Understanding changes in ontogenetic development is central to the study of human evolution. With the exception of Neanderthals, the growth patterns of fossil hominins have not been studied comprehensively because the fossil record currently lacks specimens that document both cranial and postcranial development at young ontogenetic stages. Here we describe a well-preserved 3.3-million-year-old juvenile partial skeleton of Australopithecus afarensis discovered in the Dikika research area of Ethiopia. The skull of the approximately three-year-old presumed female shows that most features diagnostic of the species are evident even at this early stage of development. The find includes many previously unknown skeletal elements from the Pliocene hominin record, including a hyoid bone that has a typical African ape morphology. The foot and other evidence from the lower limb provide clear evidence for bipedal locomotion, but the gorilla-like scapula and long and curved manual phalanges raise new questions about the importance of arboreal behaviour in the A. afarensis locomotor repertoire.

The upper part of the Pliocene Hadar Formation, central Afar, Ethiopia, has yielded a 40% complete fossil hominid skeleton (A.L. 288-1, "Lucy"). This specimen is described in detail and selected measurements and illustrations are provided.

The transition to full-time terrestrial bipedality is a hallmark of human evolution. A key correlate of human bipedalism is the development of longitudinal and transverse arches of the foot that provide a rigid propulsive lever and critical shock absorption during striding bipedal gait. Evidence for arches in the earliest well-known Australopithecus species, A. afarensis, has long been debated. A complete fourth metatarsal of A. afarensis was recently discovered at Hadar, Ethiopia. It exhibits torsion of the head relative to the base, a direct correlate of a transverse arch in humans. The orientation of the proximal and distal ends of the bone reflects a longitudinal arch. Further, the deep, flat base and tarsal facets imply that its midfoot had no ape-like midtarsal break. These features show that the A. afarensis foot was functionally like that of modern humans and support the hypothesis that this species was a committed terrestrial biped.

Carbon isotope studies of early hominins from southern Africa showed that their diets differed markedly from the diets of extant apes. Only recently, however, has a major influx of isotopic data from eastern Africa allowed for broad taxonomic, temporal, and regional comparisons among hominins. Before 4 Ma, hominins had diets that were dominated by C 3 resources and were, in that sense, similar to extant chimpanzees. By about 3.5 Ma, multiple hominin taxa began incorporating 13 C-enriched [C 4 or crassulacean acid metabolism (CAM)] foods in their diets and had highly variable carbon isotope compositions which are atypical for African mammals. By about 2.5 Ma, Paranthropus in eastern Africa diverged toward C 4 /CAM specialization and occupied an isotopic niche unknown in catarrhine primates, except in the fossil relations of grass-eating geladas (Theropithecus gelada). At the same time, other taxa (e.g., Australopithecus africanus) continued to have highly mixed and varied C 3 /C 4 diets. Overall, there is a trend toward greater consumption of 13 C-enriched foods in early hominins over time, although this trend varies by region. Hominin carbon isotope ratios also increase with postcanine tooth area and mandibular cross-sectional area, which could indicate that these foods played a role in the evolution of australopith masticatory robusticity. The 13 C-enriched resources that hominins ate remain unknown and must await additional integration of existing paleodietary proxy data and new research on the distribution, abundance, nutrition, and mechanical properties of C 4 (and CAM) plants.human evolution | hominid | paleocology D iet has long been implicated as a driving force in human evolution. Changes in the type of food consumed and the manner in which it was procured have been linked with encephalization and the emergence of bipedalism, as well as ecological, social, and cultural evolution within the hominin lineage (1-3). Given this interest, a wide variety of methods (4-8) have been used to investigate early hominin diet over the years.Stable carbon isotope analysis is a relative newcomer to early hominin dietary studies (9). Initial carbon isotope work suggested that southern African hominins and living African apes had markedly different diets (9, 10). Our ability to interpret those data in broader evolutionary terms was limited, however, because no eastern African hominins had been sampled, and because datasets from other sources, such as dental microwear (11-14), were not available. Now, however, carbon isotope data have become available for most early African hominin species, and for the first time, we can make broad taxonomic, regional, and temporal comparisons of hominin carbon isotope compositions. We can also begin to integrate the carbon isotope data with complementary information on hominin diets from other sources. This paper has a tripartite structure. The first section begins in the past and takes a brief look at why carbon isotope analysis is useful and what the first studies taught us about homin...

Taxonomic and phylogenetic analyses of great apes and humans have identified two potential areas of conflict between molecular and morphological data: phylogenetic relationships among living species and differentiation of great ape subspecies. Here we address these problems by using morphometric data. Three-dimensional landmark data from the hominoid temporal bone effectively quantify the shape of a complex element of the skull. Phylogenetic analysis using distance-based methods corroborates the molecular consensus on African ape and human phylogeny, strongly supporting a Pan-Homo clade. Phenetic differentiation of great ape subspecies is pronounced, as suggested previously by mitochondrial DNA and some morphological studies. These results show that the hominoid temporal bone contains a strong phylogenetic signal and reveal the potential for geometric morphometric analysis to shed light on phylogenetic relationships.

Our understanding of the origin of the genus Homo has been hampered by a limited fossil record in eastern Africa between 2.0 and 3.0 million years ago (Ma). Here we report the discovery of a partial hominin mandible with teeth from the Ledi-Geraru research area, Afar Regional State, Ethiopia, that establishes the presence of Homo at 2.80 to 2.75 Ma. This specimen combines primitive traits seen in early Australopithecus with derived morphology observed in later Homo, confirming that dentognathic departures from the australopith pattern occurred early in the Homo lineage. The Ledi-Geraru discovery has implications for hypotheses about the timing and place of origin of the genus Homo.

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 301 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 paleobiol- Just over three decades ago, the east African early hominin species Australopithecus afarensis was recognized as the oldest, most apelike human ancestor. Although specimens now attributed to the species had resided in fossil collections since the 1930s, the bulk of the sample was amassed during field work in the 1970s at two sites, Hadar, Ethiopia, and Laetoli, Tanzania. Today, the species' hypodigm numbers more than 400 specimens collected from a half-dozen sites, most of which are still actively being worked (Table 1). Refinements in radioisotopic dating have established the species' first and last known appearances at 3.7 and 3.0 Ma, respectively. At the time of their discovery, these specimens constituted the first informative sample of hominin fossils older than 3.0 Ma.Studies on subjects ranging from the rise of striding bipedal locomotion to the origin of the uniquely human pattern of growth and development to the evolution of hominin dietary adaptations have drawn heavily on data from the remains of A. afarensis. Taxonomic and phylogenetic research, which experienced a major renaissance in paleoanthropology beginning around the time when A. afarensis was discovered, has benefited from the extensive baseline data on fossil hominin skeletal and dental variation residing in the Hadar site-sample. Some of the research topics that focus on A. afarensis-the extent to which terrestrial bipedality was the committed form of locomotion, the degree of sexual dimorphism in body size and implications for social behavior, and the ''shape'' of the phylogenetic tree prior to the emergence of the Homo and robust australopith lineages, to name just three prominent examples-are still actively debated today, which merely drives home the message that finding solutions to scien...

The Hadar Formation in Ethiopia is a prolific source of Pliocene Hominidae attributed to the species Australopithecus afarensis. Since 1990, three seasons of field work have contributed 53 new specimens to the hominid inventory from Hadar, including the first fairly complete adult skull. Ranging from 3.0 to 3.4 million years in age (Fig. 1), the new specimens bear on key debates in hominid palaeontology, including the taxonomic implications of sample variation and the reconstruction of locomotor behaviour. They confirm the taxonomic unity of A. afarensis and constitute the largest body of evidence for about 0.9 million years of stasis in the earliest known hominid species.