Correlation of the KHS Tuff of the Kibish Formation to volcanic ash layers at other sites, and the age of early Homo sapiens (Omo I and Omo II)

Hominin specimens Omo I and Omo II from Member I of the Kibish Formation, Ethiopia are attributed to early Homo sapiens, and an age near 196 ka has been suggested for them. The KHS Tuff, within Member II of the Kibish Formation has not been directly dated at the site, but it is believed to have been deposited at or near the time of formation of sapropel S6 in the Mediterranean Sea. Electron microprobe analyses suggest that the KHS Tuff correlates with the WAVT (Waidedo Vitric Tuff) at Herto, Gona, and Konso (sample TA-55), and with Unit D at Kulkuletti in the Ethiopian Rift Valley. Konso sample TA-55 is older than 154 ka, and Unit D at Kulkuletti is dated at 183 ka. These correlations and ages provide strong support for the age originally suggested for the hominin remains Omo I and Omo II, and for correlation of times of deposition in the Kibish region with formation of sapropels in the Mediterranean Sea. The Aliyo Tuff in Member III of the Kibish Formation is dated at 104 ka, and correlates with Gademotta Unit 15 in the Ethiopian Rift Valley.     

Stratigraphy and tephra of the Kibish Formation, southwestern Ethiopia

The Kibish Formation in southwestern Ethiopia, with an aggregate thickness of ~105m, consists of lacustrine, marginal lacustrine, and deltaic deposits. It is divided into four members numbered I to IV on the basis of erosion surfaces (disconformities) between the strata of each member. It overlies the Mursi and Nkalabong formations, the latter of which is here shown to correlate with the Shungura Formation. Tephra layers in each member allow for secure correlation between geographically separated sections on the basis of the composition of their volcanic glass. Members I, III, and IV of the Kibish Formation appear to have been deposited at the same times as sapropels S7 (197ka), S4 (104ka), and S1 (8ka) in the eastern Mediterranean Sea, respectively. We correlate the KHS Tuff of the Kibish Formation with a >154-kyr-old unnamed tuff in the Konso Formation. Tephra in Member IV may derive from Mount Wenchi, a volcano situated on the divide between the Omo and Blue Nile drainage basins. Thin-bedded sedimentary layers probably represent annual deposition reflecting rapid sedimentation (~30m/kyr) of parts of the formation. This conclusion is supported by variation in paleomagnetic inclination through a sequence of these layers at KHS. Two fossils of early Homo sapiens (Omo I and Omo II) derive from Member I. Their stratigraphic placement is confirmed by analysis of the KHS Tuff in the lower part of Member II at both fossil sites. The KHS Tuff lies above a disconformity, which itself lies above the fossils at both sites. (40)Ar/(39)Ar dates provide an estimated age of ~195kyr for these fossils. Omo III, a third fossil H. sapiens, probably also derives from Member I of the Kibish Formation and is of similar age. Hominin fossils from AHS, a new site, also derive from Member I. Hominin fossils from CHS can only be placed between 104ka and 10ka, the H. sapiens specimen from JHS is most likely 9-13kyr in age, and a partial skeleton of H. sapiens from Pelvic Corner is most likely ~6.6kyr in age.     

Sapropels and the age of hominins Omo I and II, Kibish, Ethiopia

The provenance and age of two Homo sapiens fossils (Omo I and Omo II) from the Kibish Formation in southern Ethiopia have been much debated. Here we confirm that Omo I and the somewhat more primitive-looking Omo II calvariae are from similar stratigraphic levels in Member I of the Kibish Formation. Based on (40)Ar/(39)Ar age measurements on alkali feldspar crystals from pumice clasts in the Nakaa'kire Tuff, a tuffaceous bed in Member I just below the hominin levels, we place an older limit of 198+/-14ka (weighted mean age=196+/-2ka) for the hominins. A younger limit of 104+/-7ka (weighted mean age=104+/-1ka) is provided by feldspars separated from pumice clasts in the Aliyo Tuff in Member III. Geological evidence indicates rapid deposition of each member of the Kibish Formation, concurrent with deposition of sapropels in the Mediterranean Sea. The (40)Ar/(39)Ar age measurements, together with correlations with sapropels, indicate that the hominin fossils are close in age to the older limit. Our preferred estimate of the age of the hominins is 195+/-5ka, making them the earliest well-dated anatomically modern humans yet described.     

Foot bones from Omo: implications for hominid evolution

We reanalyze a hominid talus and calcaneus from Omo dating to 2.2 mya and 2.36 mya, respectively. Although both specimens occur at different localities and times, both tarsals articulate well together, suggesting a single taxon on the basis of size and function. We attribute these foot bones to early Homo on the basis of their morphology. The more modern-like tarsal morphology of these Omo foot bones makes them very similar to a talus from Koobi Fora (KNM-ER 813), a specimen attributed to Homo rudolfensis or Homo erectus. Although the Omo tarsals are a million years younger than the oldest known foot bones from Hadar, both localities demonstrate anatomical differences representing two distinct morphological patterns. Although all known hominid tarsals demonstrate clear bipedal features, the tarsal features noted below suggest that biomechanical changes did occur over time, and that certain features are associated with different hominid lineages (especially the robust australopithecines).     

Les sites archéologiques plio-pléistocènes de la formation de Nachukui, Ouest-Turkana, Kenya : bilan synthétique 1997–2001

Plio-Pleistocene archaeological sites in the Nachukui Formation, West Turkana, Kenya: synthetic results 1997–2001. Stretched along the western side of the Turkana Basin, the Nachukui Formation preserves a large number of Plio-Pleistocene archaeological sites. Research carried out by the WTAP documents hominid behavioral evolution and technical diversity, through a time period ranging from 2.35 Myr to 0.7 Myr and within a relatively precise chronostratigraphic and paleoenvironmental frame. This work is based on comprehensive excavations conducted between 1997 and 2001 at the Late Pliocene and Early Pleistocene site complexes of the formation. To cite this article: H. Roche et al., C.R. Palevol 2 (2003).     

Quaternary fossil fish from the Kibish Formation, Omo Valley, Ethiopia

The late Quaternary Kibish Formation of the Omo Valley, southwestern Ethiopia, preserves environments reflecting a history of fluctuations in the level of nearby Lake Turkana over the past 200,000 years. The Kibish Formation has yielded a diverse mammalian fauna (as well as birds and crocodiles), stone tools, and the oldest anatomically modern Homo sapiens. Fish, the most common vertebrate fossils in this unit, are reported in this study. Catfish (especially clariids and Synodontis) and Nile perch (Lates niloticus) predominate, but the gymnarchid Gymnarchus, a cyprinid (Barbus), tigerfish (Hydrocynus), pufferfish (Tetraodon), and other catfish are also present. In total, nine teleost genera are found in the Kibish Formation, representing a subset of the 37 genera that constitute the modern Omo-Turkana ichthyofauna. Several taxa present in the modern fauna, including Polypterus and members of the family Cichlidae, are not found in the Kibish deposits. Most specimens are preserved as disarticulated or broken skeletal elements, but some preservation of articulated elements (e.g., sets of vertebrae, crania with lower jaws or cleithra) also occurs. Many of the catfish and Nile perch specimens are larger than the largest reported from the modern river or lake. Faunas of Kibish Members I and III closely resemble one another; the fauna from Member IV contains only the three most common taxa (Clarias, Synodontis, Lates), though this may result from insufficient sampling. Barbed bone points have been collected from the upper part of the formation, indicating a long association between the human inhabitants and the fish fauna of the Omo Valley.     

Geochronology of the Turkana depression of northern Kenya and southern Ethiopia

Mesozoic and Cenozoic sedimentary rocks in the Turkana Depression of northern Kenya and southern Ethiopia rest on basement rocks that yield K/Ar cooling ages between 433 and 522 Ma. Proven Cretaceous strata are exposed in Lokitaung Gorge in northwest Kenya. Eocene basalts and rhyolites in Lokitaung Gorge, the Nabwal Hills, and at Kangamajoj, date between 34 and 36 Ma, recording the earliest volcanism in the region. Oligocene volcanic rocks, with associated fossiliferous sedimentary strata at Eragaleit, Nakwai, and Lokone, all west of Lake Turkana, are 23 to 28 Ma old, as is the Langaria Formation east of Lake Turkana. Lower and Middle Miocene volcanic and sedimentary sequences are present both east and west of Lake Turkana, where ages from 17.9 to 9.1 Ma have been measured at many levels. Upper Miocene strata are presently known only at Lothagam, with ages ranging from 7.4 to 6.5 Ma. Deposition of Pliocene strata of the Omo Group begins in the Omo-Turkana, Kerio, and South Turkana basins -4.3 Ma ago and continues in parts of those basins until nearly the present time, but with some gaps. These strata are linked through volcanic ash correlations at many levels, as are Pleistocene strata of the Omo Group (principally the Shungura, Koobi Fora, and Nachukui formations). (40) Ar/(39) Ar dates on many volcanic ash layers within the Omo Group, supplemented by K/Ar ages on intercalated basalts and paleomagnetic polarity stratigraphy, provide excellent age control from 4.2 to 0.75 Ma, although there is a gap in the record between -1 Ma and 0.8 Ma. Members I to III of the Kibish Formation in the lower Omo Valley record deposition between 0.2 and 0.1 Ma ago; Member IV, correlative with the Galana Boi Formation, was deposited principally between 12 and 7 ka BP.     

Paleoanthropology of the Kibish Formation, southern Ethiopia: Introduction

Cranial and skeletal remains of modern humans, Homo sapiens, were discovered in the Kibish Formation in 1967 by a team from the Kenya National Museums directed by Richard Leakey. Omo I, from Kamoya's Hominid Site (KHS), consists of much of a skeleton, including most of the cranial vault, parts of the face and mandible, and many postcranial elements. Omo II, from Paul's Hominid Site (PHS), is a virtually complete calvaria. Only a limited fauna and a few stone artifacts attributed to the Middle Stone Age were recovered in conjunction with the fossil hominids. The available dating techniques suggested a very early age, over 100 ka, for Member I, from which the Omo I and Omo II fossils were recovered. However, in subsequent decades, the reliability of the dates and the provenance of the Kibish hominids were repeatedly questioned. The papers in this volume provide a detailed stratigraphic analysis of the Kibish Formation and a series of new radiometric dates that indicate an age of 196 +/- 2 ka for Member I and 104 +/- 1 for Member III, confirming the antiquity of the lower parts of the Kibish Formation and, in turn, the fossils from Member I. Studies of the postcranial remains of Omo I indicate an overall modern human morphology with a number of primitive features. Studies of an extensive lithic record from Members I and III indicate a Middle Stone Age technology comparable to assemblages of similar age elsewhere in Ethiopia. Studies of the mammalian, avian, and fish faunas indicate overall similarities to those found in the region today, with a few distinctive differences.     

The femur of extinct bunodont otters in Africa (Carnivora,Mustelidae, Lutrinae)

This study compares fossil femora attributed to extinct African bunodont lutrines with extant mustelids and ursids to reconstruct locomotor behavior. Due to the immense size differences among taxa, shape data were used to compare morphology. Based on morphological differences, the fossil femora are suggested to belong to different taxa with different locomotor abilities and habitat preferences. The Langebaanweg femur is the oldest and has a typical mustelid morphology suggesting that it was a locomotor generalist like most mustelids. The West Turkana form is more like extant nonbunodont otters, but much larger, and may have belonged to a semiaquatic taxon. The enormous Omo femur shares some features with truly aquatic taxa (e.g., Enhydra) and is the most likely to have been fully aquatic. The same may hold true for the Hadar species as it is most similar to that from the Omo. If these femora truly belong to bunodont lutrines, then they are more diverse in postcranial morphology than in dental morphology.     

Stature-at-death of KNM-WT 15000

The specimen KNM-WT 15000 is an exceptionally complete 1.53 Myr juvenile skeleton of Homo erectus from West Turkana, Kenya. It therefore provides a unique opportunity to examine stature estimates of fossil hominids based strictly on long bone lengths. Using recovered axial and appendicular elements of KNM-WT 15000 that contributed to stature during life, we conclude that KNM-WT 15000 was much shorter at time-of-death than previous estimates that used only appendicular elements. We conservatively estimate stature-at-death at about 147 cm, although this individual could have been as short as 141 cm. Because long bone based estimates of stature also imply the axial skeletal proportion, our new stature estimate stems from the recognition of axial/appendicular disproportion in the individual KNM-WT 15000. It is possible that the peripubescent age-at-death of this specimen, and any resulting differential maturity between the appendicular and axial skeleton, may have contributed to previous overestimates of stature-at-death. However, the possibility that this individual was abnormal, as implied by axial/appendicular disproportion, remains to be fully tested. Regardless, these results suggest that some interpretations of the biology of early African Homo erectus, largely based upon KNM-WT 15000, should be viewed with caution. 5 Primate Evolution and Morphology Group, Department of Human     

Dental metric assessment of the omo fossils: implications for the phylogenetic position of Australopithecus africanus

The discovery of Australopithecus afarensis has led to new interpretations of hominid phylogeny, some of which reject A. africanus as an ancestor of Homo. Analysis of buccolingual tooth crown dimensions in australopithecines and Homo species by Johanson and White (Science 202:321-330, 1979) revealed that the South African gracile australopithecines are intermediate in size between Laetoli/hadar hominids and South African robust hominids. Homo, on the other hand, displays dimensions similar to those of A. afarensis and smaller than those of other australopithecines. These authors conclude, therefore, that A. africanus is derived in the direction of A. robustus and is not an ancestor of the Homo clade. However, there is a considerable time gap (ca. 800,000 years) between the Laetoli/Hadar specimens and the earliest Homo specimens; "gracile" hominids from Omo fit into this chronological gap and are from the same geographic area. Because the early specimens at Omo have been designated A. afarensis and the later specimens classified as Homo habilis, Omo offers a unique opportunity to test hypotheses concerning hominid evolution, especially regarding the phylogenetic status of A. africanus. Comparisons of mean cheek teeth breadths disclosed the significant (P less than or equal to 0.05) differences between the Omo sample and the Laetoli/Hadar fossils (P4, M2, and M3), the Homo fossils (P3, P4, M1, M2, and M1), and A. africanus (M3). Of the several possible interpretations of these data, it appears that the high degree of similarity between the Omo sample and the South African gracile australopithecine material warrants considering the two as geographical variants of A. africanus. The geographic, chronologic, and metric attributes of the Omo sample argue for its lineal affinity with A. afarensis and Homo. In conclusion, a consideration of hominid postcanine dental metrics provides no basis for removing A. africanus from the ancestry of the Homo lineage.     

Body size and body shape in early hominins - implications of the Gona Pelvis

Discovery of the first complete Early Pleistocene hominin pelvis, Gona BSN49/P27, attributed to Homo erectus, raises a number of issues regarding early hominin body size and shape variation. Here, acetabular breadth, femoral head breadth, and body mass calculated from femoral head breadth are compared in 37 early hominin (6.0-0.26 Ma) specimens, including BSN49/P27. Acetabular and estimated femoral head sizes in the Gona specimen fall close to the means for non-Homo specimens (Orrorin tugenesis, Australopithecus africanus, Paranthropus robustus), and well below the ranges of all previously described Early and Middle Pleistocene Homo specimens. The Gona specimen has an estimated body mass of 33.2 kg, close to the mean for the non-Homo sample (34.1 kg, range 24-51.5 kg, n = 19) and far outside the range for any previously known Homo specimen (mean = 70.5 kg; range 52-82 kg, n = 17). Inclusion of the Gona specimen within H. erectus increases inferred sexual dimorphism in body mass in this taxon to a level greater than that observed here for any other hominin taxon, and increases variation in body mass within H. erectus females to a level much greater than that observed for any living primate species. This raises questions regarding the taxonomic attribution of the Gona specimen. When considered within the context of overall variation in body breadth among early hominins, the mediolaterally very wide Gona pelvis fits within the distribution of other lower latitude Early and Middle Pleistocene specimens, and below that of higher latitude specimens. Thus, ecogeographic variation in body breadth was present among earlier hominins as it is in living humans. The increased M-L pelvic breadth in all earlier hominins relative to modern humans is related to an increase in ellipticity of the birth canal, possibly as a result of a non-rotational birth mechanism that was common to both australopithecines and archaic Homo.     

Revised stratigraphy of Area 123, Koobi Fora, Kenya, and new age estimates of its fossil mammals, including hominins

Recent geologic study shows that all hominins and nearly all other published mammalian fossils from Paleontological Collection Area 123, Koobi Fora, Kenya, derive from levels between the KBS Tuff (1.87+/-0.02 Ma) and the Lower Ileret Tuff (1.53+/-0.01 Ma). More specifically, the fossils derive from 53 m of section below the Lower Ileret Tuff, an interval in which beds vary markedly laterally, especially those units containing molluscs and algal stromatolites. The upper Burgi Member (approximately 2.00-1.87 Ma) crops out only in the southwestern part of Area 123. Adjacent Area 110 contains larger exposures of the member, and there the KBS Tuff is preserved as an airfall ash in lacustrine deposits and also as a fluvially redeposited ash. We observed no mammalian fossils in situ in this member in Area 123, but surface specimens have been documented in some monographic treatments. Fossil hominins from Area 123 were attributed to strata above the KBS Tuff in the 1970s, but later they were assigned to strata below the KBS Tuff (now called the upper Burgi Member). This study definitively places the Area 123 hominins in the KBS Member. Most of these hominins are between 1.60 and 1.65 myr in age, but the youngest may date to only 1.53 Ma, and the oldest, to 1.75 Ma. All are 0.15-0.30 myr younger than previously estimated. The new age estimates, in conjunction with published taxonomic attributions of fossils, suggest that at least two species of Homo coexisted in the region along with A. boisei until at least 1.65 Ma. Comparison of crania KNM-ER 1813 and KNM-ER 1470, which were believed to be of comparable age, is at the focus of the debate over whether Homo habilis sensu lato is in fact composed of two species: Homo habilis and Homo rudolfensis. These two crania are separated in time by approximately 0.25 myr, and therefore, arguments for their conspecificity no longer need to confront the issue of unusually high contemporaneous variation within a single species.     

Nouvelles découvertes de dents d’hominidés dans le membre Kaitio de la formation de Nachukui (1,65–1,9 Ma), Ouest du lac Turkana (Kenya)

New hominid teeth from the Kaitio member (1.65–1.9 Myr) in West Turkana (Kenya). New hominid teeth have been recovered from the archaeological sites of Kokiselei 1 and Naiyena Engol 1. These two sites are located in the west side of the Turkana Basin and belong to the Kaitio member of the Nachukui Formation. They are dated between 1.65-1.79 and 1.7-1.8 Myr respectively. The four teeth (left maxillary canine and first molar, right maxillary third molar and left mandibular third molar) discovered in Kokiselei 1 are attributed to Australopithecus boisei. The right mandibular first premolar found in Naiyena Engol 1 is referred to Homo sp. aff. ergaster. To cite this article: S. Prat et al., C. R. Palevol 2 (2003).     

New insights into the molecular phylogeny and taxonomy of mormyrids (Osteoglossiformes,Actinopterygii) in northern East Africa

Based on morphological data and analysis of mitochondrial cytochrome b gene and nuclear (S7 intron 1) DNA sequences, the phylogenetic relationships of all Pollimyrus species known from the Omo‐Turkana enclosed basin and Nile system below the Murchison Falls were solved. A mormyrid “Pollimyrus” petherici is distantly related to all other studied Pollimyrus species and clusters together with Cyphomyrus species forming with the later a monophyletic group. Moreover, the West African (but not the Congo River) populations of Cyphomyrus psittacus, the type species of the genus, seem to be conspecific to C. petherici. That is, the range of the genus Cyphomyrus is extended toward the Nile and Omo‐Turkana basins. This genus belongs to the large clade widely distributed in sub‐Saharian Africa and characterized by the presence of a chin appendage. Significance of this character for mormyrid phylogeny is discussed. Two distinct lineages of Pollimyrus occurring sympatrically in the White Nile tributaries and previously reported as the light and dark forms of Pollimyrus isidori together with five other congeneric species studied form a monophyletic group. The light form apparently represents P. isidori distributed in the Nile system downstream of the Murchison Falls and West Africa; the dark‐colored form (designated as Pollimyrus “D”) represents a distinct phylogenetic lineage inhabiting both the Omo‐Turkana and the White Nile basin. Morphological and ecological data suggest that this form may be conspecific to East African Pollimyrus nigricans or most probably represents a new species.     

Faunes et paléoenvironnements des principaux sites archéologiques plio-pléistocènes de la formation de Nachukui (Ouest-Turkana, Kenya)

Faunas and paleoenvironments from main archaeological Plio-Pleistocene sites of the Nachukui Formation (West Turkana, Kenya). The Nachukui Formation is currently under archaeological investigation, especially within the Kalochoro (2.35 – 1.9 Myr) and Kaitio (1.9 – 1.65 Myr) Members. Six main archaeological sites have been excavated from this time period, which yield rich vertebrate faunas collected in situ or in close vicinity to the site. Paleontological studies help to precise the specific diversity for each site and increase our documentation for each Member with the discovery of new taxa. They allow to provide new informations about the biotope diversities exploited by Hominids and show a climatic tendency towards more humid environment between the Members. To cite this article: J.-P. Brugal et al., C.R. Palevol 2 (2003).     

Patterns of vegetation along the Omo River in southwest Ethiopia

This study investigates the riverine vegetation along the perennial Omo River, which flows from the Ethiopian highlands to its terminus, in the southwestern lowlands, at Lake Turkana (formerly Lake Rudolf). Broadly defined to include the levee backslopes and adjacent mudflats (or ancient floodplains), the riverine zone in the lower Omo basin supports a relatively luxuriant vegetation compared with the dry grasslands in the surrounding plains environments. Habitat conditions along the lower Omo have changed significantly during the past century, primarily due to a period of reduced rainfall and river flow, a drop in lake level (L. Turkana) at the river's terminus and increased exposure of natural levees near the Omo's terminus. The floristic and physiognomic character of riverine vegetation were studied at selected sites, ranging from the relatively straight channel section in the modern delta to a strongly meandering (upstream) section of the river. A combination of open canopy woodland, shrub thicket and grassland (with scattered tree emergents) prevailed on the more recently exposed levees, in and near the modern delta; closed canopy woodland and forest predominated on fore levees in the meandering segment. Floristic diversity was relatively low at all study sites. Ficus sycomorus, Tapura fischeri, Melanodiscus oblongus, Celtis integrifolia and Trichilia roka were most significant in upstream forest sites, whereas Cordia sinensis, Acacia mellifera, Ziziphus mauritiana and Ficus sycomorus were more common in communities nearer the lake. Older forests generally contained greater diversity of more woody species, greater tree height and truck diameter than downstream levee vegetation, but they did not exhibit clear stratification. Species patchiness was broadly characteristic of the riverine zone, particularly the mudflats (ancient floodplains) extending away from the fore levees. Fires are frequently set by local inhabitants throughout the grasslands of the lower Omo Basin; within the riverine zone, they are particularly common in the mudflats but have only limited impact on woodland and forest vegetation. It is suggested that fire is a highly significant factor in the establishment of sharp boundaries between the closed canopy woodland/forest along the river and the more xerophytic vegetation of the mudflats.     

Cranium of a juvenile Australopithecus boisei from the lower Omo Basin,Ethiopia

A partial cranium of a juvenile Australopithecus boisei, recovered from the Shungura Formation in the lower Omo basin, southern Ethiopia, and dated at 2.1 m.y. B.P. , is described anatomically and compared to young and adult australopithecines, modern Homo sapiens, chimpanzees, and gorillas. A resemblance to the gracile Australopithecus is observed but is attributed mainly to the generalized appearance of the Omo specimen resulting from its young individual age. An attempt is made to reconstruct part of the ontogenetic process of A. boisei. This process is compared to the developmental changes exhibited by the African great apes and modern man and is found to combine characteristics of both.     

Intrasite spatial variation of the Omo Kibish Middle Stone Age assemblages: artifact refitting and distribution patterns

The middle-late Pleistocene Kibish Formation of the Lower Omo Valley (Ethiopia) contains some of the oldest dated Homo sapiens fossils. Archaeological excavations at the Omo Kibish between 2002 and 2003 recovered numerous stone tools from extensive horizontal exposures of two sites, KHS (dated to 195 ± 5 kyr) and BNS (dated to at least 104 ± 7 kyr). Analysis of artifact distributions, lithic-debris densities, and refitting artifact sets sheds light on site-formation processes. Both localities reveal weak patterns of differentiation, and BNS seems to have a preferred refit orientation.     

The Middle Stone Age of the northern Kenyan Rift: age and context of new archaeological sites from the Kapedo Tuffs

Rift Valley sites in southern Ethiopia and northern Kenya preserve the oldest fossil remains attributed to Homo sapiens and the earliest archaeological sites attributed to the Middle Stone Age (MSA). New localities from the Kapedo Tuffs augment the sparse sample of MSA sites from the northern Kenya Rift. Tephrostratigraphic correlation with dated pyroclastic deposits from the adjacent volcano Silali suggests an age range of 135-123 ka for archaeological sites of the Kapedo Tuffs. Comparisons of the Kapedo Tuffs archaeological assemblages with those from the adjacent Turkana and Baringo basins show broad lithic technological similarity but reveal that stone raw material availability is a key factor in explaining typologically defined archaeological variability within this region. Spatially and temporally resolved comparisons such as this provide the best means to link the biological and behavioral variation manifest in the record of early Homo sapiens.