Biomechanical interpretation of the early hominid hip

A new pelvic fragment from Swartkrans provides the opportunity to analyze the hip joint mechanics of the robust form of early hominid. The function of the lateral support system provided by the abductor muscles of the hip appears to be similar to that of the gracile early hominid from Sterkfontein. The system is well adapted for providing the lateral support necessary for efficient bipedalism. The hip extensor mechanism and hip internal rotatory system also appear to be well adapted for efficient bipedalism in a way very similar to the other early hominids. The conclusion reached is that the robust and gracile forms of South African early hominids were basically similar in their locomotor adaptation and were most likely habitual bipeds.     

How large were the australopithecines?

Stature of the African early hominids is estimated from most of the available fragments of fossil long bones by means of regression analysis. The average height of the South African gracile australopithecines is predicted to be 145.1 cm (4′9″) where n = 4 and of the South African robust forms, 152.7 cm (5′) where n = 3. The East African early hominids are somewhat taller (x = 163.0 cm or 5′4″, where n = 7). Variability in stature is high even within the same site which is probably a reflection of fairly strong sexual dimorphism in body size. Evidence is presented which suggests that at least in one form of early hominid the size proportions of fore- and hindlimbs are different than in modern man. There is also evidence that average stature may have increased through time. The most significant of these findings is that the two forms of early hominids in South Africa are possibly more similar in stature than is usually cited. This does not imply necessarily that the two forms did not differ significantly in robustness or weight.     

Dental metric assessment of the omo fossils: implications for the phylogenetic position of Australopithecus africanus

The discovery of Australopithecus afarensis has led to new interpretations of hominid phylogeny, some of which reject A. africanus as an ancestor of Homo. Analysis of buccolingual tooth crown dimensions in australopithecines and Homo species by Johanson and White (Science 202:321-330, 1979) revealed that the South African gracile australopithecines are intermediate in size between Laetoli/hadar hominids and South African robust hominids. Homo, on the other hand, displays dimensions similar to those of A. afarensis and smaller than those of other australopithecines. These authors conclude, therefore, that A. africanus is derived in the direction of A. robustus and is not an ancestor of the Homo clade. However, there is a considerable time gap (ca. 800,000 years) between the Laetoli/Hadar specimens and the earliest Homo specimens; "gracile" hominids from Omo fit into this chronological gap and are from the same geographic area. Because the early specimens at Omo have been designated A. afarensis and the later specimens classified as Homo habilis, Omo offers a unique opportunity to test hypotheses concerning hominid evolution, especially regarding the phylogenetic status of A. africanus. Comparisons of mean cheek teeth breadths disclosed the significant (P less than or equal to 0.05) differences between the Omo sample and the Laetoli/Hadar fossils (P4, M2, and M3), the Homo fossils (P3, P4, M1, M2, and M1), and A. africanus (M3). Of the several possible interpretations of these data, it appears that the high degree of similarity between the Omo sample and the South African gracile australopithecine material warrants considering the two as geographical variants of A. africanus. The geographic, chronologic, and metric attributes of the Omo sample argue for its lineal affinity with A. afarensis and Homo. In conclusion, a consideration of hominid postcanine dental metrics provides no basis for removing A. africanus from the ancestry of the Homo lineage.     

The rise of the hominids as an adaptive shift in fallback foods: plant underground storage organs (USOs) and australopith origins

We propose that a key change in the evolution of hominids from the last common ancestor shared with chimpanzees was the substitution of plant underground storage organs (USOs) for herbaceous vegetation as fallback foods. Four kinds of evidence support this hypothesis: (1) dental and masticatory adaptations of hominids in comparison with the African apes; (2) changes in australopith dentition in the fossil record; (3) paleoecological evidence for the expansion of USO-rich habitats in the late Miocene; and (4) the co-occurrence of hominid fossils with root-eating rodents. We suggest that some of the patterning in the early hominid fossil record, such as the existence of gracile and robust australopiths, may be understood in reference to this adaptive shift in the use of fallback foods. Our hypothesis implicates fallback foods as a critical limiting factor with far-reaching evolutionary effects. This complements the more common focus on adaptations to preferred foods, such as fruit and meat, in hominid evolution.     

Cranial morphometry of early hominids: facial region

We report here on early hominid facial diversity, as part of a more extensive morphometric survey of cranial variability in Pliocene and early Pleistocene Hominidae. Univariate and multivariate techniques are used to summarise variation in facial proportions in South and East African hominids, and later Quaternary groups are included as comparators in order to scale the variation displayed. The results indicate that "robust" australopithecines have longer, broader faces than the "gracile" form, but that all australopithecine species show comparable degrees of facial projection. "Robust" crania are characterised by anteriorly situated, deep malar processes that slope forwards and downwards. Smaller hominid specimens, formally or informally assigned to Homo (H. habilis, KNM-ER 1813, etc.), have individual facial dimensions that usually fall within the range of Australopithecus africanus, but which in combination reveal a significantly different morphological pattern; SK 847 shows similarly hominine facial proportions, which differ significantly from those of A. robustus specimens from Swartkrans. KNM-ER 1470 possesses a facial pattern that is basically hominine, but which in some respects mimics that of "robust" australopithecines. Early specimens referred to H. erectus possess facial proportions that contrast markedly with those of other Villafranchian hominids and which suggest differing masticatory forces, possibly reflecting a shift in dietary niche. Overall the results indicate two broad patterns of facial proportions in Hominidae: one is characteristic of Pliocene/basal Pleistocene forms with opposite polarities represented by A. boisei and H. habilis; the other pattern, which typifies hominids from the later Lower Pleistocene onwards, is first found in specimens widely regarded as early representatives of H. erectus, but which differ in which certain respects from the face of later members of that species.     

A quantitative and qualitative reanalysis of the endocast from the juvenile Paranthropus specimen l338y-6 from Omo, Ethiopia

Based on an analysis of its endocast, Holloway (1981 Am J Phys Anthropol 53:109-118) attributed the juvenile Omo L338y-6 specimen to Australopithecus africanus (i.e., gracile australopithecines) rather than to Paranthropus (Australopithecus) boisei (robust australopithecines) favored by other workers (Rak and Howell [1978] Am J Phys Anthropol 48:345-366). Holloway's attribution was based on the specimen's (1) low cranial capacity, (2) gracile-like meningeal vessels, (3) gracile-like cerebellar hemispheres, and (4) absence of an enlarged occipital/marginal (O/M) sinus system. Recent work, however, has shown that criteria 1 and 2 are not useful for sorting gracile from robust australopithecines (Culotta [1999] Science 284:1109-1111; Falk [1993] Am J Phys Anthropol 92:81-98). In this paper, we test criterion 3 by quantifying the endocranial cerebellar and occipital morphology reproduced on the Omo L338y-6 endocast, and comparing it to seven endocasts from South and East African early hominids. Our preliminary results show that metric analysis of this specimen cannot be used to sort it preferentially with either robust or gracile australopithecines. Finally, we demonstrate that, contrary to previous reports, the Omo L338y-6 endocast reproduces an enlarged left occipital sinus (criterion 4). This observation is consistent with the original attribution of the Omo specimen to robust australopithecines (Rak and Howell [1978] Am J Phys Anthropol 48:345-366). Furthermore, if Omo L338y-6 was a robust australopithecine, this discovery extends the occurrence of an enlarged O/M sinus system to one of the earliest known paranthropines. Am J Phys Anthropol 110:399-406, 1999.     

步氏巨猿牙齿大小上的变异性和南方古猿类食性假说

步氏巨猿牙齿大小上的变异性表明,在柳城巨猿洞局部地区的堆积中可能有少量时代稍晚的巨猿牙齿标本。晚期步氏巨猿与早期的相比,后部齿显著增大而前部齿则无显著差异。从步氏巨猿牙齿在大小上的演化趋势来看,南非南方古猿类中的纤细类与粗壮类之间在齿列比例上的不同不一定意味着其食性上有大的差异,纤细类与粗壮类也未必有“属”这一分类级别上的差异。     

How big were early hominids?

The recent discovery of new postcranial fossils, particularly associated body parts, of several Plio-Pleistocene hominids provides a new opportunity to assess body size in human evolution.¹ Body size plays a central role in the biology of animals because of its relationship to brain size, feeding behavior, habitat preference, social behavior, and much more. Unfortunately, the prediction of body weight from fossils is inherently inaccurate because skeletal size does not reflect body size exactly and because the fossils are from species having body proportions for which there are no analogues among modern species. The approach here is to find the relationship between body size and skeletal size in ape and human specimens of known body weight at death and to apply this knowledge to the hominid fossils, using a variety of statistical methods, knowledge of the associated partial skeletons of the of early hominids, formulae derived from a modern human sample, and, finally, common sense. The following modal weights for males and females emerge: Australopithecus afarensis, 45 and 29 kg; A. africanus, 41 and 30 kg; A. robustus, 40 and 32 kg; A. boisei, 49 and 34 kg; H. habilis, 52 and 32 kg. The best known African early H. erectus were much larger with weights ranging from 55 kg on up. These estimates imply that (1) in the earliest hominid species and the “robust” australopithecines body sizes remained small relative to modern standards, but between 2.0 and 1.7 m.y.a. there was a rapid increase to essentially modern body size with the appearance of Homo erectus; (2) the earliest species had a degree of body size sexual dimorphism well above that seen in modern humans but below that seen in modern gorillas and orangs which implies (along with other evidence) a social organization characterized by kin-related, multi-male groups with females who were not kin-related; (3) relative brain sizes increased through time; (4) there were two divergent trends in relative cheek-tooth size—a steady increase through time from A. afarensis to A. africanus to the “robust” australopithecines, and a decrease beginning with H. habilis to H. erectus to H. sapiens.     

The ischium and hip extensor mechanism in human evolution

Although it is commonly stated that the ischia of the late Pliocene–early Pleistocene hominid fossils are long and ape-like, new interpretations show this view to be fallacious. An important new theory proposed by Robinson concludes that the gracile form of early hominid was an efficient biped, but the robust form was a less efficient biped and was adapted for tree climbing. Interpretation of the ischium is crucial to this idea. The present study shows that (1) the gracile and robust australopithecine ischia had similar relative lengths and (2) that the hamstring mechanism was probably very similar in the two forms of South African early hominid.     

Body size and proportions in early hominids.

The discovery of several associated body parts of early hominids whose taxonomic identity is known inspires this study of body size and proportions in early hominids. The approach consists of finding the relationship between various measures of skeletal size and body mass in modern ape and human specimens of known body weight. This effort leads to 78 equations which predict body weight from 95 fossil specimens ranging in geological age between 4 and 1.4 mya. Predicted weights range from 10 kg to over 160 kg, but the partial associated skeletons provide the essential clues as to which predictions are most reliable. Measures of hindlimb joint size are the best and probably those equations based on the human samples are better than those based on all Hominoidea. Using hindlimb joint size of specimens of relatively certain taxonomy and assuming these measures were more like those of modern humans than of apes, the male and female averages are as follows: Australopithecus afarensis, 45 and 29 kg; A. africanus, 41 and 30 kg; A. robustus, 40 and 32 kg; A. boisei, 49 and 34 kg; H. habilis, 52 and 32 kg. These values appear to be consistent with the range of size variation seen in the entire postcranial samples that can be assigned to species. If hominoid (i.e., ape and human combined) proportions are assumed, the males would be 10 to 23 kg larger and the females 4 to 10 kg larger.     

Size- and locomotion-related aspects of hominid and anthropoid pelves: An osteometrical multivariate analysis

Two multivariate methods — the logarithmic principal component analysis (LPCA), and the logarithmic factorial analysis (LFA) — have been used tocompare the hip bone proportions of hominoids biometrically. The results have shown that size effects among apes and hominids interact to a centain extent with locomotor specializations, which are related to the attainment of more or less terrestrial behaviors. The pelvic morphology of great apes (Pongo, Pan, Gorilla) has retained numerous morphological traits — such as a gracile and elongated hip bone —, which were inherited from common adaptations to arboreal locomotion. In spite of these common traits, the African pongids (Pan, Gorilla) present two very different pelvic morphologies corresponding to two adaptative modes of terrestrial quadrupedalism. The hip bone of humans is proportionnally short and robust, most particularly at the level of its axial part. These characteristics, as well as the whole pelvic proportions, clearly indicate that gravitational forces exert a strong pressure on the pelvic walls during bipedalism. Among hominids, the transition from an australopithecine-like pelvic pattern to a human-like one corresponds to an increase of loading constraints on the hip jiont. This seems to indicate an evident change in locomotor behavior. Progression apparently became exclusively terrestrial with the genusHomo.     

Shape variation of the human pollical distal phalanx and metacarpal

Human distal pollical phalanx form has been associated with tool manufacture, and the broad tuft of this bone in Neanderthals has been suggested to be a climatic adaptation and/or an aid to a tremendously powerful grip. A wide first metacarpal head has also been proposed to be useful in distinguishing tool-dependent hominids from those less reliant on tools. In order to contribute to an evaluation of these hypotheses variation in first metacarpal and distal phalanx shape is explored among samples of modern humans and compared to that of fossil hominids. Modern humans are from the Terry Collection, Larsen Bay, a Chinese-Alaskan cemetery, Egypt, and Sully and Mobridge. Hominid fossils include AL 333w-39, SKX 5016, SK 84, Stw 294, OH 7, several Neanderthals, Skhūl 4 and 5, and Predmostí 3. Analysis involves length-width ratios, regressions of distal phalanx tuft width on base width and of metacarpal head width on length, and pattern profiles based on Z-scores with reference to the Larsen Bay sample. Larsen Bay individuals are robust, while Terry "blacks," Egyptians, and Chinese-Alaskan males tend to be gracile. Fossil hominids are most distinctive for distal phalanx radioulnar tuft and mid-shaft widths relative to length. Security of grip is one plausible explanation. While most modern samples are positively allometric for tuft width relative to base width, the Larsen Bay and fossil hominid samples are not; thus caution is advised in accepting a base-tuft width comparison as a tool-dependence marker. Separation from modern humans is not easily achieved with metacarpal measures, but the Hadar metacarpal has distinctively narrow radioulnar head width ratios. While first metacarpal head expansion among hominids may plausibly be related to tool manufacture, other activities that place stress on the metacarpophalangeal joint should also be considered.     

Petite bodies of the “robust” australopithecines

The “robust” australopithecines are often depicted as having large and powerfully built bodies to match their massive masticatory apparatus, but until 1988 the sample of postcranial remains attributed with certainty to this group was very limited. Almost nothing was known about the body of the East African “robust” australopithecine because taxonomic attribution of the postcrania was so uncertain. The body of the South African “robust” australopithecine had to be reconstructed from about a dozen isolated fragments of postcrania. Now a partial skeleton is attributed with confidence to the East African “robust” group along with several isolated bones. The South African sample has more than tripled. Analyses of this vastly expanded sample reveal that a large portion of postcrania attributed to “robust” australopithecines from Swartkrans Member 1 (35%) are from extraordinarily small-bodied individuals similar in size to a modern Pygmy weighing as little as 28 kg. These small elements include parts from the forelimb, spine, and hindlimb. About 22% of these Swartkrans 1 “robust” australopithecines are about the same size as a modern human weighing about 43 kgs and about 43% are larger than this standard but less than or equal to a 54 kg modern human. Approximately the same pattern is true for the Swartkrans 2 hominids, but taxonomic attribution is less certain. All of the Member 3 specimens are similar in size to the 45 kg standard. The partial skeleton of the East African “robust” australopithecine (KNM-ER 1500) has hindlimb joints that would correspond to a modern human of 34 kgs although the actual weight may be 5 to 10 kgs greater judging from shaft robusticity and forelimb size. The largest postcranial element attributed with some certainty to the East African “robust” australopithecine group (the talus, KNM-ER 1464) is about the same overall size as a modern human of 54 kgs, although its tibial facet is slightly smaller. Although many previous studies have hinted at the possibility that “robust” australopithecines had relatively small bodies, the new fossils provide substantial evidence that these creatures ranged from quite small to only moderate in body size relative to modern humans. These were the petite-bodied vegetarian cousins of our ancestors. Sexual dimorphism in body size appears to be greater than that in modern humans, similar to that in Pan, and less than that in Gorilla or Pongo, although such comparisons are of limited value given the small samples, poorly known body proportions, time averaging, and many other problems.     

Effects of iodine deficiency on mental and psychomotor abilities

The allometric relationships between canine base area, first molar and summed molar crown area, and the glabella–opisthocranion distance, and the direct allometric relationships between canine and molar size have been established in five primate taxa. Separate sex and combined sex ‘intraspecific’, and ‘interspecific’ regression and ‘best fit’ allometry coefficients were computed. This analysis showed that for any increase in glabella–opisthocranion length, the rate of increase in canine size exceeds the rate of increase in molar area, and ‘best fit’ solutions indicate that canine base area is positively allometric when related directly to molar crown area. These results were compared with data available for the ‘gracile’ australopithecine, A. africanus, and two ‘robust’ australopithecine taxa, A. boisei and A. robustus. The differences in canine and molar size which occur between the ‘gracile’ taxon and the two ‘robust’ taxa do not correspond to any of the trends in the comparative allometric models. Data on glabella–opisthocranion length for the fossils, meagre though they are, show that while the proportional increase in molar crown area between the taxa corresponds to comparative allometry models, the reduced canine size in the ‘robust’ taxa is against comparative allometric trends. These results indicate that, at least in terms of canine/molar proportions, the differences between the ‘gracile’ and ‘robust’ australopithecines are not merely allometric and may indicate significant dietary or behavioural differences.     

Population characteristics of extinct hominid endocranial volume

Distribution and variation statistics of hominid endocranial volume (ECV) have been investigated. Within the interpretative constraints imposed by (very) small sample sizes, the requirements for normality are met, as are those for heteroscedasticity. A significant difference in means can be demonstrated for only two comparisons. With one exception, overall distribution characteristics differ significantly in pairwise comparisons between taxa. The coefficient of variation of ECV that characterizes a group composed of all Plio-Pleistocene gracile hominids does not support a single polytypic species interpretation of this assemblage. Significant differences in the coefficient of variation exist between all possible pairs of taxa with the exception of Homo habilis and Homo erectus.     

A new pelvic fragment from swartkrans and the relationship between the robust and gracile australopithecines

A recently discovered hominid pelvic fragment from Swartkrans (SK 3155) is described in detail with particular reference to the relationship of the two presently recognized forms of australopithecines in South Africa. Results of this examination and metrical analysis indicate that the acetabulum and iliac blade of the early hominids are similar to Homo sapiens except for a unique pattern of traits: a relatively small sacral articular surface, a relatively small acetabulum, a relatively large iliac fossa, and wide lateral splaying of the iliac blades. The new Swartkrans fossil expresses these traits more strongly than does the gracile australopithecine (Sts 14) and is therefore somewhat less similar to Homo sapiens but it is very unlike any pongid.     

How different are robust and gracile capuchin monkeys? An argument for the use of sapajus and cebus

Capuchin monkey behavior has been the focus of increasing numbers of captive and field studies in recent years, clarifying behavioral and ecological differences between the two morphological types: the gracile and the robust capuchins (also referred to as untufted and tufted). Studies have tended to focus on the gracile species Cebus capucinus (fewer data are available for C. albifrons, C. olivaceus, and C. kaapori) and on Cebus apella, a name that has encompassed all of the robust capuchins since the 1960s. As a result, it is difficult to ascertain the variation within either gracile or robust types. The phylogenetic relationships between gracile and robust capuchins have also, until now, remained obscure. Recent studies have suggested two independent Pliocene radiations of capuchins stemming from a common ancestor in the Late Miocene, about 6.2 millions of years ago (Ma). The present-day gracile capuchins most likely originated in the Amazon, and the robust capuchins in the Atlantic Forest to the southeast. Sympatry between the two types is explained by a recent expansion of robust capuchins into the Amazon (ca. 400,000 years ago). Morphological data also support a division of capuchins into the same two distinct groups, and we propose the division of capuchin monkeys into two genera, Sapajus Kerr, 1792, for robust capuchins and Cebus Erxleben, 1777, for gracile capuchins, based on a review of extensive morphological, genetic, behavioral, ecological, and biogeographic evidence.     

Body weight prediction in early fossil hominids: Towards a taxon-“independent” approach

The choice of a model taxon is crucial when investigating fossil hominids that clearly do not resemble any extant species (such as Australopithecus) or show significant differences from modern human proportions (such as Homo habilis OH 62). An “interhominoid” combination is not adequate either, as scaling with body weight is strongly divergent in African apes and humans for most skeletal predictors investigated here. Therefore, in relation to a study of seven long bone dimensions, a new taxon-“independent” approach is suggested. For a given predictor, its taxonomic “independence” is restricted to the size range over which the body weight-predictor relationship for African apes and humans converges. Different predictors produce converging body weight estimates (BWEs) for different size ranges: taxon-“independent” estimates can be calculated for small- and medium-sized hominids (e. g., for weights below 50 kg) using femoral and tibial dimensions, whereas upper limb bones provide converging results for large hominids (above 50 kg). If the remains of Australopithecus afarensis really belong to one species, the relationship of male (above 60 kg) to female body weight (approximately 30 kg) does not fall within the observed range of modern hominoids. Considering Sts 14 (22 kg) to represent a small-sized Australopithecus africanus, the level of encephalization lies well above that of extant apes. If OH 62 (approximately 25 kg), with limb proportions less human-like than those of australopithecines, indeed represents Homo habilis (which has been questioned previously), an increase in relative brain size would have occurred well before full bipedality, an assumption running counter to current assumptions concerning early human evolution. © 1993 Wiley-Liss, Inc.     

Evolutionary reversals of limb proportions in early hominids? Evidence from KNM-ER 3735 (Homo habilis)

Upper-to-lower limb proportions of Homo habilis are often said to be more ape-like than those of its reputed ancestor, Australopithecus afarensis. Such proportions would either imply multiple evolutionary reversals or parallel development of a relatively short upper limb in A. afarensis and later Homo. However, assessments of limb proportions are complicated by the fragmentary nature of the two known H. habilis skeletons, OH 62 and KNM-ER 3735. Initially, KNM-ER 3735 was compared to A.L. 288-1 (A. afarensis) using a single modern human and chimpanzee as reference. Here, based on a larger comparative sample, we find that the relative size of the distal humerus, radial head, and shaft of both KNM-ER 3735 and A.L. 288-1 lie within the range of variation of modern humans, whereas their sacra are small as is the case for all early hominids. In addition, their manual phalanges are similar in having a gracile base but robust midshaft. Contrary to earlier studies, the fossils are not differentiable from each other statistically with respect to all features listed above. On the other hand, they differ in robusticity of the scapular spine and relative length of the radial neck. An exact randomization test suggests only a very low probability of finding a similar degree of difference within a single species of extant hominoids. In contrast to the consensus view, we conclude that A.L. 288-1 had a short, human-like forearm, whereas KNM-ER 3735 possessed a distinctly longer forearm and more powerful shoulder girdle. This interpretation fits with earlier conclusions that suggested human-like humerofemoral proportions but chimpanzee-like brachial proportions for Homo habilis. Thus, the scenario of a unidirectional, progressive change in limb proportions within the hominid lineage is not supported by our work.