Dental microwear and diets of African early Homo

Conventional wisdom ties the origin and early evolution of the genus Homo to environmental changes that occurred near the end of the Pliocene. The basic idea is that changing habitats led to new diets emphasizing savanna resources, such as herd mammals or underground storage organs. Fossil teeth provide the most direct evidence available for evaluating this theory. In this paper, we present a comprehensive study of dental microwear in Plio-Pleistocene Homo from Africa. We examined all available cheek teeth from Ethiopia, Kenya, Tanzania, Malawi, and South Africa and found 18 that preserved antemortem microwear. Microwear features were measured and compared for these specimens and a baseline series of five extant primate species (Cebus apella, Gorilla gorilla, Lophocebus albigena, Pan troglodytes, and Papio ursinus) and two protohistoric human foraging groups (Aleut and Arikara) with documented differences in diet and subsistence strategies. Results confirmed that dental microwear reflects diet, such that hard-object specialists tend to have more large microwear pits, whereas tough food eaters usually have more striations and smaller microwear features. Early Homo specimens clustered with baseline groups that do not prefer fracture resistant foods. Still, Homo erectus and individuals from Swartkrans Member 1 had more small pits than Homo habilis and specimens from Sterkfontein Member 5C. These results suggest that none of the early Homo groups specialized on very hard or tough foods, but that H. erectus and Swartkrans Member 1 individuals ate, at least occasionally, more brittle or tough items than other fossil hominins studied.     

Craniofacial diversity in earlyHomo and the affinities of the Sterkfontein Valley

The Sterkfontein Valley specimens SK 847 (Swartkrans Member 1) and Stw 53 (Sterkfontein Member 5) provide important evidence of earlyHomo in southern Africa. However, specific identity has been disputed, with that of SK 847 especially contentious. Opinions differ markedly as to whether the specimens are conspecific or not, whether they should be referred to East African earlyHomo species, or whether they represent new species. Morphometric analysis of facial dimensions reveals contrasting affinities for the two South African fossils, and so does not support claims for their conspecifity. Stw 53 is very like smaller East African crania referred toH. habilis, whereas SK 847 has a distinctive facial pattern. In some respects it resembles early AfricanH. erectus (=H. ergaster), but with a markedly more projecting mid-face, prominent zygomatic and unexpanded frontal region, all of which militate against inclusion in that species. The taxonomic implications of these contrasting facial affinities are briefly discussed.     

Taxonomic affinity of the early Homo cranium from Swartkrans,South Africa

A quantitative analysis that employs randomization methods and distance statistics has been undertaken in an attempt to clarify the taxonomic affinities of the partial Homo cranium (SK 847) from Member 1 of the Swartkrans Formation. Although SK 847 has been argued to represent early H. erectus, exact randomization tests reveal that the magnitude of differences between it and two crania that have been attributed to that taxon (KNM-ER 3733 and KNM-WT 15000) is highly unlikely to be encountered in a modern human sample drawn from eastern and southern Africa. Some of the variables that differentiate SK 847 from the two early H. erectus crania (e. g., nasal breadth, frontal breadth, mastoid process size) have been considered to be relevant characters in the definition of that taxon. Just as the significant differences between SK 847 and the two early H. erectus crania make attribution of the Swartkrans specimen to that taxon unlikely, the linkage of SK 847 to KNM-ER 1813, and especially Stw 53, suggests that the Swartkrans cranium may have its closest affinity with H. habilis sensu lato. Differences from KNM-ER 1813, however, hint that the South African fossils may represent a species of early Homo that has not been sampled in the Plio-Pleistocene of eastern Africa. The similarity of SK 847 and Stw 53 may support faunal evidence which suggests that Sterkfontein Member 5 and Swartkrans Member 1 are of similar geochronological age. © 1993 Wiley-Liss, Inc.     

A complete second metatarsal (StW 89) from Sterkfontein Member 4, South Africa

The functional anatomy of the hominin foot has played a crucial role in studies of locomotor evolution in human ancestors and extinct relatives. However, foot fossils are rare, often isolated, and fragmentary. Here, we describe a complete hominin second metatarsal (StW 89) from the 2.0-2.6 million year old deposits of Member 4, Sterkfontein Cave, South Africa. Like many other fossil foot bones, it displays a mosaic of derived human-like features and primitive ape-like features. StW 89 possesses a domed metatarsal head with a prominent sulcus, indicating dorsiflexion at the metatarsophalangeal joint during bipedal walking. However, while the range of motion at the metatarsophalangeal joint is human-like in dorsiflexion, it is ape-like in plantarflexion. Furthermore, StW 89 possesses internal torsion of the head, an anatomy decidedly unlike that found in humans today. Unlike other hominin second metatarsals, StW 89 has a dorsoplantarly gracile base, perhaps suggesting more midfoot laxity. In these latter two anatomies, the StW 89 second metatarsal is quite similar to the recently described second metatarsal of the partial foot from Burtele, Ethiopia. We interpret this combination of anatomies as evidence for a low medial longitudinal arch in a foot engaged in both bipedal locomotion, but also some degree of pedal, and perhaps even hallucal, grasping. Additional fossil evidence will be required to determine if differences between this bone and other second metatarsals from Sterkfontein reflect normal variation in an evolving lineage, or taxonomic diversity.     

Femoral/humeral strength in early African Homo erectus

Lower-to-upper limb-bone proportions give valuable clues to locomotor behavior in fossil taxa. However, to date only external linear dimensions have been included in such analyses of early hominins. In this study, cross-sectional measures of femoral and humeral diaphyseal strength are determined for the two most complete early Homo erectus (or ergaster) associated skeletons--the juvenile KNM-WT 15000 and the adult KNM-ER 1808. Modern comparative samples include an adult human skeletal sample representative of diverse body shapes, a human longitudinal growth series, and an adult chimpanzee sample. When compared to appropriately age-matched samples, both H. erectus specimens fall very close to modern human mean proportions and far from chimpanzee proportions (which do not overlap with those of humans). This implies very similar mechanical load-sharing between the lower and upper limbs, and by implication, similar locomotor behavior in early H. erectus and modern humans. Thus, by the earliest Pleistocene (1.7 Ma), completely modern patterns of bipedal behavior were fully established in at least one early hominin taxon.     

Dental microwear texture analysis of hominins recovered by the Olduvai Landscape Paleoanthropology Project, 1995-2007

Dental microwear analysis has proven to be a valuable tool for the reconstruction of aspects of diet in early hominins. That said, sample sizes for some groups are small, decreasing our confidence that results are representative of a given taxon and making it difficult to assess within-species variation. Here we present microwear texture data for several new specimens of Homo habilis and Paranthropus boisei from Olduvai Gorge, bringing sample sizes for these species in line with those published for most other early hominins. These data are added to those published to date, and microwear textures of the enlarged sample of H. habilis (n = 10) and P. boisei (n = 9) are compared with one another and with those of other early hominins. New results confirm that P. boisei does not have microwear patterns expected of a hard-object specialist. Further, the separate texture complexity analyses of early Homo species suggest that Homo erectus ate a broader range of foods, at least in terms of hardness, than did H. habilis, P. boisei, or the “gracile” australopiths studied. Finally, differences in scale of maximum complexity and perhaps textural fill volume between H. habilis and H. erectus are noted, suggesting further possible differences between these species in diet.     

Energetics in Homo erectus and other early hominins: the consequences of increased lower-limb length

Previous studies of daily energy expenditure (DEE) in hominin fossils have estimated locomotor costs using a formula that was based on six species, all 18 kg or less in mass, including no primates, and that has a number of other problems when applied in an ecological context. It is well established that the energetic cost of human walking is lower than that of representative mammals, particularly for individuals with long lower limbs. The current study reevaluates the daily energy expenditures of a variety of hominin species using more appropriate approaches to estimating locomotor costs. To estimate DEE for primates, I relied on published data on body mass, day range, and the percentage of time spent in various activities. Based on those data, I calculated a value for nonlocomotor DEE. I then used a variant of a method that I have suggested elsewhere to calculate the daily cost due to locomotion (DEEL) and summed the two to calculate total DEE. The more up-to-date methods for calculating the cost of travel result in lower estimates of this aspect of the energy budget than seen in previous studies. Values obtained here for DEE in various representatives of Australopithecus are lower than reported previously by around 200 kcal/day. Taking into account the greater economy of human walking, particularly the effect of the longer lower limbs found in many later Homo species, also results in lowered estimates of DEE. Elongation of the lower limbs in H. erectus reduced relative travel costs nearly 50% in comparison to A.L. 288-1 (A. afarensis). The present method for calculating DEE indicates that female H. erectus DEE was 84% greater than that of female Australopithecus; this disparity is even larger than that suggested by previous workers.     

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.     

Investigating early hominin dispersal patterns: developing a framework for climate data integration

An investigation using the Stepping Out model of early hominin dispersal out of Africa is presented here. The late arrival of early hominins into Europe, as deduced from the fossil record, is shown to be consistent with poor ability of these hominins to survive in the Eurasian landscape. The present study also extends the understanding of modelling results from the original study by Mithen and Reed (2002. Stepping out: a computer simulation of hominid dispersal from Africa. J. Hum. Evol. 43, 433-462). The representation of climate and vegetation patterns has been improved through the use of climate model output. This study demonstrates that interpretative confidence may be strengthened, and new insights gained when climate models and hominin dispersal models are integrated.     

Reappraisal of the taxonomic status of the cranium Stw 53 from the Plio/Pleistocene of Sterkfontein,in South Africa

A fossil skull, Stw 53, from the Plio/Pleistocene of Sterkfontein, in South Africa, has been referred toHomo habilis Leakey, Napier, andTobias, 1964. Reappraisal of its putative hominine affinity reveals a closer resemblance toAustralopithecus africanus Dart, 1925. The skull, as reconstructed, is too small forH. habilis; with no indication of brain expansion overA. africanus; has a facial angle outside the hominine range, but identical with that ofA. africanus; and whose teeth are not elongated but display buccolingual expansion. Although it was found in the same strata (Member 5) as stone tools, there is no causal connection. It has been dated faunistically at 2–1.5 my BP, but due to an unconformity it is suggested that it could be older. In spite of its late date, Stw 53 shows no intermediate characters which could support a trend towardsH. habilis orA. robustus Broom, 1938. It may, therefore, represent a relict population ofA. africanus.     

Cranial base morphology and temporal bone pneumatization in Asian Homo erectus

The external morphological features of the temporal bone are used frequently to determine taxonomic affinities of fossils of the genus Homo. Temporal bone pneumatization has been widely studied in great apes and in early hominids. However, this feature is rarely examined in the later hominids, particularly in Asian Homo erectus. We provide a comparative morphological and quantitative analysis of Asian Homo erectus from the sites of Ngandong, Sambungmacan, and Zhoukoudian, and of Neandertals and anatomically modern Homo sapiens in order to discuss causes and modalities of temporal bone pneumatization during hominid evolution. The evolution of temporal bone pneumatization in the genus Homo is more complex than previously described. Indeed, the Zhoukoudian fossils have a unique pattern of temporal bone pneumatization, whereas Ngandong and Sambungmacan fossils, as well as the Neandertals, more closely resemble the modern human pattern. Moreover, these Chinese fossils are characterized by a wide midvault and a relatively narrow occipital bone. Our results support the point of view that cell development does not play an active role in determining cranial base morphology. Instead, pneumatization is related to available space and to temporal bone morphology, and its development is related to correlated morphology and the relative disposition of the bones and cerebral lobes. Because variation in pneumatization is extensive within the same species, the phyletic implications of pneumatization are limited in the taxa considered here.     

Homo floresiensis: a cladistic analysis

The announcement of a new species, Homo floresiensis, a primitive hominin that survived until relatively recent times is an enormous challenge to paradigms of human evolution. Until this announcement, the dominant paradigm stipulated that: 1) only more derived hominins had emerged from Africa, and 2) H. sapiens was the only hominin since the demise of Homo erectus and Homo neanderthalensis. Resistance to H. floresiensis has been intense, and debate centers on two sets of competing hypotheses: 1) that it is a primitive hominin, and 2) that it is a modern human, either a pygmoid form or a pathological individual. Despite a range of analytical techniques having been applied to the question, no resolution has been reached. Here, we use cladistic analysis, a tool that has not, until now, been applied to the problem, to establish the phylogenetic position of the species. Our results produce two equally parsimonious phylogenetic trees. The first suggests that H. floresiensis is an early hominin that emerged after Homo rudolfensis (1.86 Ma) but before H. habilis (1.66 Ma, or after 1.9 Ma if the earlier chronology for H. habilis is retained). The second tree indicates H. floresiensis branched after Homo habilis.     

Gamma-ray spectrometric dating of late Homo erectus skulls from Ngandong and Sambungmacan, Central Java, Indonesia

Hominid fossils from Ngandong and Sambungmacan, Central Java, Indonesia, are considered to be the most anatomically derived and youngest representatives of Homo erectus. Nondestructive gamma-ray spectrometric dating of three of these Homo erectus skulls showed that all samples underwent uranium leaching. Nevertheless, we could establish minimum age estimates of around 40ka, with an upper age limit of around 60 to 70ka. This means that the Homo erectus of Java very likely survived the Toba eruption and may have been contemporaneous with the earliest Homo sapiens in Southeast Asia and Australasia.     

Speciation, diversity, and Mode 1 technologies: the impact of variability selection

Over geological timescales, organisms encounter periodic shifts in selective conditions driven by environmental change. The variability selection hypothesis suggests that increases in environmental fluctuation have led to the evolution of complex, flexible behaviours able to respond to novel and unpredictable adaptive settings. This hypothesis is tested via the framework of a single locus genetic model in which an invading ‘versatilist’ allele competes with two opposed specialists in a selection regime driven by a fluctuating environment, modelled initially as a sine wave and subsequently as an empirical climate curve covering the past 5 million years. Results demonstrate that generalist alleles achieve fixation in the sine wave environment, whilst versatilist alleles do so in the empirical environment, even at a range of very low fitness advantages over the basic generalist template. Variability selection is found to be a particularly strong force between approximately 2.5 and 1.2 Ma (millions of years ago). These results are discussed in relation to the spread of Oldowan lithics and the patterns of speciation and extinction documented in the hominin fossil record. It is suggested that the flexibility required for survival in a variable climatic regime may have been a stimulus to the development of the first stone tool technologies, whilst the ecological opportunities provided by heightened variability may have been a factor in prompting the hominin adaptive radiation evidenced during this period.     

A re-evaluation of the metric diversity within Homo erectus

Previous work by several researchers has suggested that the cranial sample from Zhoukoudian possesses a unique metric pattern relative to the African and Asian specimens assigned to Homo erectus. The current study readdresses this issue with an expanded fossil sample and a larger and more comprehensive set of cranial measurements. To test the patterns present in the assemblage, canonical variates analysis was performed using a covariance matrix generated from the Howells data set. From this, interindividual Mahalanobis distances were computed for the fossils. Random expectation statistics were then used to measure statistical significance of the Mahalanobis distances. The results show that the Zhoukoudian hominids exhibit a unique metric pattern not shared by the African and Indonesian crania sampled. In these tests the Hexian calvaria resembled the African and Indonesian specimens and differed significantly from the craniometric pattern seen in the Zhoukoudian fossils. The Zhoukoudian specimens are characterized by a wide midvault and relatively narrow occipital and frontal bones, while the African and Indonesian crania (including Hexian) have relatively broad frontal and occipital dimensions compared to their midvaults. These results do not suggest that a multiple-species scenario is necessary to encompass the variation present in the sample. Based on the current evidence it is more probable that this variation reflects polytypism influenced by environmental adaptation and/or genetic drift.     

Evidence of amelogenesis imperfecta in an early African Homo erectus

The teeth of the Homo erectus child (Garba IV) recovered from Melka Kunture Ethiopia and dated to 1.5 Ma are characterized by generalized enamel dysplasia, reduced enamel radio-opacity, and severe attrition. This combination of features is found in a large group of hereditary, generalized enamel dysplasias known as amelogenesis imperfecta (AI). SEM studies carried out on epoxy replicas of teeth from the Garba IV child, confirmed that the defects noted were developmental and not due to diagenesis. The enamel prism arrangement is abnormal and there are deep vertical furrows lacking enamel on both buccal and lingual surfaces of all molars. The lesions differ from those characteristic of linear enamel hypoplasia that form discrete horizontal lesions or pits within otherwise normal enamel. We propose that the Garba IV child is the earliest example of AI and provides a link between palaeoanthropology and molecular biology in investigations of the evolutionary history of genetic disorders.     

New 1.5 million-year-old Homo erectus maxilla from Sangiran (Central Java, Indonesia)

Sangiran (Solo Basin, Central Java, Indonesia) is the singular Homo erectus fossil locale for Early Pleistocene Southeast Asia. Sangiran is the source for more than 80 specimens in deposits with ⁴⁰Ar/³⁹Ar ages of 1.51-0.9 Ma. In April 2001, we recovered a H. erectus left maxilla fragment (preserving P³- M²) from the Sangiran site of Bapang. The find spot lies at the base of the Bapang Formation type section in cemented gravelly sands traditionally called the Grenzbank Zone. Two meters above the find spot, pumice hornblende has produced an ⁴⁰Ar/³⁹Ar age of 1.51 ± 0.08 Ma. With the addition of Bpg 2001.04, Sangiran now has five H. erectus maxillae. We compare the new maxilla with homologs representing Sangiran H. erectus, Zhoukoudian H. erectus, Western H. erectus (pooled African and Georgian specimens), and Homo habilis. Greatest contrast is with the Zhoukoudian maxillae, which appear to exhibit a derived pattern of premolar-molar relationships compared to Western and Sangiran H. erectus. The dental patterns suggest distinct demic origins for the earlier H. erectus populations represented at Sangiran and the later population represented at Zhoukoudian. These two east Asian populations, separated by 5000 km and nearly 800 k.yr., may have had separate origins from different African/west Eurasian populations.