Assessing the longitudinal structure of the early hominid foot: A two-dimensional architecture analysis

Abstract

Early hominid feet are often very fragmentary preserved and their architectural approaches stayed limited and subject to controversy. This study proposes an architectural analysis of the primate foot realised on dislocated skeleton. It is based on the angular analysis of geometrical relationships between the joint areas. We investigate the longitudinal structure of the primate foot and we present the results conceming some Australopithecus afarensis specimens from Hadar (Ethiopia) and the Homo habilis Olduvai Hominid 8 foot (Tanzania). The architectural analysis argues for the lack of a longitudinal medial arch in A. afarensis, their joints being in neutral position. On the contrary, the more recent OH8 specimen is arched both medially and laterally.

Human-like external function of the foot, and fully upright gait, confirmed in the 3.66 million year old Laetoli hominin footprints by topographic statistics, experimental footprint-formation and computer simulation

“…Nevertheless, various papers have argued that anatomical features in A. afarensis skeletal elements, including a large navicular tuberosity [5] and a well-marked peroneal groove on the fibular malleolus [55] are evidence that the medial midfoot of A. afarensis was weight-bearing, and thus that the species lacked transverse arches and/or a medial longitudinal arch. A two-dimensional analysis of articular orientations [56] also came to the same conclusion. However, a recent paper [51] argues that the form of a new fourth metatarsal of A. afarensis indicates, contrariwise, that this species did indeed have a medial longitudinal arch and lacked a mid-tarsal break.…”

A complete second metatarsal (StW 89) from Sterkfontein Member 4, South Africa

“…If the latter is correct, then some South African australopiths, while possessing a rigid lateral foot and lateral longitudinal arch (DeSilva, 2010), would have a lower and less developed medial longitudinal arch. This reconstruction of the foot would be consistent with seemingly contradictory studies finding evidence for an arch in australopiths using bones found in the lateral column (e.g., DeSilva, 2010;Ward et al, 2011), but the absence of an arch in the medial column (e.g., Berillon, 2003;Harcourt-Smith and Aiello, 2004). However, we caution about over-generalizing the arch given the range of variation in arch development in humans today and evidence that such variation may have existed in australopiths as well (DeSilva and Throckmorton, 2010).…”

The AL 333-160 fourth metatarsal from Hadar compared to that of humans, great apes, baboons and proboscis monkeys: Non-conclusive evidence for pedal arches or obligate bipedality in Hadar hominins

“…It does not include three out of five great ape species, and fails to test for alternate behaviors which may be associated to or result in these putatively bipedal characters. Moreover, the study also fails to demonstrate a causal relationship between the cited characters and the functions ascribed to them, and ignores much of the literature which quantifies African ape-like characters in the Hadar foot (Berillon, 2003(Berillon, , 2004Deloison, 2004;Sarmiento and Marcus, 2000;Stern and Susman, 1983;Susman et al, 1984). Considering that evolution proceeds as behavioral shifts through structural continuity, and necessitates localized anatomical structure to have at least a duality of function (Darwin, 1859), Ward et al's (2011a,b) claims of bipedal exclusivity for so many 4th MT characters require testing.…”

“…4a, refers the reader to reference 11, Berillon (2003), as the source of the measurements and method for measuring 4th MT cuboid facet curvature. Berillon (2003), however, does not report on 4th MT cuboid facet curvature. We suspect that Ward et al intended to reference DeSilva (2010), which in their study appears as reference 10, DeSilva (2009).…”

“…In spite of an implied flexible transverse tarsal joint the medial deflection of the distal half of the ectocuneiform facet (AL 333-79) and the lateral concavity of the shaft of the 5th MT (AL 333-78) indicate rays were directed parallel to the pedal long axis and thus the foot had compromised some of its grasping abductory ability for propulsion. Every AL 333 tarsal and metatarsal bone, individually but more so in association, suggests considerable mobility at the tarsal joints, arguing against a fixed transverse arch or a human-like longitudinal arch (see also Berillon, 2003;Harcourt-Smith, 2002). All elements indicate the tarsometatarsal joints were held against the substrate and the distal tarsal row transferred weight to the substrate (Sarmiento and Marcus, 2000).…”