Like Father, Like Son:
Assessment of the Morphological Affinities of A.L. 288–1 (A. afarensis), Sts 7 (A. africanus) and Omo119–73–2718 ( Australopithecus sp.) througha Three-Dimensional Shape Analysis of the Shoulder Joint
Julia Arias-Martorell cs 2015 PLoS ONE 10(2): e0117408 doi 10.1371/ journal.pone.0117408
martinez.perez-perez@ub.edu

The postcranial evidence for the Australopithecus genus indicates: australopiths were able bipeds,
but the morphology of the forelimbs, particularly of the shoulder girdle, suggests:
they were partially adapted to anarboreal lifestyle.
The nature of such arboreal adaptations is still unclear, as are the kind of arboreal behaviors in which apiths might have engaged.

In this study, we analyzed the shape of the shoulder joint (proximal humerus & glenoid cavity of the scapula) of 3 australopith spms with 3D geometric morphometrics
- A.L.288–1 A.afarensis,
- Sts-7 A.africanus,
- Omo 119–73–2718 Australopithecus sp.
Their morphology was compared with a wide array of living anthropoids & some additional fossil hominins:
- H.erectus KNM-WT 15000,
- H.neanderthalensis Tabun1.

Our results:
- A.L.288–1 shows mosaic traits resembling H.sapiens & Pongo,
- Sts-7 is most similar to the arboreal apes, it does not present affinities with H.sapiens.
- Omo-119–73–2718 exhibits morphological affinities with the more arboreal & partially suspensory NW monkey Lagothrix.

The shoulder of the apith spms thus shows a combination of primitive & derived traits (humeral globularity, enhancement of internal & external rotation of the joint), related to use of the arm in overhead positions.
The genus Homo spms show overall affinities with H.sapiens at the shoulder, indicating full correspondence of these hominin shoulders with the modern human morphotype.

Comment:

Very interesting & beautifully illustrated paper, thanks a lot.
Unfortunately, the interpretation only considers arboreal and terrestrial settings, without considering the possibility that australopiths - not unlike lowland gorillas, but (a lot?) more frequently - might have spent a lot of time in wetlands and forest
swamps or bais.

The authors apparently still follow the traditional interpretation that "primitive" = apelike, and "derived" = humanlike.
This is often wrong: both humans & apes are derived (in different directions), and australopiths were more primitive: they (4-1 Ma) lived near to the common ancestors (8-4 Ma) of chimps, humans & gorillas.

Another unproven preassumption is that the authors assume that "the postcranial evidence for the Australopithecus genus indicates that australopiths were able bipeds".
In fact, the postcranial evidence suggests that australopiths were orthograde ("upright"), i.e. had vertical spines most of the time, but not that they were able bipeds, on the contrary:
their wide pelvis (flaring ilia) & very valgus knees contradict cursorialism, and their curved phalanges suggest at least some arboreality, e.g. vertical climbing.

In any case, the paper makes it clear that australopiths (with globular humeral heads & enhanced humeral rotation) frequently used their arms in all directions, aside & overhead.
Paleo-anthropological evidence shows that australopiths lived in wetlands, papyrus swamps, forest swamps, lagoons etc. (e.g. Conroy 1990, Reed 1997, refs below), and isotopic, dento-gnathic & microwear data suggest
- the diet of the East-African australopiths included wetland plants & papyrus sedges,
- the South-African australopiths had a more omnivorous diet (work of P-F.Puech, N.vd.Merwe, A.Shabel & others).

The combined evidence thus suggests that most or all australopiths lived in wetlands & forest swamps, frequently wading bipedally, sometimes floating vertically, grasping branches above the bai, collecting floating vegetation, possibly including papyrus
parts (cf "aquatic herbaceous vegetation" AHV in lowland gorillas, e.g. Chadwick & Nichols 1995, Doran & McNeilage 1998, Breuer cs 2005).
This lifestyle most parsimoniously explains their well-developed shoulder mobility, e.g.
M.Verhaegen, S.Munro, P-F.Puech & M.Vaneechoutte 2011 "Early hominoids: orthograde aquarboreals in flooded forests?" pp.67-81 in M.Vaneechoutte cs eds "Was Man More Aquatic in the Past?" Bentham Sci.Publ.eBook.
For a survey, google: research Gate marc verhaegen.

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