Conclusion: Implications of KSD-VP-1/1 for Early Hominin Paleobiology and Insights into the Chimpanzee/Human Last Common Ancestor

Abstract

KSD-VP-1/1 is a 3.6 million years old (Ma) partial skeleton of Australopithecus afarensis recently discovered from the Woranso-Mille study area in the Afar region of Ethiopia. The recovered elements of this specimen, which include cervical vertebrae, a complete scapula, clavicle, numerous ribs, pelvis, and elements of the fore- and hindlimbs, greatly enhance our understanding of the paleobiology of early Australopithecus afarensis. Detailed analyses of the cervical vertebrae indicate that Australopithecus afarensis had a highly mobile neck, signaling human-like kinematics consistent with habitual upright posture and bipedalism. Elements of the shoulder girdle exhibit some primitive morphology but are overall more similar to humans than has been previously understood. This similarity is inconsistent with the notion that the Australopithecus afarensis shoulder retained primitive morphology from an African ape-like chimpanzee/human last common ancestor. Morphology of the thorax also indicates that while some individual traits may appear to superficially suggest arboreality, Australopithecus afarensis did not have an abundance of functionally significant morphological traits that would suggest high canopy arboreality as found today in large-bodied apes. Most of the inconsistencies in interpretations of early hominin paleobiology appear to stem from methodological differences, incorrect a priori assumptions, or incomplete information derived from fragmentary specimens.