(40)Ar/(39)Ar dating of Bed I, Olduvai Gorge, Tanzania, and the chronology of early Pleistocene climate change

⁴⁰Ar/³⁹Ar dating of tuffs and lavas of the late Pleistocene volcanic and sedimentary sequence of Olduvai Gorge, north-central Tanzania, provides the basis for a revision of Bed I chronostratigraphy. Bed I extends from immediately above the Naabi Ignimbrite at 2.038 ± 0.005 Ma to Tuff IF at 1.803 ± 0.002 Ma. Tuff IB, a prominent widespread marker tuff in the basin and a key to understanding hominin evolutionary chronologies and paleoclimate histories, has an age of 1.848 ± 0.003 Ma. The largest lake expansion event in the closed Olduvai lake basin during Bed I times encompassed the episode of eruption and emplacement of this tuff. This lake event is nearly coincident with the maximum precessional insolation peak of the entire Bed I/Lower Bed II interval, calculated from an astronomical model of the boreal summer orbital insolation time-series. The succeeding precessional peak also apparently coincides with the next youngest expansion of paleo-Lake Olduvai. The extreme wet/dry climate shifts seen in the upper part of Bed I occur during an Earth-orbital eccentricity maximum, similar to episodic lake expansions documented elsewhere in the East African Rift during the Neogene.     

The puzzle from JK2—A femur and a tibial fragment (O.H.34) from Olduvai Gorge,Tanzania

During excavations in Bed III, Olduvai Gorge, Tanzania in 1962, a slender fossil femur and part of a tibial shaft were recovered. Their strange appearance resulted in their neglect for many years. Anatomical examination now confirms that these bones are hominid, probably hominine, yet distorted in form. The distortion does not appear to be the result of pathology but due to damage and abrasion while in the deposits; deposits dated at approximately 1 million years B.P. O.H. 34 is the first hominid to be recovered from Bed III, Olduvai Gorge.     

Examining time trends in the Oldowan technology at Beds I and II,Olduvai Gorge

The lithic analysis of the Bed I and II assemblages from Olduvai Gorge reveals both static and dynamic time trends in early hominids' technology from 1.8 to 1.2 m.y.a. The Bed I Oldowan (1.87-1.75 m.y.a.) is characterized by the least effort strategy in terms of raw material exploitation and tool production. The inclusion of new raw material, chert, for toolmaking in the following Developed Oldowan A (DOA, 1.65-1.53 m.y.a.) facilitated more distinctive and variable flaking strategies depending on the kind of raw materials. The unique characters of DOA are explainable by this raw material factor, rather than technological development of hominids. The disappearance of chert in the subsequent Developed Oldowan B and Acheulian (1.53-1.2 m.y.a.) necessitated a shift in tool production strategy more similar to that of Bed I Oldowan than DOA. However, the evidence suggests that Bed II hominids might have been more skillful toolmakers, intensive tool-users, and engaged in more active transport of stone tools than the Bed I predecessors. Koobi Fora hominids maintained a more static tool-using behavior than their Olduvai counterparts due mainly to a stable supply of raw materials. They differed from Olduvai hominids in terms of less battering of cores, consistent transport behavior, and few productions of side-struck flakes, indicating a regional variation of toolmaking and using practice. However, they shared with Olduvai hominids a temporal trend toward the production of larger flakes from larger cores after 1.6 m.y.a. Increased intake of animal resources and the expansion of ranging area of Homo ergaster would have led to the development of technological organization. Technological changes in the Oldowan industry are attested at Olduvai Gorge, Koobi Fora, and Sterkfontein, suggesting that it was a pan-African synchronous phenomenon, beginning at 1.5 m.y.a.     

The age and stratigraphic position of Olduvai Hominid I

A short history of Olduvai Hominid I is given. On the basis of absolute and relative dating its position in the Naisiusiu Bed, part of the former Bed V, is affirmed. Some connection, on morphological grounds, with other hominids in East Africa is postulated, as well as with cultural material.     

Analysis of orientation patterns in Olduvai Bed I assemblages using GIS techniques: implications for site formation processes

Mary Leakey’s excavations at Olduvai Beds I and II provided an unparalleled wealth of data on the archaeology of the early Pleistocene. We have been able to obtain axial orientations of the Bed I bone and stone tools by applying GIS methods to the site plans contained in the Olduvai Volume 3 monograph (Leakey, 1971). Our analysis indicates that the Bed I assemblages show preferred orientations, probably caused by natural agents such as water disturbance. These results, based on new GIS techniques applied to paleoanthropological studies, have important implications for the understanding of the formative agents of Olduvai sites and the behavioral meaning of the bone and lithic accumulations in Bed I.     

Soricidae (Mammalia) from the Early Pleistocene of Olduvai Gorge, Tanzania

Soricid remains collected from Bed I of Olduvai Gorge are described. The great majority of the specimens are mandibles. A survey of the mandibles of living African species revealed many differences in characters of the lower teeth and jaw that can be used for identification. On the basis of these characters, nine species are distinguished in the Olduvai collection, of which six are well enough preserved to permit a discussion of their relationships to living species. Three new species and one new subspecies are described. All the Olduvai shrews differ in some respects from their nearest living relatives; three species are close to species from Makapansgat, Swartkrans and Sterkfontein, RSA, though there appear to be slight differences. A change in the soricid fauna takes place within Bed I, interpreted as due to increasing aridity.     

A new species of cormorant (Aves: Phalacrocoracidae) from the Pleistocene of Olduvai Gorge,Tanzania

Phalacrocorax owrei nov. sp. is a small cormorant from the Lower Pleistocene of Olduvai Gorge. Osteological proportions are established for the four subgenera of Phalacrocorax, and P. owrei is assigned to the subgenus Stictocarbo. The species was the most abundant bird in the Bed I deposits and is also represented by a few specimens in the middle part of Bed II. Its last known appearance coincides with a change in the local environment when the climate became more arid and the Olduvai Lake became more saline and more alkaline. At other localities in Bed II the extinct P. tanzanice occurs, as well as P. africanus and P. corbo, which breed on the African lakes and seacoast today.     

Scavenging or Hunting in Early Hominids: Theoretical Framework and Tests

Evidence from Bed I, Olduvai, supports the hypothesis that scavenging, not hunting, was the major meat-procurement strategy of hominids between 2 and 1.7 million years ago. Data used to evaluate the hunting and scavenging hypotheses are derived from studying cut marks on Bed I bovids, comparing adaptations necessary for scavenging with those of early hominids, and a pa-leoecological reconstruction of Bed I carcass biotnass, carnivore guild, and hominidforaging area.     

Vegetation during UMBI and deposition of Tuff IF at Olduvai Gorge, Tanzania (ca. 1.8 Ma) based on phytoliths and plant remains

As part of ongoing research at Olduvai Gorge, Tanzania, to determine the detailed paleoenvironmental setting during Bed I and Bed II times and occupation of the basin by early hominins, we present the results of phytolith analyses of Tuff IF which is the uppermost unit of Bed I. Phytoliths were identified in most of the levels and localities on the eastern paleolake margin, but there are not always sufficient numbers of identifiable morphologies to infer the specific type of vegetation due to dissolution. Some surge surfaces and reworked tuff surfaces were vegetated between successive ash falls, as indicated by root-markings and the presence of a variety of phytolith morphotypes. Dicotyledonous wood/bark types were dominant except at the FLK N site just above Tuff IF when monocots are dominant and for the palm-dominated sample from the reworked channel cutting down into Tuff IF at FLK N. The area between the two fault scarps bounding the HWK Compartment, approximately 1 km wide, was vegetated at various time intervals between some of the surges and during the reworking of the Tuff. By lowermost Bed II times the eastern margin was fully vegetated again. Climate and tectonic activity probably controlled the fluctuating lake levels but locally the paleorelief and drainage were probably the controlling factors for the vegetation changes. These data support a scenario of small groups of hominins making brief visits to the paleolake during uppermost Bed I times, followed by a more desirable vegetative environment during lowermost Bed II times.     

Late Pliocene grassland from Olduvai Gorge,Tanzania

The Olduvai fossil plants documented by us in this paper are the first direct evidence for open grassland in the late Neogene of Africa based on macroplant remains. Silicified remains of herbaceous ground cover are exceptionally well preserved in situ within Late Pliocene sediments below the initial pyroclastic ash surge unit of Tuff IF in the uppermost part of Bed I, Olduvai Gorge, northern Tanzania. Published radiometric and palaeomagnetic dates place this grass layer between 1.839 + 0.005 Ma and 1.785 + 0.01 Ma. Exposed at localities on the south side of the Gorge this herbaceous ground cover grew on a floodplain developed on a dried out lake bed, following pronounced lake retreat of saline–alkaline palaeo-Lake Olduvai during a developing dry climatic phase. Sheathed basal culms, rhizomes and roots are interpreted as those of one or more small mat-forming grasses or less likely, sedges. Small dicotyledonous herbs were probably also present. The proximity of adjacent plants indicates a relatively dense ground cover. Roots extended at least 8 cm below the ground surface. Aerial parts of the plants were absent or were not preserved when the weathered basal culms were covered by a thin layer of brown waxy clay, followed by fallout of pyroclastic ash. Both units were mostly eroded away prior to emplacement of a wet, cool pyroclastic surge which then buried and preserved in situ remnants of the herbaceous ground cover. Preservation of the semi-woody rhizomes implies well-drained soils, otherwise the plant material would have quickly rotted. Collections from discontinuous exposures indicate the grassland covered an area of at least a few hectares. This open grassland would have provided grazing for the Late Pliocene fauna.     

The Ngorongoro Volcanic Highland and its relationships to volcanic deposits at Olduvai Gorge and East African Rift volcanism

The Ngorongoro Volcanic Highland (NVH), situated adjacent and to the east of Olduvai Gorge in northern Tanzania, is the source of the immense quantities of lava, ignimbrite, air fall ash, and volcaniclastic debris that occur interbedded in the Plio-Pleistocene sedimentary deposits in the Laetoli and Olduvai areas. These volcanics have proven crucial to unraveling stratigraphic correlations, the age of these successions, the archaeological and paleontological remains, as well as the source materials from which the bulk of the stone tools were manufactured. The NVH towers some 2,000 m above the Olduvai and Laetoli landscapes, affecting local climate, run-off, and providing varying elevation - climate controlled ecosystem, habitats, and riparian corridors extending into the Olduvai and Laetoli lowlands. The NVH also plays a crucial role in addressing the genesis and history of East African Rift (EAR) magmatism in northern Tanzania.In this contribution, we provide age and petrochemical compositions of the major NVH centers: Lemagurut, basalt to benmorite, 2.4-2.2 Ma; Satiman, tephrite to phonolite, 4.6-3.5 Ma; Oldeani, basalt to trachyandesite, 1.6-1.5 Ma; Ngorongoro, basalt to rhyolite, 2.3-2.0 Ma; Olmoti, basalt to trachyte, 2.0-1.8 Ma; Embagai, nephelinite to phonolite, 1.2-0.6 Ma; and Engelosin, phonolite, 3-2.7 Ma. We then discuss how these correlate in time and composition with volcanics preserved at Olduvai Gorge. Finally, we place this into context with our current understanding as to the eruptive history of the NVH and relationship to East African Rift volcanism.     

Archaeological predictions for hominid land use in the paleo-Olduvai Basin, Tanzania, during lowermost Bed II times

We present a preliminary predictive model of Oldowan stone artefact and scavenged larger mammal bone assemblages for 11 landscape facets modeled earlier to occur across a large portion (>300 km²) of the paleo-Olduvai Basin during lowermost Bed II times. This second phase of model-building is based on our earlier characterizations of the basin's landscape ecostructure and the inter-facet distribution of key resources and hazards probably encountered by Late Pliocene hominids (Peters & Blumenschine, 1995, 1996). Our current extension of the model of hominid–landscape interactions specifies additional theoretical components, including: (1) the assumed capabilities of Oldowan hominids (presumablyHomo habilis, primarily); (2) the landscape-facet-specific tasks they carried out; (3) the immediate stone and bone task residues they produced; and (4) the predicted composition, condition, density, and clustering of stone artefact and butchered and unbutchered bone assemblages for each facet. We develop ecological linkages between these new and formerly reported modeling components, the most fundamental of which is the facet-specific degree of tree/shrub cover abundance, and the correlated degree of competition among larger carnivores and hominids for scavengeable larger mammal carcasses. These factors condition variability among landscape facets in scavenging opportunities encountered by hominids, which in our model is the major predictor of bone and stone artefact assemblage composition. The predictive value of scavenging reflects the bias of paleoanthropological traces toward technology and butchery in their landscape context, but the model is surprisingly insensitive to what are usually thought to be critical social components of hominid land use. The predictions for the traces of hominid–landscape interactions modeled herein can be tested in the future against the landscape archaeological sample being excavated from lowermost Bed II by the Olduvai Landscape Paleoanthropology Project.     

Paleoanthropological applications of amino acid racemization dating of fossil bones and teeth

The general principals of the amino acid racemization based dating technique are discussed. The results obtained at Olduvai Gorge (Tanzania) and Zhoukoudian (China) are presented as an illustration of the paleoanthropological application of racemization dating. Tooth enamel provides the best material for the racemization dating of Middle to Lower Pleistocene deposits, although in some cases bones also yield reliable ages. The racemization method provides a means of dating teeth and bones which are too old for radiocarbon dating. Only small samples are required and processing procedures are straightforward. The technique is particularly useful in paleoanthropological studies since hominid fossils can be directly dated.     

Vegetation and plant food reconstruction of lowermost Bed II, Olduvai Gorge, using modern analogs

Vegetation and plant foods for hominins of lowermost Bed II, Olduvai Gorge were modeled by examining vegetation in modern habitats in northern Tanzania (Lake Manyara, Ngorongoro, Serengeti) that are analogous to the paleolandscape in terms of climate, land forms, and soil types, as indicated by previous paleoenvironmental studies of Olduvai. Plant species in the modern habitats were identified in a series of sample plots, and those known to be eaten by modern humans, chimpanzees, or baboons were considered potentially edible for early hominins. Within the 50-80 kyr deposition of lowermost Bed II, periods of drier climate were characterized by low lake stands and a broad eastern lacustrine plain containing a mosaic of springs, marsh, woodland, and edaphic grassland. Based on results of this study, plant food diversity in each of those habitats was relatively low, but the mosaic nature of the area meant that hominins could reach several different habitat types within short distances, with access to potential plant foods including marsh plants, grass grains, roots, shrub fruits, edible parts from palms, leafy herbaceous plants, and Acacia pods, flowers, and gum. Based on Manyara analogs, a greater variety of plant foods, such as tree fruits (e.g., Ficus, Trichilia) and the roots and fruits of shrubs (e.g., Cordia, Salvadora) would be expected further east along the rivers in the lacustrine terrace and alluvial fans. Interfluves of the alluvial fans were probably less wooded and offered relatively fewer varieties of plant foods, but there is sparse paleoenvironmental evidence for the character of Olduvai's alluvial fans, making the choice of appropriate modern analogs difficult. In the western side of the basin, based on modern analogs in the Serengeti, riverine habitats provided the greatest variety of edible plant food species (e.g., Acacia, Grewia, Justicia). If the interfluves were grassland, then a large variety of potentially edible grasses and forbs were present seasonally. Periods of wetter climate resulted in a much expanded paleolake and a shrinking of the eastern lacustrine plain mosaic into a narrow zone. The dominant landscape features were then forest-lined rivers in the eastern alluvial fans, and rivers in the western side of the paleo-Olduvai basin were also better watered at these times, supporting denser woody vegetation with large varieties of edible fruits, leaves, and underground parts.     

Environments and hominin activities across the FLK Peninsula during Zinjanthropus times (1.84 Ma), Olduvai Gorge, Tanzania

We establish through 13 excavations the landscape context and nature of hominin activities across the Zinjanthropus land surface from which the Leakeys recovered the FLK 22 and FLK NN 1 paleoanthropological assemblages. The land surface was created by fluvial incision of the eastern margin of paleo-Lake Olduvai following a major lake withdrawal. Erosion was uneven, leaving a peninsula bounded by a river channel, the FLK Fault, and a freshwater wetland. This FLK Peninsula supported groves of trees that attracted hominins and carnivores, and that preserved the dense concentrations of carcass remains and stone tools they left behind, including those at FLK 22. Some carcasses appear to have been acquired at the ecotone of the Peninsula and Wetland, where another dense artifact and bone assemblage accumulated. A lesser topographic high at the edge of a Typha marsh in the Wetland was the site of FLK NN 1 and a scatter of large stone tools used possibly for rootstock processing.Our landscape reconstruction delimits the vegetation mosaic indicated by previous work and provides a topographical explanation for the existence of FLK 22 and FLK NN 1. Both are unexpected if the FLK area was the flat, featureless lake margin terrain typical of lake basins similar to paleo-Olduvai. The results show that the Leakeys’ sites were not isolated occupation floors but rather parts of a land surface utilized intensively by hominins. Although commonly considered to have been home bases, their likely high predation risk, evidenced by large carnivore feeding traces and the remains of four hominin individuals, suggests visits to them were brief and limited to feeding. Finally, stratigraphic observations confirm that FLK NN 3 accumulated on an older land surface, refuting the hypothesis that the OH 8 foot found there is the same individual as the OH 35 leg from FLK 22.     

Landscape distribution of Oldowan stone artifact assemblages across the fault compartments of the eastern Olduvai Lake Basin during early lowermost Bed II times

The density and composition of Oldowan stone artifact assemblages deposited during the first ca. 20,000 years of lowermost Bed II times show a recurrent pattern of variation across recognized synsedimentary faults that compartmentalized landscapes of the eastern Olduvai Lake Basin. When active, the faults created minor topographic relief. The upthrown fault footwalls accumulated assemblages with relatively high densities of artifacts, including types retaining potential usefulness, particularly volcanic flaked pieces, manuports, pounded pieces, and split cobbles. Values for these assemblage characteristics decline toward the lower-lying hangingwall of the fault compartments, accompanied by an increase in the proportionate weight of artifact assemblages comprising quartzite, particularly flaking shatter and potentially useful detached pieces. Values reverse once again at faults, either on the downthrown, hangingwall side or on the upthrown side. The patterns are stronger for the volcanic components of the artifact assemblages than for the quartzite components, reflecting the additional influence of distance from the local source on quartzite assemblage characteristics reported previously. The landscape distributions of artifact assemblages are consistent with a landscape-fault model in which minor fault-induced topographic relief at times created a mosaic of vegetation environments repeated within each of the three fault compartments of the lake margin and distal alluvial fan. The fault-compartmentalized landscape model is currently supported only by sediment thickness and facies changes across synsedimentary faults, but it provides predictions for spatial variation in the cover abundance of trees, freshwater reservoirs and associated distributions of resources and hazards associated with stone artifact use and discard that can be tested if sample sizes of key paleoenvironmental indicators are increased.     

Neandertals,competition, and the origin of modern human behavior in the Levant

The East Mediterranean Levant is a small region, but its paleoanthropological record looms large in debates about the origin of modern humans and the fate of the Neandertals. For most of the twentieth century, the Levantine paleoanthropological record supported models of continuity and evolutionary transition between Neandertals and early modern humans. Recent advances in radiometric dating have challenged these models by reversing the chronological relationship between Levantine Neandertals and early modern humans. This revised chronostratigraphy for Levantine Middle Paleolithic human fossils raises interesting questions about the evolutionary relationship between Neandertals and early modern humans. A reconsideration of this relationship moves us closer to understanding the long delay between the origin of morphologically modern‐looking humans during the Middle Paleolithic (>130 Kyr) and the adaptive radiation of modern humans into Eurasia around the time of the transition from the Middle to Upper Paleolithic (50 to 30 Kyr).     

Cranial remains of Homo erectus from Beds II and IV,Olduvai Gorge,Tanzania

Cranial remains of hominids 9 and 12 from Olduvai Gorge are described in detail. O.H. 9 consists of a heavily built braincase, partly damaged and lacking the face, while O.H. 12 is less complete. The Bed II specimen is about 1.2 million years in age and shows anatomical similarities to the cranium designated ER-3733 from Koobi Fora, east of Lake Turkana. Together these African fossils provide valuable information about Homo erectus in the later Lower Pleistocene. Comparisons of O.H. 9 with several of the Choukoutien crania are also carried out. These Chinese and other Asian remains of Homo erectus cannot be placed in a secure chronological framework, but all of the material should be studied systematically in order to assess relatedness among what must be several different populations.     

Unraveling hominin behavior at another anthropogenic site from Olduvai Gorge (Tanzania): new archaeological and taphonomic research at BK, Upper Bed II

New archaeological excavations and research at BK, Upper Bed II (Olduvai Gorge, Tanzania) have yielded a rich and unbiased collection of fossil bones. These new excavations show that BK is a stratified deposit formed in a riverine setting close to an alluvial plain. The present taphonomic study reveals the second-largest collection of hominin-modified bones from Olduvai, with abundant cut marks found on most of the anatomical areas preserved. Meat and marrow exploitation is reconstructed using the taphonomic signatures left on the bones by hominins. Highly cut-marked long limb shafts, especially those of upper limb bones, suggest that hominins at BK were actively engaged in acquiring small and middle-sized animals using strategies other than passive scavenging. The exploitation of large-sized game (Pelorovis) by Lower Pleistocene hominins, as suggested by previous researchers, is supported by the present study.