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Controversy over the early ancestry of hominin evolution

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  • Controversy over the early ancestry of hominin evolution

    Before about 1970 all the ancestor fossils of hominins could fit into cardboard box, but since thousands of fossils have been discovered all over Africa and Asia that have established a relatively good consistent hominin evolution dating bact to about 4.4 million years ag with the australpithecines Lucy (3.2 million years) and her distant cousin Ardi.' {4.4 million years ago). What we are also finding is a diversity of cousins at the various stages of hominin evolution that in and of themselves went extinct and and not a direct ancestor to humans like Australpithecus Robustus and A. boisei. One problem is the definition of what is a species making it difficult to define specific ancestrial lineages in hominins and life in general. Recent finds in hominin evolution and evolution in general is that evolution takes place in a diversity of what was previously called species, subspecies and related varieties

    Older hominin primate ancestors and there cousins have less fossil evidence, and search for a direct ancestor is more illusive. The claims of direct hominin ancestry is more difficult and sometimes controversial like the Sahelanthropus tchadensis (6.8 to 7.2 million years ago). The following articles illustrate the controversy of claiming direct hominin ancestral lineages of hominins. My view is insufficient information to draw any conclusions as to direct hominin ancestry older than Lucy and Ardi. I also find reason to doubt scientific conclusions that too narrowly define species to reach their conclusions.

    Source: https://phys.org/news/2020-11-partial-left-femur-sahelanthropus-tchadensis.html



    Study of partial left femur suggests Sahelanthropus tchadensis was not a hominin after all


    by Bob Yirka , Phys.org
    Cast of the Sahelanthropus tchadensis holotype cranium TM 266-01-060-1, dubbed Toumaï, in facio-lateral view. Specimen of Anthropology Molecular and Imaging Synthesis of Toulouse. Credit: Didier Descouens/CC BY-SA 4.0
    A small team of researchers from France, Italy and the U.S., has found evidence that suggests Sahelanthropus tchadensis was not a hominin, and thus was not the earliest known human ancestor. In their paper published in Journal of Human Evolution, the group describes their study of the fossilized leg bone and what it showed them.

    Back in 2001, a CNAR team of four led by a Frenchman, Alain Beauvilain, and three Chadians, Adoum Mahamat, Djimdoumalbaye Ahounta, and Gongdibé Fanoné, discovered the fossilized remains of Sahelanthropus tchadensis at a site in the Djurab Desert in Chad. Subsequent study of the remains by Brunet and his team showed them to be between 6.8 and 7.2 million years old. They also found evidence indicating that the specimen walked upright and was therefore a hominin and a human ancestor. And because of the timeline, the find was described as the earliest known ancestor (prior to the find, "Lucy" was the earliest known ancestor—she had been dated back to approximately 3.2 million years ago.) The evidence the team reported depended mainly on the size of the teeth and marks on the back of the skull. After Brunet published a paper describing the team's findings, many in the field refused to recognize the work because it had been published in a journal that was not peer reviewed and he refused to allow access to the fossilized remains. In this new effort, the researchers claim to have found evidence suggesting that Sahelanthropus tchadensis did not walk upright and thus was not a hominin, but was instead an ape ancestor.

    © Copyright Original Source



    This article makes the claim of direct hominin ancestry:

    Source: https://phys.org/news/2022-08-sahelanthropus-oldest-humanity-bipedal.html



    Sahelanthropus, the oldest representative of humanity, was indeed bipedal


    by CNRS
    Left: 3D models of the postcranial material of Sahelanthropus tchadensis. From left to right: the femur, in posterior and medial view; the right and left ulnae, in anterior and lateral view. Right: Example of analysis performed to interpret the locomotor mode of Sahelanthropus tchadensis. 3D cortical thickness variation map for the femurs of (from left to right) Sahelanthropus, an extant human, a chimpanzee and a gorilla (in posterior view). This analysis enables us to understand the variations of mechanical constraints on the femur and to interpret these constraints in terms of locomotor mode. Credit: © Franck Guy / PALEVOPRIM / CNRS – University of Poitiers
    The acquisition of bipedalism is considered to be a decisive step in human evolution. Nevertheless, there is no consensus on its modalities and age, notably due to the lack of fossil remains. A research team, involving researchers from the CNRS, the University of Poitiers and their Chadian partners, examined three limb bones from the oldest human representative currently identified, Sahelanthropus tchadensis. Published in Nature on August 24, 2022, this study reinforces the idea of bipedalism being acquired very early in our history, at a time still associated with the ability to move on four limbs in trees.

    At 7 million years old, Sahelanthropus tchadensis is considered the oldest representative species of humanity. Its description dates back to 2001 when the Franco-Chadian Paleoanthropological Mission (MPFT) discovered the remains of several individuals at Toros-Menalla in the Djurab Desert (Chad), including a very well-preserved cranium. This cranium, and in particular the orientation and anterior position of the occipital foramen where the vertebral column is inserted, indicates a mode of locomotion on two legs, suggesting that it was capable of bipedalism.

    © Copyright Original Source


    Last edited by shunyadragon; 08-26-2022, 09:42 AM.
    Glendower: I can call spirits from the vasty deep.
    Hotspur: Why, so can I, or so can any man;
    But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

    go with the flow the river knows . . .

    Frank

    I do not know, therefore everything is in pencil.

  • #2
    "claiming direct hominin ancestral lineages of hominins" for fossils that old is at best a crap shoot. The odds are way too good that it could represent an evolutionary dead-end -- an offshoot -- rather than a direct descendant.

    Haven't we learned anything in the last few decades?

    I'm always still in trouble again

    "You're by far the worst poster on TWeb" and "TWeb's biggest liar" --starlight (the guy who says Stalin was a right-winger)
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    • #3
      Originally posted by rogue06 View Post
      "claiming direct hominin ancestral lineages of hominins" for fossils that old is at best a crap shoot. The odds are way too good that it could represent an evolutionary dead-end -- an offshoot -- rather than a direct descendant.

      Haven't we learned anything in the last few decades?
      I describe the problem as 'insufficient information' to draw conclusions, and emphasis focusing on the fossil evidence itself without artificially stretching the conclusions support an agenda. I have a yes/no/maybe concerning the conclusions of both articles.
      Glendower: I can call spirits from the vasty deep.
      Hotspur: Why, so can I, or so can any man;
      But will they come when you do call for them? Shakespeare’s Henry IV, Part 1, Act III:

      go with the flow the river knows . . .

      Frank

      I do not know, therefore everything is in pencil.

      Comment

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