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South African skeleton shows humans learnt to walk upright in the trees


The analysis of the world’s most complete skeleton of an early human ancestor, conducted by a research collaboration involving the University of Liverpool, offers conclusive evidence that human ancestors became efficient upright walkers while they were still substantially tree dwelling animals.

South African skeleton shows humans learnt to walk upright in the trees
Professor Ronald Clarke with Little Foot [Credit: University of Liverpool]
The first bones of the 3.67 million old skeleton, specimen StW 573 nicknamed ‘Little Foot’, were 12 foot bones and leg bone fragments identified in boxes in the 1990s. The rest of the skeleton has undergone two decades of painstaking excavation, cleaning, restoring and analysis. It was found in a very deep cavern, with the bone embedded in a concrete-like matrix. The bone is very delicate and in some cases literally paper-thin. However, it has given scientists a far greater understanding of how our species evolved.


Limbs intact

The over 90% complete skeleton of an old female, much more than twice as complete as the famous Lucy, and considerably older as well, Little Foot is a member of the genus Australopithecus, a widespread and varied genus of hominins to which Lucy belonged, and which was an early precursor to modern-day Homo sapiens which appeared roughly 300,000 years ago. Little Foot is the first fossil of Australopithecus ever to have been discovered with its limbs intact.

South African skeleton shows humans learnt to walk upright in the trees
Little Foot’s fossil bones [Credit: Patrick Landmann/Science Photo Library]
The studies support the argument of her discoverer, Professor Ronald Clarke of the University of the Witwatersrand, that there were two species of Australopithecus living at the same time in South Africa’s ‘Cradle of Humankind’, Australopithecus africanus, which was small, like Lucy, and probably primarily tree-dwelling, and Australopithecus prometheus, which was probably just within the range of modern human stature.


Important finding

As part of the study, which has been reported in Nature Science, Professor Robin Crompton, Honorary University of Liverpool Research Associate in Musculoskeletal Biology, and his colleagues analysed how she would have walked.


Professor Crompton, states: “This hominin, for the first time in the fossil record, had longer lower limbs than upper limbs, like ourselves. This is an important finding, as the slightly older hominin Ardipithecus, which came before Australopithecus, had longer arms than legs – more like other great apes such as the gorilla.


“That means she was being selected for long stride length in bipedalism. Moreover, unlike Lucy, ‘Littlefoot’ had a hip joint like our own, able to transmit large forces from the trunk to the leg and vice versa. Although Little Foot’s legs were longer than her arms, they had not yet achieved the great relative leg length found in humans. Thus, she would not have been as good at carrying objects as we are. However, she would have been much better at climbing trees than modern humans.

“It is most likely that she would have resided in an area that was a mix of tropical rainforest, broken woodland and grassland, through which she would roam around. She would have lived primarily on forest fruits and leaves”

Source: University of Liverpool [December 10, 2018]

TANN

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1 comment :

  1. Fantastic discovery, thanks a lot. It seems to confirm that South- & East-Africa (and probably other regions of Africa as well) during the Pliocene were full of different species of australopithecines. All these australopiths were no "human ancestors", of course. The traditional idea that they were human ancestors (to the exclusion of Pan & Gorilla) is based on a statistically impossible assumption: that all hominid fossils (possibly thousands) are closer relatives of Homo than of Pan or Gorilla, although there are 6 or 7 extant chimp, bonobo & gorilla species, and there's only 1 extant human species. This is incredibly anthropocentric (pre-darwinian, in fact): orangutans Pongo (the Asian great apes) do have hundreds of fossil relatives (e.g. Siva-, Giganto-, Indo-, Lufeng-, possibly Ankara-pithecus etc.), so there's no reason to suppose that Pan & Gorilla would not have had fossil relatives, yet for some reason (read: anthropocentrism), it's widely accepted that the African apes had no or almost no fossil relatives.
    Most anthropologists still assume that the australopiths had a lot of "human" traits believed to express "bipedalism" (read: "therefore human Ancestors"): flat feet, valgus knees, low iliac blades, vertical spines etc., and small canines & thick cheekteeth enamel are also believed to be human-specific. But, in fact, most of not all of these traits are not human-derived, but are hominid- or even hominoid-primitive, but lost in the African apes (often in parallel), e.g.
    - Many Miocene hominoids fossil already had thicker enamel (e.g. Afro- & Griphopithecus c 14 Ma) and/or smaller canines than extant African apes.
    - Vertical spines & remarkably humanlike lumbar vertebrae were already present in e.g. Morotopithecus (c 20 Ma). These, of course, don't express bipedal running, but, according to comparative biology, suggest vertical climbing and/or bipedal wading (australopiths indeed typically fossilized in forest swamps or wetlands, e.g. Reed 1997 JHE 32:289).
    - Low pelvises as in humans, gibbons & monkeys (still without the iliac elongation seen in great apes) are the primitive condition.
    - Valgus knees are an adaptation for having long femoral necks (an adaptation for femoral abduction, together with the flaring ilia) but at the same time keeping hip, knee & ankle joints in 1 line while standing upright (which is more stable): the longer & more horizontal the femoral neck, the more valgus the knee has to be to bring the 3 leg joints in 1 line.
    - Flat feet with adducted big toes are still seen in prenatal chimp fetuses, who have "a foot resembling that of man in that its great toe points forward ... Only as it approaches its birth size does its foot acquire the appearance of a hand. At no stage of its development does the human foot resemble that of an adult ape" (Carleton Coon "The Story of Man" p.12), IOW, human feet might in several respects be more primitive than chimpanzee (& probably also gorilla) feet.
    For a less human-biased view of hominoid & hominid evolution, google "Ape and Human Evolution 2018 biology vs anthropocentrism" (PPT).

    Most likely, different australopiths (presumably in parallel in East- & South-Africa) lived in more or less open or closed flooded forests & wetlands, some of them spent more time in the swamps wading bipedally much like bonobos & lowland gorillas still do sometimes (google e.g. "gorilla bai" & "bonobo wading"), others spent more time in the trees, often climbing vertically in the branches above the swamps, as we predicted several years ago in a paper in TREE (Verhaegen, Puech & Munro 2002 "Aquarboreal Ancestors?" Trends Ecol.Evol.17:212-217), some were probably more frugi-, others more herbivorous (e.g. frequently feeding on "aquatic herbaceous vegetation" (AHV) like papyrus sedges & waterlily parts).

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