Cross-sectional morphology of the SK 82 and 97 proximal femora.

Computed tomography scans of the proximal femoral shaft of the South African "robust" australopithecine, A. robustus, reveal a total morphological pattern that is similar to the specimen attributed to A. boisei in East Africa but unlike that of Homo erectus or modern human femora. Like femora attributed to H. erectus, SK 82 and 97 have very thick cortices, although they do not have the extreme increase in mediolateral buttressing that is so characteristic of H. erectus. And unlike H. erectus or modern humans, their femoral heads are very small relative to shaft strength. These features are consistent with both increased overall mechanical loading of the postcranial skeleton and a possibly slightly altered pattern of bipedal gait relative to that of H. erectus and modern humans.

Body proportions of Australopithecus afarensis and A. africanus and the origin of the genus Homo.

New discoveries of A. africanus fossils from Member 4 Sterkfontein reveal a body form quite unlike earlier Australopithecus species. The new adult material consists of over 48 fore- and hindlimb specimens and includes an associated partial skeleton, Stw 431. The forelimbs and relatively large: the average size of their joints corresponds to a modern human with body mass of 53 kg. The hindlimbs are much smaller with an average size matching a modern human of only 33 kg. Analyses of the Stw 431 partial skeleton confirm these results. In contrast, A. afarensis and anamensis more closely approximate a human pattern of forelimb joint size. This is an unanticipated complication in our understanding of early human evolution. In general, craniodental morphology tracks time in species of Australopithecus: A. anamensis (3.5-4.1 Ma) is the the most primitive with a strongly sloping symphysis, large canine roots, etc., A. afarensis (3.0-3.6 Ma) is less primitive, and A. africanus (2.6-3.0 Ma) shares many derived characteristics with early Homo (e.g., expanded brain, reduced canine, bicuspid lower third premolar, reduced prognathism, greater flexion of the cranial base, deeper TMJ). the new postcranial material, however, reveals an apparently primitive morphology of relatively large forelimb and small hindlimb joints resembling more the pongid than the human pattern. More pongid-like proportions are also present in the two known associated partial skeletons of H. habilis (OH 62 KNM-ER 3735). This may imply either (1) that A. africanus and H. habilis evolved craniodental characters in parallel with the lineage leading to later Homo, or (2) that fore- to hindlimb proportions of A. afarensis (and perhaps A. anamensis) evolved independent of the lineage leading to Homo and does not imply a close phylogenetic link with Homo. Both of these explanations or any other phylogeny imply homoplasy.

Tempo and mode in human evolution.

The quickening pace of paleontological discovery is matched by rapid developments in geochronology. These new data show that the pattern of morphological change in the hominid lineage was mosaic. Adaptations essential to bipedalism appeared early, but some locomotor features changed much later. Relative to the highly derived postcrania of the earliest hominids, the craniodental complex was quite primitive (i.e., like the reconstructed last common ancestor with the African great apes). The pattern of craniodental change among successively younger species of Hominidae implies extensive parallel evolution between at least two lineages in features related to mastication. Relative brain size increased slightly among successively younger species of Australopithecus, expanded significantly with the appearance of Homo, but within early Homo remained at about half the size of Homo sapiens for almost a million years. Many apparent trends in human evolution may actually be due to the accumulation of relatively rapid shifts in successive species.

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.

Femoral lengths and stature in Plio-Pleistocene hominids.

This study reports the femoral lengths of 31 Plio-Pleistocene hominids dated between 3.1 and 0.7 million years ago, and uses those lengths to estimate stature by way of the femur-stature ratio reported by Feldesman et al. (Am. J. Phys. Anthropol. 78:219-220, 1989). By this method the average female Australopithecus afarensis is 105 cm and the average male is 151 cm. The respective values are 115 and 138 cm for A. africanus. As defined by Howell (In VJ Maglio and HBS Cooke (eds): The Evolution of African Mammals. Cambridge: Harvard University Press, 1978) and Johanson et al. (Kirtlandia 28:1-14, 1978), Homo habilis is a sexually dimorphic species, with females standing 118 cm and males 157 cm. Such apparently strong dimorphism may be due to the possibility that there are actually two species of nonrobust hominids between 2 and 1.7 m.y.a. The estimate for the female Australopithecus boisei is 124 cm and for the male, 137 cm, but these estimates are especially difficult to be certain of because there are no femora that can be positively identified as male A. boisei. Australopithecus robustus is estimated to be 110 cm (female) and 132 cm (male). African Homo erectus stood 160 cm (female) and 180 cm (male). From these estimates several generalizations are apparent. First, there is apparently strong sexual dimorphism in stature in A. afarensis and H. habilis, but less in the other species. Second, the "robust" australopithecines were relatively small statured. Third, it is apparently not true that humans have been getting progressively taller throughout their evolutionary history. Some individuals were as tall as modern humans 3 m.y.a., by 2 m.y.a. one individual stood about 173 cm, and by 1.7 m.y.a. a stature of 180+ cm was not uncommon.

Relative cheek-tooth size in Australopithecus.

Until the discovery of Australopithecus afarensis, cheek-tooth megadontia was unequivocally one of the defining characteristics of the australopithecine grade in human evolution along with bipedalism and small brains. This species, however, has an average postcanine area of 757 mm2, which is more like Homo habilis (759 mm2) than A. africanus (856 mm2). But what is its relative cheek-tooth size in comparison to body size? One approach to this question is to compare postcanine tooth area to estimated body weight. By this method all Australopithecus species are megadont: they have cheek teeth 1.7 to 2.3 times larger than modern hominoids of similar body size. The series from A. afarensis to A. africanus to A. robustus to A. boisei shows strong positive allometry indicating increasing megadontia through time. The series from H. habilis to H. erectus to H. sapiens shows strong negative allometry which implies a sharp reduction in the relative size of the posterior teeth. Postcanine megadontia in Australopithecus species can also be demonstrated by comparing tooth size and body size in associated skeletons: A. afarensis (represented by A.L. 288-1) has a cheek-tooth size 2.8 times larger than expected from modern hominoids; A. africanus (Sts 7) and A. robustus (TM 1517) are over twice the expected size. The evolutionary transition from the megadont condition of Australopithecus to the trend of decreasing megadontia seen in the Homo lineage may have occurred between 3.0 and 2.5 m.y. from A. afarensis to H.habilis but other evidence indicates that it is more likely to have occurred between 2.5 to 2.0 m.y. from an A. africanus-like form to H. habilis.

The capitate of Australopithecus afarensis and A. africanus.

The capitates of Australopithecus afarensis (AL 288-lw and AL 333-40) and A. africanus (TM 1526) have the identical combination of modern pongid, modern hominid, and unique characteristics. These traits include the combination of a length that is proximodistally shortened (Homo sapiens-like), a facet for the second metacarpal that is distolaterally facing (unique), the reduced styloid process on the third metacarpal (pongidlike), a dorsally placed trapezoid facet (pongidlike), mediolaterally constricted metacarpal III facet (pongidlike), a prominent palmar beak (pongidlike), a single elongated facet for the second metacarpal (H. sapiens-like), a waisted neck (pongidlike), and a reduced amount of "cupping" in the third metacarpal facet (H. sapiens-like). In overall shape the bones are more like H. sapiens than other extant hominids, although they are uniquely different. The two A. afarensis capitates provide no evidence that there are two postcranial morphotypes at Hadar. Available evidence shows that A. afarensis and A. africanus are strikingly similar postcranially. The morphological differences between the capitate of Australopithecus and H. sapiens may relate to the retention of climbing ability and an absence of certain grip capabilities in these early hominids.

Miocene hominoid palatofacial morphology.

The palatofacial morphology of Proconsul africanus, P. nyanzae, P. major and Sivapithecus meteai is compared to extant catarrhines. The early Miocene hominoids (Proconsul) are unlike modern great apes, but retain a primitive catarrhine pattern more similar to some extant cercopthecoids. By middle Miocene times the typical hominoid palatofacial morphology can be recognized in at least one species (S. meteai) and this corresponds to the evolution of the postcranium in which the hominoid pattern is also only recognizable by the middle Miocene.

Bioenergetics and the origin of hominid bipedalism.

Compared to most quadrupedal mammals, humans are energetically inefficient when running at high speeds. This fact can be taken to mean that human dipedalism evolved for reasons other than to reduce relative energy cost durding locomotion. Recalculation of the energy expending expended during human walking at normal speeds shows that 1) human bipedalism is at least as efficient as typical mammalian quadrupedalism and 2) human gait is much more efficient than bipedal or quadrupedal locomotion in the chimpanzee. We conclude that bipedalism bestowed an energetic advantage on the Miocene hominoid ancestors of the Hominidae.

Morphological affinities of Pan paniscus.

Although the pygmy chimpanzee (Pan paniscus) is more similar to man than is the common chimpanzee (Pan troglodytes) in some traits, the resemblance is due primarily to the smaller size and concomitant allometric generalization of the former. The two species of chimpanzees are equally good models for the common ancestry of African apes and man.

The femur in early human evolution.

Uni- and multivariate analyses of 5 fossil and 215 extant hominoid femora show that two morphological patterns of hominid femora existed about two million years ago. Femora classified as Homo sp. indet. (KNMER 1472 and 1481) are more like Homo sapiens although not identical. Those classified as Australopithecus robustus (SK 82 and 97) and A. boisei (KNM-ER 1503) are similar to one another but uniquely different from any living hominoid. The strong mophological constrasts imply biomechanical and possible locomotor differences, although these are as yet unknown.

Relative femoral head size in early hominids.

Relative growth of the human femur head is studied by a logarithmic principal components method. Growth rates differ according to the population sampled and the other body dimensions being compared, and especially according to sex. The results do not support biomechanical assumptions of strongly positive allometry of the femur head, which have been used to argue that the australopithecine hip joint was not relatively small.

Fore- and hindlimb proportions in Plio-Pleistocene hominids.

Associated fore- and hindlimb parts of five individuals are known from the hominid Plio-Pleistocene fossil collections in Africa. Four of these have been classified as Australopithecus and show definite evidence that in comparison with humans, forelimbs were relatively large and hindlimbs were relatively small. The fourth individual, placed in the genus Homo, has human proportions. These findings do not necessarily imply locomotor differences: the forelimbs may have been relatively long in Australopithecus simply because they were as yet not completely reduced from their generalized hominoid ancestral state.

Analysis of the hominoid os coxae by Cartesian coordinates.

This study is based upon 48 3-dimensional coordinates taken on 4 fossil hominid and 127 extant hominoid coxal bones. The follis include Sts 14, SK 3155, MLD 7, and MLD 25. The comparative sample consists of 42 Homo sapiens, 27 Pan troglodytes, 29 Gorilla gorilla and 29 Pongo pygmaeus. The coordinates improve the metrical representation of the bone beyond what can be done with linear measurements because the shape complexity of the os coxae is so great. The coordinates are rotated and translated so that all bones are in a standard position. The coordinates are then standardized for each specimen by dividing all coordinates by the pooled standard deviation of X, Y, and Z coordinates. These data are treated to standard statistical analyses including analysis of variance, Penrose size and shape statistics, principal coordinates and components, and canonical variates analysis. The data are then further altered by using some specimen as a standard and rotating each specimen until the total squared distance between its coordinates and those of the standard are minimized. The same statistics are applied to these "best fit" data. The results show a high degree of agreement between the methods. The hominid os coxae are dundamentally different from the other hominoids and the fossil hominids share the basic hominid configuration but with some unique differences.

The association between Harris lines and enamel hypoplasia in prehistoric California Indians.

Hypoplastic defects of tooth enamel and Harris lines in the long bones have been heralded as potentially useful indicators of health conditions in prehistoric populations. Both result from temporary cessation of growth processes due to similar types of disease, malnutrition, or other metabolic insult. An association test for the first six years of life was conducted on a large series of prehistoric California Indians, using femora and canines from young adults. No significant association was found. This is ascribable to differences in etiology and stability.