Donald C. Johanson

Complete Fourth Metatarsal and Arches in the Foot of Australopithecus afarensis

A long bone of the foot of an early human indicates that its foot was stiff and arched, as in modern humans. 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.

Anterior dental microwear in Australopithecus afarensis: comparisons with human and nonhuman primates

Abstract Dental microwear observed on the incisors and the canine/premolar complex of Australopithecus afarensis is described. Comparisons are made with three groups of extant African primates: Pan troglodytes troglodytes, Gorilla gorilla gorilla, and Papio hamadryas. Additional comparisons are made with a prehistoric Eskimo dental sample recovered from Point Hope, Alaska. Six distinct types of incisal dental microwear are found in these groups. These include fine wear striae, polish, small pits, large pits, gouges, and microflakes. These microwear types are related to suggested dietary conditions, feeding behaviors, and dental functions. It is shown that each species exhibits a different set of microwear types. Results of this study show that incisal dental microwear in A. afarensis is most similar to that observed in Gorilla, and to a lesser extent, in Papio. It is suggested that the incisors of A. afarensis were used to strip leaves and to chew hard foods such as roots, seeds, and rhizomes. Dental microwear observed on the canine/premolar complex of A. afarensis indicates that these teeth did not serve a shearing/slicing function as they do in modern apes or in baboons. Rather, it appears that the canine/premolar complex of A. afarensis was used primarily to puncture-crush food.

The pygmy chimpanzee is not a living missing link in human evolution

Phylogenetic reconstruction should incorporate knowledge of the fossil record. Recent suggestions that the pygmy chimpanzee can serve as a living missing link are contra fossil evidence and are rejected.

New discoveries of pliocene hominids and artifacts in Hadar: International Afar Research Expedition to Ethiopia (fourth and fifth field seasons, 1975–1977)

Abstract This note enumerates the paleontological discoveries of the Afar Expedition in 1975–1977.

The strategy of paleoanthropology: Early African hominids annual luncheon address: AAPA 1996

Discoveries of fossil hominids, particularly at Olduvai Gorge, Tanzania, in the late 1950s and early 1960s served as an important catalyst for stimulating the multi-interdisciplinary approach which now characterizes African paleoanthropology. While discovery of fossil hominids will always play a central role, it is the strategic implementation of a diverse set of inquiries which promises to generate the most rewarding and comprehensive details of how we became human. Field work by the Omo Research Expedition and the Koobi Fora Research Project contributed significantly to development of the strategy of paleoanthropology, emphasizing integration of specialists from geology, biology and the social sciences. In Ethiopia the ongoing Hadar Research Project has applied the integrated, multidimensional strategy of paleoanthropology resulting in important additions to our understanding of early hominid origins. The pace of fossil hominid discoveries is picking up in Africa, and there is every reason to believe that major contributions to human evolutionary studies will be forthcoming.

Aspects of Mandibular Ontogeny in Australopithecus afarensis

Human and ape mandibles differ in the proportion of adult size attained at equivalent dental emergence stages; for most dimensions human mandibles are more advanced. These dissimilarities in pattern of growth underlie the vastly different adult mandibular morphologies of these taxa. Australopithecus mandibles represent a third distinctive mandibular morphology, but the pattern of its mandibular growth remains underexplored. The Australopithecus afarensis sample from the Hadar site, Ethiopia, ca. 3.4–3.0 Ma, is represented by three infant (pre-M1 emergence) and two juvenile (pre-M3 emergence) mandibles. A recently recovered mandible, A.L. 1920-1, though edentulous, appears to capture an A. afarensis individual during M2 emergence, thus bridging these developmental stages. In this chapter, we (1) describe three new infant/juvenile A. afarensis mandibles and confirm that the suite of features used to distinguish A. afarensis from other taxa is present early in ontogeny, and (2) investigate how the A. afarensis mandible changes in size and shape throughout growth in comparison to humans and chimpanzees . Our results indicate that A. afarensis resembles humans more than chimpanzees in its percentage of adult corpus breadth attained at successive stages of dental emergence. A. afarensis is also more similar to humans in corpus cross-sectional shape changes throughout ontogeny. We suggest that canine reduction may have had an important influence on the growth trajectory of the A. afarensis mandibular corpus such that, as in humans, it achieved adult values relatively early. Our results underscore the importance of considering the influence of the developing dentition on both juvenile and adult mandibular morphology.