South African Australopithecines Research Articles

Towards the restoration of ancient hominid craniofacial anatomy: Chimpanzee morphology reveals covariation between craniometrics and facial soft tissue thickness.

In modern humans, facial soft tissue thicknesses have been shown to covary with craniometric dimensions. However, to date it has not been confirmed whether these relationships are shared with non-human apes. In this study, we analyze these relationships in chimpanzees (Pan troglodytes) with the aim of producing regression models for approximating facial soft tissue thicknesses in Plio-Pleistocene hominids. Using CT scans of 19 subjects, 637 soft tissue, and 349 craniometric measurements, statistically significant multiple regression models were established for 26 points on the face and head. Examination of regression model validity resulted in minimal differences between observed and predicted soft tissue thickness values. Assessment of interspecies compatibility using a bonobo (Pan paniscus) and modern human subject resulted in minimal differences for the bonobo but large differences for the modern human. These results clearly show that (1) soft tissue thicknesses covary with craniometric dimensions in P. troglodytes, (2) confirms that such covariation is uniformly present in both extant Homo and Pan species, and (3) suggests that chimp-derived regression models have interspecies compatibility with hominids who have similar craniometric dimensions to P. troglodytes. As the craniometric dimensions of early hominids, such as South African australopithecines, are more similar to P. troglodytes than those of H. sapiens, chimpanzee-derived regression models may be used for approximating their craniofacial anatomy. It is hoped that the results of the present study and the reference dataset for facial soft tissue thicknesses of chimpanzees it provides will encourage further research into this topic.

Social Behavior of Early Hominins

Interest in the evolution of human behavior has always featured large in evolutionary biology, challenging the imaginations not just of paleoanthropologists and archeologists, but also of virtually any scientific discipline that touches on human evolution. It certainly has sparked the popular imagination for more than a century, inspiring books and films; pop culture theories; and of course skepticism, doubt, and even hostility. Ever since the first hominin fossils were found, it seems to have been almost irresistible to engage in speculation about the behavior of our ancestors and close relatives, and the exercise continues to the present. For example, Dart (1957) notably emphasized a predilection to violence and power associated with carnivory in the “osteodontokeratic” culture of South African australopithecines. Campbell (1971) takes as a given that human behavior evolved from a chimpanzee-like social system. Washburn and Lancaster (1968) emphasize the role of “Man the Hunter” in the social evolution of hominins. In contrast, Tanner (1987) emphasized the role of gathering in social evolution. Lovejoy (1981) emphasized male provisioning of females in the development of pair-bonds. Wrangham et al. (1999) emphasize the role of cooking in the transformation from an-ape-like to human-like social system. I could go on for pages listing papers offering an enormous variety of models and hypotheses based on an equally wide variety of evidences. Perhaps because it is so easy to tell stories about human behavior, it is easy to dismiss hypotheses about hominin behavior as unsupportable assertion, steeped in preconceptions and cultural bias, and lacking in any real scientific merit. But over the years, the fossil record of human evolution has grown substantially, including not just fossil hominins but a treasure trove of environmental and ecological data. At the same time, behavioral ecology, especially of primates, has built a tremendous body of knowledge about the evolutionary and ecological basis of behavior that has provided extraordinary insight into human behavior. The combination of progress in these disciplines is allowing more and more systematic and scientific approaches to Int J Primatol (2012) 33:1247–1250 DOI 10.1007/s10764-012-9641-0

Upper Molar Cusp Dimensions of South African Australopithecines

Recently, a number of articles have been published on the mechanisms of dental development, and in particular on the genetic control of dental formation. As a specific example of the potential of this kind of research for paleoanthropological studies, cusp areas of upper molars of two species of South African Australopithecines (Australopithecus africanus, A. robustus) have been examined. The results suggest notable differences between the two species, possibly related to markedly different developmental pathways that are still far from clear in their details.

Dental development and upper molar cusp dimensions of South African australopithecines

In recent years a number of papers have been published on the mechanisms of dental development, and in particular on the genetic control of dental formation. As a specific example of the potential of this kind of research for paleoanthropological studies, cusp areas of upper molars of two species of South African australopithecines (Australopithecus africanus, A. robustus) have been examined. The results suggest notable differences between the two species, possibly related to different developmental pathways, although details need clarifying.

The South African australopithecines: A palaeodemographic analysis

Anthropologists, demographers and historians alike are continually seeking information about demographic profiles of prehistoric and ancient human populations. There are many different approaches relevant to the problem, yet direct evidence of the demographic structure of any archaeological population is primarily provided by analysis of human skeletal and dental remains. This offers a possibility of extending demographic inferences back to Pliocene — Early Pleistocene times, which, in turn, would enhance our understanding of the principles of human survival, adaptation, social interaction and demographic evolution of man. Data on the age distribution of South African australopithecines has been analysed using life-table analysis, based on a stationary population model. The estimated demographic profile is the evaluated and interpreted within a framework of biological, cultural and ecological circumstances. It is concluded that palaeodemography, if carefully undertaken, can play a real and pragmatic role in understanding the demographic history of man.

Hip bone trabecular architecture shows uniquely distinctive locomotor behaviour in South African australopithecines

Cancellous bone retains structural and behavioural properties which are time and strain-rate dependent. As the orientation of the trabeculae (trajectories) follows the direction of the principal strains imposed by daily loadings, habitual postural and locomotor behaviours are responsible for a variety of trabecular architectures and site-specific textural arrangements of the pelvic cancellous network. With respect to the great ape condition, the human trabecular pattern is characterized by a distinctive ilioischial bundle, an undivided sacropubic bundle, and a full diagonal crossing (∼100°) over the acetabulum between the ilioischial and the sacropubic bundles. Advanced digital image processing (DIP) of hip bone radiographs has revealed that adolescent and adult South African australopithecines retained an incompletely developed human-like trabecular pattern associated with gait-related features that are unique among the extant primates.

Further data about venous channels in South African Plio-Pleistocene hominids.

Original data about venous channels in South African Plio-Pleistocene hominids are discussed. To assess possible changes in blood volume flow of fossil hominids, we test whether dimensions of three extracranial venous foramina were different between Australopithecus africanus and Australopithecus (Paranthropus) robustus. Moreover, providing further data about the small sample of South African Plio-Pleistocene hominids, we also attempt to re-analyse the incidence of divided hypoglossal canals and four emissary foramina in a very large sample of extant African apes representing all ages, species and subspecies, in A. africanus and in "robust australopithecines". Up to now, only very poor data on extracranial dimensions of venous foramina were available for fossil hominids. However, this topic provides interesting information about the modifications of volume flow during human evolution. Assuming that in fossil hominids, as in humans, dimensions of condylar and mastoid foramina, as well as those of jugular foramina, depended on volume flow through them, we conclude, first, that volume flow through internal jugular veins was comparable in South African australopithecines, extant chimpanzees and humans, and second, that, in comparison with the extant less-encephalized chimpanzees (presumably reflecting the ancestral condition), volume flow was higher through condylar veins in A. (P.) robustus. This increase was responsible for a significantly greater amount of blood drainage from the brain (and consequently an increased arterial blood supply). We support the view that encephalization was the prevailing functional explanation for volume flow increase through condylar veins in A. (P.) robustus, in comparison with its ancestor with its presumably more ape-like degree of encephalization. Considering the incidence of emissary canals and foramina, significant differences between A. africanus, "robust australopithecines" and all the extant African ape species, were tested statistically. Concerning the condylar canal, we did not find differences between "robust australopithecines" and extant African apes. Concerning the incidence of divided hypoglossal canals, mastoid canals, parietal and occipital foramina, no difference was found between extant African apes, A. africanus and "robust australopithecines". High frequencies of either condylar or mastoid canals cannot be regarded as a "pongid condition". Moreover, we did not find convincing data to support the hypothesis that mastoid emissary veins (partly representing a putative "radiator" for cooling the brain) were selected in A. africanus, in comparison with "robust australopithecines".

New Isotopic and Sedimentological Measurements of the Thabaseek Deposits (South Africa) and the Dating of the Taung Hominid

Earlier attempts to date the Taung hominid type specimen of Australopithecus africanus Dart yielded conflicting results. Recent faunal studies pointed to an age of 2.3 myr. Radioisotopic results suggested 1.0 myr. New uranium studies reveal that the Thabaseek (the oldest Taung tufa) was not a closed system and that younger uranium entered the tufa after initial deposition, producing an apparent isotopic age younger than the age of deposition. The Thabaseek isotopic dates provide only a terminus ad quem and this technique is therefore not applicable to the older Taung tufas. Delson's dating (2.3 myr) of cercopithecoids from Hrdlicka's pinnacle ca. 50 m from the hominid site provides the best available approximation to the age of the hominid. In our new Taung excavation, stratigraphic analysis indicates that the hominid may somewhat predate most identified fauna. Sedimentologically the hominid matrix proves to be of fluvial deposition, and hence closely resembles one Hrdlicka deposit, both samples differing appreciably from all other Taung samples which bespeak eolian deposition. Thus, the conditions under which the hominid-bearing stratum was deposited were virtually identical to those pertaining to one of the Hrdlicka deposits. The newest results show that Taung was not the youngest South African australopithecine site and eliminate the discrepancy between the relative ages of the Taung A. africanus africanus and the Sterkfontein A. africanus transvaalensis.

Présence de Saccostomus (Rodentia, Mammalia) a Olduvai Bed I (Tanzanie, Pléistocène inférieur). Implications phylétiques et paléobiogéographiques

Many Saccostomus dental remains are found at Olduvai Bed I (Tanzania, 1.7 Myr). Their description and their comparison with their modern equivalents allow to attribute them to S. cf. mearnsi. They show better affinities with the modern Kijungu (Tanzania) S. mearnsi population of lesser size. S. cf. mearnsi of Olduvai Bed I could derive by size reduction of its molars from S. major of Laetolil Beds at Laetoli (Tanzania, 3.7–3.5 Myr). A revision of the Saccostomus fossil record allows to suggest a major-meamsi divergence between 3.7–2.5 Myr and a meamsi-campestris probably later (between 1.7 and 0.3 Myr). The discussion of the repartition of fossil Saccostomus shows that its absence from Ethiopia, Kenya and South African australopithecine caves during pliocene and lower pleistocene times could be due to biogeographical causes (Rift evolution structure) rather than to ecological or taphonomical ones.

Dental development in South African australopithecines. Part I: Problems of pattern and chronology

AbstractIt is well known that humans take about twice as long as apes to mature. The traditional view that such delayed maturation was already present in australopithecines has been called into question during the past several years. We have approached this problem by looking at patterns of dental development in gracile and robust australopithecines from South Africa and comparing them to patterns found in extant humans and apes. We have employed both 2 and 3 dimensional computed tomography in our research. The dental growth patterns in these two australopithecine morphs differ, particularly in M1/I1 development. The robust australopithecines are more humanlike and the gracile australopithecines more apelike in this feature (“humanlike” and “apelike” are not used in any taxonomic sense). Pattern and chronology of dental development must be considered separately. Several major problem areas for future research are identified, most of which revolve around the issue of intra‐ versus interspecific variation.

Dental development in South African australopithecines. Part II: Dental stage assessment

AbstractDental development stages of six immature Australopithecus robustus individuals from Swarktrans (SK 61, SK 62, SK 63, SK 64, SK 438, SK 3978) and seven immature Australopithecus africanus individuals from Taung, Sterkfontein, and Makapans (Taung 1, Sts 2, Sts 8, Sts 18, Sts 24, Stw 327, MLD 2) are described. These stages were assessed using the system devised by Demirjian and colleagues and were based on a data set comprising over 350 computed tomographic (CT) scans taken at 1 and 2 mm slice intervals. It is concluded that patterns of dental development may have differed between A. robustus and A. africanus even though the chronology of development (i.e., the length of time for dental development to occur) may have proceeded relatively rapidly in both species. These data provide unique information regarding the timing and pattern of dental maturation in austral‐opithecines and can be used to compare and contrast developmental patterns among early hominids, modern humans, and nonhuman primates.

Hominoid dental maturation

Traditional analyses of dental eruption pattern and enamel attrition suggested that the South African australopithecines exhibited a human-like or delayed maturation rate. Recent work has challenged this view by proposing that early hominids matured at a rate more like extant apes. We show that relative growth rates of ape and human dental structures are essentially similar, and that pattern differences in calcification stem from hominid incisor and canine reduction with concomitant facial reorganization. Pattern of dental development alone cannot be used to infer rates of somatic maturation.

Cerebral Cortices of East African Early Hominids

An endocast of the frontal lobe of a reconstructed skull, which is approximately 2 million years old, from the Koobi Fora region of Kenya appears to represent the oldest human-like cortical sulcal pattern in the fossil record, while the endocast from another skull from the same region produces an endocast that appears apelike in its frontal lobe and similar to endocasts from earlier South African australopithecines. New analysis of paleoanatomical evidence thus indicates that at least two taxa of early hominids coexisted in East Africa.

The Application of a Normalizing Statistic to the Dental Metricies of the South African Australopithecines

This study assesses the utility of T-scores for discerning taxonomic categories in Plio-Pleistocene hominids by analysis of the dental metrics of the South African australopithecines. The hominids are divided into robust and gracile samples and T-scores and correlations between these samples are determined. Following a limited comparison of correlations between two non-human primate species the australopithecine T-scores and correlations are suggested to be close to the levels expected if the differences between samples were explained by sexual dimorphism.

Revisiting the South African Taung australopithecine endocast: The position of the lunate sulcus as determined by the stereoplotting technique

AbstractFalk's (1980a) claims regarding the pongid‐like disposition of convolutional patterns on the South African australopithecine endocasts are critically examined. Using a stereoplotter apparatus and a small sample of chimpanzee brain casts, the angular coordinates of the lunate sulcus are recorded, and placed as such on the Taung and SK 1585 endocasts. The resulting location of such pongid‐oriented lunate sulci violates the gross morphology of the australopithecine endocasts. Relative brain: body weight ratios for Australopithecus are shown to be advanced over any of the pongids. In addition, evidence is provided from LeGros Clark's (1947) paper that controverts certain of Falk's claims regarding his methods. It is concluded that the secondary sulci and gyri on the now available australopithecine endocasts are not clear enough to warrant unambiguous demonstration; with regard to the lunate sulcus, the Taung endocast does not show a pongid pattern.

A reanalysis of the South African australopithecine natural endocasts.

Sulcal patterns of six previously available South African australopithecine natural endocasts are reexamined and compared to sulcal patterns of 17 human, 12 gorilla and six chimpanzee brains. In addition, a seventh natural endocast, from STS 58, is described for the first time and compared to an artificial endocast from the same specimen. Using the Taung endocast as a focal point, it is shown that sulcal patterns reproduced on natural endocasts of australopithecines appear to be pongid-like rather than human-like. Contrary to earlier descriptions, the lunate sulcus occupies a rostral position similar to that found in pongids. Since South African australopithecine brains do not appear to be reorganized along human lines at a gross external neuroanatomical level, the concept of neurological reorganization is best applied at finer neurological levels, perhaps at the level of the neuron or at a neurochemical level. Thus, future studies by comparative neuroscientists are more likely to elucidate the fine details of neurological reorganization that occurred during early human evolution than are studies by paleontologists who directly observe the australopithecine fossil record of natural endocasts.

The natural history of the helicoidal occlusal plane and its evolution in early Homo.

In modern man the pitch of the occlusal plane may vary along the tooth-row. When anterior cheek-teeth show a plane sloping upward palatally, whilst that on posterior cheek-teeth slopes upward buccally, there results a twisted or helicoidal occlusal plane (Ackermann). Several hypotheses have been proposed for the structural basis of the helicoidal occlusal plane. Campbell's proposal ('25) has gained widest acceptance, namely that the helicoid results from anteroposterior differences in upper and lower alveolar arch width. In the early 1960s, while studying the Olduvai hominids assigned to Homo habilis, the author noted changing occlusal slopes along the tooth-row and a slight helicoid, although these featues had not been noted in other early hominids. Subsequently, Wallace showed a total absence of the helicoid from South African australopithecines, and its presence in Swartkrans Homo, SK 45 and SK 80. Recent studies confirm the presence of the helicoid in all available specimens of H. habilis, including Stw 53 found at Sterkfontein in 1976. Hence, this trait may distinguish between Australopithecus and early Homo. Measurements of the maxillary arch widths have shown that, whereas in Australopithecus arch widths increase to a maximum at M3, in early Homo maxillary arch widths are greatest at M2. The decline in posterior maxillary arch width is part of a general reduction of that region. Thus despite striking elongation of premolars and M1 in early Homo, M2 and M3 are mesiodistally abbreviated. It is hypothesized that the onset of posterior arch reduction, with the appearance of a helicoid, was a structural and functional concomitant of the transition from the presumed australopithecine ancestor to H. habilis.

Chronology and biology of the South African australopithecines

Based on a 10 months' visit to Southern and Eastern Africa, an attempt is made to contribute to the faunal correlation and the palaeecology of the Transvaal cave deposits; conclusions are mainly drawn from evidence of the fossil Cercopithecoids, but light is shed on the sympatric Australopithecines of Makapansgat, as well. It is suggested that Early Man could have lived only underneath rock-shelters near the ancient cave entrances; the highly diversified fossil fauna of the Makapansgat breccia indicates a very varied biotope; the fossil Cercopithecoids of this site are very primitive and correlate well with a Plio-Pleistocene age.

Primate models for australopithecine sexual dimorphism

AbstractSeveral different models of sexual dimorphism in the South African australopithecines are compared with sexual dimorphism in the living primates. Australopithecine dimorphism is placed in an evolutionary context, and contrasting trends in the hominid and pongid lineages are shown. Evidence suggesting that the australopithecines were an extremely polytypic taxon is presented, and a high level of both inter‐ and intra‐population variation is indicated.

Paleoecology of South African Australopithecines: Taung Revisited

The environmental context and stratigraphic position of the first australopithecine discovery, at Taung, South Africa, need to be reconsidered, since the Taung juvenile, as Australopithecus africanus, is the type specimen of the gracile lineage of Plio-Pleistocene hominids. Recent study of the site and its regional setting shows that two generalizations widely held today are either incorrect or dubious. In particular, the Taung hominid is found in deposits that clearly indicate a subhumid or humid environment and not a semidesert, thus questioning the original basis for hypotheses concerning an ecological differentiation of gracile and robust australopithecines. Furthermore, the Taung specimen relates to a younger geomorphologic cycle than postulated by F. E. Peabody, and this cycle appears to immediately predate the Middle Pleistocene "Younger Gravels" of the Vaal River. This and other, faunal criteria suggest that Taung is contemporary with or even younger than Swartkrans and Kromdraai rather than broadly coeval with Sterkfontein and Makapansgat. By implication, the Taung hominid may postdate the arrival of true Homo in southern Africa, opening up a new range of problems concerning the phylogeny and ecological adaptations of the australopithecines.