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Like father, like son: assessment of the morphological affinities of A.L. 288-1 (A. afarensis), Sts 7 (A. africanus) and Omo 119-73-2718 (Australopithecus sp.) through a three-dimensional shape analysis of the shoulder joint.

Arias-Martorell J, Potau JM, Bello-Hellegouarch G, Pérez-Pérez A - PLoS ONE (2015)

Bottom Line: The morphology of the specimens was compared with that of a wide array of living anthropoid taxa and some additional fossil hominins (the Homo erectus specimen KNM-WT 15000 and the H. neanderthalensis specimen Tabun 1).The shoulder of the australopith specimens thus shows a combination of primitive and derived traits (humeral globularity, enhancement of internal and external rotation of the joint), related to use of the arm in overhead positions.The genus Homo specimens show overall affinities with H. sapiens at the shoulder, indicating full correspondence of these hominin shoulders with the modern human morphotype.

View Article: PubMed Central - PubMed

Affiliation: Departament de Biologia Animal, Universitat de Barcelona, Barcelona, Spain.

ABSTRACT
The postcranial evidence for the Australopithecus genus indicates that australopiths were able bipeds; however, the morphology of the forelimbs and particularly that of the shoulder girdle suggests that they were partially adapted to an arboreal lifestyle. The nature of such arboreal adaptations is still unclear, as are the kind of arboreal behaviors in which australopiths might have engaged. In this study we analyzed the shape of the shoulder joint (proximal humerus and glenoid cavity of the scapula) of three australopith specimens: A.L. 288-1 (A. afarensis), Sts 7 (A. africanus) and Omo 119-73-2718 (Australopithecus sp.) with three-dimensional geometric morphometrics. The morphology of the specimens was compared with that of a wide array of living anthropoid taxa and some additional fossil hominins (the Homo erectus specimen KNM-WT 15000 and the H. neanderthalensis specimen Tabun 1). Our results indicate that A.L. 288-1 shows mosaic traits resembling H. sapiens and Pongo, whereas the Sts 7 shoulder is most similar to the arboreal apes and does not present affinities with H. sapiens. Omo 119-73-2718 exhibits morphological affinities with the more arboreal and partially suspensory New World monkey Lagothrix. The shoulder of the australopith specimens thus shows a combination of primitive and derived traits (humeral globularity, enhancement of internal and external rotation of the joint), related to use of the arm in overhead positions. The genus Homo specimens show overall affinities with H. sapiens at the shoulder, indicating full correspondence of these hominin shoulders with the modern human morphotype.

Show MeSH
3D models of the three australopiths—A.L. 288–1r (A. afarensis), Sts 7 (A. africanus) and Omo 119–73–2718 (Australopithecus sp.)—proximal humeri included in the study with a sample of extant taxa.The humeri are shown in proximal and posterior views. Pongo is shown as a representative of the arboreal ape shape and Lagothrix as a representative of a more generalized arboreal shape. The humeri are at the same scale for interpretative purposes.
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pone.0117408.g009: 3D models of the three australopiths—A.L. 288–1r (A. afarensis), Sts 7 (A. africanus) and Omo 119–73–2718 (Australopithecus sp.)—proximal humeri included in the study with a sample of extant taxa.The humeri are shown in proximal and posterior views. Pongo is shown as a representative of the arboreal ape shape and Lagothrix as a representative of a more generalized arboreal shape. The humeri are at the same scale for interpretative purposes.

Mentions: The proximal humerus morphology of A.L. 288–1r (A. afarensis) exhibits mixed characteristics, showing some affinities with the modern humans (Fig. 3a, Table 5) and Pongo in the bgPCA (Fig. 2a) and with the smaller taxa (hylobatids, Ateles and Lagothrix) (Figs. 4a, 5a and 7). With the arboreal apes and atelines, A.L. 288–1r shares the position and shape of the greater tubercle insertions, but the positioning of the humeral head with respect to the tubercles as well as its overall shape is more similar to the modern human morphotype (Fig. 9). A mosaic nature has been found for a number of postcranial structures in early hominins, including the forelimb and the shoulder region [14,64–66,67], and A. afarensis specimens have been described as showing more modern-looking characteristics than later australopiths for other cranial and postcranial regions (e.g., [68]). However, a study by Lague [61] on allometric changes in the distal humerus indicated that for particularly small early hominin specimens (such as A.L. 288–1r, to which the study specifically refers) if shape changes are analyzed without accounting for the size-shape variation of the comparison sample (i.e., modern humans), the morphological associations of this region could appear more human-like. If the regression of humeral shape onto CS (Fig. 5a) is considered, A.L. 288–1r exhibits a CS value more similar to the small taxa of the study and a proximal humeral shape within the upper ranges of those groups (Ateles, Lagothrix, hylobatids). The CS value is also well within the lower ranges of Pongo, but it is clearly far from the ranges of modern humans. However, in the size-shape PCA (the PCA of the residuals of the CS-shape regression, Fig. 6a), A.L. 288–1r does not differ morphologically from the modern humans for the two first PCs, appearing more human-like again than more modern (fossil) taxa (Sts7 and Omo 119–73–2718), as suggested by McHenry and Brown [68].


Like father, like son: assessment of the morphological affinities of A.L. 288-1 (A. afarensis), Sts 7 (A. africanus) and Omo 119-73-2718 (Australopithecus sp.) through a three-dimensional shape analysis of the shoulder joint.

Arias-Martorell J, Potau JM, Bello-Hellegouarch G, Pérez-Pérez A - PLoS ONE (2015)

3D models of the three australopiths—A.L. 288–1r (A. afarensis), Sts 7 (A. africanus) and Omo 119–73–2718 (Australopithecus sp.)—proximal humeri included in the study with a sample of extant taxa.The humeri are shown in proximal and posterior views. Pongo is shown as a representative of the arboreal ape shape and Lagothrix as a representative of a more generalized arboreal shape. The humeri are at the same scale for interpretative purposes.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4317181&req=5

pone.0117408.g009: 3D models of the three australopiths—A.L. 288–1r (A. afarensis), Sts 7 (A. africanus) and Omo 119–73–2718 (Australopithecus sp.)—proximal humeri included in the study with a sample of extant taxa.The humeri are shown in proximal and posterior views. Pongo is shown as a representative of the arboreal ape shape and Lagothrix as a representative of a more generalized arboreal shape. The humeri are at the same scale for interpretative purposes.
Mentions: The proximal humerus morphology of A.L. 288–1r (A. afarensis) exhibits mixed characteristics, showing some affinities with the modern humans (Fig. 3a, Table 5) and Pongo in the bgPCA (Fig. 2a) and with the smaller taxa (hylobatids, Ateles and Lagothrix) (Figs. 4a, 5a and 7). With the arboreal apes and atelines, A.L. 288–1r shares the position and shape of the greater tubercle insertions, but the positioning of the humeral head with respect to the tubercles as well as its overall shape is more similar to the modern human morphotype (Fig. 9). A mosaic nature has been found for a number of postcranial structures in early hominins, including the forelimb and the shoulder region [14,64–66,67], and A. afarensis specimens have been described as showing more modern-looking characteristics than later australopiths for other cranial and postcranial regions (e.g., [68]). However, a study by Lague [61] on allometric changes in the distal humerus indicated that for particularly small early hominin specimens (such as A.L. 288–1r, to which the study specifically refers) if shape changes are analyzed without accounting for the size-shape variation of the comparison sample (i.e., modern humans), the morphological associations of this region could appear more human-like. If the regression of humeral shape onto CS (Fig. 5a) is considered, A.L. 288–1r exhibits a CS value more similar to the small taxa of the study and a proximal humeral shape within the upper ranges of those groups (Ateles, Lagothrix, hylobatids). The CS value is also well within the lower ranges of Pongo, but it is clearly far from the ranges of modern humans. However, in the size-shape PCA (the PCA of the residuals of the CS-shape regression, Fig. 6a), A.L. 288–1r does not differ morphologically from the modern humans for the two first PCs, appearing more human-like again than more modern (fossil) taxa (Sts7 and Omo 119–73–2718), as suggested by McHenry and Brown [68].

Bottom Line: The morphology of the specimens was compared with that of a wide array of living anthropoid taxa and some additional fossil hominins (the Homo erectus specimen KNM-WT 15000 and the H. neanderthalensis specimen Tabun 1).The shoulder of the australopith specimens thus shows a combination of primitive and derived traits (humeral globularity, enhancement of internal and external rotation of the joint), related to use of the arm in overhead positions.The genus Homo specimens show overall affinities with H. sapiens at the shoulder, indicating full correspondence of these hominin shoulders with the modern human morphotype.

View Article: PubMed Central - PubMed

Affiliation: Departament de Biologia Animal, Universitat de Barcelona, Barcelona, Spain.

ABSTRACT
The postcranial evidence for the Australopithecus genus indicates that australopiths were able bipeds; however, the morphology of the forelimbs and particularly that of the shoulder girdle suggests that they were partially adapted to an arboreal lifestyle. The nature of such arboreal adaptations is still unclear, as are the kind of arboreal behaviors in which australopiths might have engaged. In this study we analyzed the shape of the shoulder joint (proximal humerus and glenoid cavity of the scapula) of three australopith specimens: A.L. 288-1 (A. afarensis), Sts 7 (A. africanus) and Omo 119-73-2718 (Australopithecus sp.) with three-dimensional geometric morphometrics. The morphology of the specimens was compared with that of a wide array of living anthropoid taxa and some additional fossil hominins (the Homo erectus specimen KNM-WT 15000 and the H. neanderthalensis specimen Tabun 1). Our results indicate that A.L. 288-1 shows mosaic traits resembling H. sapiens and Pongo, whereas the Sts 7 shoulder is most similar to the arboreal apes and does not present affinities with H. sapiens. Omo 119-73-2718 exhibits morphological affinities with the more arboreal and partially suspensory New World monkey Lagothrix. The shoulder of the australopith specimens thus shows a combination of primitive and derived traits (humeral globularity, enhancement of internal and external rotation of the joint), related to use of the arm in overhead positions. The genus Homo specimens show overall affinities with H. sapiens at the shoulder, indicating full correspondence of these hominin shoulders with the modern human morphotype.

Show MeSH