The massive fossil humerus from the Oldowan horizon of Gombore I, Melka Kunture (Ethiopia, &gt;1.39 Ma)

While there is broad agreement that early hominins practiced some form of terrestrial bipedality, there is also evidence that arboreal behavior remained a part of the locomotor repertoire in some taxa, and that bipedal locomotion may not have been identical to that of modern humans. It has been difficult to evaluate such evidence, however, because of the possibility that early hominins retained primitive traits (such as relatively long upper limbs) of little contemporaneous adaptive significance. Here we examine bone structural properties of the femur and humerus in the Australopithecus afarensis A.L. 288–1 ("Lucy", 3.2 Myr) that are known to be developmentally plastic, and compare them with other early hominins, modern humans, and modern chimpanzees. Cross-sectional images were obtained from micro-CT scans of the original specimens and used to derive section properties of the diaphyses, as well as superior and inferior cortical thicknesses of the femoral neck. A.L. 288–1 shows femoral/humeral diaphyseal strength proportions that are intermediate between those of modern humans and chimpanzees, indicating more mechanical loading of the forelimb than in modern humans, and by implication, a significant arboreal locomotor component. Several features of the proximal femur in A.L. 288–1 and other australopiths, including relative femoral head size, distribution of cortical bone in the femoral neck, and cross-sectional shape of the proximal shaft, support the inference of a bipedal gait pattern that differed slightly from that of modern humans, involving more lateral deviation of the body center of mass over the support limb, which would have entailed increased cost of terrestrial locomotion. There is also evidence consistent with increased muscular strength among australopiths in both the forelimb and hind limb, possibly reflecting metabolic trade-offs between muscle and brain development during hominin evolution. Together these findings imply significant differences in both locomotor behavior and ecology between australopiths and later Homo.

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“…Sources: 1) Present study; 2) Ruff, 1995 [65]; 3) Ruff, 2008 [33]; 4) Di Vincenzo et al, 2015 [76]; 5) L. Rodriguez, pers. comm.…”

Section: Methodsmentioning

confidence: 99%

Limb Bone Structural Proportions and Locomotor Behavior in A.L. 288-1 ("Lucy")

et al. 2016

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“…It was discovered in 1976 in the Oldowan tool-bearing level of Gombore I, one of the early to middle Pleistocene localities forming the Melka Kunture archaeological and paleontological site complex along the Upper Awash Valley, on the Ethiopian highlands (Chavaillon and Piperno, 2004;Gallotti and Mussi, 2015). Originally reported by Chavaillon and co-workers (1977) and by Senut (1979;see also Senut, 1981a, b), GOM IB has been more recently investigated by Puymerail et al (2014) and by Di Vincenzo et al (2015). A refinement of the chronologies at Melka Kunture (Morgan et al, 2012;Tamrat et al, 2014) indicates that GOM IB is 1.6-1.5 Ma old (Morgan, 2014: pers.…”

Section: Methodsmentioning

confidence: 99%

“…In its original description, Susman stated that "(t)his specimen is a reasonably good match for TM 1517 in both size and shape, and on this basis it most likely belongs to Paranthropus" (Susman, 1989: 462). However, based on its cross-sectional shape and comparisons with the expanded record at Swartkrans, this specimen has since been allocated to Homo (Lague, 2015;Susman et al, 2001; Braga et al, 2016a, b;Broom, 1938b;Broom and Schepers, 1946;Bruxelles et al, 2016;Churchill et al, 2013;Di Vincenzo et al, 2015;Lague, 2014Lague, , 2015Lague and Jungers, 1996;McHenry and Brown, 2008;Ryan and Sukhdeo, 2016;Senut, 1981a;Skinner et al, 2013;Straus, 1948;Susman, 1989;Susman et al, 2001;Thackeray et al, 2001 SK 24600 Swartkrans Chavaillon et al, 1977;Churchill et al, 2013;Di Vincenzo et al, 2015;Puymerail et al, 2014;Ryan and Sukhdeo, 2016;Senut, 1979Senut, , 1981a a In some papers cited in this study, the taxon Paranthropus is subsumed within Australopithecus. b Braga et al, 2016a, b;Bruxelles et al, 2016.…”

Section: Methodsmentioning

confidence: 99%

“…An interesting case is represented by the long-term debate about the allocation to Paranthropus (or australopith s.l., following some authors) or Homo of isolated remains of the distal humerus remains (e.g., Bacon, 2000;Churchill et al, 2013;Di Vincenzo et al, 2015;Lague, 2014Lague, , 2015Lague and Jungers, 1996;Patterson and Howells, 1967;Senut, 1981a;Susman, 1989;Susman et al, 2001). While potentially well suited for assessing postcranial variation because of their abundance in the record and the biomechanical specificities of the hominin elbow joint, Plio-Pleistocene specimens from both eastern and southern Africa have nonetheless been the matter of frequent controversial attributions (rev.…”

Section: Introductionmentioning

confidence: 99%

“…in Di Vincenzo et al, 2015). Conversely, a poorly distinct coronoid area, a more distal positioning of the lateral epicondyle relative to the capitulum, a thick and medially oriented medial epicondyle (epitrochlea), a more vertically developed (thus, sub-rounded) and anteriorly projecting capitulum, and a proportionally anteroposteriorly expanded contour of the distal shaft are more typical human features (e.g., Di Vincenzo et al, 2015;Domínguez-Rodrigo et al, 2013;Lague, 2014;Susman, 1989;Susman et al, 2001). Also, the presence of a distally flaring sharp supracondylar crest, also present in apes (Lague, 2015), seems more common in later Homo than in Paranthropus, even if rather variable in its occurrence and degree of development within the same fossil sample (Lague, 2015).…”

Section: Introductionmentioning

confidence: 99%

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