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Re: Basicranial flexion

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  • Mario Petrinovich
    ... Yes. And they do have shock absorbing S-shaped necks (just like we have S-shaped backbone), and absorbing air sacks. But still, the impact is huge, and I
    Message 1 of 10 , May 1, 2006
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      Rob Dudman:
      > Bok, Mario.......

      : ))) Bok, Rob...

      > > What about basicranial flexion in plunge diving byrds?
      > > Anybody has any info? Backbone could push bones of skull.
      > > Although
      > > they dive bill first, not top of head first, like we do. And
      > > they do
      > > have very flexible, apsorbing necks. But maybe the push of
      > > backbone had some inpact on bones of skull of those birds.
      > >
      > Thanks for your response. At a guess I'd suggest that the over-
      > all
      > shape made by pointed beak, long slender neck and no shoulders,
      > breaks the water in much the same way as a spear-point and so
      > reduces the impact to a minimum. ---Rob.

      Yes. And they do have shock absorbing S-shaped necks (just
      like we have S-shaped backbone), and absorbing air sacks. But
      still, the impact is huge, and I guess they do need an off-center
      attachment point between backbone and skull. This attachment point
      could have some peculiarities. Although, the difference between
      weight of a bird and an ape also is huge, so it could be that
      peculiarities are greater in ape.
      Anyway, this is valid idea.
      Now, imagine this. We were the only animal in the position
      to have that shift (because we were the only heavy animal that
      plunge dives). This shift is responsible for our increased
      vocabularity (if this is the right expression). And we were in the
      right position (whole day floating in the sea), where we had the
      need for increased vocabularity. Next thing you know, we excange a
      lot of information between us, : ). -- Mario
    • strangetruther
      ... over- ... When birds dive like this, and gannets must be the supreme example, the idea is to get the neck as straight as possible so the stresses are taken
      Message 2 of 10 , May 14, 2006
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        --- In AAT@yahoogroups.com, "Mario Petrinovich"
        <mario.petrinovic1@...> wrote:
        >
        > Rob Dudman:
        > > Bok, Mario.......
        >
        > : ))) Bok, Rob...
        >
        > > > What about basicranial flexion in plunge diving byrds?
        > > > Anybody has any info? Backbone could push bones of skull.
        > > > Although
        > > > they dive bill first, not top of head first, like we do. And
        > > > they do
        > > > have very flexible, apsorbing necks. But maybe the push of
        > > > backbone had some inpact on bones of skull of those birds.
        > > >
        > > Thanks for your response. At a guess I'd suggest that the
        over-
        > > all
        > > shape made by pointed beak, long slender neck and no shoulders,
        > > breaks the water in much the same way as a spear-point and so
        > > reduces the impact to a minimum. ---Rob.
        >
        > Yes. And they do have shock absorbing S-shaped necks (just
        > like we have S-shaped backbone), and absorbing air sacks. But
        > still, the impact is huge, and I guess they do need an off-center
        > attachment point between backbone and skull. This attachment point
        > could have some peculiarities. Although, the difference between
        > weight of a bird and an ape also is huge, so it could be that
        > peculiarities are greater in ape.
        > Anyway, this is valid idea.
        > Now, imagine this. We were the only animal in the position
        > to have that shift (because we were the only heavy animal that
        > plunge dives). This shift is responsible for our increased
        > vocabularity (if this is the right expression). And we were in the
        > right position (whole day floating in the sea), where we had the
        > need for increased vocabularity. Next thing you know, we excange a
        > lot of information between us, : ). -- Mario
        >

        When birds dive like this, and gannets must be the supreme example,
        the idea is to get the neck as straight as possible so the stresses
        are taken by lognitudinal pressure straight down the cervical
        column, rather than asking the muscles to do it, which would require
        very fast changes as the load was suddenly experienced. There would
        be little cushioning benefit since anything the head could cope with
        the rest of the body could. It's not like cushioning in the leg
        joints to protect the higher sections from shocks the foot has to
        endure.

        I doubt if an S-shape in any part of the backbone in humans was
        caused by evolutionary pressure by headfirst diving; on the rare
        occasions when they did plunge in, they'd probably go in bum-first.

        Cordially, and "Hello list",


        Strangetruther
      • Marc Verhaegen
        ... Most of the time, yes, I think you re right: see sea gypsies etc. ... Welcome, Strangetruther. --Marc
        Message 3 of 10 , May 21, 2006
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          > > > > What about basicranial flexion in plunge diving byrds?
          > > > > Anybody has any info? Backbone could push bones of skull.
          > > > > Although
          > > > > they dive bill first, not top of head first, like we do. And
          > > > > they do
          > > > > have very flexible, apsorbing necks. But maybe the push of
          > > > > backbone had some inpact on bones of skull of those birds.

          > > > Thanks for your response. At a guess I'd suggest that the
          > over-
          > > > all
          > > > shape made by pointed beak, long slender neck and no shoulders,
          > > > breaks the water in much the same way as a spear-point and so
          > > > reduces the impact to a minimum. ---Rob.

          > > Yes. And they do have shock absorbing S-shaped necks (just
          > > like we have S-shaped backbone), and absorbing air sacks. But
          > > still, the impact is huge, and I guess they do need an off-center
          > > attachment point between backbone and skull. This attachment point
          > > could have some peculiarities. Although, the difference between
          > > weight of a bird and an ape also is huge, so it could be that
          > > peculiarities are greater in ape.
          > > Anyway, this is valid idea.
          > > Now, imagine this. We were the only animal in the position
          > > to have that shift (because we were the only heavy animal that
          > > plunge dives). This shift is responsible for our increased
          > > vocabularity (if this is the right expression). And we were in the
          > > right position (whole day floating in the sea), where we had the
          > > need for increased vocabularity. Next thing you know, we excange a
          > > lot of information between us, : ). -- Mario

          > When birds dive like this, and gannets must be the supreme example,
          > the idea is to get the neck as straight as possible so the stresses
          > are taken by lognitudinal pressure straight down the cervical
          > column, rather than asking the muscles to do it, which would require
          > very fast changes as the load was suddenly experienced. There would
          > be little cushioning benefit since anything the head could cope with
          > the rest of the body could. It's not like cushioning in the leg
          > joints to protect the higher sections from shocks the foot has to
          > endure.
          > I doubt if an S-shape in any part of the backbone in humans was
          > caused by evolutionary pressure by headfirst diving; on the rare
          > occasions when they did plunge in, they'd probably go in bum-first.

          Most of the time, yes, I think you're right: see sea gypsies etc.

          > Cordially, and "Hello list",

          Welcome, Strangetruther.

          --Marc
        • Marc Verhaegen
          Basicranial flexion in the evolution of Homo: new analyses of an old model M Bastir, A Rosas, C Stringer, JM de la Cuétara, R Kruszynski, CF Ross & MJ Ravosa
          Message 4 of 10 , Feb 3, 2009
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            Basicranial flexion in the evolution of Homo: new analyses of an old model

            M Bastir, A Rosas, C Stringer, JM de la Cuétara, R Kruszynski, CF Ross & MJ
            Ravosa 2009 AAPA abstracts

            Understanding variation in the basicranium is of central importance to
            paleoanthropology because of its fundamental structural role in skull
            development and evolution. At the beginning of the 20th century it was
            suggested that encephalisation plays a role in producing flexion between
            midline basicranial elements. It has been proposed that basicranial flexion
            is also influenced by the size or shape of the face. This hypothesis was
            further refined during the 1950s by the Swiss anatomist Biegert, who
            suggested that brain size and facial size act as antagonists on basicranial
            flexion. Biegert¹s model is particularly relevant for understanding aspects
            of Neanderthal skull evolution because one important and unresolved problem
            is that these large-brained hominins have slightly less flexed basicrania
            than equally large-brained modern humans. We addressed this hypothesis by
            applying geometric morphometrics to a large comparative dataset of
            radiographic and/or CT images of adult non-human primates, hominin fossils
            and humans (29 species, 142 individuals). Multiple, multivariate regression
            and thin plate splines analyses suggest that basicranial evolution is highly
            significantly influenced by both brain size and face size. Our data show
            that in addition to brain size, the prime factor of basicranial evolution in
            Homo, facial size importantly influences basicranial morphology and
            orientation. These interactions can explain why, despite their similar brain
            sizes, Neanderthals as well as some Mid-Pleistocene humans have less flexed
            cranial bases than modern humans. To gain a detailed understanding of the
            multifactorial inputs into basicranial flexion, future studies should also
            focus on the underlying factors of facial size evolution.

            _____

            Biegert : CC & facial size act as antagonists on BCF?
            - large CC = high BCF
            - large face = small BCF

            Hn have slightly less BCF < Hs.

            IMO this problem is not so difficult:
            - BCF in Hs = when standing/walking vertically, our face is oriented less
            upward, more downward, to where we're going,
            - less BCF in Hn = when swimming horizontally, their face was directed less
            downward than it had been in Hs, more upward, to where they were swimming.

            The flat skull, the heavy supra-orbital torus (protecting the more
            anteriorly placed eyes), the slightly more dorsal foramen magnum in archaic
            Homo (He>Hn) are all adaptations to looking forward in more pronograde He-Hn
            (swimming, vs.orthogradely walking Hs).
            In He-Hn the eyes are placed +-before the brain skull (therefore a heavy
            torus is needed), in Hs +-under the brain skull (no torus any more: our eyes
            are proteced by the brain skull).

            --Marc
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