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.     

Microstratigraphy of the Kibish hominin sites KHS and PHS, Lower Omo Valley, Ethiopia

Detailed stratigraphic analysis of the Omo I and Omo II fossil localities confirms both the relational and sequential context reported by Butzer in 1969. The two fossils derive from approximately the same level within upper Member I of the Kibish Formation. Additional features of the local stratigraphic sequences indicate a complex history of depositional events, minor erosional surfaces, and weak soil formation throughout upper Member I.     

The Middle Stone Age archaeology of the Lower Omo Valley Kibish Formation: excavations, lithic assemblages, and inferred patterns of early Homo sapiens behavior

This paper describes the excavation, stratigraphy, and lithic assemblages of Middle Stone Age sites from the Omo Kibish Formation (Lower Omo Valley, southwestern Ethiopia). Three sites were excavated, two in Kibish Member I (KHS and AHS) and one at the base of Member III (BNS). The assemblages are dominated by relatively high-quality raw materials procured as pebbles from local gravels. The principal modes of core preparation are radial/centripetal Levallois and discoidal. Retouched tools are rare. Foliate bifaces are present, as are larger tools, such as handaxes, picks, and lanceolates, but these are more common among surface finds than among excavated assemblages. Middle Stone Age assemblages shed light on the adaptations of the earliest-known Homo sapiens populations in Africa.     

The large-mammal fauna from the Kibish Formation

The Kibish faunal remains are useful for reconstructing the habitat of the earliest documented Homo sapiens and for understanding the community within which early modern humans existed. A diverse assemblage of large mammals, including many species of bovids, suids, and equids, has been recovered from the Kibish Formation. There are no extinct large mammals represented in the fossil assemblage, and the overall taxonomic composition of the fossil fauna is similar to the modern-day wildlife community living near the Omo River. The fossil faunal assemblage shows a paucity of arboreal primates, and carnivore species are rare. However, the faunal sample includes possible Cephalophus (duiker) remains and Hylochoerus meinertzhageni (giant forest hog), taxa that are extremely rare in the African fossil record, and both indicate more closed habitats. Comparative analyses of the Kibish faunal remains using the ecological-diversity approach document close associations with edaphic grassland and woodland vegetation types. These vegetation forms are similar to current habitats surrounding the Omo River.     

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.     

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.     

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.     

Stratigraphic context of fossil hominids from the Omo group deposits: northern Turkana Basin, Kenya and Ethiopia

The chronometric framework developed for Plio-Pleistocene deposits of the northern Turkana Basin is reviewed in light of recent advances in lithostratigraphy, geochemical correlation, paleomagnetic stratigraphy, and isotopic dating. The sequence is tightly controlled by 20 precise ages on volcanic materials. These ages are internally consistent but are at variance with estimates for the boundaries of the magnetic polarity time scale by about 0.07 my. This discrepancy can be only partially resolved at present. Based on the established chronometric framework and stratigraphic sequences, depositional ages can be estimated for significant marker beds. These ages can in turn be used to constrain the 449 hominid specimens thus far reported from the basin. Ages for most hominid specimens can be estimated with a precision of +/- 0.05 my. In addition, the chronometric framework will be applicable to other paleontological collections, archeological excavations, and future discoveries in the basin.     

Analysis of an early hominid ulna from the Omo basin,Ethiopia

The discovery (in 1971) of a nearly complete right ulna from the Shungura Formation of the Omo basin provides the opportunity to analyze the forelimb structure of the Australopithecus boisei form of early hominid. Results from multivariate morphometric analyses show that this bone is unique in shape among the extant hominoids although it is most similar to Pan and Homo. Despite its long slender shaft and large distal articular surface the bone's overall morphology is quite unlike Pongo.     

Depositional environments, archeological occurrences and hominids from Members E and F of the Shungura Formation (Omo basin, Ethiopia)

The several known archeological occurrences from the Shungura Formation (Members E and F) are discussed within the context of their particular depositional and paleoenvironmental settings, and the broader context of the Pliocene of the Turkana Basin. These assemblages date from 2·3–2·4 Ma, and are among the oldest yet known in Africa. In situ archeological assemblages are restricted to the distal edge of fluviatile levees, behind gallery forests and at the edge of open savanna. Extensive and rather dense scatters of slightly disturbed quartz artifacts are linked to large expanses of braided stream situations. Lag components are derived from stream beds. There is no available evidence of occupation either under riverine or deltaic forest settings or on dryland. Hominid skeletal remains from this interval, none of which occur at or are directly associated with such archeological occurrences, are attributed to two hominid taxa. Most specimens represent a “robust” australopithecine and are attributed here to A. aethiopicus. A few hominid teeth are attributed to aff. Homo sp.     

Fish remains from the Plio-Pleistocene Shungura Formation, Omo River basin, Ethiopia

Thousands of vertebrate fossils have been recovered from the lower Omo River Valley, in southern Ethiopia, however, fishes have been poorly reported. Here we describe fossil fish remains deriving from the Shungura Formation, part of the Omo Group of deposits ranging in date from 1.8 to 3.4 my. Two new species are reported, Sindacharax omoensis (Characiformes) and Lates arambourgi (Perciformes), which suggest greater diversity of these genera than previously documented.     

Further morphometric studies of the ulna from the Omo Basin, Ethiopia.

A reanalysis of the L40-19 fossil ulna from the Omo Basin, Ethiopia is presented. Using covariance adjustment rather than ratios to correct metric data for variations due to body size, a comparative sample reflecting 21 contemporary Anthropoid taxa, and both distribution-free and multivariate statistical procedures, this study indicates that the earlier conclusion drawn by McHenry et al. ('76), viz., that the fossil is "unique" among Hominoids, is essentially correct. This study also concludes, however, that although the fossil is projected closer to Pan and Homo than to Pongo, the distances are considerably greater than found between behaviorally similar modern forms. Consequently, aside from assigning the fossil on morphometric grounds to the Hominoidea, little else can be said about its possible locomotor habits or its ancestry.     

A description of the Omo I postcranial skeleton, including newly discovered fossils

Recent fieldwork in the Kibish Formation has expanded our knowledge of the geological, archaeological, and faunal context of the Omo I skeleton, the earliest known anatomically modern human. In the course of this fieldwork, several additional fragments of the skeleton were recovered: a middle manual phalanx, a distal manual phalanx, a right talus, a large and a small fragment of the left os coxae, a portion of the distal diaphysis of the right femur that conjoins with the distal epiphysis recovered in 1967, and a costal fragment. Some researchers have described the original postcranial fragments of Omo I as anatomically modern but have noted that a variety of aspects of the specimen's morphology depart from the usual anatomy of many recent populations. Reanalysis confirms this conclusion. Some of the unusual features in Omo I--a medially facing radial tuberosity, a laterally flaring facet on the talus for the lateral malleolus, and reduced dorsovolar curvature of the base of metacarpal I--are shared with Neandertals, some early modern humans from Skhul and Qafzeh, and some individuals from the European Gravettian, raising the possibility that Eurasian early modern humans inherited these features from an African predecessor rather than Neandertals. The fragment of the os coxae does not unambiguously diagnose Omo I's sex: the greater sciatic notch is intermediate in form, the acetabulum is large (male?), and a preauricular sulcus is present (female?). The preserved portion of the left humerus suggests that Omo I was quite tall, perhaps 178-182 cm, but the first metatarsal suggests a shorter stature of 162-173 cm. The morphology of the auricular surface of the os coxae suggests a young adult age.     

Inventory of remains of Hominidae from Pliocene-Pleistocene formations of the lower Omo basin, Ethiopia (1967-1972)

Since its initiation in 1966 the Omo Research Expedition has recovered a series of hominid fossils, in association with many vertebrate taxa, from formations of Pliocene/Pleistocene age from the lower Omo basin, southern Ethiopia. These fossiliferous formations span a time range from over 4.2 m.y. to about 1.4 m. y. on the basis of K/A age determination. Hominid remains have been found so far to occur at two localities in the upper part of the Usno Formation (～ 2.9 m.y.) and in the Shungura Formation at 79 localities from successive Members B through levels postdating J, a time span between 3 m.y. and 1.4 m.y. The remains—inventoried here according to skeletal part, locality and stratigraphic level, age and situation—include numerous isolated and associated teeth, mandibles, partial maxillae, portions of crania, and elements of the postcranial skeleton.     

A fossil baboon skull from the lower Omo basin,southwest Ethiopia

A well-preserved fossil skull assignable to the genusPapio was discovered in the late Pliocene deposits at the “White Sands locality” of the lower Omo basin, southwest Ethiopia in November 1978. This skull obviously belongs to a male baboon which is morphologically somewhat different from the extant species ofPapio and closely resemblesPapio baringensis R. E. F. Leakey, 1969. Its muzzle is not only long but comparatively wide and robust with a very flat dorsum, an almost quadrate vertical cross section, short and obtuse maxillary ridges and virtually absent maxillary fossae, and its zygomatic portion flares laterally to widen the large temporal process of the zygomatic bone. The post-orbital constriction is very marked, the temporal fossa is squarish in basal view, and the sagittal crest is placed rather posteriorly and meets a large nuchal crest, all of which suggest heavy temporal musculature. The incisors are lacking but were probably not as small as inP. baringensis. As a result of morphological comparisons with extant and fossil species ofPapio, this newly discovered skull was considered to represent a new species,Papio quadratirostris.     

Shell-Filled Burrows in the Upper Oligocene Antigua Formation,Antigua, Lesser Antilles

Limestones of the Upper Oligocene Antigua Formation of Antigua contain unusual burrows filled with the densely packed debris of shelly benthos. Unlined burrows (Planolites?) in deep-water biofacies at Half Moon Bay, parish of Saint Philip, are packed with a monospecific assemblage of large benthic foraminiferans (Lepidocyclina canelli Lemoine &; Douvillé) and a single brachiopod valve, Tichosina sp. A similar burrow in shallower-water biofacies at Hughes Point, parish of Saint Philip, is packed with echinoderm debris and, particularly, test fragments of the spatangoid echinoid Lovenia n. sp. Fragments of the same echinoid fill a conical burrow, Bergaueria isp. The latter is probably a physical accumulation, the common fragments of echinoid being washed into an empty burrow. In contrast, the infill of Planolites? isp. is more likely to be an accumulation mediated by the burrower.     

Taphonomy and compositional fidelity of Quaternary fossil assemblages of terrestrial gastropods from carbonate-rich environments of the Canary Islands

Quaternary aeolian deposits of the Canary Islands contain well‐preserved terrestrial gastropods, providing a suitable setting for assessing the taphonomy and compositional fidelity of their fossil record over ~13 kyr. Nine beds (12, 513 shells) have been analysed in terms of multivariate taphonomic and palaeoecological variables, taxonomic composition, and the stratigraphic and palaeontological context. Shells are affected by carbonate coatings, colour loss and fragmentation. Shell preservation is size‐specific: juveniles are less fragmented and show colour preservation more commonly than adults. In palaeosols, the adult shell density correlates negatively with the proportion of fragmented adults, negatively with the proportion of juveniles, and positively with the proportion of adults with coatings. High bioturbation intensity in palaeosols is associated with low shell fragmentation and high proportion of shells with coatings. These relationships imply that high adult density in palaeosols was driven by an increase in shell production rate (related to a decrease in predation rates on adults and a decrease in juvenile mortality) and a decrease in shell destruction rate (related to an increase in durability enhanced by carbonate precipitation). In dunes, the relationships between taphonomic alteration, shell density and bioturbation are insignificant. However, dune assemblages are characterized by a lower frequency of shells with coatings and higher rates of colour loss, indicating lower shell durability in dunes than in palaeosols. Additionally, non‐random differences in the coating proportion among palaeosols imply substantial temporal variation in the rate of carbonate crust formation, reflecting long‐term changes in bioturbation intensity that covaries positively with shell preservation. Dunes and palaeosols do not differ in species abundances despite differences in the degree of shell alteration, suggesting that both weakly and strongly altered assemblages offer data with a high compositional fidelity. Carbonate‐rich terrestrial deposits originating in arid conditions can enhance the preservation of gastropods and result in fossil assemblages that are suitable for palaeoecological and palaeoenvironmental studies of terrestrial ecosystems.     

A new hominid parietal from Bodo, Middle Awash Valley, Ethiopia

A piece of left parietal of a Middle Pleistocene hominid, recovered from the Upper Bodo Sand Unit, in the Middle Awash, Ethiopia, is described anatomically and compared to Middle Pleistocene hominids and modern Homo sapiens. It bears several primitive features and has important implications for the original Bodo skull, found at the same stratigraphic level in the same area. The new fossil skull represents a different individual from the original Bodo skull.     

Spatial behaviours of Early Oldowan toolmakers in the Shungura Formation (Lower Omo Valley,Ethiopia): Proposal for an integrated approach

The spatial relationships of the Early Oldowan toolmakers with their environment have been so far addressed through raw material procurement analyses and the characterization of hominid habitat. This paper proposes to integrate these two approaches into a broader spatial analysis encompassing archaeological and environmental data (palaeontological, geological and isotopic data) from Member F and lower Member G of the Shungura Formation (Lower Omo Valley, Ethiopia). Heterogeneity in data resolution induces a multiscale approach with three levels of analysis. The level of occurrence complex allows focusing on the characterization of archaeological occurrences and on their environmental settings. The level of “study area” allows working on hominid habitats and on their raw material procurement behaviours. Finally, at the Shungura Formation scale, we can address temporal issues related to the evolution of spatial behaviours between Member F and the lower part of Member G, ca. 2.3 to 2 million years (Ma).