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.

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.

Anatomical descriptions are presented for the foot bones recovered from the Hadar Formation during the 1974-1977 field seasons inclusive. The following are anatomical descriptions of the foot bones recovered by the International Afar Research Expedition during the field seasons of 1974-1977, inclusive (Johanson et al., this volume). The foot bones from the partial skeleton from A.L. 288 are described separately (Johanson et al., this volume).Anatomical nomenclature follows general usage and Trotter and Peterson (1966). Measurements are those in general use or are described. Morphometric, biomechanical, and kinematic studies are currently in progress and results will be reported subsequently. These descriptions are organized by anatomical region: Tarsal bones are described first, followed by metatarsal bones and phalanges. The associated partial foot skeleton A.L. 333-115 is described separately. All measurements are in millimeters. DESCRIPTIONS TARSALS A.L. 333-75: fragment of right talus (Fig. 31-K) PreservationThis fragment consists of a perfectly preserved right talar head. It is severed from the body of the talus by a transverse section through the neck, preserving only a small portion of the trochlear articular surface and the most distal portion of the talar sulcus.Morphology The distal navicular articular surface is a convex oval with a maximum diameter of 23.9. A small triangular facet is present on the inferomedial corner of the navicular surface for articulation with the plantar calcaneonavicular ligament. The anterior and Preservation

The fossil hominid hand bone collection from the Pliocene Hadar Formation, Ethiopia, is described anatomically. These hand bones, all from A.L. (Afar Locality) 333 and 333w, constitute the largest sample of hominid manus remains thus far recovered from the Plio-Pleistocene of Africa.The Hadar hominid hand bones constitute the most compete collection yet recovered from any African Plio-Pleistocene site. They are assigned to Australopithecus afarensis (Johanson et al., 1978;Johanson and White, 1979) The Hadar assemblage markedly increases the Plio-Pleistocene hominid manus fossil record and includes several elements previously unrecovered: complete hamate, pisiform, and second, third, and fourth metacarpals. The collection is also unique among African remains because there are abundant clearly associated cranial and postcranial specimens of A. afarensis. Another significant feature of these bones is the presence of duplicate specimens. This provides us with the opportunity to observe individual hand variation within a single early hominid species. Those from A.L. 3331 333w represent a minimum of five individuals, including a juvenile (2-6 years of age) and an adolescent.The bulk of the Hadar hand fossils were recovered from the 3331333~ locality, but two specimens, a capitate and a proximal phalanx, are from A.L. 288. The latter elements are described elsewhere (Johanson et al., this volume). No comparative analysis or biomechanical or functional interpretations will be entered. Measurements are presented in Tables 1 and 2. See appendix 1 for definition of measurements. The descriptions are organized by region: Carpal bones are described first, followed by metacarpals and phalanges. DESCRIF'MONS CARPALSA.L. 333-40 (Fig. 1A-F) The specimen is a right capitate. Preservation. This capitate is excellently preserved with only two small erosional foci at the dorsomedial and ventromedial margins of the lunate facet.The specimen is rather bulky, having a moderately expanded head and Morphology.

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A large sample of Pliocene fossil hominid remains has been recovered from the African sites of Hadar in Ethiopia and Laetolil in Tanzania. These collections, dating approximately between 2.9 and 3.8 million years ago, constitute the earliest substantial record of the family Hominidae. This article assesses the phylogenetic relationships of the newly discovered fossil hominids and provides a taxonomy consistent with that assessment. A new taxon, Australopithecus afarensis, has been created to accommodate these Pliocene hominid fossils.

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