.The third late Oligocene locality,

Nakwai, is near the Miocene site ofLoperot site, but slightly to the north(028 260N, 358 550E). Here, in 1987,Benson Kyongo noticed a concentra-tion of fossils eroding from the top ofa small hill (Fig. 2). This site, initiallyknown as ‘‘Benson’s site,’’ was exten-sively sieved over two KFRP field sea-sons in 1989 and 1990. Several well-preserved hominoid isolated teeth anda variety of small mammals and othervertebrate taxa were recovered. Morerecent field expeditions (2007-2010)surveyed in the proximity of Benson’s

site3 and recovered additional collec-tions of fossils from this site and otherlocalities nearby. Because these fossil-iferous outcrops are found in the Nak-wai area, this is the name now given tothese sites. Initial interpretation of thegeology of the area suggests that Nak-wai is an extensive series of terrestrialsediment with several fossiliferouslocalities underlying massive floodbasalts (Rassmussen, personal com-munication).

Nakwai is significantly older thanpreviously worked sites in the proxim-ity of Loperot. Faunal correlationsindicate a late Oligocene age, similarto Losodok.3 Recently, sedimentaryoutcrops between Nakwai and Lokonewere traced in an attempt to assessthe relative ages of these two impor-tant sites. It appears likely that thesetwo sites derive from one sedimentarysequence, with Nakwai overlying theolder deposits at Lokone (Rasmussen,personal communication). The faunalassemblages from the two sites areconsistent with this interpretation.

Late Oligocene NonprimateFaunas

Table 1 lists published mammalianspecies for the Oligocene sites of theTurkana Basin. These are based on pre-

liminary publications of recently discov-ered localities; it is expected that addi-tional taxa will be described. However,these preliminary results provide a gen-eral framework for understanding thefaunas of the Oligocene of Turkanaand their affinities with other sites inthe region as well as further afield.

Lokone

The vertebrate fauna from Lokoneincludes over 100 specimens of small,intermediate, and large species. Theseinclude at least five orders of actino-pterygiian fishes, crocodiles, and apaleomedusid turtle. At present, at leastsix orders of mammals are known,19,28

including a single primate. Only themammals are currently identifiedbeyond the ordinal level.Organic geochemistry and pollen

analyses demonstrate that sedimen-tation occurred in a wide, deepfreshwater lacustrine environment sur-rounded by a mosaic of semi-decidu-ous forests and humid woodlands,29

with rainfall heavier than 1,000 mm/year. This reconstruction is supportedby the fish and paleomedusid turtle,which are indicative of a freshwaterlake in the region.19 More analysis ofthis material may be useful in recog-nizing new taxa and learning moreabout regional environments.All mammals show affinities with

the Fayum fauna of Egypt, ratherthan with younger Miocene localitiesin the Turkana Basin region. Thelarger mammals include aff. Phiomia,a proboscidean, and a possible newspecies of the anthracothere Bothriog-enys. Two creodonts, Apterodon sp.aff. gaudryi, and aff. Masrasector, arealso Oligocene forms. The formerappears more derived than the threespecies of the Fayum or the early Oligo-cene European species. The latter isknown only from a tooth fragment.19 Asmall saghatheriine hyrax, possiblyrepresenting a new taxon, is alsoknown from Lokone. It, too, seemsmore similar to Oligocene Fayumforms than any later hyraxes.19 A singlerodent, Metaphiomys cf. schaubi, rep-resented by a single molar, is similarto M. schaubi found in the lowersequence of the Jebel Qatrani Forma-tion in the Fayum and in one level atthe base of the upper sequence.19,30–33

M. schaubi is also known from Zellahin Libya.19,34 It differs from Metaphi-

Figure 2. Fossil collecting at the Late Oligocene locality of Nakwai or ‘‘Benson’s Site’’.Photo courtesy of Tab Rasmussen. [Color figure can be viewed in the online issue, whichis available at wileyonlinelibrary.com.]

240 Leakey et al. ARTICLE

omys cf. beadnelli35 from the Oligo-cene site of Rukwa in Tanzania.19

Ducrocq et al.19 propose that theage of Lokone is late early Oligoceneor early late Oligocene. The probosci-dean from Lokone is very similar to

Phiomia major from Chilga, whilesome of the taxa, particularly Aptero-don and Bothriogenys, display a mor-phology more advanced than that oftheir closest relatives in the Fayumupper fossiliferous levels (approxi-

mately 34 to 29 Ma)33,36 and slightlymore advanced than that of the taxafrom Chilga, Ethiopia.2,20 A high levelof faunal continuity in the Oligocene,over distances greater than 3,000 km,is indicated by most mammal taxafrom Lokone, which have close rela-tives in the Fayum and other NorthAfrican late Oligocene sites.19 Thesimilarities of the mammals fromLokone to those of the Fayum, ratherthan younger Miocene taxa from theTurkana Basin or anywhere in EastAfrica, supports the notion that theintroduction of northern immigrantsinto East Africa had yet to begin whenthe fossils of Lokone were deposited.

Losodok and Nakwai

The most recent revisions of the fau-nas from Losodok and Nakwai areby Rasmussen and Gutierrez3 and

the subject of Gutierrez’s disserta-tion.37 Comparisons of the Nakwai

fauna with that from Losodok indi-

cate these two sites are of similar age.The well-dated late Oligocene Eraga-

leit Beds and Nakwai share at least sixspecies. Losodok and Nakwai appearto be slightly younger than Lokonebased on a somewhat more advancedfauna and the presence at Nakwai of asingle northern immigrant, Mioprio-don hodopeus, the earliest knownrecord of Carnivora in Africa.There appear to be taphonomic dif-

ferences in the fauna from Losodokand Nakwai. Losodok preserves largermammals in the rapidly depositedcoarse conglomerates, whereas at Nak-wai the majority of the mammals aresmall and derive from a fine-grainedoverbank palaeosol at the small Ben-son’s site, which was extensivelyscreened. Some of the fossils fromother localities at Nakwai are larger. Itis likely that the Losodok fauna, whichis dated between 27 and 24 Ma, iscloser to the younger age since its faunais less primitive than that found in the27 Ma Ethiopian Chilga deposits.3

There is little faunal continuitybetween Losodok and Nakwai andyounger early Miocene sites in EastAfrica. Only Mioprionodon hodopeusties Losodok and Nakwai to the Mio-cene. All other published materialbelongs to orders and families alreadypresent in the Oligocene of Africa.

TABLE 1. Faunal List of Oligocene Sites From Turkana

Taxon LokoneLosodok/Nakwai Comments

PrimatesParapithecidaeLokonepithecus manai X

Family incertae sedisKamoyapithecus hamiltoni X

RodentiaPhiomyidaeMetaphiomys cf. schaubi XDiamantomys timius X

CreodontaHyaenodontidaeApterodon sp. aff. gaudryi Xaff. Masrasector? XMlanyama sugu XHyainailouros sp. X

CarnivoraViverridaeMioprionodon hodopeus X

HyracoideaGeniohyidaeBrachyhyrax oligocenus X

PachyhyracidaeGen et sp nov. (aff.Pachyhyracina)

X Isolated teeth notdescribed in Cenozoic Mammalsof Africa as suggested in3

SaghatheriidaeSaghatheriinae indet. XThyrohyrax kenyaensis XT. microdon X

TitanohyracidaeAfrohyrax sp. nov. X Unnamed due to

poor preservationPliohyracidaeMeroehyrax kyongoi X

ArtiodactylaAnthracotheriidaeaff. Bothriogenys XBrachyodus sp. indet. X

EmbrithopodaArsinoitheriidaeArsinoitherium X

ProboscideaPalaeomastodontidaeaff. Phiomia X

MammutidaeLosodokodon losodokius X

DeinotheriidaeGen et sp nov. X Originally ssigned to

Prodeinotherium, butGutierrez37 statesthat it is a new genusand species.

GomphotheriidaeGenus indet. X

ARTICLE Faunal Change in the Turkana Basin 241

Some material may represent the ear-liest species of genera better repre-

sented in the Miocene but belonging to

orders well known in the Oligocene of

Africa. For example, the thryonomioid

rodent Diamantomys is very common

in the early Miocene. The earliest spe-

cies of this genus, D. timius, is from

Losodok.3 While this genus is previ-

ously unknown in the Oligocene, the

thryonomioids are well known from

the Fayum of Egypt. Therefore, Dia-

mantomys timius does not represent

an immigration from Eurasia.Like the Fayum deposits, both Loso-

dok and Nakwai have a diverse hyrax

fauna. These include species of some

genera previously unknown later than

the Oligocene, such as Thyrohyrax ken-

yaensis, the tiny T. microdon, an enig-

matic hyrax (described as genus and

species nov. by Rasmussen and Gutier-

rez)3 and aff. Pachyhyrax.37 Moreover,

Rasmussen and Gutierrez described

primitive species of genera also found

in the Miocene: Brachyhyrax oligoce-nus, Meroehyrax kyongoi, and an

unnamed, probably new species attrib-

uted to Afrohyrax. Poor preservation of

the material prevents Rasmussen and

Gutierrez from naming a new species.

Meroehyrax batae is known from

Rusinga and Bukwa. Brachyhyrax

aequatorialis is a rare taxon docu-

mented from Songhor and Napak,38,39

while Afrohyrax championi was origi-

nally described at Moruorot by Ara-

mbourg13 and has since been recog-

nized in sites such as Rusinga, Song-

hor, Bukwa, and Maboko Island.3 A.championi was reconstructed by

Whithworth40 as a cursorial animal

suggestive of open habitats. There are

no described postcrania of the new spe-

cies from either Losodok or Nakwai to

indicate whether this was also the case

in Afrohyrax sp. nov.All other taxa from Losodok and

Nakwai are typical Oligocene taxa.These include an indeterminate spe-cies of Arsinotherium, a large Oligo-cene form that is not known beyondthe Oligocene. In addition, there areseveral proboscideans; Losodokodonlosodokius is very likely the earliestmammutid recorded. Some materialfrom Nakwai originally placed byRasmussen and Gutierrez3 in Prodei-

notherium may represent a new genusand species of a new subfamily.37

Deinotheres include Chilgatheriumharrisi, previously known from Chilgain Ethiopia.2 There are also speci-mens assigned to Gomphotheriidaeindeterminate. There are two creo-donts from Losodok: Hyainailourussp. and a new genusMlanyama.

Most known Oligoceneorders actually diversifiedin the early Miocenerather than beingreplaced, the exceptionbeing the extinction ofembrithopods and thetaxonomic decline of thehyraxes. Additionally,various northernimmigrants appeared ina piecemeal fashion, notsimultaneously, withcarnivores apparentlybeing the first to enterAfrica in the lateOligocene.3

Late Oligocene Primates

Kamoyapithecus hamiltoni is fromLosodok and Nakwai. This enigmaticprimate from the late Oligocene is typ-ically regarded as a catarrhine,41 but itsrelationships with Miocene cercopithe-coids and hominoids is unclear.Kamoyapithecus retains many primi-tive features similar to Aegyptopithecusfrom the early Oligocene of Egypt, suchas the cross-sectional morphology ofthe upper canine, but differs fromAegyptopithecus in its thicker enameland more robust and flatter upperteeth.3 Other similarities with primitiveOligocene stem catarrhines include itsrelatively broad upper molars, rela-tively narrow trigon, a broad lingualcingulum, M2 with a large hypoconeset close to the trigon, and crowns inwhich the buccal part is distinctlyshorter than the lingual moiety.26,41

Gutierrez37 describes three otherprimates from Losodok and Nakwai.

These include several teeth that areassigned to Propliopithecus sp., a ge-nus from the Fayum, which, apartfrom a single specimen from Mal-embe in Angola,42 is previouslyunknown in sub-Saharan Africa.A new parapithecid primate, Lokone-

pithecus manai, was recently namedfrom Lokone.28 This taxon is quiteprimitive compared to the Fayum para-pithecids of the upper Jebel QatraniFormation.28 The authors suggest thatit is perhaps a relict species that per-sisted into the later part of the Oligo-cene.

Discussion

Before the discovery of theseTurkana Basin sites there was nofossil record of African faunas imme-diately prior to the Oligocene-Miocene boundary.5 These late Oli-gocene faunas, together with theslightly earlier fauna from Chilga,Ethiopia, provide a relatively contin-uous record from 27 Ma to close to23 Ma, and inform the nature of thechange from the Oligocene to theMiocene. Rasmussen and Gutierrez3

proposed the name African Mid-Tertiary Event (AMTE) for this fau-nal change, suggesting that this wasa rather rapid transition. However,the changes were likely to have beenmore complex and to have includedseveral different processes ratherthan a single event. Most known Oli-gocene orders actually diversified inthe early Miocene rather than beingreplaced, the exception being theextinction of embrithopods and thetaxonomic decline of the hyraxes.Additionally, various northern immi-grants appeared in a piecemeal fash-ion, not simultaneously, with carni-vores apparently being the first toenter Africa in the late Oligocene.Why changes in the endemic groupsoccurred as they did, and what proc-esses led to migration of certain Eur-asian taxa before or after othersarrived in Africa is still a matter forfurther research.In-depth ecological reconstructions

of the Losodok and Nakwai sites arelacking, mainly due to the scarcityof nonmammalian fossils and thelow abundance of remains recoveredso far.37 Large terrestrial mammalsdominate the combined Losodok and

242 Leakey et al. ARTICLE

Nakwai localities. The only previ-ously published mammals that maybe easily assigned to more arborealhabitats are Kamoyapithecus andperhaps Mioprionodon. Brachyodusand Arsinoitherium and some of theproboscideans are often associatedwith the presence of water. In con-trast, the Fayum forest43 has more pri-mates and other arboreal taxa. How-ever, Gutierrez’s dissertation,37 whichincludes new undescribed mammalsfrom Nakwai and Losodok, preliminar-ily compared the mammals of theupper levels of the Fayum and thosefrom the early Miocene of Songhor tothe combined Losodok and Nakwaifaunal record. Her conclusions indicatea higher-level taxonomic and ecologicsimilarity between the upper levels ofthe Fayum and Losodok and Nakwai,but not between either one and Song-hor. The collection from Songhor, as isconsistent with previous works,appears to sample a more forestedenvironment, while in the other twoOligocene faunas are consistent with aclosed woodland type of environment.Nevertheless, until more fossils are col-lected and a more detailed taphonomicanalysis is performed, a preliminaryinterpretation of the Losodok and Nak-wai habitats is consistent with wood-lands and the presence of water eitherfluvial or lacustrine.

EARLY MIOCENE

Early Miocene Sites

The early Miocene localities at Mor-uorot and Loperot were first noted inthe 1930s13 1940s, respectively.44

They were extensively collected byexpeditions from the University ofCalifornia,23–25,45,46 but primates ofthis age were not found in the Tur-kana Basin until much later. EarlyMiocene localities are now knownboth on the eastern and westernshores of the lake, and almost allhave yielded catarrhine primates. Thefact that each site has a distinctivestratigraphy suggests that they mostlikely are depositionally unrelated toeach other. The majority of the Tur-kana Basin Miocene sites date tobetween 18 and 17 Ma, althoughKajong, to the east of the lake,appears to be slightly earlier than this.Thus, all of the sites appear to date tothe latest early Miocene.12,27,47,48

East of the lake, five early Miocenesites are known, four to the west orsouthwest of Lake Chew Bahir, andone near the southern end of Lake Tur-kana (Fig. 1). Harris and Watkins47 dis-covered the site of Buluk, on the south-ern end of the Suregei plateau (Fig. 3).Following Harris and Watkins’47 initialreport of fossils at Buluk, the site wasresurveyed in 1983 by the KFRP. Exten-sive fossil remains were recovered,including more than two species ofhominoid and one cercopithecoid (Ta-ble 2).14,18 The geology of Buluk, a smallexposure of claystones with coarsesandstones and conglomerate channelfills in the Buluk Member of the BakateFormation, has been described byWatkins.49 The site is dated at about 17Ma.50 This site has produced the great-est diversity of early Miocene taxafrom east of Lake Turkana.

There are several early Miocene sitesnorth of Buluk in both northern Kenyaand southern Ethiopia (Fig. 1). The areanear Fejej, in southern Ethiopia, con-tains a mosaic of scattered sedimentarydeposits ranging from Oligocenethrough Pleistocene.51–53 The Miocenedeposits (Fig. 4), very near the Kenyaborder, have yielded a variety of mostlylarge mammals similar to those ofBuluk, as well as numerous remains ofplant fossils, including wood, fruit, andseeds.48,54–56 These deposits, assignedto the Bakate Formation, have an esti-mated age of greater than 16.2 Mabased on a dated basalt.54

Just south of the Fejej Miocenedeposits are several patches of simi-lar-aged fossiliferous deposits innorthern Kenya that were firstreported by Watkins49 and later exam-ined more extensively in 1995 and1996.48,57 These sites, like those fromBuluk, have an approximate age of 17Ma.50,58 The early Miocene sedimentsunconformably overlie older Oligo-cene rocks of the Nabwal and Langa-ria Formations. The sites have namesdenoting the region, but not the geo-logical formations or units yieldingthe fossils. The strata lie stratigraphi-cally below the basalt that forms thebase of the Buluk sequence. Both theNabwal site and the Irile site haveyielded a small fauna, including pri-mates, of mammals that are broadlysimilar to those reported fromBuluk.48 In 2004, excavations at Bulukand Nabwal led to the recovery ofadditional primate and other mamma-lian faunas from these localities.59

About 150 km to the south ofBuluk, Williamson and Savage60

reported a fauna from the KajongFormation, northeast of Loiyangalaninear the southern end of Lake Tur-kana. It is likely to be over 19 Ma.12

This site (formerly Mwiti) wasinitially surveyed by the KFRP in1973. Several fossils were discoveredincluding two proboscideans, one arelatively complete skull. Unfortu-nately, subsequent work by Savage,

Figure 3. The early Miocene site of Buluk, East of Lake Turkana. [Color figure can beviewed in the online issue, which is available at wileyonlinelibrary.com.]

ARTICLE Faunal Change in the Turkana Basin 243

Coryndon and Williamson did notproduce many additional fossils.To the west of Lake Turkana, the

early Miocene sites are in generallarger than those to the east andhave produced a greater diversity ofmammalian species (Fig. 1, Table 3).Five sites are known, the majoritydating to �17 Ma. There are twosites of this age in the LothidokRange, Kalodirr and Moruorot.The site of Kalodirr (Fig. 5) was

discovered by the KFRP in 1985when Kamoya Kimeu found thealmost complete skull and mandibleof a previously unknown hominoid.The geology of Kalodirr, on the west-ern slopes of the Lothidok range,was described by Boschetto and col-leagues.27 Most of the fossils recov-ered from the Kalodirr locality werefrom the Kalodirr Member of theLothidok Formation, situated abovethe Kalakol Basalts, and the regionbetween the Kalodirr and NaserteTuffs, respectively dated at 17.5 Maand 16.8 Ma (Fig. 2).27,61

Close to Moruorot Hill, in thesoutheast of the Lothidok Range, isan early Miocene locality divided bythe river Almononet, which cutsthrough the southern end of the Loth-idok Range. In these localities, Mor-uorot North and Moruorot South, theNaserte Tuff is the highest tuff in thesection, so that the fauna from Mor-uorot is older than 16.8 Ma.27

Thirty kilometers north of Losodokthere is a small locality, Locherangan,which was surveyed, excavated, anddescribed by Anyonge.62 The middleof the sequence contains two alteredtuffs, the upper one giving an age of17.5 Ma, which is comparable to theage of Kalodirr and Moruorot. Thefossils were deposited in a lacustrinesetting with some fluviatile influence.They were recovered on the surfaceof the uppermost stratigraphic unit.62

The fossil-bearing strata extend 2 kmto the southwest of the main locality.Fossiliferous outcrops in the Loperot

area were some of the earliest to bediscovered in the Turkana Basin,63,64

but apart from early descriptions ofsome of this fauna,46,65–68 little atten-tion has been given to these Miocenesediments. Joubert69 has given theonly comprehensive account of the ge-ology of the Loperot area, but he does

TABLE 2. Faunal List for Miocene Sites West of Lake Turkana: Kalodirr and Moruorot

Taxon Kalodirr Moruorot

PrimatesDendropithecidaeSimiolus enjiessi X X

ProconsulidaeAfropithecinaeAfropithecus turkanensis X X

NyanzapithecinaeTurkanapithecus kalakolenis X ?

InsectivoraMacroscelidaeMiosengi butleri X

ErinaceomorphaErinaecidaecf. Gymnuerchinus X

RodentiaThryonomyidaeParaphiomys stromeri Xcf. Apodecter sp nov (large) I Xcf. Apodecter sp nov (large) II Xcf. Apodecter sp nov (med) X

MyophiomyidaeElmerimys woodi X X

Pedetedidaecf. Megapedetes sp (small) X

Afrocricedontidaecf. Notocricetodon sp nov X

LagomorphaOchotonidaeKenyalagomys minor X

CreodontaHyaenodontidaeAnasinopa leakeyi X XIsohyaenodon andrewsi XIsohyaenodon sp. nov. Xcf. Hyainailourus X

CarnivoraAmphicyonidaeCynelos macrodon X X

BarbourfelidaeAfrosmilus turkanae X Xcf. Afrosmilus sp. nov. X

Viveridaecf. Kichechia sp nov X XGen. nov. sp. nov. X

HyracoideaTitanohyracidaeAfrohyrax championi X X

ProboscideaDeinotheriidaeProdeinotherium hobleyi X

GomphotheriidaeProtanancus macinnesi X Xcf. Gomphotherium X

PerrisodactylaChalicotheridaeGen. Indet X

RhinocerotidaeTurkanatherium acutirostratum X XRusingaceros leakeyi

ArtiodactylaX X

AnthracotheriidaeBrachyodus aequatorialis X X

Continued

244 Leakey et al. ARTICLE

not provide sections for the fossil sites.In 1987, the KFRP briefly prospectedin this area, recovering several verte-brate fossils.

Early Miocene NonprimateFaunas

The Turkana Basin early Miocenesites have yielded significant vertebratefaunas (see Leakey and Walker,14

Leakey and Leakey,15,16, Anyonge,62

and Savage and Williamson70 for pre-liminary faunal lists for Buluk, Kajong,Kalodirr, Locherangan, Loperot, andMoruorot). Table 2 is a preliminary listof mammalian taxa from Loperot andMoruorot; Table 3 is a similar list ofthose at Buluk, Fejej, Nabwal, andIrile. Relatively few detailed descrip-tions of the nonprimate mammalianfauna have been published.46,65–68,71–74

Detailed analyses and revisions of thefaunas have yet to be attempted. Thefaunal list from Kajong includes sev-eral taxa, but the most complete aretwo proboscidean specimens, a com-plete skull and mandible of Archaeobe-lodon filholi73 and a left upper molarassigned to Gomphotherium sp.74

Grossman75 recently completed anal-yses of the Kalodirr fauna and a revi-sion of the Moruorot fauna as thetopic of his doctoral dissertation.Grossman’s unpublished thesis iden-tified a number of new genera andspecies, some of which may repre-sent the earliest occurrence in sub-

Saharan Africa of Eurasian lineages(for example, Listriodon), whileothers are the oldest known mem-bers of endemic African mammals(such as Macroscelidinae).72,75

A comparison of Tables 2 and 3shows that there are differencesamong the sites on either side of thelake, the most apparent being amongthe Suidae. The pigs from Kalodirrinclude Listriodon, Kenyasus, andNamachoerus.75,76 These are lacking atBuluk, where the suid community is

composed of Lopholistriodon, Ngur-uwe, and Megalochoerus.77,78 Addition-ally, cercopithecoid primates are foundonly at Buluk and Nabwal. Buluk andNabwal lack very small mammals, sothese cannot be compared directly.Without detailed paleoenvironmen-

tal reconstructions, these differencesare hard to explain. However, recentwork describing silicified tree trunksup to several meters in diameterfrom the top of Sibiloit and fromBuluk and Nabwal56 show that largetrees were present at this time atthese localities. These contrast, tosome extent, with Grossman’s75 analy-ses of the mammalian faunas of Kalo-dirr and Moruorot, which suggestedrelatively more open-canopy wood-lands at both sites. Fossil leaves fromthe Kalodirr Tuffs also appear to bethose of broad-leaved plants, somesuggesting rather wet conditions.Other studies suggest that there wereswamps in the area.61,79 In contrast,Madden23 suggested that the paleoen-vironment was open and semi-arid.Grossman’s75 analyses of the Mor-

uorot and Kalodirr faunas indicatewooded, relatively open habitats atboth sites, in contrast to the forestedenvironments suggested by the fau-nas from sites of similar age inWestern Kenya near Lake Victoria(Fig. 6). The western Kenya sites rep-resent a temporal succession with

TABLE 2. (Continued)

Taxon Kalodirr MoruorotSivameryx africanus X X

SuidaeCainochoerinaeKenyasus rusingensis X X

LopholistriodontinaeNamachoerus moruoroti X X

ListriodontinaeListriodon jeanneli X X

SanitheriidaeDiamantohyus africanus X X

TragulidaeDorcatherium chappuisi X XDorcatherium pigotti X XAfrotragulus moruorotensis X X

GiraffoideaCanthumeryx sirtensis X XGen et sp nov I XGenus et sp nov II X

ClimacoceratidaeClimacoceras cf. africanus X

Figure 4. FJ-18, an early Miocene site near Fejej in southern Ethiopia. [Color figure can beviewed in the online issue, which is available at wileyonlinelibrary.com.]

ARTICLE Faunal Change in the Turkana Basin 245

apparent differences between olderand younger sites.38,80 In particular,the faunas from the older sites(Songhor, Koru, Legetet) are markedlydifferent from those of the Turkanalocalities and share very few taxa. Theyounger fauna from Rusinga hassome similarities to that from Kalo-dirr and Moruorot, although it is stillmore similar to the fauna from Song-hor than to that of the Turkanasites.75 These differences betweenRusinga and the Turkana sites appearto be related to habitat differences.For example, macroscelideans arepresent at both Rusinga and Kalodirr,but those found at Rusinga are rhyn-chocyonines, which inhabit closed-canopy habitats81; at Kalodirr, onlymacroscelidines, an open habitat sub-family, are present.72

Early Miocene Primates

The early Miocene of Africa isresplendent with primitive apes andmonkeys (see Harrison,41 Miller andcoworkers,82 and Jablonski and Frost83

for recent descriptions and discus-sions). Most early Miocene primateswere known from numerous sitesnear Lake Victoria in western Kenya,and a few in eastern Uganda, firstpublished in 1929.84,85 These formedthe basis for our hypotheses abouthominoid evolution. There is con-siderable debate about the exactrelationships of early Miocenenoncercopithecoid catarrhines tomodern hominoids. Some treat allearly Miocene apes as stem homi-noids outside the modern Hominoi-dea. For example Harrison41 includesAfropithecus and Turkanapithecus inthe family Proconsulidae in the super-family Proconsuloidea (Afropithecusin the subfamily Afropithecinae andTurkanapithecus in the subfamilyNyanzapithecinae). He includes Sim-iolus in the Dendropithecoidea,another catarrhine superfamily. Wediscuss early Miocene apes as part ofthe Hominoidea, partly for brevity’ssake, since their affinity with modernapes may be due only to a lack ofderived cercopithecoid features.The sites of the Turkana Basin have

yielded at least three species of homi-noid previously unrecognized else-where. The large-bodied Afropithecus

TABLE 3. Faunal List for the Early Miocene Sites East of Lake Turkana:Buluk, Nabwal, Irile And Fejej

Taxon Buluk Nabwal Irile Fejej

PrimatesDendropithecidaeSimiolus enjiessi X

ProconsulidaeAfropithecinaeAfropithecus turkanensis X X X

Cercopithecoideaindet X X

VictoriapithecidaeNoropithecus bulukensis Xcf. Noropithecus fleaglei X

CreodontaHyaenodontidaeHyainailourus nyanzae X X Xcf. Hyainailourus X

CarnivoraAmphicyonidaeCynelos macrodon X X

FelidaeIndet X

HyracoideaGeniohyidaeBrachyhyrax cf. aequatorialis X

ProboscideaDeinotheriidaeProdeinotherium hobleyi X X X X

GomphotheriidaeArchaeobelodon aff. filholi X X X Xcf. Choerolophodon X XIndet X X

PerissodactylaRhinocerotidaeTurkanatherium acutirostratum X X XBrachypotherium sp nov? XRusingaceros leakeyi XChilotheridium pattersoni XChilotheridium sp. XParadiceros muikiri Xcf. Paradiceros Xindet X X X

ArtiodactylaAnthracotheriidaeBrachyodus aequatorialis X XAfromeryx zelteni X X X

SuidaeLopholistriodontinaeLopholistriodon pickfordi X

KubanochoerinaeKubanochoerus massai Xcf. Libychochoerus XMegalochoerus cf. khinzikiberus X X XM. marymuunguae X X cfcf. Nguruwe kijiuvum X

SanitheriidaeDiamantohyus africanus X

TragulidaeDorcatherium chappuisi X X XDorcatherium pigotti X Xindet X

Giraffoideacf. Canthumeryx XIndet X X

246 Leakey et al. ARTICLE

turkanensis, with an estimated bodymass between 30 and 55 kg,41,86 andthe medium-sized Turkanapithecuskalakolensis, with males weighing�10 kg (Harrison41), are known fromrelatively complete crania. The thirdspecies, Simiolus enjiessi, is consider-ably smaller, with males estimated tohave weighed �6 kg and females �4kg.41,87,88 These represent the onlynoncercopithecoid primate taxa ofthis age in the Turkana basin,although Anyonge62 suggests that atLocherangan there may be a fourthhominoid represented by a wornupper third molar and a deciduousupper incisor that compares withthat of Limnopithecus. Cercopithe-coids of this age, as elsewhere inAfrica, are absent from most sitesbut have been recovered from Bulukand Nabwal.18,57,82

Afropithecus turkanensis [Leakey

and Leakey, 1985]

In 1985, Leakey and Walker14

reported the discovery of a new homi-noid from the Miocene site of Buluk,northern Kenya. The hominoid wasrepresented by six specimens, the

most complete being an associatedmandibular and maxillary fragment(KNM-WS 11599) and a mandibularfragment (KNM-WS 124). Because ofthe many morphological similaritiesto Sivapithecus seen in the Bulukspecimens, it was initially thoughtthat this was an early species of theEurasian Sivapithecus, known fromthe Siwaliks in Pakistan.14 Subse-quently, additional specimens of alarge ape were recovered from Kalo-dirr, on the western shores of thelake. The most complete of thesespecimens comprises a snout, facialskeleton, and frontal (KNM-WK16999; Fig. 7), and a mandible lack-ing the ascending rami (KNM-WK16840).15 The total sample of 18specimens showed the same complexof characters as the Buluk ‘‘Sivapi-thecus’’ described previously, makingit clear that only one species wasrepresented at the two sites. TheBuluk and Kalodirr large hominoidwas named a new genus and species,Afropithecus turkanensis. Subsequentprospecting at Kalodirr led to an evenlarger sample of 46 specimens of A.turkanensis. The size variation withinthe Afropithecus sample indicates that

this taxon had a considerable degreeof sexual dimorphism that can beaccommodated within a single spe-cies. Afropithecus displays a mixtureof characters, many of which areprimitive and similar to features inearly Miocene hominoids and Oligo-cene catarrhines.90,91 Features incommon with the much smaller (6-8kg) Oligocene Aegyptopithecus zeuxis,a species geologically almost twice asold from the Jebel Qatrani Forma-tion of the Fayum Depression inEgypt, appear to represent primitivecharacters retained over millions ofyears. If this interpretation is correct,then these features define the natureof the primitive facial morphology.Support for this interpretation camerecently with the discovery of a faceof a medium- sized fossil catarrhine,Saadanius hijazensis from Saudi Ara-bia (29-28 Ma),90 which displaysmany of the same primitive featuresthat are suggestive of phylogeneticcontinuity.Leakey and Walker86 suggested that

the pattern of facial and mandibularbuttressing, massive chewing muscu-lature with large strong anterior teeth,procumbent incisors supported by aprojecting premaxilla, and upper andlower canines with large stout roots,together with heavy canine wear,point to Afropithecus being a sclero-carp forager. More support for thishypothesis came from analyses ofcanine morphology.92 This combina-tion of characters is not seen in othercatarrhines, but compares with that ofthe New World pitheciines describedby Kinzey.93 Afropithecus had rela-tively thick enamel, which formed ina manner similar to that of otherMiocene hominoids, and may havepermitted the exploitation of a widervariety of food resources.94

Postcranially, Afropithecus showsmany similarities with Proconsul,and was most likely a slow-movingarboreal quadruped. The postcranialanatomy is thought to be close to theprimitive condition for hominoids.95

Turkanapithecus kalakolensis

[Leakey and Leakey, 1986]

This species is represented by a rathersmall number of individuals compris-ing the type, KNM-WK 16950, a well-preserved male cranium and mandible

Figure 5. The early Miocene site of Kalodirr in West Turkana that yielded the skulls of Afro-pithecus and Turkanapithecus. Photo courtesy of James Rossie. [Color figure can beviewed in the online issue, which is available at wileyonlinelibrary.com.]

ARTICLE Faunal Change in the Turkana Basin 247

(Fig. 7) and probably associated post-cranial elements that include a right fe-mur, proximal and distal left radius,left metacarpal I, and fragments ofphalanges, rib, and vertebrae; a frag-ment of maxilla, KNM-WK 16957; anda complete proximal phalanx, KNM-WK 16954. The type cranium (Fig. 8)is relatively complete, preserving thefacial region, partial calvaria, andexamples of all the upper teeth exceptthe incisors. It is slightly smaller thanthe type skull of Proconsul africanus,KNM-RU 7290. The associated mandi-ble preserves the mandibular bodywith the left m2 and right m3 andmuch of the left ramus.16

The cranium has a relatively shortface, a well-defined broad snout,rather small orbits, a large interorbitaldistance and a rather shallow and nar-row palate. Judging from the dentineexposure, which becomes visible withrelatively little wear, the teeth appear

to have rather thin enamel. The man-dibular body is shallow and deeper atthe symphysis. The postcranial mor-phology is neither ape-like nor mon-key-like. Turkanapithecus was mostlikely an arboreal quadruped similarin its locomotor repertoire to that ofProconsul, but possibly with enhancedclimbing abilities.95

Simiolus enjiessi

[Leakey and Leakey, 1987]

The genus Simiolus was firstdescribed in 198717 after the discov-ery of five cranial and four postcra-nial specimens of a small-bodied apeat Kalodirr. The type specimenincludes the right mandibular bodywith i1-m3, a fragment of left maxillawith the canine and P3, and most ofthe postcanine dentition. A well-pre-served gracile juvenile mandible(KNM-WK 16956) was also recov-

ered, but this unfortunately lacksmuch of the dentition. Diagnosticcharacters of the dentition of Simio-lus include the moderately high-crowned and buccolingually com-pressed female upper canines, therather triangular outline of the upperP3, the very slight buccal flare of theupper P4, the mesiodistally ratherlong upper and lower molars withelevated cusps and crests, the strongtransverse crest linking the hypoconeand metacone, the narrow and smalllower incisors in relation to the

Figure 8. The cranium of Turkanapithecuskalakolensis from Kalodirr. [Color figure canbe viewed in the online issue, which isavailable at wileyonlinelibrary.com.]

Figure 6. Habitat reconstructions of selected Miocene localities compares with modernAfrican habitats using ecological structure analysis (redrawn from Grossman75). Plot offirst two principal components is based on body mass, diet and locomotion of faunalassemblages comparing Miocene sites with modern sites and comparing Miocene siteswith each other. Solid squares: Closed canopy habitats; open triangles: open canopyhabitats; open stars: Early andMiddle Miocene localities. 1: Seredou, 2: Amani, 3: Irangi, 4:Semliki A, 5: Sokoke-Gedi, 6: Budongo, 7: Kakamega, 8: Lemera, 9: Rwenzori Forest, 10:Mount Kenya, 11: Semliki B1, 12: Legaja, 13: Jebel Mara, 14: Rwenzori, 15: Kapiti Plains, 16:Karamoja, 17: Tsavo, 18: Gabiro, 19: Banagi, 20: Rukwa, 21: Serengeti, 22: Kafue Flats.Notice that Moruorot and Kalodirr cluster withmodern open canopy sites along PC 1whileSonghor and Rusinga cluster with modern closed canopy sites. Middle Miocene Mabokoand Fort Ternan also cluster with Kalodirr and Moruorot, suggesting that some aridificationoccurred in the Lake Victoria region during the Early to Middle Miocene transition. All Mio-cene sites are distinct from modern sites along PC 2, probably reflecting differencesamong the two groups caused by a combination of floral differences and taphonomicbiases. Data for modern sites courtesy of Peter Andrews.

Figure 7. Thecraniumandarticulatedmandi-ble of Afropithecus turkanensis from Kalodirr.[Color figure can be viewed in the onlineissue, which is available at wileyonlinelibrary.com.]

248 Leakey et al. ARTICLE

lower molars, and the bilaterallycompressed lower p3 with a long andsteep honing facet.Postcranial elements of Simiolus

enjiessi have been recovered fromKalodirr, Moruorot, and Buluk, andinclude at least 13 limb bones andone vertebra. Rose and coworkers87

noted that these postcranial elementsare similar to those of other AfricanMiocene small-bodied genera, includ-ing Dendropithecus, Micropithecus,Limnopithecus, and Kalepithecus. Thefunctional morphology of the postcra-nial elements is unlike that of otherMiocene catarrhines or any extantanthropoids, resembling instead fea-tures of platyrrhine primates.87,96

Comparative analyses suggest thatalthough arboreal quadrupedalismwas an important part of the locomo-tor repertoire, additional featuresindicate some suspensory capability.

Cercopithecoidea

In the Turkana Basin, early cercopi-thecoids are described only fromBuluk and Nabwal18,57,82 and includetwo species of a new genus, Noropi-thecus.82 The Buluk cercopithecoidwas initially assigned to the subfam-ily Victoriapithecinae, and to the ge-nus Prohylobates.18 Due to the frag-mentary nature of the North AfricanProhylobates material, no clear mor-phological characters could bediscerned that would distinguishbetween the Buluk monkey, Prohylo-bates, and Victoriapithecus fromMaboko Island on Lake Victoria,western Kenya. Because the genericname Prohylobates had priority, thefifteen specimens from Buluk weretentatively assigned to this genus.18

More recent surveys at Buluk and fur-ther discoveries of Prohylobates tandyi

from Wadi Moghra, Egypt, have clari-fied some of these taxonomic issues.The Buluk cercopithecoid (Fig. 9) isnow recognized as a distinct genusand species, Noropithecus buluken-sis.82 A single cercopithecoid speci-men, a right partial mandible withthe m1 and m2 crowns, the roots ofp3-m1, and part of the mandibularbody and symphyseal region recov-ered from Nabwal57 is assigned byMiller and colleagues82 to a new spe-cies, cf. Noropithecus fleaglei (Fig. 9).

Discussion

The sites in Turkana have very dif-ferent primate assemblages from thenumerous sites in Western Kenya,such as Songhor, Koru or Rusinga.The Turkana faunas have fewer pri-mate taxa than those in westernKenya and lack any strepsirrhines,suggesting that the open woodlandsites are associated with lower pri-mate taxonomic diversity than thosein forested environments. Cercopi-thecoids are rarely found in the earlyMiocene but, where they do occur,the habitats are often inferred to beopen woodland rather than forest.75,97

Until recently, sites in western Kenyaand eastern Uganda provided all thedata we had on early hominoids. Thedifferent taxa and paleoenvironmentsin the Turkana Basin offer a freshperspective on the interpretation ofthese early hominoids.75

MIDDLE MIOCENE

Middle Miocene Sites

The Lothidok Formation includestwo Middle Miocene sites in theKalatum Member dated between13.8-12.2 Ma.27 These two sites, Eshaand Atirr, are in proximity to theMoruorot localities and stratigraphi-cally lie within the Kalatum Memberof the Lothidok Formation (Figs. 1and 2). The Esha locality is situatedalong the north-south flowingNakwal Esha River, north of EshaHill and west of Moruorot Hill (38170N, 358 480E). Atirr is situatedabout 6 km south of Moruorot Hillon the east side of the LothidokRange (38 130N and 358 510E). TheKalatum Member is believed to bebetween approximately 13.2 Ma, the

Figure 9. Fossil cercopithecoid monkeys from the early Miocene sites of Buluk and Nabwal.From top to bottom: lateral, occlusal, and medial views of the type specimens of Noropi-thecus bulukensis (left) and cf. Noropithecus fleaglei (right). Photos courtesy of Ellen Miller

ARTICLE Faunal Change in the Turkana Basin 249

age of the Kamurunyang lahar, and12.2 Ma, the age of the Loperibasalts that overlay the LothidokFormation. Since the Loperi basaltsunconformably overlay the KalatumMember, the age is likely to be closerto 13.2 Ma. Atirr is a little older than13.2 Ma, since the fossiliferous strataare directly overlaid by the typeKamurunyang lahar.

Middle Miocene NonprimateFaunas

Esha was very briefly surveyed bythe KFRP early in 1987. Approxi-mately fifty specimens were col-lected, including bovids, giraffids,gomphotheres, anthracotheres, a sin-gle suid, and a hominoid uppercanine. Atirr was also prospected inthe same year, and although fewerspecimens were collected there, thefauna included an almost completerhino cranium. The Esha and Atirrfossils were unwittingly includedwith the earlier Moruorot fauna byGrossman,75 rather than being ana-lyzed separately. We now know thatthe bovids assigned to Moruorot areactually from Esha and Atirr, andare different from the ones knownfrom Fort Ternan. This is also truefor other specimens from otherorders, such as the carnivores andthe perissodactyls, again highlightingthe importance of the Miocene sitesof the Turkana Basin. Esha and Atirrare the only middle Miocene sitesknown in the Turkana Basin. Theabsence of horses at these relativelysmall localities is consistent with anage older than 10.5 Ma.

Middle Miocene Primates

A single well-preserved hominoidspecimen was recovered from Esha,an upper canine that appears to rep-resent Kenyapithecus wickeri. Severalother tooth fragments that may beprimate were also recovered. Kenyapi-thecus is best known from FortTernan, dated at �14 Ma. It is consid-ered by some researchers to be themost likely candidate for the earliestknown African hominoid. Harrison41

includes Kenyapithecus in the Homi-noidea and the Family Hominidae.

Discussion

Esha and Atirr are the only MiddleMiocene sites known in the TurkanaBasin. Sites of this age anywhere inEast Africa are few. The faunas fromsuch sites are thus important. Therhino cranium recovered from Atirr,as well as the hominoid canine fromEsha, indicate that future field workat these sites could be rewarding.

LATE MIOCENE

Late Miocene Sites

Lothagam, situated to the south ofthe Turkwell River and to the west ofthe Napudet Range, is the only lateMiocene site known in the TurkanaBasin. Its most fossiliferous sedimentsdate from >7.4 Ma to the late Plio-cene, �3.5-3.0 Ma. Only the lowermoststrata of the Nawata Formation con-cern us here. The Nawata Formationis divided into two members, Upperand Lower, separated by a well-datedMarker Tuff (6.54 Ma). The UpperNawata unfortunately has no datedhorizons above the Marker Tuff, butthe Purple Marker, which separatesthe Upper Nawata and the overlyingApak member of the Nachukui Forma-tion is believed to be about 5 Ma,though it may be younger.11,98,99

Late Miocene NonprimateFaunas

The Lothagam sequence providesevidence of major faunal change andcorresponding habitat change thattook place between 7.5 and 5 Ma.11

Many last appearances of taxa com-mon earlier in the Miocene are docu-mented, together with first appearan-ces of lineages that dominate thelater Pliocene and Pleistocene fau-nas. Bobe100 describes the late Mio-cene Lothagam fauna in detail in thecontext of the later Pliocene andPleistocene faunas. The late Mioceneradiation of C4 grasses appears tohave been a major driving force forthis faunal turnover event, whichcorresponds to the time of the diver-gence of the ape and hominin line-ages. Analyses of stable isotopes indental enamel show C4 vegetationcontributing a significant dietary

component of many large herbivoresfor the first time in Africa.9,11,101,102

The shift to a grazing diet of C4 vege-tation was not, however, simultane-ous in the diverse herbivorous fami-lies, but occurred at different times,with the equids being the first toswitch to a full C4 diet beginning at9.9 Ma.9,10 The sequence of sitesthat, together with Lothagam, docu-ment the timing and course of thisdietary change in the most commonherbivorous lineages, includes theslightly older sites Nakali, Nachola,and Samburu Hills in the SugutaValley to the south of Lake Tur-kana.10

Late Miocene Primates

Although a rich fossil fauna hasbeen recovered from late Miocenesediments at Lothagam, only threespecimens that may represent earlyhominins are known. One of these, amandibular fragment, was recoveredby Patterson’s Harvard expedition in1965.103 A half upper molar and alower incisor were recovered by theKFRP in 1990 and 1992, respec-tively.104 In view of the extensive anddiverse faunal assemblage recoveredfrom the Nawata Formation, com-prising over 1,000 mammalian speci-mens, it is surprising, and perhapssignificant, that hominins are absentuntil a time close to 5 Ma. Monkeys,on the other hand, are relatively com-mon in the Nawata Formation.105

Over 80% are papionins, apparentlyrepresenting only one species; theremaining 20% are colobines of atleast three species. Interestingly, theselate Miocene monkeys all exhibit sim-ilar morphological characters of theirpostcranial skeleton that indicate ter-restrial locomotion. In contrast, theirdietary adaptations differ, colobinesapparently eating seeds and someleaves, and cercopithecines eatinglargely fruits.105

Discussion

Lothagam is an exceptional site forthe numerous beautifully preservedand unusually complete fossils thathave been found there. These fossils,together with accurate dating of theNawata Formation, have provided a

250 Leakey et al. ARTICLE

unique record of this significant timeinterval.

CONCLUSIONS

The late Oligocene and Miocenewere intervals during which majorevolutionary changes in mammalianfaunas occurred and modern line-ages within many mammalian Orders,including Primates, emerged. Twosignificant turnover episodes punctu-ate this time interval, one initiating atthe Oligocene-Miocene boundary andthe other in the late Miocene. Eachmarks a turning point in the evolu-tion of mammalian families andeach has relevance for the evolutionof higher primates. The formerinvolved reintegration of the Africancontinent with Eurasia resulted in theappearance of many northernmigrants into faunas previously domi-nated by endemic African taxa. As aresult, some African endemics, suchas proboscideans, were able to diver-sify and expand out of Africa. Others,such as Embrithopoda, did not sur-vive. While the northern immigrantsentered Africa only gradually, someendemics, hyracoids in particular,were unable to maintain their levelsof diversity, probably because of com-petition with pecoran artiodactyls.The latter episode heralded theappearance of many herbivorousgrazing mammals into open countryniches as a radiation of C4 grassesopened new habitats.106 The late Mio-cene turnover also saw the appear-ance of the direct ancestors of manymodern species and the disappear-ance of more archaic taxa.Each of these episodes has signifi-

cance in primate evolution. The lateOligocene-Miocene turnover wasmarked by an adaptive radiation ofstem hominoids. The presence ofKamoyapithecus in the Turkana Ba-sin, together with the recent discov-ery of Saadanius in Saudi Arabia,90

are key to an understanding of theevolution of the earliest hominoidsand cercopithecoids. The presence inthe Turkana Basin of Afropithecus,which shares certain characters withAegyptopithecus and Saadanius, isalso important in this context. Thecercopithecoids from Buluk andNabwal provide evidence of diversity

in these early monkeys. The faunasfrom the early Miocene Turkana sitesappear to derive from wooded ratherthan forested environments, and thusprovide new insights into a timeinterval in East Africa previouslyknown largely from the forested sitesof western Kenya. The TurkanaBasin late early Miocene hominoids,which include the genera Afropithe-cus, Turkanapithecus, and Simiolus,as well as the new cercopithecoidgenus Noropithecus, provide a newunderstanding of the diversity ofhominoids and cercopithecoids andtheir habitats at this time.

ACKNOWLEDGMENTS

The work described in this paperhas benefitted from the efforts ofmany people over many decades byeveryone associated with the KoobiFora Research Project, in particularBrad Boschetto, John Harris, RonWatkins, as well as John Kappelman,Tab Rasmussen, Ellen Miller, andTom Bown. This research was sup-ported in part by funds from theNational Science Foundation, TheNational Geographic Society, and theLSB Leakey Foundation. AndreaBaden, Ian Wallace, and Luci Betti-Nash assisted with the manuscript.

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