African Hominin Research Articles

Understanding ancient hominin dispersals using artefactual data: a phylogeographic analysis of Acheulean handaxes.

BackgroundReconstructing the dispersal patterns of extinct hominins remains a challenging but essential goal. One means of supplementing fossil evidence is to utilize archaeological evidence in the form of stone tools. Based on broad dating patterns, it has long been thought that the appearance of Acheulean handaxe technologies outside of Africa was the result of hominin dispersals, yet independent tests of this hypothesis remain rare. Cultural transmission theory leads to a prediction of a strong African versus non-African phylogeographic pattern in handaxe datasets, if the African Acheulean hypothesis is to be supported.Methodology/Principal FindingsHere, this prediction is tested using an intercontinental dataset of Acheulean handaxes and a biological phylogenetic method (maximum parsimony). The analyses produce a tree consistent with the phylogeographic prediction. Moreover, a bootstrap analysis provides evidence that this pattern is robust, and the maximum parsimony tree is also shown to be statistically different from a tree constrained by stone raw materials.Conclusions/SignificanceThese results demonstrate that nested analyses of behavioural data, utilizing methods drawn from biology, have the potential to shed light on ancient hominin dispersals. This is an encouraging prospect for human palaeobiology since sample sizes for lithic artefacts are many orders of magnitude higher than those of fossil data. These analyses also suggest that the sustained occurrence of Acheulean handaxe technologies in regions such as Europe and the Indian subcontinent resulted from dispersals by African hominin populations.

Speleothem preservation and diagenesis in South African hominin sites implications for paleoenvironments and geochronology

AbstractPlio‐Pleistocene speleothems from australopithecine‐bearing caves of South Africa have the potential to yield paleoenvironmental and geochronological information using isotope geochemistry. Prior to such studies it is important to assess the preservation of geochemical signals within the calcitic and aragonitic speleothems, given the tendency of aragonitic speleothems to recrystallize to calcite. This study documents the geochemical suitability of speleothems from the principal hominin‐bearing deposits of South Africa. We use petrography, together with stable isotope and trace element analysis, to identify the occurrence of primary aragonite, primary calcite, and secondary calcite. This study highlights the presence of diagenetic alteration at many of the sites, often observed as interbedded primary and secondary fabrics. Trace element and stable isotopic values distinguish primary calcite from secondary calcite and offer insights into geochemical aspects of the past cave environment. δ13C values of the primary and secondary calcites range from +6 to −9‰ and δ18O values range from −4 to −6‰. The data are thus typical of meteoric calcites with highly variable δ13C and relatively invariant δ18O. High carbon isotope values in these deposits are associated with the effects of recrystallization and rapid outgassing of CO2 during precipitation. Mg/Ca and Sr/Ca ratios differ between primary and secondary calcite speleothems, aiding their identification. Carbon and oxygen isotope values in primary calcite reflect the proportion of C3 and C4 vegetation in the local environment and the oxygen isotope composition of rainfall. Primary calcite speleothems preserve the pristine geochemical signals vital for ongoing paleoenvironmental and geochronological research. © 2009 Wiley Periodicals, Inc.

Dietary adaptations of South African australopiths: inference from enamel prism attitude

The angle at which enamel prisms approach the wear surface holds information with regard to the stiffness of the tissue, as well as its wear resistance. Hence, analyses of prism orientation may shed light on questions of whether the thick enamel in hominins has evolved to confer stiffness or wear resistance to the teeth and may thus inform about the diet and behavioural ecology of these species. This was explored for Paranthropus robustus and Australopithecus africanus, whereby a distinction was made between prisms at the Phase I and Phase II facets. The results were compared with those obtained for Theropithecus, Macaca, and Potamochoerus for whom behavioural and/or experimental data are available, and were interpreted against simple mechanical principles. The South African hominins differ significantly in their relationships between wear facets and prism angulations. Teeth of P. robustus are better adapted to more vertical loads during mastication (Phase I), whereas those of A. africanus are better adapted to cope with more laterally-directed loads (Phase II) commonly associated with roll-crush and mastication. Overall, teeth of P. robustus appear stiffer, while those of A. africanus seem more wear resistant.

Enamel-dentine junction (EDJ) morphology distinguishes the lower molars of Australopithecus africanus and Paranthropus robustus

Tooth crown morphology plays a central role in hominin systematics, but the removal of the original outer enamel surface by dental attrition often eliminates from consideration the type of detailed crown morphology that has been shown to discriminate among hominin taxa. This reduces the size of samples available for study. The enamel-dentine junction (EDJ) is the developmental precursor and primary contributor to the morphology of the unworn outer enamel surface, and its morphology is only affected after considerable attrition. In this paper, we explore whether the form of the EDJ can be used to distinguish between the mandibular molars of two southern African fossil hominins: Paranthropus (or Australopithecus) robustus and Australopithecus africanus. After micro-computed tomographic scanning the molar sample, we made high-resolution images of the EDJ and used geometric morphometrics to compare EDJ shape differences between species, in addition to documenting metameric variation along the molar row within each species. Landmarks were collected along the marginal ridge that runs between adjacent dentine horns and around the circumference of the cervix. Our results suggest that the morphology of the EDJ can distinguish lower molars of these southern African hominins, and it can discriminate first, second, and third molars within each taxon. These results confirm previous findings that the EDJ preserves taxonomically valuable shape information in worn teeth. Mean differences in EDJ shape, in particular dentine horn height, crown height, and cervix shape, are more marked between adjacent molars within each taxon than for the same molar between the two taxa.

Locomotion and posture from the common hominoid ancestor to fully modern hominins, with special reference to the last common panin/hominin ancestor.

Based on our knowledge of locomotor biomechanics and ecology we predict the locomotion and posture of the last common ancestors of (a) great and lesser apes and their close fossil relatives (hominoids); (b) chimpanzees, bonobos and modern humans (hominines); and (c) modern humans and their fossil relatives (hominins). We evaluate our propositions against the fossil record in the context of a broader review of evolution of the locomotor system from the earliest hominoids of modern aspect (crown hominoids) to early modern Homo sapiens. While some early East African stem hominoids were pronograde, it appears that the adaptations which best characterize the crown hominoids are orthogrady and an ability to abduct the arm above the shoulder - rather than, as is often thought, manual suspension sensu stricto. At 7-9 Ma (not much earlier than the likely 4-8 Ma divergence date for panins and hominins, see Bradley, 2008) there were crown hominoids in southern Europe which were adapted to moving in an orthograde posture, supported primarily on the hindlimb, in an arboreal, and possibly for Oreopithecus, a terrestrial context. By 7 Ma, Sahelanthropus provides evidence of a Central African hominin, panin or possibly gorilline adapted to orthogrady, and both orthogrady and habitually highly extended postures of the hip are evident in the arboreal East African protohominin Orrorin at 6 Ma. If the traditional idea that hominins passed through a terrestrial 'knuckle-walking' phase is correct, not only does it have to be explained how a quadrupedal gait typified by flexed postures of the hindlimb could have preadapted the body for the hominin acquisition of straight-legged erect bipedality, but we would have to accept a transition from stem-hominoid pronogrady to crown hominoid orthogrady, back again to pronogrady in the African apes and then back to orthogrady in hominins. Hand-assisted arboreal bipedality, which is part of a continuum of orthograde behaviours, is used by modern orangutans to forage among the small branches at the periphery of trees where the core hominoid dietary resource, ripe fruit, is most often to be found. Derivation of habitual terrestrial bipedality from arboreal hand-assisted bipedality requires fewer transitions, and is also kinematically and kinetically more parsimonious.

Cranio-dental evidence of a hominin-like hyper-masticatory apparatus in Oreopithecus bambolii. Was the swamp ape a human ancestor?

The phylogeny of Oreopithecus bambolii has been controversial since Johannes Hurzeler first argued that the Late Miocene (Tortonian) primate was a fossil hominin. While most paleontologist currently exclude Oreopithecus from human ancestry, recent postcranial evidence of hominin-like bipedalism and power precision grips in Oreopithecus has rekindled interest in the fossil Italian hominoid. In this study, a comparative review of hominoid cranio-dental morphology indicates that Oreopithecus possessed a suite of hominin-like characteristics that were apparently functionally related to powerful folivorous mastication. Since the oreopithecine dentition exhibited exceptional adaptations for folivory relative to most other extant and extinct hominoids, the accessory development of a hominin-like hyper-masticatory cranio-mandibular apparatus to further enhance plant comminution and digestibility is not surprising. However, the combination of hominin-like locomotive, manual, and masticatory functional attributes appears to substantiate Hurzeler's designation of O. bambolii as a Late Miocene hominin. Additionally, an extensive compilation of hominoid cranio-dental and postcranial characteristics strongly supports a close phylogenetic relationship between Oreopithecus and the earliest African hominins Sahelanthropus and Australopithecus. The wetland paleoecology of the Tortonian island of Tuscany–Sardinia suggests that Oreopithecus was a specialized semiaquatic folivore who apparently waded bipedally into freshwater swamps to feed on aquatic plants. However, the extensive wear on the oreopithecine canines and incisors along with their manual precision grips may indicate that freshwater invertebrates were also included in their diets. Such specialized aquatic feeding behavior by these ancient Italian swamp apes seems to support Alister Hardy's hypothesis that human bipedalism and power precision grips were inherited from Late Miocene hominin ancestors who originally utilized such functional attributes for aquatic foraging in shallow water environments. Additionally, the remarkably hominin-like cranio-dental morphology of O. bambolii suggests that modern omnivorous humans probably inherited a significant number of their cranio-dental characteristics from these highly specialized aquatic plant eating hominins.

Statistical and biological definitions of “anatomically modern” humans: Suggestions for a unified approach to modern morphology

AbstractMuch of the recent literature on the origin of modern humans has been plagued by an inability of the participants in the debate to agree on what constitutes “anatomically modern” morphology. An upshot of this disagreement has been an ongoing set of debates over which specimens are or are not anatomically modern and whether various fossil specimens such as the Florisbad cranium, Vindija Neanderthals, Klasies River Mouth mandibles, or Skhul‐Qafzeh hominins, all of which arguably possess some supposedly “modern” traits, qualify as genuinely “modern.” Such decisions frequently have implications with regard to how we reconstruct later hominin phylogenies and, ultimately, how we reconstruct the behaviors, adaptations, and evolution of Middle‐Late Pleistocene African hominins and their contemporaries.

Tracking changing environments using stable carbon isotopes in fossil tooth enamel: an example from the South African hominin sites

The environmental contexts of the karstic hominin sites in South Africa have been established largely by means of faunal associations; taken together these data suggest a trend from relatively closed and more mesic to open, drier environments from about 3 to 1.5 Ma. Vrba argued for a major shift within this trend ca. 2.4–2.6 Ma, an influential proposal that posited links between bovid (and hominin) radiation in Africa and the intensification of Northern Hemisphere Glaciation. Yet faunal approaches often rely on habitat and feeding preferences of modern taxa that may differ from those of their extinct predecessors. Here we explore ways of extending 13C/ 12C data from fossil mammals beyond denoting “presence” or “absence” of C 4 grasses using the evolution of open environments in South Africa as a case study. To do so we calculated the relative proportions of C 3-, mixed-, and C 4-feeding herbivores for all the hominin sites for which we have sufficient data based on 13C/ 12C analyses of fossil tooth enamel. The results confirm a general trend towards more open environments since 3 Ma, but they also emphasize a marked change to open grassy habitats in the latest Pliocene/early Pleistocene. Mean 13C/ 12C for large felids also mirrored this trend.

Plio-Pleistocene facies environments from the KBS Member, Koobi Fora Formation: implications for climate controls on the development of lake-margin hominin habitats in the northeast Turkana Basin (northwest Kenya)

Climate change is hypothesized as a cause of major events of Plio-Pleistocene East African hominin evolution, but the vertically discontinuous and laterally confined nature of the relevant geological records has led to difficulties with assessing probable links between the two. High-resolution sedimentary sequences from lacustrine settings can provide comprehensive data of environmental changes and detailed correlations with well-established orbital and marine records of climate. Hominin-bearing deposits from Koobi Fora Ridge localities in the northeast Turkana Basin of Kenya are an archive of Plio-Pleistocene lake-margin sedimentation though significant developmental junctures of northern African climates, East African environments, and hominin evolution. This study examines alluvial channel and floodplain, nearshore lacustrine, and offshore lacustrine facies environments for the approximately 136-m-thick KBS Member (Koobi Fora Formation) exposed at the Koobi Fora Ridge. Aspects of the facies environments record information on the changing hydrosedimentary dynamics of the lake margin and give insights into potential climatic controls. Seasonal/yearly climate changes are represented by the varve-like laminations in offshore mudstones and the slickensides, dish-shaped fractures, and other paleosol features overprinted on floodplain strata. Vertical shifts between facies environments, however, are interpreted to indicate lake-level fluctuations deriving from longer-term, dry-wet periods in monsoonal rainfall. Recurrence periods for the inferred lake-level changes range from about 10,000 to 50,000 years, and several are consistent with the average estimated timescales of orbital precession (∼20,000 years) and obliquity (∼40,000 years). KBS Member facies environments from the Koobi Fora Ridge document the development of lake-margin hominin habitats in the northeast Turkana Basin. Environmental changes in these habitats may be a result of monsoonal rainfall variations that derive from orbital insolation and/or glacial forcing.

Mammalian body size changes and Plio-Pleistocene environmental shifts: implications for understanding hominin evolution in eastern and southern Africa

This study examines geographic and temporal variation in three mammalian taxa co-occurring in eastern and southern Africa. The selected taxa—the spotted hyena ( Crocuta crocuta), the plains zebra ( Equus burchellii), and the impala ( Aepyceros melampus)—are geographically widespread in modern times and are abundant in eastern and southern African Plio-Pleistocene fossil sites. Craniodental measurements of modern conspecifics from known geographic locations are compared using multivariate statistical methods to discern patterns of modern geographic variation within taxa. Modern and fossil samples are statistically compared to assess the nature and extent of inferred shifts in body size, both between modern samples and through time in each region. These results indicate that modern spotted hyenas and plains zebras exhibit mainly size variation between regions, with southern African samples possessing statistically larger craniodental metrics than eastern African samples. Comparison of fossil and modern samples reveals that the fossil assemblages do not show the same pattern of geographic variation. Significant temporal changes are more numerous between fossil and modern eastern African samples, and these changes are not mirrored by similar changes in the southern African samples. The changes experienced by taxa in eastern Africa appear to have been more extreme and wide-ranging than those in southern Africa, a presumed refugium. This result accords well with genetic studies of several large mammal species and paleoenvironmental studies suggesting that eastern African localized environments were more affected by tectonism and volcanism than were those in southern Africa. This study suggests that different evolutionary scenarios may have existed within Africa during the Plio-Pleistocene, but that both regions played unique and complementary roles in the evolution of African hominins and the broader faunal community.

Blue Nile incision on the Ethiopian Plateau: Pulsed plateau growth, Pliocene uplift, and hominin evolution

The 1.6-km-deep Gorge of the Nile, a rival of the Grand Canyon, resulted from the deep incision of the Blue Nile drainage into the uplifted Ethiopian Plateau. Understanding the incision history of the plateau is crucial to unraveling the Cenozoic tectonoclimatic evolution of the region, particularly because the region has long been used as a natural laboratory to understand the geodynamics of continental rifting and the evolution of hominins. We undertake a quantitative geomorphologic approach integrating field, geographic information system (GIS), and digital elevation model (DEM) data to analyze incision (volume, long-term rates, and spatiotemporal variability) and river longitudinal profiles of the Blue Nile drainage. Previously published isotopic ages of the Cenozoic volcanic rocks are used to constrain long-term incision rates through geologic time. Our data argue that (1) the Blue Nile drainage has removed at least 93,200 km 3 of rocks from the northwestern Ethiopian Plateau since ca. 29 Ma (early Oligocene) through a three-phase (ca. 29–10 Ma, ca. 10–6 Ma, and ca. 6 Ma to present) incision, where long-term incision rates increased rapidly and episodically in the late Miocene (ca. 10 Ma and ca. 6 Ma); (2) being out-ofphase with the past climatic events and in-phase with the main volcanic episodes of the region, this episodic increase of incision rate is suggestive of episodic growth of the plateau; (3) of the ~2-km rock uplift of the plateau since ca. 30 Ma, 0.3 km was due to isostatic uplift related to erosional unloading, and the rest was due to other tectonic activities; (4) the extremely rapid long-term incision rate increase, thus a rapid uplift of the plateau, ca. 6 Ma might be related to lithospheric foundering, caused by ponded plume material beneath the Ethiopian Plateau and aided by huge tectonic stresses related to the Messinian salinity crisis of the Mediterranean Sea. These events could have caused the plateau to rise >1 km within a few m.y. in the early Pliocene. This uplift history of the Ethiopian Plateau can shed critical light on the geodynamics of the Afar mantle plume and the evolution of the East African hominins via climate change.

Darwin, South Africa and the emergence of the genus Homo

The genus Homo has been identified in early Pleistocene deposits at Sterkfontein, Swartkrans and Kromdraai in South Africa. However, the boundary between Homo and australopithecines is not clearly distinct. Examples are given whereby certain specimens attributed to Homo have been assigned instead to an australopithecine, or vice versa. Remarkably, the earliest purported Homo from Africa 2.4 Ma), specimen KNM-BC 1 from Chemeron (Baringo area) in Kenya, is morphologically very similar to the type specimen of Paranthropus robustus from Kromdraai, at least 1.95 Ma. It is suggested that the emergence of Homo was more of a gradual phenomenon, associated with genetic drift and a spectrum of morphological variability in space and time, rather than a punctuated ‘Homo event’. This view is assessed in relation to a statement by Charles Darwin in The Descent of Man, published in 1871, and in relation to African hominins dated between 1.5 and 2.5 Ma.

Dental microwear texture analysis shows within-species diet variability in fossil hominins

Reconstructing the diets of extinct hominins is essential to understanding the paleobiology and evolutionary history of our lineage. Dental microwear, the study of microscopic tooth-wear resulting from use, provides direct evidence of what an individual ate in the past. Unfortunately, established methods of studying microwear are plagued with low repeatability and high observer error. Here we apply an objective, repeatable approach for studying three-dimensional microwear surface texture to extinct South African hominins. Scanning confocal microscopy together with scale-sensitive fractal analysis are used to characterize the complexity and anisotropy of microwear. Results for living primates show that this approach can distinguish among diets characterized by different fracture properties. When applied to hominins, microwear texture analysis indicates that Australopithecus africanus microwear is more anisotropic, but also more variable in anisotropy than Paranthropus robustus. This latter species has more complex microwear textures, but is also more variable in complexity than A. africanus. This suggests that A. africanus ate more tough foods and P. robustus consumed more hard and brittle items, but that both had variable and overlapping diets.

Beyond prosody and infant-directed speech: Affective, social construction of meaning in the origins of language

Our starting point for the origins of language goes beyond prosody or infant-directed speech to highlight the affective, multimodal, and co-constructed nature of meaning-making that was likely present before the split between African great apes and hominins. Analysis of vocal and gestural caregiving practices in hominins, and of meaning-making via gestural interaction in African great apes, supports our thesis.

Analysis and significance of linear enamel hypoplasia in Plio‐Pleistocene hominins

This study of linear enamel hypoplasia (LEH) in Plio-Pleistocene hominins builds on a previous study (Guatelli-Steinberg [2003] Am. J. Phys. Anthropol. 120:309-322) that focused on LEH in early South African hominins. The present study is more comprehensive, encompassing dental specimens of hominins from East Africa as well, including early Homo. As a developmental defect of enamel, LEH is used in anthropological contexts to reveal information about physiological stress. However, intrinsic aspects of enamel development and morphology can affect the expression of LEH, complicating efforts to understand the significance of these defects. In this study, the analysis of LEH is conducted with respect to enamel development and morphology. It is predicted that Paranthropus should have fewer defects on its canine teeth than Australopithecus and Homo, owing to its abbreviated period of enamel formation. This prediction is supported: Paranthropus has statistically significantly fewer defects per canine than Australopithecus and Homo. The previous study demonstrated that despite the wider spacing of perikymata on the teeth of South African Paranthropus, defects on the canine teeth of this genus were not wider than those of Australopithecus. A multiple linear regression analysis in that study, as well as a separate analysis in the present study, indicate that the number of perikymata within defects is a better predictor of defect width than perikymata spacing. In this study, it was additionally found that the average number of perikymata within Australopithecus defects is statistically significantly greater than it is in Paranthropus, thus explaining why Paranthropus defects are not wider than those of Australopithecus. The biological significance of this difference in the number of perikymata within the defects of Australopithecus and Paranthropus is considered in light of several factors, including: 1) the possibility that other intrinsic attributes of enamel morphology may be involved (specifically the faster extension rates of Paranthropus that result in shallower defects), 2) generic differences in the canalization of enamel development, and 3) generic differences in the duration of disruptions to enamel growth.

Macroscopic and microscopic analyses of linear enamel hypoplasia in Plio-Pleistocene South African hominins with respect to aspects of enamel development and morphology.

This study uses macroscopic and microscopic methods to analyze the expression of linear enamel hypoplasia (LEH) in Plio-Pleistocene South African hominins. LEH is a developmental defect of enamel that is used in many anthropological contexts as a physiological stress indicator. Previous research has not settled the question as to whether differences in LEH expression exist between Paranthropus and Australopithecus and if they exist, to what extent these differences might be explained simply by taxonomic differences in enamel development and morphology rather than by differential stress experience. In this study, the analysis of LEH is conducted with respect to differences between Paranthropus and Australopithecus in aspects of enamel development and morphology that are thought to influence LEH expression. Two factors impacting LEH expression are considered: the duration of enamel formation, and the spacing of perikymata. It is predicted that if the first factor strongly influences the expression of LEH, then there should be fewer defects per tooth in Paranthropus because of its abbreviated crown formation spans (and fast extension rates) relative to Australopithecus. It is also predicted that because Australopithecus has more densely packed perikymata in comparable regions of the crown than Paranthropus, this taxon should, on average, have narrower defects than Paranthropus. To address these questions, 200 Australopithecus and 137 Paranthropus teeth were examined for LEH, and the analysis of defect width with respect to perikymata spacing was conducted on tooth impressions examined under a scanning electron microscope using INCA (Oxford Instruments) measurement software. Data support the first prediction: Australopithecus does have significantly more defects per canine tooth than Paranthropus. Data do not support the second prediction in large part because several Australopithecus specimens have wide groove defects in which perikymata are not visible and enamel is irregular. Such wide grooves are not predicted by perikymata spacing such that alternative explanations, including taxonomic differences in ameloblast sensitivity and the duration/severity of disruptions to enamel growth, must be considered.