Lucy's Flat Feet: The Relationship between the Ankle and Rearfoot Arching in Early Hominins

BACKGROUND. In the Plio-Pleistocene, the hominin foot evolved from a grasping appendage to a stiff, propulsive lever. Central to this transition was the development of the longitudinal arch, a structure that helps store elastic energy and stiffen the foot during bipedal locomotion. Direct evidence for arch evolution, however, has been somewhat elusive given the failure of soft-tissue to fossilize. Paleoanthropologists have relied on footprints and bony correlates of arch development, though little consensus has emerged as to when the arch evolved. METHODOLOGY/PRINCIPAL FINDINGS. Here, we present evidence from radiographs of modern humans (n=261) that the set of the distal tibia in the sagittal plane, henceforth referred to as the tibial arch angle, is related to rearfoot arching. Non-human primates have a posteriorly directed tibial arch angle, while most humans have an anteriorly directed tibial arch angle. Those humans with a posteriorly directed tibial arch angle (8%) have significantly lower talocalcaneal and talar declination angles, both measures of an asymptomatic flatfoot. Application of these results to the hominin fossil record reveals that a well developed rearfoot arch had evolved in Australopithecus afarensis. However, as in humans today, Australopithecus populations exhibited individual variation in foot morphology and arch development, and "Lucy" (A.L. 288-1), a 3.18 Myr-old female Australopithecus, likely possessed asymptomatic flat feet. Additional distal tibiae from the Plio-Pleistocene show variation in tibial arch angles, including two early Homo tibiae that also have slightly posteriorly directed tibial arch angles. CONCLUSIONS/SIGNIFICANCE. This study finds that the rearfoot arch was present in the genus Australopithecus. However, the female Australopithecus afarensis "Lucy" has an ankle morphology consistent with non-pathological flat-footedness. This study suggests that, as in humans today, there was variation in arch development in Plio-Pleistocene hominins.Leakey Foundatio

Homo naledi, a new species of the genus Homo

Homo naledi es una especie previamente desconocida de homínido extinto descubierta dentro de la Cámara Dinaledi del sistema de cuevas Rising Star, en el Cradle of Humankind, Sudáfrica. Esta especie se caracteriza por tener una masa corporal y estatura similar a las poblaciones humanas de cuerpo pequeño, pero un volumen endocraneal pequeño similar al de los australopitecos. La morfología craneal de H. naledi es única, pero se asemeja más a las especies tempranas de Homo, incluyendo Homo erectus, Homo habilis o Homo rudolfensis. Aunque primitiva, la dentición es generalmente pequeña y simple en su morfología oclusal. H. naledi presenta adaptaciones manipulativas de la mano y la muñeca similares a las humanas. También exhibe un pie y miembro inferior similares a los humanos. Estos aspectos humanos se contrastan en el postcráneo con un tronco, hombro, pelvis y fémur proximal más primitivos o similares a los australopitecos. Representando al menos 15 individuos con la mayoría de los elementos esqueléticos repetidos múltiples veces, esta es la mayor colección de una sola especie de homínidos descubierta en África.National Geographic SocietyThe National Research Foundation of South Africa (WARF)The Palaeontological Scientific TrustLyda Hill FoundationWisconsin Alumni Research Foundation (WARF)Texas A and M UniversityDepto. de Biodiversidad, Ecología y EvoluciónFac. de Ciencias BiológicasTRUEpu