The 1959 discovery of the hominin fossil Zinjanthropus boisei brought the world's attention to the rich records at Olduvai Gorge, Tanzania. Subsequent excavations of archaeological level 22 (FLK Zinj) Bed I uncovered remains of Homo habilis and a high-density collection of fossils and Oldowan stone tools. The occurrence of this unusual collection of bones and tools at this specific location has been controversial for decades. We present paleoecological data that provide new insights into the origin of FLK Zinj. Our recent excavations 200 m north of the site uncovered a 0.5-m-thick tufa mound draped by Tuff IC, in the same stratigraphic horizon as level 22. Stable isotope analyses indicate that the carbonates were deposited by a freshwater spring. Phytolith analysis of the waxy clay under Tuff IC revealed abundant woody dicotyledon and palm phytoliths, indicating that the site was wooded to densely wooded. The time equivalency and close physical proximity of the two environments indicate the two are related. This study has provided the first documented evidence of springs in Bed I and these data have important implications for the interpretation of hominin behavior in meat acquisition and the ongoing debate on scavenging versus hunting.

Renewed excavations at FLK Zinj and its surrounding landscape have yielded valuable information regarding its paleoecological situation and the prehistoric behavioral function of the site. The density of materials at the main cluster of the site excavated by Leakey contrasts with the bone and lithic scatters surrounding the site. The location of FLK Zinj, situated a few hundred meters away from a freshwater spring, would have enabled hominins access to water, plants and game. The appeal of the spot for hominins (also explained by the presence of a wooded habitat) is confirmed by inferences of its redundant use prior and during the formation of the FLK Zinj paleosol, as witnessed by materials accumulated both under and on the waxy clay deposit that constitutes the FLK Zinj stratum. The single-cluster nature of the site indicates central-place behavior and evidence is provided that hominins occupied the site at a time of very low predation hazards in the area.

The records of early hominins are commonly localized both temporally and spatially even in archaeologically rich basins like Olduvai Gorge, Tanzania. The FLK North site was discovered in 1960, but the reason for the exact location of this dense concentration of fossils and stone tools on a lake-margin flat has not been explained. We present new geological and geochemical information from six excavations in upper Bed I, which revealed up to 1.4-m-thick carbonate deposits, attesting to the presence of freshwater springs in the area surrounding FLK North. The δ18O signatures of the tufa are typical for meteoric water that has evolved during evaporation. Tuff IF that caps the sequence was deposited on uneven topography with the highest area a low-relief ridge between two faults at the archaeological site and lowest areas being sites of groundwater discharge. The model proposed here is that rainfall on adjacent highlands was transported to the basin where faults acted as conduits for water. Similar hydrogeological settings at modern lakes Manyara and Eyasi, currently support lush groundwater forest and woodland despite arid climate. FLK North may have been an “oasis” offering freshwater and shelter for consuming meat by both carnivores and hominins.

The phytolith content of 10 samples collected immediately under Tuff IF (~ 1.785 Ma) at FLK N and other surrounding localities (~ 2 km²) provides a direct botanical evidence for woody vegetation in the eastern margin of Olduvai Gorge during uppermost Bed I time. Observation and counting of 143 phytolith types (5 to >150 μ) reveal dense but heterogeneous woody cover (~ 40–90%) of unidentified trees and/or shrubs and palms associated to the freshwater springs surrounding FLK N, and more open formation (presumably ~ 25–70% woody cover) in the southeast at localities VEK, HWK W and HWK E. The paleovegetation is best described as groundwater palm forest/woodland or bushland, which current analogue may be found near Lake Manyara in similar hydrogeological context (freshwater springs near saline/alkaline lake). Re-evaluating the published pollen data based on this analogy shows that 70% of the pollen signal at FLK N may be attributed to thicket-woodland, Acacia groundwater woodland, gallery and groundwater forests; while < 30% is attributed to swamp herbage and grasslands. Micro-botanical, isotopic, and taphonomical studies of faunal remains converge on the same conclusion that the area surrounding FLK N, which attracted both carnivores and hominins in the early Pleistocene, was densely wooded during uppermost Bed I time.

From excavation at FLK North levels 1–2 in 1960–1962, Mary Leakey reported approximately 1200 Oldowan artifacts and 3300 large mammal fossils as a hominin “living floor”. Preliminary taphonomic analysis by Bunn seemed supportive, based on the presence of some cut-marked bones, the concentration of several dozen bovid individuals, and the relative abundance of limbs and mandibles over other axial elements. Recent taphonomic analysis of Leakey's entire fossil assemblage by Domínguez-Rodrigo and Barba, however, documents a minor hominin role at the site, contrasted to the dominant role of carnivores. Felids brought prey animals; hyenas scavenged from abandoned felid meals. At different times, hominins butchered several bovids and discarded artifacts at this dynamic location. Since 2006, renewed excavations at FLK North and other sites by the Olduvai Paleoanthropology and Paleoecology Project (TOPPP) have expanded artifact and fossil samples and implemented new analytical approaches to clarify taphonomic histories of the Olduvai paleolandscape. At FLK North, > 1000 new large mammal fossils from levels 1 to 2 show minimal butchery evidence amid abundant evidence of carnivore gnawing/fracture, rodent gnawing, and sediment abrasion. To help guide future excavation and analyses, we have developed several alternative working hypotheses of site formation.

FLK North is one of the densest concentrations of fossils found in Olduvai Gorge. A recent taphonomic re-evaluation of the collection excavated by Leakey at the site suggests that it was a palimpsest in which most of the animals were accumulated and modified by carnivores. The lithic tools therefore seem to have an independent depositional history from most of the fauna. The present study, based on new excavations, expands the evidence supporting this interpretation and demonstrates a thicker deposit than was reported by Leakey, including new archaeological levels. It also shows that in the few instances where hominins butchered carcasses, meat, not marrow, was their main target. This argues against passive scavenging hypotheses, which emphasize the dietary role of marrow, and instead underscores the importance of meat in the diet of early Pleistocene hominins.

Recent work at FLK North (FLK N) has unearthed a new archaeological assemblage recovered with precise control of its stratigraphic position. In the present work, the technological study of the new lithic sample is described. The results show the co-occurrence in the same site of different technological behaviors. At FLK N, hominins were involved in both percussion/battering activities and through freehand and bipolar knapping, in core reduction. However, the reconstruction of the operational sequences shows that core reduction was probably a marginal behavior, while percussion/battering activities occurred more regularly throughout the sequence. If hominins were not involved in regular carcass processing, as recent taphonomic studies suggest, then hominins' sporadic and low-impact visits to the site over a long period of time must have been driven by other activities probably linked to the exploitation of alternative resources. Plant processing could have been a plausible explanation for hominin presence at FLK N.

Age profiling of fossil faunal samples relies on the correlation of animal tooth-wear patterns with life history stages, but the criteria used to infer these stages are not necessarily valid. Here we redefine some commonly used prey age classes, such as “juvenile,” “prime-age adult,” and “old adult,” based on the variable characteristics of tooth wear that we have observed in different ungulate size classes, and argue that prey vulnerability to predation is not so clearly predicted by the simplified age classes in widespread use by zooarchaeologists. We recommend instead classifying the youngest animal remains as either young juvenile or subadult juvenile, and adult remains as early prime, late prime or old, and provide specific criteria of dental eruption and occlusal wear for making these determinations. We argue this refined age profiling system, when used in combination with other types of zooarchaeological and taphonomic data, can provide accurate inferences of faunal accumulation processes.

The world’s first archaeological traces from 2.6 million years ago (Ma) at Gona, in Ethiopia, include sharp-edged cutting tools and cut-marked animal bones, which indicate consumption of skeletal muscle by early hominin butchers. From that point, evidence of hominin meat-eating becomes increasingly more common throughout the Pleistocene archaeological record. Thus, the substantive debate about hominin meat-eating now centers on mode(s) of carcass resource acquisition. Two prominent hypotheses suggest, alternatively, (1) that early Homo hunted ungulate prey by running them to physiological failure and then dispatching them, or (2) that early Homo was relegated to passively scavenging carcass residues abandoned by carnivore predators. Various paleontologically testable predictions can be formulated for both hypotheses. Here we test four predictions concerning age-frequency distributions for bovids that contributed carcass remains to the 1.8 Ma. old FLK 22 Zinjanthropus (FLK Zinj, Olduvai Gorge, Tanzania) fauna, which zooarchaeological and taphonomic data indicate was formed predominantly by early Homo. In all but one case, the bovid mortality data from FLK Zinj violate test predictions of the endurance running-hunting and passive scavenging hypotheses. When combined with other taphonomic data, these results falsify both hypotheses, and lead to the hypothesis that early Homo operated successfully as an ambush predator.

The Bed-I series of Olduvai Gorge (Tanzania) is a reference site in human evolution, having yielded the holotypes of Paranthropus boisei and Homo habilis, together with manufactured artefacts and abundant large and micro-fauna. Excavations in Olduvai Gorge have been recently resumed, with new aims and new results. This paper presents the results of the taphonomic analysis carried out on a fossil small-mammal assemblage recovered from FLK NW level 20, a layer overlying Tuff C, dated from 1.84 Ma. The analysis provides good evidence of a category 1 predator, most likely a barn owl, as the predator of the bone assemblage. Trampling and sediment compression might influence postdepositional breakage of the bones. This study is especially relevant since previous taphonomic analyses carried out at levels above and below this sample led to inconclusive results due to a low number of fossils (Fernández-Jalvo et al., 1998). The new sample provides new information to reconstruct the paleoenvironmental context in which early hominins inhabited.

Bulk geochemistry of ~ 1.8 Ma lacustrine claystone at Olduvai Gorge, Tanzania, is controlled principally by the geochemistry of ultrafine (< 0.1 μm), authigenic clay minerals. Authigenic clays have an average structural formula of (Si3.83Al0.17)(Al0.43Fe0.49Mg0.84)(Na0.99K0.22Ca0.16)O10(OH)2; octahedral composition varies, with Mg/(Al + Fe) ranging from 0.7 to 2.3. These clay minerals have a complex history of interaction with saline, alkaline water, followed by secondary diagenetic reactions that leached Mg in freshwater paleoenvironments. Lateral variations in whole-rock and clay geochemistry show westward enrichment in Mg, from Mgoct = 0.6–1.6. This is consistent with persistence of saline, alkaline Paleolake Olduvai to the west, and the presence of groundwater wetlands and other freshwater paleoenvironments to the east. Stone artifact mass density also varies systematically across the basal Bed II deposits, ranging from 100.0 to 104.3 g of artifacts per cubic meter of excavated sediment. Significant correlation is found between clay geochemistry and the density of artifacts excavated from associated archeological trenches (r2 = 0.59, p < 0.01). This relationship supports models of hominin land use in which artifact use and discard is concentrated near freshwater paleoenvironments such as wetlands associated with surface and groundwater discharge. Independent paleoenvironmental proxies such as clay geochemistry allow quantitative hypothesis testing to improve our understanding of early hominin behavior and paleoecology.