Stretching the time span of hominin evolution at Kromdraai (Gauteng,South Africa): Recent discoveries

The Plio-Pleistocene locality of Kromdraai B has yielded the type specimen of Paranthropus robustus, as well as 27 additional fossil hominin specimens. In a number of both cranial and dental features, the states shown by the Kromdraai Paranthropus are more conservative when compared to the more derived conditions displayed by both South African conspecifics and the post-2.3 Ma eastern African Paranthropus boisei. Since 2014, we excavated the earliest known infilling of the Kromdraai cave system in a previously unexplored area. This new locality provided as yet 2200 identifiable macrovertebrate fossils, including 22 hominins, all tied in the earliest part of the stratigraphic sequence, representing three distinct depositional periods. Since we report here, for the first time, the occurrence of fossil hominins in Members 1 and 2, our discoveries stretch the time span of hominin evolution at Kromdraai and contribute to a better understanding of the origin of Paranthropus in southern Africa.     

Cercopithecoid primate postcranial fossils from Cooper's D,South Africa

Among several highly fossiliferous localities in the Bloubank Valley (Gauteng, South Africa), the Cooper's Cave System has been known since 1938 and has produced a rich fossil assemblage, including some remains of the early hominin Paranthropus robustus. In 2001, excavations began at a new locality, Cooper's D, which dates to ～1.4-1.5 Ma. Although hominins are relatively rare in the assemblage, remains of cercopithecoid primates are much more common. Craniodental fossils currently indicate the possible presence of at least three large-bodied cercopithecoid primate genera at Cooper's D: Gorgopithecus, Papio, and Theropithecus. In this study, we identify and describe > 100 cercopithecoid primate postcranial fossils representing all regions of the appendicular skeleton. The specimens come from several age classes and size morphs; more than one third of the fossils described are from sub-adult and juvenile individuals. The adult postcranial fossils vary substantially in size, with body masses estimated between 30 and 60 kg (from 16 of the better preserved specimens). The functional morphology of the postcranial remains indicate that these elements come from animals that likely utilized terrestrial substrates, but they remain difficult to definitively attribute to Gorgopithecus, Theropithecus, or Papio given the absence of associated skeletons. The smaller specimens likely belong to Papio while the larger ones can be attributed to the other two genera. Because Cooper's D has also yielded fossils of the early hominin Paranthropus robustus, this raises the question of how these four large-bodied, mostly terrestrial primates sympatrically utilized the landscape.     

New Australopithecus robustus fossils and associated U-Pb dates from Cooper's Cave (Gauteng, South Africa)

Australopithecus robustus is one of the best represented hominin taxa in Africa, with hundreds of specimens recovered from six fossil localities in the Bloubank Valley area of Gauteng Province, South Africa. However, precise geochronological ages are presently lacking for these fossil cave infills. In this paper, we provide a detailed geological background to a series of hominin fossils retrieved from the newly investigated deposit of Cooper's D (located partway between Sterkfontein and Kromdraai in the Bloubank Valley), including uranium-lead (U-Pb) ages for speleothem material associated with A. robustus. U-Pb dating of a basal speleothem underlying the entire deposit results in a maximum age of 1.526 (±0.088) Ma for Cooper's D. A second U-Pb date of ca. 1.4 Ma is produced from a flowstone layer above this basal speleothem; since this upper flowstone is not a capping flowstone, and fossiliferous sediments are preserved above this layer, some of the hominins might be slightly younger than the calculated age. As a result, we can broadly constrain the age of the hominins from Cooper's D to between 1.5 and approximately 1.4 Ma. Extinct fauna recorded in this comparatively young deposit raise the possibility that the Bloubank Valley region of South Africa represented a more stable environmental refugium for taxa relative to tectonically more active East Africa. The sediments of the deposit likely infilled rapidly during periods when arid conditions prevailed in the paleoenvironment, although it is unclear whether sediment deposition and bone deposition were necessarily contemporaneous occurrences. We reconstruct the paleoenvironment of Cooper's D as predominantly grassland, with nearby woodlands and a permanent water source. The hominin teeth recovered from Cooper's D are all from juveniles and can be confidently assigned to A. robustus. In addition, two juvenile mandibular fragments and an adult thoracic vertebra are tentatively attributed to A. robustus.     

Early Homo at Kromdraai B: probabilistic and morphological analysis of the lower dentition

Kromdraai B, situated less than 2 km east of Sterkfontein, in the Gauteng province of South Africa, has yielded 27 specimens, attributed to a single Plio-Pleistocene hominid species, including the type specimen of Paranthropus (Australopithecus) robustus. By using resampling and morphological analysis, and after considering the most diagnostic features that have been used in the past for the lower dentition, we here suggest that one specimen from Kromdraai B, KB 5223, is clearly distinct from P. robustus and represents early Homo. To cite this article: J. Braga, J.F. Thackeray, C. R. Palevol 2 (2003).     

Civettictis braini nov. sp. (Mammalia: Carnivora), a new viverrid from the hominin-bearing site of Kromdraai (Gauteng,South Africa)

A new Plio-Pleistocene viverrid species is described based on two newly discovered maxillae (KW 10141 and KW 10383) from the recent excavations at the hominin-bearing site of Kromdraai (Gauteng, South Africa). This major site allows us to address the conundrum of Paranthropus and Homo origins in South Africa and presents a highly diverse carnivore spectrum (at least 22 species) including herpestids and viverrids. Civettictis braini nov. sp. is a viverrid species comparable in size to the extant African civet Civettictis civetta (Schreber, 1776). However C. braini nov. sp. differs significantly from the extant species in its dental proportions. Its canine and three premolars (P1–P3) are relatively robust, while its carnassials (P4) and two molars (M1, M2) are extremely reduced. This new species supplements our knowledge on carnivore taxonomic diversity and paleoecology in Southern Africa about 2 millions of years ago.     

The enigmatic molar from Gondolin, South Africa: Implications for Paranthropus paleobiology

The specific attribution of the large hominin M₂ (GDA-2) from Gondolin has significant implications for the paleobiology of Paranthropus. If it is a specimen of Paranthropus robustus it impacts that species' size range, and if it belongs to Paranthropus boisei it has important biogeographic implications. We evaluate crown size, cusp proportions and the likelihood of encountering a large-bodied mammal species in both East and South Africa in the Early Pleistocene. The tooth falls well outside the P. robustus sample range, and comfortably within that for penecontemporaneous P. boisei. Analyses of sample range, distribution and variability suggest that it is possible, albeit unlikely to find a M₂ of this size in the current P. robustus sample. However, taphonomic agents - carnivore (particularly leopard) feeding behaviors - have likely skewed the size distribution of the Swartkrans and Drimolen P. robustus assemblage. In particular, assemblages of large-bodied mammals accumulated by leopards typically display high proportions of juveniles and smaller adults. The skew in the P. robustus sample is consistent with this type of assemblage. Morphological evidence in the form of cusp proportions is congruent with GDA-2 representing P. robustus rather than P. boisei. The comparatively small number of large-bodied mammal species common to both South and East Africa in the Early Pleistocene suggests a low probability of encountering an herbivorous australopith in both. Our results are most consistent with the interpretation of the Gondolin molar as a very large specimen of P. robustus. This, in turn, suggests that large, presumptive male, specimens are rare, and that the levels of size variation (sexual dimorphism) previously ascribed to this species are likely to be gross underestimates.     

The mid-face of lower Pleistocene hominins and its bearing on the attribution of SK 847 and StW 53

SK 847 and StW 53 have often been cited as evidence for early Homo in South Africa. To examine whether midfacial morphology is in agreement with these attributions, we analyze Euclidean distances calculated from 3-D coordinates on the maxillae of SK 847 and StW 53, as well as Australopithecus africanus (Sts 5, Sts 71), Paranthropus robustus (SK 46, SK 48, SK 52, SK 83), early Homo (KNM-ER 1813, KNM-ER 1805, KNM-ER 3733, KNM-WT 15000), P. boisei (KNM-ER 406, KNM-WT 17000, KNM-WT 17400), Gorilla gorilla (n = 116), Homo sapiens (n = 342), Pan paniscus (n = 21) and P. troglodytes (n = 65). Multivariate analyses separate extant hominoids suggesting we have captured taxonomic affinity. With the exception of SK 847 and SK 52, South African fossils tend to cluster together. P. robustus differs substantially from East African robust megadonts. SK 847 and StW 53 resemble the East African Homo specimens that are the most australopith-like, such as KNM-WT 15000 and KNM-ER 1813. The resemblance between StW 53 and Homo is driven partly by similarities in maxillary size. When distances are scaled, StW 53 aligns with A. africanus, while SK 847 clusters primarily with early Homo.     

Body size and body shape in early hominins - implications of the Gona Pelvis

Discovery of the first complete Early Pleistocene hominin pelvis, Gona BSN49/P27, attributed to Homo erectus, raises a number of issues regarding early hominin body size and shape variation. Here, acetabular breadth, femoral head breadth, and body mass calculated from femoral head breadth are compared in 37 early hominin (6.0-0.26 Ma) specimens, including BSN49/P27. Acetabular and estimated femoral head sizes in the Gona specimen fall close to the means for non-Homo specimens (Orrorin tugenesis, Australopithecus africanus, Paranthropus robustus), and well below the ranges of all previously described Early and Middle Pleistocene Homo specimens. The Gona specimen has an estimated body mass of 33.2 kg, close to the mean for the non-Homo sample (34.1 kg, range 24-51.5 kg, n = 19) and far outside the range for any previously known Homo specimen (mean = 70.5 kg; range 52-82 kg, n = 17). Inclusion of the Gona specimen within H. erectus increases inferred sexual dimorphism in body mass in this taxon to a level greater than that observed here for any other hominin taxon, and increases variation in body mass within H. erectus females to a level much greater than that observed for any living primate species. This raises questions regarding the taxonomic attribution of the Gona specimen. When considered within the context of overall variation in body breadth among early hominins, the mediolaterally very wide Gona pelvis fits within the distribution of other lower latitude Early and Middle Pleistocene specimens, and below that of higher latitude specimens. Thus, ecogeographic variation in body breadth was present among earlier hominins as it is in living humans. The increased M-L pelvic breadth in all earlier hominins relative to modern humans is related to an increase in ellipticity of the birth canal, possibly as a result of a non-rotational birth mechanism that was common to both australopithecines and archaic Homo.     

The paleoanthropology of Hadar,Ethiopia

Field research at the fossil-bearing deposits in the Afar Depression began in the 1970s. Prior to this, hominin fossils older than 3.0 Mya consisted of only a handful of fragments. During Phase I, the International Afar Research Expedition to Hadar, Ethiopia collected some 240 fossil hominins from Hadar over a time range of 3.0–3.4 Mya. Along with hominin fossils from Laetoli, they were deemed a new species, Australopithecus afarensis. This taxon was posited as the last common ancestor to robust Australopithecus and the Homo lineage in eastern Africa. Phase II research under the Hadar Research Project has added strength to the Phase I results, including the first association of a Homo fossil with stone tools at 2.4 Mya. This presentation is a cursory synopsis of the importance and implications of the hominin fossils recovered at Hadar during over the last 34 years.     

Early Pleistocene human mandible from Sima del Elefante (TE) cave site in Sierra de Atapuerca (Spain): a comparative morphological study

We present a detailed morphological comparative study of the hominin mandible ATE9-1 recovered in 2007 from the Sima del Elefante cave site in Sierra de Atapuerca, Burgos, northern Spain. Paleomagnetic analyses, biostratigraphical studies, and quantitative data obtained through nuclide cosmogenic methods, place this specimen in the Early Pleistocene (1.2-1.3 Ma). This finding, together with archaeological evidence from different European sites, suggests that Western Europe was colonised shortly after the first hominin expansion out of Africa around the Olduvai subchron. Our analysis of the ATE9-1 mandible includes a geometric morphometric analysis of the lower second premolar (LP₄), a combined and detailed external and internal assessment of ATE9-1 roots through CT and microCT techniques, as well as a comparative study of mandibular and other dental features. This analysis reveals some primitive Homo traits on the external aspect of the symphysis and the dentition shared with early African Homo and the Dmanisi hominins. In contrast, other mandibular traits on the internal aspect of the symphysis are derived with regard to African early Homo, indicating unexpectedly large departures from patterns observed in Africa. Reaching the most occidental part of the Eurasian continent implies that the first African emigrants had to cross narrow corridors and to overcome geographic barriers favouring genetic drift, long isolation periods, and adaptation to new climatic and seasonal conditions. Given these conditions and that we are dealing with a long time period, it is possible that one or more speciation events could have occurred in this extreme part of Eurasia during the Early Pleistocene, originating in the lineages represented by the Sima del Elefante-TE9 hominins and possibly by the Gran Dolina-TD6 hominins. In the absence of any additional evidence, we prefer not include the specimen ATE9-1 in any named taxon and refer to it as Homo sp.     

First Early Hominin from Central Africa (Ishango,Democratic Republic of Congo)

Despite uncontested evidence for fossils belonging to the early hominin genus Australopithecus in East Africa from at least 4.2 million years ago (Ma), and from Chad by 3.5 Ma, thus far there has been no convincing evidence of Australopithecus, Paranthropus or early Homo from the western (Albertine) branch of the Rift Valley. Here we report the discovery of an isolated upper molar (#Ish25) from the Western Rift Valley site of Ishango in Central Africa in a derived context, overlying beds dated to between ca. 2.6 to 2.0 Ma. We used µCT imaging to compare its external and internal macro-morphology to upper molars of australopiths, and fossil and recent Homo. We show that the size and shape of the enamel-dentine junction (EDJ) surface discriminate between Plio-Pleistocene and post-Lower Pleistocene hominins, and that the Ishango molar clusters with australopiths and early Homo from East and southern Africa. A reassessment of the archaeological context of the specimen is consistent with the morphological evidence and suggest that early hominins were occupying this region by at least 2 Ma.     

Improved age control on early Homo fossils from the upper Burgi Member at Koobi Fora,Kenya

To address questions regarding the evolutionary origin, radiation and dispersal of the genus Homo, it is crucial to be able to place the occurrence of hominin fossils in a high-resolution chronological framework. The period around 2 Ma (millions of years ago) in eastern Africa is of particular interest as it is at this time that a more substantial fossil record of the genus Homo is first found. Here we combine magnetostratigraphy and strontium (Sr) isotope stratigraphy to improve age control on hominin-bearing upper Burgi (UBU) deposits in Areas 105 and 131 on the Karari Ridge in the eastern Turkana Basin (Kenya). We identify the base of the Olduvai subchron (bC2n) plus a short isolated interval of consistently normal polarity that we interpret to be the Pre-Olduvai event. Combined with precession-forced (∼20 kyr [thousands of years]) wet–dry climate cycles resolved by Sr isotope ratios, the magnetostratigraphic data allow us to construct an age model for the UBU deposits. We provide detailed age constraints for 15 hominin fossils from Area 131, showing that key specimens such as cranium KNM-ER 1470, partial face KNM-ER 62000 and mandibles KNM-ER 1482, KNM-ER 1801, and KNM-ER 1802 can be constrained between 1.945 ± 0.004 and 2.058 ± 0.034 Ma, and thus older than previously estimated. The new ages are consistent with a temporal overlap of two species of early Homo that can be distinguished by their facial morphology. Further, our results show that in this time interval, hominins occurred throughout the wet–dry climate cycles, supporting the hypothesis that the lacustrine Turkana Basin was a refugium during regionally dry periods. By establishing the observed first appearance datum of a marine-derived stingray in UBU deposits at 2.058 ± 0.034 Ma, we show that at this time the Turkana Basin was hydrographically connected to the Indian Ocean, facilitating dispersal of fauna between these areas. From a biogeographical perspective, we propose that the Indian Ocean coastal strip should be considered as a possible source area for one or more of the multiple Homo species in the Turkana Basin from over 2 Ma onwards.     

The SKX 1084 hominin patella from Swartkrans Member 2, South Africa: An integrated analysis of its outer morphology and inner structure

SKX 1084 is an isolated partial patella from Swartkrans Member 2, South Africa, attributed to a small-bodied Paranthropus robustus. This study provides complementary information on its outer conformation and, for the first time for a fossil hominin patella, documents its inner structure in the perspective of adding biomechanically-related evidence to clarify its identity. We used X-ray micro-tomography to investigate SKX 1084 and to extract homologous information from a sample of 12 recent human, one Neanderthal, and two adult Pan, patellae. We used geometric morphometrics to compare the outer equatorial contours. In SKX 1084, we identified two cancellous bony spots suitable for textural assessment (trabecular bone volume fraction, trabecular thickness, degree of anisotropy), and two related virtual slices for measuring the maximum cortico-trabecular thickness (CTT) of the articular surface. SKX 1084 shows a more complex articular shape than that for Pan, but still simpler than typical in Homo sapiens. At all sites, its CTT is thinner compared to Pan and approaches the condition in humans. This is also true for the expanded volume of the cancellous network. However, at both investigated spots, SKX 1084 is systematically intermediate between Homo and Pan for trabecular bone volume fraction and trabecular thickness, a pattern already shown in previous analyses on other Paranthropus postcranial remains. In the absence of any structural signal from patellae unambiguously sampling Paranthropus, as well as of comparable evidence extracted from specimens representing early Homo, our results do not allow rejection of the original taxonomic attribution of SKX 1084.     

Variation in enamel thickness within the genus Homo

Recent humans and their fossil relatives are classified as having thick molar enamel, one of very few dental traits that distinguish hominins from living African apes. However, little is known about enamel thickness in the earliest members of the genus Homo, and recent studies of later Homo report considerable intra- and inter-specific variation. In order to assess taxonomic, geographic, and temporal trends in enamel thickness, we applied micro-computed tomographic imaging to 150 fossil Homo teeth spanning two million years. Early Homo postcanine teeth from Africa and Asia show highly variable average and relative enamel thickness (AET and RET) values. Three molars from South Africa exceed Homo AET and RET ranges, resembling the hyper thick Paranthropus condition. Most later Homo groups (archaic European and north African Homo, and fossil and recent Homo sapiens) possess absolutely and relatively thick enamel across the entire dentition. In contrast, Neanderthals show relatively thin enamel in their incisors, canines, premolars, and molars, although incisor AET values are similar to H. sapiens. Comparisons of recent and fossil H. sapiens reveal that dental size reduction has led to a disproportionate decrease in coronal dentine compared with enamel (although both are reduced), leading to relatively thicker enamel in recent humans. General characterizations of hominins as having ‘thick enamel’ thus oversimplify a surprisingly variable craniodental trait with limited taxonomic utility within a genus. Moreover, estimates of dental attrition rates employed in paleodemographic reconstruction may be biased when this variation is not considered. Additional research is necessary to reconstruct hominin dietary ecology since thick enamel is not a prerequisite for hard-object feeding, and it is present in most later Homo species despite advances in technology and food processing.     

Re-appraisal of the stratigraphy and determination of new U-Pb dates for the Sterkfontein hominin site, South Africa

Sterkfontein Caves is the single richest early hominin site in the world with deposits yielding one or more species of Australopithecus and possible early Homo, as well as an extensive faunal collection. The inability to date the southern African cave sites accurately or precisely has hindered attempts to integrate the hominin fossil evidence into pan-African scenarios about human evolutionary history, and especially hominin biogeography. We have used U-Pb and U-Th techniques to date sheets of calcium carbonate flowstone inter-bedded between the fossiliferous sediments. For the first time, absolute age ranges can be assigned to the fossil-bearing deposits: Member 2 is between 2.8 ± 0.28 and 2.6 ± 0.30 Ma and Member 4 between 2.65 ± 0.30 and 2.01 ± 0.05 Ma. The age of 2.01 ± 0.05 Ma for the top of Member 4 constrains the last appearance of Australopithecus africanus to 2 Ma. In the Silberberg Grotto we have reproduced the U-Pb age of ∼2.2 Ma of for the flowstones associated with StW573. We believe that these deposits, including the fossil and the flowstones, accumulated rapidly around 2.2 Ma. The stratigraphy of the site is complex as sediments are exposed both in the underground chambers and at surface. We present a new interpretation of the stratigraphy based on surface mapping, boreholes logs and U-Pb ages. Every effort was made to retain the Member system, however, only Members 2 and 4 are recognized in the boreholes. We propose that the deposits formally known as Member 3 are in fact the distal equivalents of Member 4. The sediments of Members 2 and 4 consisted of cone-like deposits and probably never filled up the cave. The U-Th ages show that there are substantial deposits younger than 400 ka in the underground cave, underlying the older deposits, highlighting again that these cave fills are not simple layer-cakes.     

Oldest Evidence of Toolmaking Hominins in a Grassland-Dominated Ecosystem

Background

Major biological and cultural innovations in late Pliocene hominin evolution are frequently linked to the spread or fluctuating presence of C₄ grass in African ecosystems. Whereas the deep sea record of global climatic change provides indirect evidence for an increase in C₄ vegetation with a shift towards a cooler, drier and more variable global climatic regime beginning approximately 3 million years ago (Ma), evidence for grassland-dominated ecosystems in continental Africa and hominin activities within such ecosystems have been lacking.

Methodology/Principal Findings

We report stable isotopic analyses of pedogenic carbonates and ungulate enamel, as well as faunal data from ∼2.0 Ma archeological occurrences at Kanjera South, Kenya. These document repeated hominin activities within a grassland-dominated ecosystem.

Conclusions/Significance

These data demonstrate what hitherto had been speculated based on indirect evidence: that grassland-dominated ecosystems did in fact exist during the Plio-Pleistocene, and that early Homo was active in open settings. Comparison with other Oldowan occurrences indicates that by 2.0 Ma hominins, almost certainly of the genus Homo, used a broad spectrum of habitats in East Africa, from open grassland to riparian forest. This strongly contrasts with the habitat usage of Australopithecus, and may signal an important shift in hominin landscape usage.     

First hominine remains from a ∼1.0 million year old bone bed at Cornelia-Uitzoek, Free State Province, South Africa

We report here on evidence of early Homo around 1.0 Ma (millions of years ago) in the central plains of southern Africa. The human material, a first upper molar, was discovered during the systematic excavation of a densely-packed bone bed in the basal part of the sedimentary sequence at the Cornelia-Uitzoek fossil vertebrate locality. We dated this sequence by palaeomagnetism and correlated the bone bed to the Jaramillo subchron, between 1.07 and 0.99 Ma. This makes the specimen the oldest southern African hominine remains outside the dolomitic karst landscapes of northern South Africa. Cornelia-Uitzoek is the type locality of the Cornelian Land Mammal Age. The fauna contains an archaic component, reflecting previous biogeographic links with East Africa, and a derived component, suggesting incipient southern endemism. The bone bed is considered to be the result of the bone collecting behaviour of a large predator, possibly spotted hyaenas. Acheulian artefacts are found in small numbers within the bone bed among the fossil vertebrates, reflecting the penecontemporaneous presence of people in the immediate vicinity of the occurrence. The hominine tooth was recovered from the central, deeper part of the bone bed. In size, it clusters with southern African early Homo and it is also morphologically similar. We propose that the early Homo specimen forms part of an archaic component in the fauna, in parallel with the other archaic faunal elements at Uitzoek. This supports an emergent pattern of archaic survivors in the southern landscape at this time, but also demonstrates the presence of early Homo in the central plains of southern Africa, beyond the dolomitic karst areas.     

Emergence of the genus Homo: From concept to taxonomy

The main goal of this paper is to present an overview of hypotheses concerning early Homo specimens and to discuss the definition of the genus Homo in the light of recent discoveries. For some authors, all the specimens attributed to early Homo belong to one unique species. For others, this group (Homo habilis sensu lato) is heterogeneous and could be splitted into two groups: H. habilis and Homo rudolfensis. Some researchers have also proposed to put the species habilis and rudolfensis into the genera Australopithecus or Kenyanthropus. Therefore, two scenarios concerning first humans seem to emerge. An emergence of the genus Homo, as early as 2.8 Ma, with Homo sp. specimens and the species H. habilis and H. rudolfensis, another at 1.9 Ma with Homo ergaster. According to the recent archaeological and paleoanthropological discoveries, these criteria often considered to be crucial for the definition of the genus Homo, as the cranial capacity, the humanlike manipulative abilities, the habitual erect posture and bipedal gait, the language ability and the capacity to make tools are now obsolete.