Cultural beginnings: Plio-Pleistocene archaeological occurrences

Cultural beginnings: Plio-Pleistocene archaeological occurrences from the Afar, Ethiopia J O H N W. K. H A R R I S

Abstract

In the time interval between approximately 2.5 million years and 1.5 million years ago and against a background of changing environmental conditions and the emergence of highly diversified populations of early hominids, the earliest archaeological occurrences have been documented from a number of localities in the Rift Valley of East Africa. These have been attributed to the Oldowan Industrial Complex. More recently, broadly comparable archaeological occurrences have been discovered from Hadar and the Middle Awash located in adjacent areas of the Afar, in Ethiopia. This paper summarizes the age, context and characteristics of these occurrences and offers preliminary comments on their contribution to greater understanding of early hominid adaptive patterns of behavior.

R6sum6

Les plus anciennes d6couvertes arch~ologiques document~es proviennent de la vallfe du Rift en Afrique orientale, datant d'il y a entre 1,5 et 2,5 millions d'ann6es et se trouvant au sein d'une p6riode d'6volution des milieux et d'apparition d'esp~ces tr6s diversifi6es d'hominides. Ces dfcouvertes ont 6t6 attribufes au complexe industriel Oldowayen. Derni~rement, des tbuilles dans l 'Hadar et le moyen bassin de l'Awash, situ6s dans des terres adjacentes ~t l'Afar en Ethiopie, ont mises ~ d6couvert de trouvailles g6n6ralement comparables. Le prdsent article r6sume l'~ge, le contexte et les caractfristiques de ces dfcouvertes et prfsente des commentaires pr6liminaires quant ~ leur r61e possible dans une comprehension approfondie de m6thodes d'adaptation du comportement chez les anciens hominides.

There is a growing body of evidence to indicate that climatic fluctuations and relatively rapid environmental changes occurred in the Great Rift Valley of eastern Africa during the time :interval from approximately 2.5 myr (million years) to 1.5 myr. Studies of the geology, geochemistry, palynology, and paleontology at important fossiliferous and artifact-bearing localities in the Lake Turkana basin, for example, suggest that climatically induced ,ecological changes were probably the result of a reduction in rainfall (Bonnefille 1976; de

4 John W. K. Ilarris

Heinzelin etal. 1976; Eck 1976; Gentry 1976;Jaeger and Wesselman 1976; Cerling etal. 1977; M. G. Leakey I980). Floral and faunal changes were reflected in the replacement of moisture loving, closed forest and woodland savanna species by others adapted to drier and more open bush and savanna grassland. At Olduvai Gorge, research indicates that environmental changes were partly the result of palaeogeographical changes due to faulting as well as to climatic changes from moister to drier and more arid conditions (Hay 1976; Bonnefille and Riollet 1980). It is against this background of environmental transition that there appears in the East African fossil record evidence for diversified populations of early hominids as well as, in the form of stone artifacts, the earliest material manifestations of culturally elaborated behavior.

Although there is only one hominid-bearing locality, the Shungura Formation, in the Lower Omo Valley of Ethiopia, hominid populations were presumably widespread in East Africa in the time period 2.5 to 2 myr (Howell and Coppens 1976). Moreover, various but as yet unspecified selection pressures resulting in part from the environmental changes were operating on hominid populations. These led to the differentiation and ultimately to the speciation of the hominids, accounting for the presence of at least two and possibly three species in the East African fossil record by about 2 million years ago. Figure 1 shows that

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Figure 1 Early hominid species found in the fossil record of East Africa and the kinds and timing of anatomical and behavioral changes that took place during the Plio-Pleistocene.

Cultural beginnings 5

these species would include Homo habilis, which exhibits significant brain expansion compared to earlier hominids, the robust australopithecine, Australopithecus boisei, and perhaps a more gracile form, Australopithecus africanus (Howell 1978; Walker and Leakey 1978). The trend to brain expansion continues in the Homo lineage with the replacement of Homo habilis by Homo erectus at 1.5 myr (R. E. F. Leakey 1976; Walker et al. 1982). By that time, residual gracile australopithecine populations had become extinct, and although examples ofAustralopithecus boisei still occur in the fossil record, this form too becomes extinct by approximately 1 myr (Howell 1978).

It is in the same strata that yield evidence for highly diversified hominid populations that the earliest archaeological occurrences have been recorded. Following large scale excavations in Bed I and Bed II at Olduvai Gorge, the nature and character of these occurrences were described and defined by Mary D. Leakey (1971). The artifact occurrences recovered f?om Bed I became the type set of the Oldowan Industry, and in more recent years similar occurrences have been documented and described, for example from the Omo, Koobi Fora, Melka Konture and Chesowanja (Chavaillon 1976; Merrick 1976; Isaac 1976; Harris 1978; Chavaillon et al. 1979; Gowlett et al. 1981). Clearly, because of the widespread nature of these early stone artifact occurrences, the Oldowan warrants full recognition as an Industrial Complex (Bishop and Clark 1965; Clark et al. 1966).

Finally, the data available indicate that the inception of stone tool manufacture and use closely coincides with the appearance of larger-brained hominid forms attributed to the genus Homo (Isaac 1978; Harris 1980). Moreover, these simple stone artifacts should not be viewed simply as evidence of a capacity for toolmaking; they also provide clues to a broad range of adaptive behaviors on the part of some early hominid populations. Figure 1 shows the timing of significant adaptive shifts in behavior as reflected in the archaeological and fossil hominid record. Furthermore, as Isaac (1981 ) has pointed out, it is widely believed that some of the innovative and adaptive behaviors that initiated the formation of the archaeological record may also have been significant determinants in the trend towards brain expansion. This paper summarizes the age, the context and the characteristics of recently discovered archaeological occurrences fbund in the Plio-Pleistocene deposits at Hadar and the Middle Awash, in Ethiopia, and offers preliminary comments on their behavioral significance.

Hadar and the Middle Awash are situated close to the banks of the Awash River in adjacent areas of the low-lying Afar Depression at the northeast terminus of the Ethiopian Rift Valley. Figure 2 shows their location in relation to Plio-Pleistocene hominid and archaeological sites found elsewhere in or on the flanks of the Rift Valley of eastern Africa. Both study areas constitute a portion of the west central Afar sedimentary basin, which is a N-S trending elongate sedimentary structure that runs parallel and adjacent to the Ethiopian Western Escarpment (Taieb 1974; Taieb et al. 1976). In this trough-shaped depression fluvial, deltaic, and lacustrine sediments accumulated, preserving a unique paleontological and archaeological record for the late Cenozoic of eastern Africa (Johanson et al. 1982; Kalb, Oswald et al. 1982; Clark et al. in prep.). The Plio-Pleistocene archaeological occurrences reported here sample two separate time intervals during the sedimentary history of the west central Afar basin. The age of the Hadar occurrences is estimated to lie between 2.4 myr and 2.7 myr, whereas the earliest occurrences from the Middle Awash are approximately 1.3 myr to 1.5 myr.

6 John W. K. Harris

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Hadar

Since 1973 multidisciplinary palaeoanthropological studies by the International Afar Research Expedition at Hadar have contributed significantly towards a greater understanding of our zoological family, the Hominidae, during the Pliocene. Surveys undertaken in sedimentary deposits of the Hadar Formation over four successive field seasons (1973-1976/77) recovered abundant vertebrate fauna, including numerous well-preserved hominid specimens and the oldest known stone artifacts (Johanson and Coppens 1976; Johanson and Taieb 1976, 1978;Johanson etal. 1978, 1982; Corvinus and Roche 1976, 1980; Roche and Tiercelin 1977, 1980; Harris and Johanson 1982; Harris in press). Geological, paleontological and geophysical studies have established the stratigraphy and nomenclature and provided a chronological and biostratigraphical framework for assessing the age of the hominid and artifact finds (Taieb et al. 1976; Taieb and Tiercelin 1979; Gray et aI. 1980; Gray 1980; Aronson et al. 1977; Schmitt et al. 1980; Walter 1980; Walter and Aronson 1982).

Over 240 hominid specimens, representing a minimum of 35 individuals, have been recovered from the Hadar Formation and these have been attributed to one taxon, Australopithecus afarensis ~ohanson et al. 1978; Johanson and White 1979). Figure 3 shows that, on the basis of the geochronology, the hominid fbssils span a time range of approximately 3.0 myr to 3.5 myr. Palaeoenvironmental reconstruction indicates that the early hominid localities sample low energy channel and floodplain lake margin depositional environments situated in low-lying areas of an alluvial plain that was intermittently inundated by lake waters (Taieb and Tiercelin 1979; Gray et al. 1980).

In contrast to the hominid finds, the early stone artifact localities come from higher up in the stratigraphic sequence and are thus younger in age. Furthermore, the nature of their geological context indicates past depositional environments associated with high energy streams located on the alluvial plain between the plateau and the lake margin. Figure 3 shows their age to lie between approximately 2.4 myr and 2.7 myr. Stone artifacts of this great antiquity were first discovered by Gudren Corvinus to the west of the main hominid-bearing localities in an area where downcutting by the Gona River is today exposing sections of the upper beds of the Hadar Formation (Corvinus 1976; Corvinus and Roche 1976; Taieb and Tiercelin 1979). Evidence for the age, the nature of the geological contexts and the characteristics of the Gona River archaeological occurrences are discussed below.

Stratigraphy and dating

The sequence of Plio-Pleistocene sediments of the Hadar Formation so far studied extends over an area of 65 square kilometers. This sequence is well exposed today in badtand topography as a result of dissection by the Awash River and its tributaries. The Hadar Formation has an aggregate thickness of 280 meters and, due to the presence of laterally extensive marker beds (mainly volcanic tufts), has been subdivided into fbur stratigraphic members: the Basal Member, the Sidi Hakoma Member, the Denan Dora Member and the Kada Hadar Member (Taieb et al. 1976). The sediments comprise lacustrine, lake margin and associated fluvial deposits related to an extensive Plio-Pleistocene lake that periodically fluctuated and inundated the entire sedimentary basin.

8 .John I4/. K. Harris

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The stone artifacts were discovered stratified in fluvial deposits belonging to the upper

beds of the Kada Hadar Member (KH) exposed along the banks of the Gona River and in the badland topography to the west of the river. The most informative archaeological localities are situated approximately 8 km upstream from the confluence with the Awash River where a welt-exposed stratified sequence of coarse gravel and cobble conglomeratic deposits interbedded with finer-grained sands, silts and tephra deposits reached an aggregate thickness of 30 to 40 m. The stone artifacts were found in derived channel contexts and in their lateral fine-grained silty floodplain equivalents (Roche and Tiercelin 1980; Harris and

Johanson 1982; Harris in press). Figure 3 illustrates the stratigraphic relationships of the artifact-bearing conglomerates

and silts to the AST-1, AST-2, and AST-3 tephra horizons in the Gona River section. In particular, the AST-2 tephra has proved to be an important stratigraphic marker for correlation and also a crucial horizon for determining the age of the artifacts. It has been correlated in the field and by feldspar chemistries to the BKT-2 tephra. These identifications have been one of the principal means of correlating the Gona River section and sediments of the Kada Hadar member exposed to the east in the Sidi Hakoma and Kada Hadar tributaries (Taieb et al. t 978; Walter 1980). In the initial publications (Roche and Tiercelin 1977, 1980) the estimate for the age of the artifacts was based on potassium argon and fission track age determinations on the BKT-2 tephra, the correlative of AST-2, which yielded dates of 2.6 -+ 0.23 myr and 2.58 + 0.23 myr respectively (Aronson et al. 1977). These dates have been revised and more recent K-Ar age determinations show the BKT-2 tephra to be 2.88 + 0.2 myr (Walter and Aronson 1982). The reliability of this new date is corroborated by a fission track age determination of 2.7 + 0.22 myr on the AST-2 tephra that is within the range of uncertainty of the K-Ar age (Walter 1980). Taken together these dates set important new maximum limits on the age of the artifacts.

The palaeomagnetic polarity data collected from the Hadar Formation, when calibrated against the absolute age determinations on the tephra horizons, show that the upper beds of the Kada Hadar Member belong within the Gauss normal epoch following the short Kaena reversed event, and thus have an age of between 2.4 myr and 2.8 myr (Aronson et aI. 1977; Schmitt et al. 1980). The minimum age limit is in concordance with a new fission track date on the BKT-3 tephra outcropping near the top of the Kada Hadar Member, which yielded an age of 2.4 + 0 .4myr (Walter 1980). Therefore, on the basis of absolute age determinations, the palaeomagnetic stratigraphy and stratigraphic correlation, the Gona stone artifacts range in age between approximately 2.4 myr and 2.7 myr, and are substantially older than the earliest archaeological occurrences fbund elsewhere in the Rift Valley of eastern Africa. The earliest artifacts reported from Member E and Member F in the Shungura Formation at the Omo River are of the order of 2.1 myr (Chavaitlon 1976; Merrick 1976). Further to the south, the earliest artifacts found in the Lower Member of the Koobi Fora Formation east of Lake Turkana and in Bed I at Olduvai Gorge are dated to t.8 myr (Drake et al. 1980; McDougall et al. 1980; Curtis and Hay 1972).

The sites: context and assemblage characteristics

Archaeological studies at Hadar leading to tile recovery of Pliocene age stone artifacts were initiated by Corvinus in 1973 and 1974. Much of this earlier work, however, was

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concentrated on surveying the extensive fluvial gravels and sands that uncomformably

mantle the Plio-Pleistocene Hadar Formation (Taieb et al. 1976). These surveys and small scale excavations undertaken principally along the banks of the Sidi Hakoma and Kada

Hadar tributaries produced biface and flake occurrences found in derived channel contexts. The artifact occurrences are classified as Acheutian due to the diagnostic bifacial artifact forms present. They are of Middle Pleistocene age (Corvinus 1975, 1976; Corvinus and Roche 1976, 1980). In 1974, the archaeological survey was extended west to include sedimentary exposures in the Gona River drainage. At one locality, Afaredo I (renamed Kada Gona t), several whole flakes made ofbasatt were discovered and are reported to be derived from a calcareous tuffaceous silt within the upper beds of the Hadar Formation

(Corvinus 1976). No excavation was undertaken; however, in light of this important discovery, the survey was continued by H~l~ne Roche in 1976 and by the author in 1977 and several new occurrences of stone artifacts were found near the Gona River. Figure 4 shows the location of the Kada Gona 2-3-4 site and the West Gona site in well-exposed fluvial deposits of the Kada Hadar Member, which are several kilometers downstream to the south of the Afaredo site.

Kada Gona 2-3-4 site

The investigation of this site was undertaken by Roche and Tiercelin in 1976. Short reports were published on the stone artifacts, which were recovered from two stratigraphic levels in the local sedimentary sequence on the east bank of the Gona River: the middle conglomerate and the upper conglomerate (Roche and Tiercelin 1977, 1980). In the stratigraphic interval between the middle and upper conglomerates, there are interbedded deposits of clays, sands, silts and the AST-2 tephra horizon. The in situ stone artifacts were found dispersed in secondarily derived contexts. The presence of large clasts the size of cobbles and the massive thickness of the conglomerates illustrate the high energy nature of the stream channel deposits. These features of the depositional environments, when taken together with the abraded physical condition of the stone artifacts, indicate transported and redeposited materials. The 16 trachyte and basalt artifacts recovered in situ from the middle conglomerate comprise both unifacially and bifacially flaked cobbles (chopper cores), cores (including polyhedrons) and whole flakes. On a sample often cores the dimensions ranged in size from 113 mm/80 mm/4t mm for the largest specimen and 71 mm/53 mm/42 mm fbr the smallest. The whole flakes measured from 119 mm/63 mm/33 mm to 39.5 mm/34.5 mm/ 11 mm in length, breadth and thickness. In addition, five cores were derived from the upper conglomerate. Although the sample is small, the Kada Gona 2-3-4 stone artifacts are

classified as belonging to the Oldowan Industrial Complex on morphological/typological and technological grounds as well as by the size range of the cores and flakes. They are comparable to the stone assemblages recovered from Bed I at Olduvai Gorge, described by M. D. Leakey (1971), and from the Lower and Upper Members of the Koobi Fora Formation, east of Lake Turkana, described by Isaac (1976) and Harris (1978). From a behavioral point of view, the stone artifacts provide important evidence for the tool making capacities of early hominids living on the surrounding terrain. Furthermore, the geological evidence shows that local streams during periods of high energy flow were transporting clasts of cobble size in their bed load. The cobbles were being deposited and incorporated in

12 John I47. K. Harris

conglomerates that were presumably at times exposed, oft~ring a readily available and important source of raw material.

West Gona site

The site was discovered in badland deposits of the Kada Hadar Member found outcropping west of the Gona River during archaeological survey and geological reconnaissance by

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Figure 5 a) West Gona archaeological site plan. b) West Gona local site stratigraphy.


Harris and Taieb in January 1977 (Fig. 4). Two concentrations consisting of stone artifacts and fossilized bone were found on the surface, and a small test excavation revealed a low density archaeological occurrence stratified in fine-grained silt floodplain deposits. These stone artifact and bone occurrences represent real anomalies in the distribution pattern of archaeological traces of hominid activities across the landscape because, but for one or two small concentrations found elsewhere, over the rest of the surveyed area stone artifacts are missing and the sediments are generally poorly fossiliferous. Preliminary field correlation shows that the site stratigraphically overlies the middle conglomerate and the 2.7 + 0.2 myr AST-2 tephra exposed in the main Gona river section (see Fig. 3). It was possible to trace the beds in the field and no major unconformities were observed between the two areas. A preliminary date of 2.4 million years is therefore suggested for the West Gona artifacts based on the minimum age for the Kada Hadar Member (Aronson et al. 1977; Schmitt et al. 1980).

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14 John W. K. Harris

This would make them younger than the earliest artifacts found on the east bank; more precise stratigraphic relationships must await further detailed geological mapping.

Figure 5a shows the site plan and Figure 5b summarizes the local stratigraphic sequence.

Figure 6 shows that the in situ stone artifacts and fragmentary bone occur as a low density

concentration scattered within a 20 to 30 cm lens of sandy silt. The archaeological occurrence

appears to be in primary context. The low energy nature of the sedimentary environment of deposition as well as lack of size sorting or preferred orientation and the fresh condition of the

stone artifacts suggest that the archaeological occurrence was minimally disturbed during site formation and by subsequent burial processes.

Preliminary palaeogeographical reconstruction shows that in the lower part of the section

there is evidence for high energy stream activity. On the basis of the upward-fining fluvial

sequence, it would appear that the stream migrated laterally away from the locality, and fine-grained sands and silts were deposited in a low" energy floodplain environment. The

archaeological occurrence provides evidence for hominid activities located on a stream bank or adjacent floodplain subject to seasonal flooding. The onset of ponded and marshy

conditions is shown by the deposition of massive beds of clays containing root casts capping

the sequence. No artifacts were found in the clays; such environments were probably less suitable for hominid occupation.

The surface stone artifacts were concentrated in two low density patches near the base of eroded exposures of the Kada Hadar Member. A small test excavation (Fig. 7) measuring

10 m 2 located at the southern end of the outcrop (Locality 2) yielded 19 stone artifacts and five bone fragments. This low density scatter was concentrated vertically over 10-15 cm

Figure 7 The excavation at locality 2, West Gona archaeological site with the Gona River in tile background, at Hadar.


within a lens of sandy silt (SZ). The areal boundaries of the occurrence were not defined. A

chopper/core found in the same lithologic horizon of a geological trench at the edge of the

excavation indicates that the archaeological horizon extends laterally further to the west.

Table t shows the composition of the stone assemblage, which comprises two basic classes of artifact forms: flaked cobbles and whole and fragmentary broken flakes (Fig. 8: 1,2). The

flaked cobbles are small (< 100 mm) and the presence of several generations of flake scars

testifies to core reduction sequences. The extremities or edges are sharp and there is no evidence for blunting or abrasion to suggest their utilization as implements or 'tools'. For this

reason the flaked cobbles are classified as 'cores' (sensu stricto) rather than being placed in a

chopper ' tool' category following the typological system devised by M. D. Leakey (1971).

The whole flakes and flake fragments exhibit noticeable striking platforms and pronounced

bulbs of percussion. A number of the flakes have cortical dorsal surfaces, possibly suggesting

that some flaking was done by hominids at the site. Both trachyte and basalt were used for

stone artifact manufacture. Although no unmodified cobbles or 'manuports ' were found in the excavated occurrence, a readily available source of raw material was probably close at

hand. A maximum dimension of 100 mm was measured on basalt cobbles incorporated in the basal conglomeratic horizon at the site; this provides an index of the size of clast

transported in the bed load of the local streams and corresponds to that of the flaked cobbles

found at the site. I t is likely then, that cobbles of a similar size were available for artifact manufacture in nearby conglomerates at the time of hominid occupation.

Table 1 West Gona archaeological site.

SURFACE Location 1 Location 2 Location 2

EXCAVATED range of maximum mean dimension (mm) (mm)

Core (chopper) 2 - - 1 Whole flakes 6 5 5 Flake fragments 7 4 12 Core fragments 1 5 1

TOTAL 16 14 19

Bone fragments 7 3 5

95-84 90 72-26 42 51-14 33 81

The faunal remains are ti 'agmentary and only one specimen is identifiable to taxon: a small piece of the plate of an elephant molar. The co-occurrence of stone artifacts and bone appears

to be more than a fortuitous association. The low energy environment of deposition in addition to the fresh condition of the stone artifacts and the lack of size sorting (specimens range in maximum dimension from 84 mm-14 mm) suggest that the occurrence was the result of hominid activities rather than an accumulation concentrated by fluvial processes. This has an important bearing on a range of questions related to the diet and subsistence activities of Pliocene hominids, which will be fully explored in future site investigations.

The artifact sample from the West Gona site is indistinguishable in terms of morphological and technological characteristics from the artifacts recovered from the Kada Gona 2-3-4 site. The presence of pieces of smaller size in the whole flake and flake fragment categories of the


Figure 8 1. ~Core' (chopper) from the West Gona archaeological site, Hadar. Note the presence of several generations of flake scars indicating that the *core' has been considerably reduced. 2. Sample of the excavated occurrence of whole flakes from the West Gona archaeological site, Hadar.


West Gona assemblage is presumably due to the relatively undisturbed sedimentary context. Overall both assemblages show clear affinities to the artifact occurrences found in Olduvai

Gorge Bed 1 and the Koobi Fora Formation, east of Lake Turkana, attributed to the Oldowan Industrial Complex (M. D. Leakey 1971; Isaac 1976; Harris 1978). One class of artifact, retouched or trimmed pieces, is clearly missing, perhaps due to sampling error. The Gona River artifacts contrast with the artifacts recovered from Member F of the Shungura Formation at the Omo River mainly as a consequence of differences in raw materials (Chavaillon 1976; Merrick and Merrick 1976). The Omo artifacts were made on quartz, which shatters on impact and produces large numbers of small angular pieces. As a result, the greater proportion of these assemblages consists of very small flakes and angular fragments which are of limited value for comparative purposes.

Middle Awash

Systematic archaeological survey of the Middle Awash was undertaken in 1981 as part of a multidisciplinary palaeoanthropological investigation coordinated byJ . D. Clark and T. D. White. The study area is located along the center of the Awash River valley, south of Hadar and north of the town of Gewani (Fig. 2). Extensive deposits of Miocene, Pliocene and Pleistocene sediments are found outcropping along the eastern and the western Awash Valley margins as well as in the basin center. These proved to be richly fossiliferous (including hominids) and contain a virtually uninterrupted paleontological record over the last six million years. FossiIiferous deposits of Pleistocene age are particularly well exposed east of the present-day Awash River, which bisects the study area. Survey of this area located numerous archaeological occurrences that provide evidence for hominid occupation over the last 1.5 million years (Clark et al. in prep.).

Figure 9 shows the location of Early Pleistocene Oldowan and Middle Pleistocene Acheulian occurrences. These were discovered in laterally extensive deposits of fluvial sediments between Meadura and Matabaietu. To the north of Meadura, concentrations of Middle Stone Age and Later Stone Age materials were found in late Pleistocene and Holocene sediments. In addition, early Acheulian artifacts were discovered during a brief survey of Pleistocene deposits on the west side of the Awash River, demonstrating that area's potential and thus high priority for further large scale survey. In this section, discussion will center on a description of the Oldowan occurrences, the earliest archaeological traces of hominid occupation in the Middle Awash. Preliminary reports on the overall results of the 1981 palaeoanthropological investigations are in preparation and will be published elsewhere (Clark et al. in prep.).

M. Taieb (1974) was the first to realize the palaeoanthropological significance of the Middle Awash during geologic reconnaissance in the late 1960's. In 1971, he guided a group from the Pan African Congress to exposures containing early stone artifacts north of Gewani (Abebe et al. 1976). Small scale exploratory studies of the Middle Awash archaeology were subsequently undertaken by J. Kalb and a Southern Methodist University group coordinated by F. Wendorffor short periods between 1975 and 1978 (Kalb 1978; Kalb, Jolly et al. 1982). A diverse group of archaeological occurrences was discovered including one described from Matabaietu containing Oldowan type artifacts with a suggested age of 2 myr (Larson 1977). The occurrence consisted of heavily patinated finds that were not in situ and,

18 John Pr; K. Harris

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Figure 9 Lower and Middle Pleistocene archaeological sites located east of the Awash River in the central part of the Middle Awash study area.


as is explained below, the designation of Matabaietu as an Oldowan locality remains problematic. During survey in 1981, the earliest stratified occurrences of Oldowan artifacts

were found in previously undiscovered localities in the Bodo drainage. In the time available, several surface samples of stone artifacts were identified, plotted, lifted and removed to the National Museum of Ethiopia in Addis Ababa for study. One small excavation was undertaken that yielded stone artifacts together with fragmentary fauna in a fine-grained sedimentary context. As the study of the artifacts is still in progress, only brief preliminary comments are offered on the stratigraphy and age of the occurrences, their context, and morphological/typological characteristics.

The geological sequence comprises thick fluvial, deltaic and lacustrine sediments intercalated with volcanic tuffaceous horizons that accumulated in the basin over the last 6 million years. A recently published geological summary of the Middle Awash deposits forms a basis for describing the stratigraphical provenience of the earliest stone artifact occurrences (Kalb, Oswald et al. 1982). These are found in the early Pleistocene 'Middle Bodo' beds. As yet no artifacts have been recovered from the Pliocene 'Lower Bodo' beds or outcrops of equivalent age surveyed from Wee-ee to Meadura.

Figure 9 shows the locations of Oldowan occurrences being exposed today along the eroded margins of ephemeral streams in the Bodo area. The localities are clustered in two fault-bounded blocks of sediment that are informally called the 'Middle Bodo' beds following Kalb, Oswald et al. (1982). The northern block contains diagnostic suids, equids, and bovids, which indicate an age of 1.3 myr to 1.5 myr (White pers. comm.; Clark et al. in prep.). Stone artifacts and fragmentary fossilized fauna occur stratified together in river sands and gravels in the northern block. These elements are found in lateral silty bank and overbank deposits, some of which, in the southern block, overlie a grey vitric tuff. The stratigraphic relationships of the northern and southern archaeological occurrences at Bodo remain to be worked out in detail and geochronologic work by R. Walter on the volcanic units is in progress.

The most informative site, designated BOD-A3, is situated in the southern block near the headwaters of the Ounda Bodo catchment. Nearly 400 stone artifacts and numerous fragmentary faunal remains were found in relatively fresh condition scattered over a steep-sided outcrop of fine-grained fluvial deposits. Table 2 shows that surface artifacts include several flake scraper forms as well as modified and utilized flakes and cobbles, including hammerstones. The major proportion of the assemblage consists of cores, unmodified flakes and flaking debitage. A further 45 stone specimens were recovered in situ

from a 10 m 2 excavation. Basalt was the preferred raw material but artifacts were also made of rhyolite, ignimbrite and chert.

The great majority of faunal specimens are highly fragmentary and the long bone fragments occasionally display longitudinal and spiral fractures (R. Blumenschine pers. comm.). No cutmarks have been found. Up to six species are present including several bovids, an equid, an elephant, and possibly a hippo. Most specimens derive from a large bovid species which, unlike the other taxa, is well represented by most classes of skeletal parts. The fresh condition, lack of size sorting, lack of preferred orientation and sedimentary context of the specimens indicate a low energy environment of silty river overbank deposition. This suggests an archaeological occurrence in primary context or, at most, minimally disturbed.

Several similar archaeological occurrences were found nearby in overbank silty deposits.


Close to one of these, designated BOD-A4, clay samples were collected from a cone-shaped, reddish discolored area. Analysis by M. Barbetti of the University of Sidney Radiocarbon

Laboratory showed that the samples were baked in antiquity. In recent years, the question of the antiquity of hominid control of fire in Africa has been reopened with reports of baked clay

within archaeological horizons at Koobi Fora, Chesowanja and Gadeb (Barbetti et al. 1978,

1980; Gowlett et al. 1981). In view of the controversial nature of this evidence and due to the

fact that these localized discolored areas are widespread phenomena in the Middle Awash, further detailed excavation, sectioning, and sampling will be undertaken at BOD-A4 and

elsewhere in an effort to determine the agencies that caused them to be baked.

Table 2 Middle Awash archaeological sites.

B O D A 3 B O D A 5 H A R A 6 Surface Excav. Surface Excav. Surface Excav.

Scraper 5 3 Discoid 1 Sub-spheroid 1 Miscellaneous 4

Mod. flakes, frags. 6 3 Mod. cobble 3 Hammerstone 2

Flakes 187 24 25 Flake frags. 127 17 9 Cores 30 2 17 Core frags./chunk 27 4

Cobbles 2 n = 389 n = 45 n = 65

1

34 17 7

1 n = 60

In contrast to the Oldowan finds in fine-grained depositional environments, two artifact

occurrences in fluvial sands and gravels were located near the banks of the Kada Bodo (northern block). One of these, BOD-A5, yielded 70 artifacts including a variety of subtypes

ofsmal t cores, several small retouched flakes, unmodified whole flakes and fragments (Fig. 10). Several specimens were observed in situ in a well-exposed, carbonate cemented

sandstone. The stone artifact occurrences sampled at Bodo show morphological and technological

features in common with those stone assemblages recovered from Olduvai Bed 1 and from

the KBS Tuff unit at Koobi Fora, which were classified under a typological system devised by M. D. Leakey (t 971 ). The diminutive and exhausted nature of the flaked cobbles suggest that the Middle Awash 'tools' represent the by-products of least-effort solutions to the production of small, sharp-edged flakes. Therefore, we formally adopted a classificatory system treating the flaked cobbles as 'cores' instead of 'tools', following Clark and Kleindienst (1974). Without exception, the specimens so far recovered fail in the subcategory of unspecialized 'cores' because there is no evidence for preparation of the flaking surface or striking platfbrms. The overall diminutive nature of the artifacts is reflected in that, almost without exception, the 'cores', flakes and fragments are smaller than 100 mm in maximum dimension. Furthermore, the stone artifact assemblages are distinguishable fi'om the


Figure 10 Cores (top) and whole flakes (bottom) recovered from the surface of the Oldowan site Bodo A5, Middle Awash.

Acheulian assemblages tbund elsewhere in the Middle Awash inasmuch as they are completely devoid of bifaces.

Survey elsewhere on the east side of the Middle Awash produced stone artifact occurrences that can only tentatively be assigned to the Oldowan Industrial Complex. At Matabaietu, in addition to relocating a site where a surface Oldowan occurrence had been previously reported (Larson 1977), small numbers of heavily patinated artifacts were found at several other localities on the surface amongst well preserved bones of elephant and hippo. No significance is attached to these associations, however, because of the deflated nature of the deposits and the probability that geological processes were responsible for the surface accumulation of stone artifacts and bone. Contrary to earlier publications (Larson 1977; Kalb, Jolly et al. 1982), the designation of Matabaietu as an Oldowan locality remains problematic until further field studies are undertaken and well-defined, stratified archaeological occurrences are discovered and excavated.

The small core and flake component typical of the Oldowan is also characteristic of three archaeological occurrences discovered in Middle Pleistocene sediments at Hargufia, north of Bodo. At locality HAR-A6, 60 surface artit~tcts derived from tuffaceous silty sand deposits were comprised of small amorphously flaked cobbles, diminutive 'cores', small flakes and fragments (Table 2). Their age and stratigraphic position relative to other archaeological occurrences at Hargufia as well as to other Oldowan occurrences in the Middle Awash remain to be determined.


Implications of the Hadar and Middle Awash archaeological occurrences

Cultural affinities

The Gona River artifact occurrences indicate that by approximately 2.5 million years ago early hominids had already mastered the art of simple percussion stone flaking. The discovery of cores and the residue from flaking reduction sequences--whole flakes and broken flakes--attest to a rudimentary knowledge of the use of conchoidal fracture to produce simple stone implements. In this preliminary report, the West Gona sample of flaked cobbles are treated as cores. This classification is based firstly on the lack of abrasion on the sharp angular 'core' edges. Secondly, more recent studies on artifact assemblages of similar character suggest that flaked cobbles or 'cores' are likely to represent the by-products of least-effort solutions to obtain sharp-edged flakes, which then served as 'tools' (Bunn et al. 1980; Toth 1982). On the other hand, if Mary Leakey's typology (1971) based upon morphological criteria is adopted, then amongst the combined sample of flaked cobbles from the West Gona and the Kada Gona 2-3-4 sites, choppers, polyhedrons and discoids, which are characteristic of the 'shaped tool' category, are clearly present. Therefore, the occurrences t?om the Gona River are attributed to the Oldowan Industrial Complex because of broad similarities, in technological and morphological features and in the overall assemblage composition, to well-defined occurrences described particularly from Olduvai Gorge Bed I and the Koobi Fora Formation, east of Lake Turkana (M. D. Leakey 1971; Isaac and Harris 1978). In addition, occurrences of this character belonging to a 'core' or 'core tool' and flake craft tradition are compatible with the definition of the dominant lithic technology of mode 1: chopper tools and flakes (G. Clark 1969). However, the Gona artifacts are significantly older and predate previously documented Oldowan type occurrences by approximately 500,000 years.

The earliest stratified archaeological assemblages recovered from Bodo in the Middle Awash are similarly characterized by small 'cores' and flakes with the addition of various flake scraper forms and miscellaneously trimmed pieces. This trend towards relatively more diversified artifact forms is seen in assemblages recovered from the Upper Member of the Koobi Fora Formation, attributed to the Karari Industry, and in those belonging to the Developed Oldowan A found in Middle Bed II at Olduvai Gorge, which also date to approximately 1.5 myr (Harris 1978; M. D. Leakey 1971). In every instance, however, these assemblages, on the basis of stratigraphy and absolute age determinations, are older than assemblages that provide evidence for the removal of large flakes (larger than 100-150 mm) and contain bifaces, and which have been variously attributed to the Developed Oldowan B and the Acheulian Industrial Complex in East Africa (Fig. 11). Therefore, the Bodo assemblages, as well as the Karari and Developed Oldowan A assemblages on technological and morphological grounds belong to a 'core' or 'core tool' and flake tradition and are most parsimoniously accommodated in the Oldowan Industrial Complex.

Behavioral inferences

The distribution pattern of stone artifacts in relationship to palaeogeographicat features across ancient landscapes is a potential source of information regarding early hominid

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land-use and settlement patterns. Preliminary studies at the West Gona site indicate archaeological traces of hominid activities close to the margin of a stream channel. This is consistent with the overall tendency for the earliest archaeological sites to be situated close to stream courses (Isaac 1982). This choice of location was probably determined by several factors. In addition to the advantages of water, shade and shelter, plant foods, which presumably constituted the greater part of the diet of early hominids, are found in their greatest abundance in these better-watered areas of the landscape. Furthermore, in the case of the Gona River sites, raw materials for stone tool manufacture were readily available in nearby stream conglomerates.

The geological context of the earliest archaeological occurrences at Bodo in the Middle Awash indicates that hominid occupation sites were also located in and around the margins of stream channels. The 'Middle Bodo' beds show two contrasting lithofacies: fossiliferous and artifact-bearing gravels, sands and silts, and massive beds of clays, generally non-fossiliferous and lacking in stone artifacts. Preliminary palaeogeographical reconstruction based upon characteristics of these contrasting depositional environments together with the distributional pattern of archaeological traces over the landscape suggest hominids were locating their occupation sites close to the margins of local tributary stream channels in the more elevated hinterland of the sedimentary basin and avoiding the low-lying swampy floodplain of the palaeo-Awash in the center of the basin (Clark et al. in prep.). This should be taken only as a working hypothesis. For example, a similar sort of pattern to the distribution of a set of archaeological 'sites' with an age of 1.5 myr was observed in the Koobi Fora basin (Harris 1978; Harris and Isaac 1980). The majority of the archaeological 'sites' were situated away from the lakeshore in the interior of the sedimentary basin; however, as more became known of the study area, less conspicuous archaeological traces of the presence of hominids in lake margin environments were found. These included several much lower density artifact occurrences and a fossilized faunal occurrence completely devoid of any stone artifacts, yet containing several bones exhibiting cut marks that could only have been made by a stone implement (Isaac et al. 1976; Bunn 1982). Both Hadar and the Middle Awash provide rare opportunities for conducting similar sorts of studies leading to a greater understanding of early hominid land-use.

The presence of artifacts in the geological record may signify changes in the diet or show certain dietary preferences by some hominids fbr food items requiring stone implements in their acquisition and/or preparation (Mann, 1972). In view of marked environmental changes brought about by more arid conditions as documented in the Lake Turkana basin and the Afar, interspecific and intraspecific competition for already existing food resources or the search for alternative food resources to maintain stable populations would have been heightened between 2.5 myr and 2 myr (Bonnefille 1976; Cerling et al. 1977; Gasse et al.

1980). Circumstantial evidence from the co-occurrence of stone artifacts and fragmentary fauna at the West Gona site suggests hominid activities related to the preparation and consumption of meat. This remains to be proven, but it is clear that the pristine sharp flakes and fragments found at the site would have fimctioned adequately as knives for cutting through hide and slicing through muscle or sinew. It is suggested that some populations of early hominids, presumably in part as a response to changing environmental conditions, were extending their food resource base to include meat in their diet. More importantly, certain adaptive advantages would result from hominids adopting a diet that included a high


protein source such as meat, not the least of which would be in terms of fitness potential

compared to other hominid populations with less nutritious diets obtained perhaps from less predictable sources (Milton 1981).

In some instances, sites characterized by the concentration of stone artifacts and fragmentary faunal remains have been referred to as 'home bases' (Isaac 1978). Sites of this nature found in Bed I at Olduvai and in the Koobi Fora Formation, east of Lake Turkana, illustrate the idea that new adaptive strategies involving a set of concomitant behaviors including the transport oftbod and materials, tool making, meat eating and food sharing had become established by the Early Pleistocene (M. D. Leakey 1971; Potts and Shipman 1981; Isaac 1981; Bunn et al. 1980). In light of the hominid and archaeological discoveries at Hadar, these sorts of adaptive behaviors may have taken place significantly earlier in time.

Site 333, located in deposits of the Denen Dora Member at Hadar, offers indirect evidence of a different kind from an earlier time horizon (~ 3.0 myr). Here the fragmentary fossilized remains of at least 13 hominid infants, juveniles and adults were recovered. This suggests that early hominids congregated in groups ~ohanson 1976}. Thus it is possible that selection pressures were already operating favoring behaviors such as social role differentiation associated with cooperative subsistence strategies and reciprocal food sharing in order to maintain cohesive social groups consisting of adults, children and perhaps aged or non-productive members. Furthermore, it has been pointed out that such social behavioral adaptations favored through natural selection may have had a profound influence on the reorganization and expansion of the brain (Holloway 1973; Wolpoff 1980; Isaac 1981).

Therefore, the Gona River archaeological occurrences become a critical factor in determining what sort of behavioral adaptations were manifested by at least 2.5 million years ago. The discovery of early stone artifacts denotes a shift in foraging behaviors which required the utilization ofsimpte stone implements with sharp as well as blunted edges. The manufacture of opportunistically flaked objects with sharp edges, in particular, presumably arose out of new sets of activities requiring simple cutting, scraping or piercing devices, marking the beginning of an awareness in the relationship between form and function. As suggested above, their association with fragmentary bone at the West Gona site possibly indicates a broadening of the food resource base by some populations of hominids to include the consumption of meat. Also, the low energy fine-grained nature of the sedimentary deposits containing the artifacts at the site provides evidence for the transportation of stone by early hominids. Cobblestones, later flaked at the 'site', and/or already fabricated stone artifacts were transported from a source area and were concentrated on the floodplain near the margins of a stream as a result of hominid activities. Until large scale excavations are undertaken at the West Gona site and the co-occurrence of stone artifacts and faunal remains is described and defined in detail, any further elaboration of behavioral adaptations based upon the present archaeological evidence would be premature.

Although hominid activities related to the manufacture and use of simple stone artifacts may reflect a growing advance in mental capacity, whether or not these represent the behavioral manifestations of a larger-brained hominid remains a critical but an unresolved issue. Unfortunately, there is only one locality, the Shungura Formation in the Omo River Valley, yielding hominid specimens from the fossil record sampling the time range (2.5 myr-2.0 myr) bearing on this issue (Howell and Coppens 1976; Howell 1978; Boaz 1979). Here the earliest specimens attributed to Homo date approximately 2.2 million years to 2.0


million years and are contemporary with the earliest remains of another species, Australopithecus boisei, although some authors have suggested that this robust australopithecine may have emerged at an earlier time (Coppens 1980; Grine 1981). However, the remains are fragmentary and provide no information on trends towards brain expansion. The issue may be resolved in the future by a comprehensive survey tbr hominid remains in the Gona Area, particularly in the large and well-exposed deposits to the west of the river. The survey has so far been concentrated in the east and on older deposits, which have yielded hominid specimens attributed to a primitive australopithecine, Australopithecus afarensis (see Fig. 3).

The Middle Awash Oldowan archaeological occurrences promise to provide further evidence for reconstructing early hominid adaptive patterns of behavior from slightly younger ranges of time, approximately 1.5 million years ago. Of potentially great significance is the evidence for fire. This takes the form of localized patches of clay, which were baked by fire in antiquity (Clark et al. in prep.). Although these traces of fire appear to be widespread phenomena in the Middle Awash, they were observed and in one case sampled close to one of the Oldowan archaeological sites in the Bodo locality. One possibility is that the fire was the result of hominid activities. Only humans have learned to overcome a fear of fire that is instinctive amongst animals. Thus, in very real terms, the controlled use of fire by early hominids would have had an important adaptive advantage as a means of protection against larger animals and, more particularly, carnivores. On the one hand, it would have facilitated moves into new and unfamiliar habitats and, on the other, occupation and more efficient exploitation of drier and more open grassland habitats where bush and tree cover were more restricted.

It is important to realize that, beginning approximately 1.5 million years ago, there are archaeological traces that indicate not only the occupation by early hominids of more elevated areas on the high plateau such as Gadeb (Clark and Kurashina 1979), but that the drier and presumably more open grassy hinterlands of sedimentary basins in the floor of the Rift were being more intensively occupied, as for example at Karari near Koobi Fora (Harris 1978; Harris and Isaac 1980). This archaeological evidence for the movements of hominid groups into highland environments and for the intensification of occupation of others coincides with the earliest reported traces of fire on early hominid occupation 'sites' at Chesowanja and Gadeb as well as anomalous but so far inconclusive results from the Karari, near Koobi Fora (Barbetti et al. 1978, 1980; Gowlett et al. 1981; Harris 1982). In view of the controversial nature of this evidence the Middle Awash research group is currently treating the controlled use of fire by early hominids as one of several working hypotheses to account for the baked clay patches, particularly where they occur in close proximity to the archaeological occurrences.

Conclusion

The earliest occurrences of stone artifhcts attributed to the Oldowan Industrial Complex have been described from stratified deposits at the Gona River in the Hadar study area with an age of approximately 2.5 million years. It was suggested that in part as a response to environmental changes towards drier and more arid conditions some populations of early hominids broadened their subsistence base. The utilization of stone as a raw material probably arose out of the necessity to produce sharp- and perhaps blunt-edged implements

Cultural beginnings' 27

following an adaptive shift in foraging behaviors. Preliminary insights into the range of activities of Pliocene-age hominids have been described. These studies show that the Gona River deposits will be a major source of information in the future for the elucidation of adaptive patterns of behavior of early hominids from late Pliocene periods of time that are otherwise poorly known in East Africa.

Similarly, preliminary descriptions have been given on the context and characteristics of Oldowan archaeological occurrences found in deposits in the Middle Awash dating to approximately 1.5 myr. Future studies of these concentrations of fragmentary but diagnostic faunas and stone artifacts and their differential distribution across the landscape will provide opportunities to define a range of adaptive behaviors and to document systematically the land-use patterns of early hominids occupying the basin. In addition, the Middle Awash provides a unique opportunity for testing the hypothesis that early hominids had learned the controlled use of fire.

Acknowledgements

My participation at Hadar was the result of an invitation from Donald Johanson and Maurice Taieb, co-directors of the International Afar Research Expedition. I am grateful for their assistance in the field as well as to the Ethiopian and foreign members of the project, particularly Tom Gray, Bill Kimbell and Bob Walter, who helped with the excavation. Desmond Clark invited me to join the Middle Awash Research Project and the success of the archaeological survey was due to all participants in the group. Palaeoanthropological fieldwork at Hadar and the Middle Awash was made possible by grants from the National Science Foundation, the National Geographic Society and the L. S. B. Leakey Foundation, which are gratefully acknowledged. I also thank the Provisional Military Government of Socialist Ethiopia for permission to work at Hadar and the Middle Awash.

The preparation of this manuscript was made possible by funding from the Graduate School, University of Wisconsin-Milwaukee and the Holt Family Charitable Trust. Karin Harris and Mary Korenic helped in its preparation, and I thank Michele Patin for skilled drafting and Barbara Gittings for typing.

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Cultural beginnings: Plio-Pleistocene archaeological occurrences