Was “Lucy” more human than her “child”? Observations on early hominid postcranial skeletons

Fully adult partial skeletons attributed to Australopithecus afarensis (AL 288-1, “Lucy”) and to Homo habilis (OH 62, “Lucy's child”), respectively, both include remains from upper and lower limbs. Relationships between various limb bone dimensions of these skeletons are compared to those of modern African apes and humans. Surprisingly, it emerges that OH 62 displays closer similarities to African apes than does AL 288-1. Yet A. afarensis, whose skeleton is dated more than 1 million years earlier, is commonly supposed to be the ancestor of Homo habilis. If OH 62, classified as Homo habilis by its discoverers, does indeed represent a stage intermediate between A. afarensis and later Homo, a revised interpretation of the course of human evolution would be necessary.     

Estimation of the ancestral effective population sizes of African great apes under different selection regimes

Reliable estimates of ancestral effective population sizes are necessary to unveil the population-level phenomena that shaped the phylogeny and molecular evolution of the African great apes. Although several methods have previously been applied to infer ancestral effective population sizes, an analysis of the influence of the selective regime on the estimates of ancestral demography has not been thoroughly conducted. In this study, three independent data sets under different selective regimes were used were composed to tackle this issue. The results showed that selection had a significant impact on the estimates of ancestral effective population sizes of the African great apes. The inference of the ancestral demography of African great apes was affected by the selection regime. The effects, however, were not homogeneous along the ancestral populations of great apes. The effective population size of the ancestor of humans and chimpanzees was more impacted by the selection regime when compared to the same parameter in the ancestor of humans, chimpanzees and gorillas. Because the selection regime influenced the estimates of ancestral effective population size, it is reasonable to assume that a portion of the discrepancy found in previous studies that inferred the ancestral effective population size may be attributable to the differential action of selection on the genes sampled.     

Evolutionary Development in Australopithecus africanus

Evolutionary developmental biology is quickly transforming our understanding of how lineages evolve through the modification of ontogenetic processes. Yet, while great strides have been made in the study of neontological forms, it is much more difficult to apply the principles of evo-devo to the miserly fossil record. Because fossils are static entities, we as researchers can only infer evolution and development by drawing connections between them. The choices of how we join specimens together??juveniles to adults to study ontogeny, taxon to taxon to study evolution??can dramatically affect our results. Here, I examine paedomorphism in the fossil hominin species Australopithecus africanus. Using extant African apes as proxies for ancestral hominin morphology, I demonstrate that Sts 71 is most similar to a sub-adult African ape, suggesting that A. africanus is paedomorphic relative to the presumed ancestral form. I then plot ontogenetic size and shape in extant great apes, humans, and A. africanus in order to assess patterns of ontogenetic allometry. Results indicate that ontogenetic allometry in A. africanus, subsequent to M1 occlusion is similar to that in modern humans and bonobos; gorillas, chimpanzees, and orangutans share a different pattern of size-shape relationship. Combined with results from the analysis of paedomorphism plus knowledge about the developmental chronologies of this group, these findings suggest that paedomorphism in A. africanus arises relatively early in ontogeny.     

New postcranial fossils of Australopithecus afarensis from Hadar, Ethiopia (1990-2007)

Renewed fieldwork at Hadar, Ethiopia, from 1990 to 2007, by a team based at the Institute of Human Origins, Arizona State University, resulted in the recovery of 49 new postcranial fossils attributed to Australopithecus afarensis. These fossils include elements from both the upper and lower limbs as well as the axial skeleton, and increase the sample size of previously known elements for A. afarensis. The expanded Hadar sample provides evidence of multiple new individuals that are intermediate in size between the smallest and largest individuals previously documented, and so support the hypothesis that a single dimorphic species is represented. Consideration of the functional anatomy of the new fossils supports the hypothesis that no functional or behavioral differences need to be invoked to explain the morphological variation between large and small A. afarensis individuals. Several specimens provide important new data about this species, including new vertebrae supporting the hypothesis that A. afarensis may have had a more human-like thoracic form than previously appreciated, with an invaginated thoracic vertebral column. A distal pollical phalanx confirms the presence of a human-like flexor pollicis longus muscle in A. afarensis. The new fossils include the first complete fourth metatarsal known for A. afarensis. This specimen exhibits the dorsoplantarly expanded base, axial torsion and domed head typical of humans, revealing the presence of human-like permanent longitudinal and transverse arches and extension of the metatarsophalangeal joints as in human-like heel-off during gait. The new Hadar postcranial fossils provide a more complete picture of postcranial functional anatomy, and individual and temporal variation within this sample. They provide the basis for further in-depth analyses of the behavioral and evolutionary significance of A. afarensis anatomy, and greater insight into the biology and evolution of these early hominins.     

The evolution of hominoid cranial diversity: A quantitative genetic approach

Hominoid cranial evolution is characterized by substantial phenotypic diversity, yet the cause of this variability has rarely been explored. Quantitative genetic techniques for investigating evolutionary processes underlying morphological divergence are dependent on the availability of good ancestral models, a problem in hominoids where the fossil record is fragmentary and poorly understood. Here, we use a maximum likelihood approach based on a Brownian motion model of evolutionary change to estimate nested hypothetical ancestral forms from 15 extant hominoid taxa. These ancestors were then used to calculate rates of evolution along each branch of a phylogenetic tree using Lande's generalized genetic distance. Our results show that hominoid cranial evolution is characterized by strong stabilizing selection. Only two instances of directional selection were detected; the divergence of Homo from its last common ancestor with Pan, and the divergence of the lesser apes from their last common ancestor with the great apes. In these two cases, selection gradients reconstructed to identify the specific traits undergoing selection indicated that selection on basicranial flexion, cranial vault expansion, and facial retraction characterizes the divergence of Homo, whereas the divergence of the lesser apes was defined by selection on neurocranial size reduction.     

Disproportionate Cochlear Length in Genus Homo Shows a High Phylogenetic Signal during Apes’ Hearing Evolution

Changes in lifestyles and body weight affected mammal life-history evolution but little is known about how they shaped species’ sensory systems. Since auditory sensitivity impacts communication tasks and environmental acoustic awareness, it may have represented a deciding factor during mammal evolution, including apes. Here, we statistically measure the influence of phylogeny and allometry on the variation of five cochlear morphological features associated with hearing capacities across 22 living and 5 fossil catarrhine species. We find high phylogenetic signals for absolute and relative cochlear length only. Comparisons between fossil cochleae and reconstructed ape ancestral morphotypes show that Australopithecus absolute and relative cochlear lengths are explicable by phylogeny and concordant with the hypothetized ((Pan,Homo),Gorilla) and (Pan,Homo) most recent common ancestors. Conversely, deviations of the Paranthropus oval window area from these most recent common ancestors are not explicable by phylogeny and body weight alone, but suggest instead rapid evolutionary changes (directional selection) of its hearing organ. Premodern (Homo erectus) and modern human cochleae set apart from living non-human catarrhines and australopiths. They show cochlear relative lengths and oval window areas larger than expected for their body mass, two features corresponding to increased low-frequency sensitivity more recent than 2 million years ago. The uniqueness of the “hypertrophied” cochlea in the genus Homo (as opposed to the australopiths) and the significantly high phylogenetic signal of this organ among apes indicate its usefulness to identify homologies and monophyletic groups in the hominid fossil record.     

Social cognition,Stag Hunts,and the evolution of language

According to the socio-cognitive revolution (SCR) hypothesis, humans but not other great apes acquire language because only we possess the socio-cognitive abilities required for Gricean communication, which is a pre-requisite of language development. On this view, language emerged only following a socio-cognitive revolution in the hominin lineage that took place after the split of the Pan-Homo clade. In this paper, I argue that the SCR hypothesis is wrong. The driving forces in language evolution were not sweeping biologically driven changes to hominin social cognition. Our LCA with non-human great apes was likely already a Gricean communicator, and what came with evolution was not a raft of new socio-cognitive abilities, but subtle tweaks to existing ones. It was these tweaks, operating in conjunction with more dramatic ecological changes and a significant increase in general processing power, that set our ancestors on the road to language.     

Postnatal temporal bone ontogeny in Pan,Gorilla, and Homo,and the implications for temporal bone ontogeny in Australopithecus afarensis

Assessments of temporal bone morphology have played an important role in taxonomic and phylogenetic evaluations of fossil taxa, and recent three‐dimensional analyses of this region have supported the utility of the temporal bone for testing taxonomic and phylogenetic hypotheses. But while clinical analyses have examined aspects of temporal bone ontogeny in humans, the ontogeny of the temporal bone in non‐human taxa is less well documented. This study examines ontogenetic allometry of the temporal bone in order to address several research questions related to the pattern and trajectory of temporal bone shape change during ontogeny in the African apes and humans. We further apply these data to a preliminary analysis of temporal bone ontogeny in Australopithecus afarensis. Three‐dimensional landmarks were digitized on an ontogenetic series of specimens of Homo sapiens, Pan troglodytes, Pan paniscus, and Gorilla gorilla. Data were analyzed using geometric morphometric methods, and shape changes throughout ontogeny in relation to size were compared. Results of these analyses indicate that, despite broadly similar patterns, African apes and humans show marked differences in development of the mandibular fossa and tympanic portions of the temporal bone. These findings indicate divergent, rather than parallel, postnatal ontogenetic allometric trajectories for temporal bone shape in these taxa. The pattern of temporal bone shape change with size exhibited by A. afarensis showed some affinities to that of humans, but was most similar to extant African apes, particularly Gorilla. Am J Phys Anthropol 151:630–642, 2013. © 2013 Wiley Periodicals, Inc.     

Evolution of femur and tibia in higher primates: Adaptive morphological patterns and phylogenetic diversity

Seventy six metrical traits measured on the femur and tibia of three higher primate groups —Ceboidea, Cercopithecoidea, Hominoidea have been processed by various univariate and multivariate statistical methods to survey the process of evolution of the morphology of the femur and tibia in higher primates. Intragroup and intergroup variability, similarity and differences as well as various aspects of scaling and sexual dimorphism have been analyzed to study adaptive trends and phylogenetic diversity in higher primates, in individual superfamilies and to explore the adaptive morphological pattern of early hominids and basic differences between hominids and pongids. Two basic morphotypes of the femur and tibia in higher primates have been determined. They are (1) advanced hominoid morphotype (hominids and pongids) and (2) ancestral higher primate morphotype (platyrrhine and cattarrhine monkeys, early hominoids, and hylobatids). Cebid lower limb bones are adapted to arboreal quadrupedalism with antipronograde features while femur and tibia of cercopithecid monkeys are basically adapted to the semi-arboreal locomotion. Early hominoids (Proconsul) and hylobatids are morphologically different from pongids; some features are close toAteles or other monkey species. Pongids and hominids are taken as one major morphological group with different scaling and some functional and morphological similarities. Numerous analogous features were described on the lower limb skeleton ofPan andPongo showing analogous ecological parameters in their evolution. Major morphological and biomechanical trends are analyzed. It is argued that early advanced hominoid morphology is ancestral both to the pongids and to early hominids. The progressive morphological trend in early hominids has been found fromA. afarensis with ancestral hominid morphology, toH. habilis with an elongated femur and structural features similar to advanced hominids. A detailed phylogenetic analysis of higher primate femur and tibia is also presented.     

Critique of ‘Australopithecus afarensis’ as a single species based on dental metrics and morphology

Leonard andHegmon (1987) compare a series of dental metrics of ‘Australopithecus afarensis Johanson, White, andCoppens, 1978’ with criteria for modern apes, to test the hypothesis that ‘A. afarensis’ represents a single species. They also compare the morphology of the lower third premolar. The dental breadth of ‘A. afarensis’ shows a wide range of variation, particularly in the lower third premolar morphology which displays greater variation than in modern apes—yet the study concludes that the single species hypothesis cannot be rejected. The study is flawed by applying criteria for pongids inappropriate for a hominid. When ‘A. afarensis’ is compared with criteria for hominids, the range of variation in dental size, breadth, and third premolar morphology is greater than that in any hominid species. The single species hypothesis is, therefore, once again rejected. Moreover, the name ‘A. afarensis’ is preoccupied byPraeanthropus africanus (Weinert) and must be dropped.     

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.     

Dating of the human-ape splitting by a molecular clock of mitochondrial DNA

Summary A new statistical method for estimating divergence dates of species from DNA sequence data by a molecular clock approach is developed. This method takes into account effectively the information contained in a set of DNA sequence data. The molecular clock of mitochondrial DNA (mtDNA) was calibrated by setting the date of divergence between primates and ungulates at the Cretaceous-Tertiary boundary (65 million years ago), when the extinction of dinosaurs occurred. A generalized leastsquares method was applied in fitting a model to mtDNA sequence data, and the clock gave dates of 92.3±11.7, 13.3±1.5, 10.9±1.2, 3.7±0.6, and 2.7±0.6 million years ago (where the second of each pair of numbers is the standard deviation) for the separation of mouse, gibbon, orangutan, gorilla, and chimpanzee, respectively, from the line leading to humans. Although there is some uncertainty in the clock, this dating may pose a problem for the widely believed hypothesis that the bipedal creatureAustralopithecus afarensis, which lived some 3.7 million years ago at Laetoli in Tanzania and at Hadar in Ethiopia, was ancestral to man and evolved after the human-ape splitting. Another likelier possibility is that mtDNA was transferred through hybridization between a proto-human and a protochimpanzee after the former had developed bipedalism.     

Metatarsophalangeal joint function and positional behavior in Australopithecus afarensis

Recent discussions of the pedal morphology of Australopithecus afarensis have led to conflicting interpretations of australopithecine locomotor behavior. We report the results of a study using computer aided design (CAD) software that provides a quantitative assessment of the functional morphology of australopithecine metatarsophalangeal joints. The sample includes A. afarensis, Homo sapiens, Pan troglodytes, Gorilla gorilla, and Pongo pygmaeus. Angular measurements of the articular surfaces relative to the long axes of the metatarsals and phalanges were taken to determine whether the articular surfaces are plantarly or dorsally oriented. Humans have the most dorsally oriented articular surfaces of the proximal pedal phalanges. This trait appears to be functionally associated with dorsiflexion during bipedal stride. Pongo has the most plantarly oriented articular surfaces of the proximal pedal phalanges, probably reflecting an emphasis on plantarflexion in arboreal positional behaviors, while the African hominoids are intermediate between Pongo and Homo for this characteristic. A. afarensis falls midway between the African apes and humans. Results from an analysis of metatarsal heads are inconclusive with regard to the functional morphology of A. afarensis. Overall, the results are consistent with other evidence indicating that A. afarensis was a capable climber. © 1994 Wiley-Liss, Inc.     

Cladistic relationships of extant and fossil hominoids

There is general agreement that the hominoid primates form a monophyletic group, that the extant great apes and humans form a second clade within that group with the gibbons as the sister group, and that the African apes and humans form a third clade. Although it has recently been proposed that humans and orang utans are sister taxa and also that the great apes form a clade to the exclusion of humans, our analysis, particularly of the molecular evidence, supports the existence of an African ape and human clade. The major problem in hominoid phylogeny at present is the relationships of the species within this clade: morphological data generally support the existence of an African ape clade which is the sister group to humans; some molecular data also support this conclusion, but most molecular evidence indicates the existence of a chimpanzee/human clade. We have cladistically re-analysed the DNA and protein sequence data for which apomorphic character states can be assessed. It is clear that there is a high degree of homoplasy whichever branching pattern is produced, with some characters supporting the existence of a chimpanzee/human clade and others supporting an African ape clade. When the cladistic analyses of morphological and molecular data are combined we believe that the most parsimonious interpretation of the data is that the African apes form a clade which is the sister taxon of the human (i.e., Australopithecus, Homo and Paranthropus) clade.This paper is not intended as a survey of all hominoid fossils but as a study of branching points in hominoid evolution and fossils are included which are relevant to this branching pattern. The analysis of fossil taxa in this study leads us to conclude that Proconsul is the sister taxon to the later Hominoidea. A number of middle Miocene forms such as Dryopithecus, Kenyapithecus, Heliopithecus and Afropithecus are shown to share derived characters with great apes and humans and provide evidence for the divergence of that clade from the gibbon lineage prior to 18 Ma. The position that Sivapithecus represents the sister group of the orang utan clade is supported here and shows that the orang utan lineage had diverged from the African ape and human lineage prior to 11·5 Ma. There is unfortunately no definitive fossil cvidence on branching sequences within the African ape and human clade, although a new specimen from Samburu, Kenya may be related to the gorilla.     

Loss of air sacs improved hominin speech abilities

In this paper, the acoustic-perceptual effects of air sacs are investigated. Using an adaptive hearing experiment, it is shown that air sacs reduce the perceptual effect of vowel-like articulations. Air sacs are a feature of the vocal tract of all great apes, except humans. Because the presence or absence of air sacs is correlated with the anatomy of the hyoid bone, a probable minimum and maximum date of the loss of air sacs can be estimated from fossil hyoid bones. Australopithecus afarensis still had air sacs about 3.3 Ma, while Homo heidelbergensis, some 600 000 years ago and Homo neandethalensis some 60 000 years ago, did no longer. The reduced distinctiveness of articulations produced with an air sac is in line with the hypothesis that air sacs were selected against because of the evolution of complex vocal communication. This relation between complex vocal communication and fossil evidence may help to get a firmer estimate of when speech first evolved.     

Speciation and paraphyly in western mediterranean hares (Lepus castroviejoi,L. europaeus,L. granatensis,andL. capensis) revealed by mitochondrial DNA phylogeny

Mitochondrial DNA (mtDNA) variation among specimens of the northwestern African hare (Lepus capensis schlumbergeri) and three European hares sampled in Spain (L. castroviejoi andL. granatensis, which are endemic to the Iberian Peninsula, andL. europaeus) was analyzed using seven restriction endonucleases. Fourteen haplotypes were found among the 34 animals examined. Restriction site maps were constructed and the phylogeny of the haplotypes was inferred. mtDNA ofL. capensis was the most divergent, which is consistent with its allopatric African distribution and with an African origin of European hares. We estimated that mtDNA in hares diverges at a rate of 1.5–1.8% per MY assuming that the European and African populations separated 5–6 MYBP. Maximum intraspecies nucleotide divergences were 1.3% inL. capensis, 2.7% inL. castroviejoi, and 2.3% inL. granatensis but 13.0% inL. europaeus. The latter species contained two main mtDNA lineages, one on the branch leading toL. castroviejoi and the other on that leading toL. granatensis. The separation of these two lineages from theL. castroviejoi orL. granatensis lineages appears to be much older than the first paleontological record ofL. europaeus in the Iberian peninsula. This suggests that the apparent polyphyly ofL. europaeus is due not to secondary introgression, but to the retention of ancestral polymorphism inL. europaeus. The results suggest thatL. europaeus either has evolved as a very large population for a long time or has been fractionated. Such a pattern of persistence of very divergent lineages has also been reported in other species of highly mobile terrestrial mammals. As far as mtDNA is concerned,L. europaeus appears to be the common phylogenetic trunk which has diversified during dispersion over the European continent and from whichL. castroviejoi andL. granatensis speciated separately in southwest Europe.     

Hominid-pongid distinctiveness in the miocene-pliocene fossil record: The lothagam mandible

The Lothagam mandibular fragment, found in 1967 west of Lake Turkana, Kenya, has been dated to 5.5 million years ago. This date is significant because it may lie within the suggested time range during which the hominid and pongid clades diverged. Because of its fragmentary condition and great age, this specimen has run the gamut of taxonomic assignations, from ramapithecine to pongid to hominid. These three nomenclatural categories serve as the basis for three hypotheses tested in this study. First, morphological and metric comparisons between Lothagam and a sample of Euroafrican ramapithecines address the hypothesis of “Lothagam as predi-vergence hominoid.” Second, comparisons with a sample of Pan test the “Lothagam as postdivergence, African protopongid” hypothesis. Finally, samples of Australopithecus afarensis and A. africanus were utilized to evaluate the hypothesis of “Lothagam as postdivergence, early hominid.” Unlike previous studies attempting to ascertain the evolutionary affinities of this enigmatic fossil, this work benefits from the large sample of A. afarensis specimens now generally available for study. Metric and morphological comparisons demonstrate Lothagam's affinity to A. afarensis in sharing derived, hominid states in such features as the mental foramen vertical position, the ascending ramus origin, the breadth of the alveolar margin, the reduction of the hypoconulid, the dimensions of the M₁ and the dimensions of the mandibular corpus. It is suggested that the dental/gnathic features enumerated in this study can be employed to distinguish ancestral hominid from pongid in future Mio/Pliocene paleontological discoveries.     

The Belohdelie frontal: new evidence of early hominid cranial morphology from the Afar of Ethiopia

Study of the Belohdelie frontal has demonstrated that this four-million-year-old specimen belongs to a very generalized hominid that may be close to the divergence point of the hominid and African ape clades. Features associated with the temporalis muscle in the Belohdelie frontal and other new hominids from Hadar (AL 333-125) and West Turkana (KNM-ER 17000) suggest that the earliest hominids shared a large anterior component of this muscle relative to the extinct and extant apes. Results of this study support the phylogenetic hypothesis put forward by many workers that A. afarensis gave rise to the “robust” Australopithecus and A. africanus clades.     

Genetic aspects in hominid evolution

Genomic comparison between apes and humans have made important contributions to our understanding of human evolution. The modern period of karyological comparisons between humans and other primates began about forty years ago and has been marked by a series of technical revolutions. In the 1960s pioneering genetic and chromosomal comparisons of human and great apes suggested, as had Darwin a century before, that our closest relative were the African apes. Early immunological analyses placed human/apes divergence at about five million year ago. Acceptance of man’s late divergence from the African apes was delayed by the scarcity of paleontological evidence coupled with a fallacious Asiatic origin hypothesis of the hominoids. Chromosome banding techniques in the seventies and high resolution methods in the eighties allowed a detailed comparison of the chromosomes between closely related primates and reinforced the hypothesis of an African origin for humans. It was clearly shown that humans were more closely related to African apes than to the orang-utan. The last decade has seen a vigorous integration of molecular and cytogenetic. This powerful combination promises to be quite fruitful because chromosomes can be compared directly at the DNA level. Fluorescentin situ hybridisation (FISH), chromosome painting, is a colourful technique for establishing chromosomal homology between species. Results obtained by FISH over the last ten years have resolved the cytogenetic problem of the homology between humans, apes, hylobates and Old World monkeys and defined the chromosomal syntenies and major translocations involved in the genome evolution of higher primates.     

Size and shape variation in Australopithecus afarensis proximal femora

The degree of size and shape variation in the A. afarensis fossil sample has been interpreted in a variety of ways. Size variation has been described as exceeding that of extant hominoids, similar to that of strongly sexually dimorphic hominoids, and best matched to modern humans. The degree of shape variation has been characterized both as great and negligible. Recent fieldwork has increased the proximal femoral sample, providing new data with which to examine variation. The proximal femur of A. afarensis is analyzed in a comparative framework in order to gauge the magnitude of size and shape variation in this element.Seven of the best-preserved A. afarensis proximal femora contribute to the analysis (A.L. 128-1, A.L. 152-2, A.L. 211-1, A.L. 288-1ap, A.L. 333-3, A.L. 333-123, A.L. 827-1). Comparative samples from Pan, Pongo, Gorilla, and Homo provide context for interpreting variation among the fossils. The coefficient of variation (CV) of linear measurements is used to estimate size variation. Bootstrap resampling of CVs from extant hominoids provides distributions for comparison to A. afarensis CVs. Ratios of linear measurements provide scale-free shape variables that are used in pairwise comparisons. The Euclidean distance between pairs of A. afarensis are compared to the Euclidean distances between extant hominoid pairs.As found in some earlier analyses, size variation in A. afarensis is accommodated best in gorillas and orangutans. The magnitude of difference in shape between A. afarensis pairs is exceeded by most taxa, indicating that shape variation is not extreme. These general findings are contradicted by a few instances of excessive size and shape variation. These are uncharacteristic results and could point to temporal bias, although other alternatives are explored. The signal from the proximal femur is that size variation in A. afarensis is like that of the strongly sexually dimorphic apes, and shape variation is well within the range of most hominoids irrespective of their degree of size dimorphism.