In the 1970s, mid-Pliocene hominin fossils were found at the sites of Hadar in Ethiopia and Laetoli in Tanzania. These samples constituted the first substantial evidence for hominins older than 3.0 Ma and were notable for some remarkable discoveries, such as the "Lucy" partial skeleton and the abundant remains from the A.L. 333 locality at Hadar and the hominin footprint trail at Laetoli. The Hadar and Laetoli fossils were ultimately assigned to the novel hominin species Australopithecus afarensis, which at the time was the most plesiomorphic and geologically ancient hominin taxon. The discovery and naming of A. afarensis coincided with important developments in theory and methodology in paleoanthropology; in addition, important fossil and genetic discoveries were changing expectations about hominin divergence dates from extant African apes. This coincidence of events ensured that A. afarensis figured prominently in the last 30 years of paleoanthropological research. Here, the 30+ year history of discovery, analysis, and interpretation of A. afarensis and its contexts are summarized and synthesized. Research on A. afarensis continues and subject areas in which further investigation is needed to resolve ongoing debates regarding the paleobiology of this species are highlighted.

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"Lucy" redux: a review of research on Australopithecus afarensis.

Descriptions of the upper limb skeleton of Homo floresiensis

Development of the femoral bicondylar angle in hominid bipedalism

Did the first hominids have a short developmental period similar to that of the great apes or a longer period closer to that of modern humans? Evidence from studies on dental and facial growth favors the first point of view. Additional evidence presented in this report is provided by a morphogenetic analysis of the lower limb. Some morphological modifications undergone by the human femur during infantile and adolescent growth are shown to be excellent markers of different developmental stages. The angular remodelling of the femoral diaphysis, which results in femoral bicondylar angle, is a marker of infancy, while the reshaping of the distal femoral epiphysis is a marker of adolescence. This reshaping of the bony epiphysis consists of the strong projection of the external lip of the femoral trochlea, the increase of the radius of curvature of the external condyle, and the anteroposterior lengthening of the whole epiphysis. The growth spurt in linear dimensions of the femur, characteristic of human adolescence, is shown to be associated with qualitative changes of the distal femoral epiphysis engendered by the late closure of the distal epiphysis.



The femur of the first hominids (Australopithecus afarensis) shows only features of infantile growth, whereas characters of both precocious and later growth are typical of later hominids (Homo). The absence of the derived epiphyseal features in Australopithecus would be linked to their early epiphyseal closure and short adolescent growth period; their presence in Homo would have been promoted by their delayed epiphyseal closure and prolonged adolescent growth period. The transition from Australopithecus to Homo appears to have involved a heterochronic process of time hypermorphosis (Gould, [1977], Ontogeny and Phylogeny [Cambridge: Harvard University Press]) in which the size of the femur increases, the epiphysis is modified, and the period of peripubertal growth is prolonged. The shape of the distal epiphyses of KNM-WT 15000, an immature Homo erectus (Brown et al. [1985] Nature 316:788–792), lies clearly within the range of modern human adolescents. In contradiction to Smith's ([1993] in A. Walker and R. Leakey [eds.]: The Nariokotome Homo erectus Skeleton [Cambridge: Harvard University Press], pp. 195–220) hypothetical reconstruction of life span of Homo erectus, we infer that a growth spurt had begun with Homo erectus but was probably less pronounced and of shorter duration than in modern humans. Our findings on the femur are consistent with studies of the growth on the hominid pelvis (Berge [1996] in LF Marcus, M Corti, A Loy, G Naylor, and DE Slice [eds.]: Advances in Morphometrics [Chicago: Plenum Publishing Corp.], pp. 441–448). It is suggested that the lengthening of the adolescent growth period, from Australopithecus to Homo, would have been also associated with the shape changes of the pelvis and with the lengthening of the lower limbs. Am J Phys Anthropol 107:163–178, 1998. © 1998 Wiley-Liss, Inc.

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Short Adolescence in Early Hominids: Infantile and Adolescent Growth of the Human Femur

Three different human femoro-tibial characters are selected as functionally relevant and derived hominid characters: femoral bicondylar angle, shape of the femoral distal epiphysis, and the tibial insertion of the lateral meniscus. The timing and mode of formation of these characters are investigated during human ontogeny and are shown to differ considerably. The available hominid fossils (Australopithecus afarensis and early Homo) are interpreted in the light of this ontogenetic analysis with the conclusion that, during hominid evolution, different modes of selection of these features must have occurred. In modern humans, the femoral bicondylar angle proves to be an epigenetic functional feature, which develops during early childhood growth. It is present in all australopithecines and we suggest that it developed following a change in their locomotor behavior and not upon a genomic change: the early practice of bipedal walking, with adducted knee joints, in the locomotor repertoire of infant australopithecines, was sufficient to promote this angle. Later in hominid evolution, the knee joint evolved from having a single insertion of the lateral meniscus on the tibia to a double one. While Australopithecus afarensis exhibits a single insertion, early Homo clearly exhibits a double insertion of the lateral meniscus on the tibia. The double insertion restricts the mobility of the meniscus on the tibial plateau, indicating a habitual practice of full extension movements of the knee joint. Among modern humans, the posterior insertion of the lateral meniscus appears early in fetal life. Consequently in early Homo, this new selected feature developed directly as a result of a genomic change. The derived shape of human distal femoral epiphysis includes a prominence of the lateral lip of the femoral trochlea, an elliptical profile of the lateral condyle, and an anteroposterior lengthening of the epiphysis. Analysis of human fetal and neonatal distal epiphyses shows that the prominence of the lateral lip of the trochlea arises before any use, and thus appears to be genetically determined. However, the postnatal development of this joint shows that this feature is also modified epigenetically by use. It is argued that the hominid femoro- patellar joint would have been reshaped following the process of genetic assimilation (Waddington (1942) Nature 3811:563-565). The prominence of the lateral lip of the femoral trochlea was probably selected following a

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Ontogeny and phylogeny of femoro‐tibial characters in humans and hominid fossils: Functional influence and genetic determinism

Numerous studies of the bicondylar angle of the adult femur have been carried out in human anatomy, paleoanthropology and primatology. The aim of this paper is to study the evolution of this angle in relation to age and acquisition of walking in young children. Seventy-seven radiographs of children, ranging from 5 months to 17 years postnatally, and of four dead newborn were analysed. The measurements concern the bicondylar angle (A.O.F.), the collo-diaphyseal angle (A.C.D.), the length of the femoral neck (L.N.) and of the femur (L.F.) and the interacetabular distance (D.I.A.). Some children were x-rayed at different ages, which permits a longitudinal as well cross-sectional study. The results show that there is no sexual dimorphism and that the increase in the angle is closely related to the age of the child. The bicondylar angle starts at 0° at birth and then increases progressively with growth to reach adult values of at least 6°-8° between 4 and 8 years postnatally. In adults, the mean values are between 8° and 11° and the maximum range is between 6° and 14°. The obliquity angle corresponds to an angular remodeling of the femoral diaphysis, which is independant of the growth and shape of the distal femoral epiphysis. The tibio-femoral angle measures the evolution of a physiologic phenomenon, from the load “in varus” to the load “in valgus” of the lower limb. It is linked with the bicondylar angle but is different from it.

J. P. Damsin

Papers

Evolution of the angle of obliquity of the femoral diaphysis during growth--correlations.