Instances of divergence of intermediate developmental stage, conserving later form?

Discussion in 'Biology & Genetics' started by Buckaroo Banzai, Jan 26, 2015.

  1. Buckaroo Banzai Mentat Registered Senior Member

    Somewhat like the very early stages of embryos can be "radically" different (well, at least inasmuch a blob of nearly undifferentiated cells can differ in shape from another, I think), but converge later on -- but on not-so-early stages, and specially with evolutionary novelties in-between.

    Also somewhat like (and more like) caterpillars are extended larval stages, and some other insects can almost "skip" the larval stage altogether, at least in the sense that they won't be "autonomous" larvae, but will hatch as "mini-adults" or something like it. That happens while butterfiles and moths didn't "evolve from catterpillars", but had this developmental stage stretched for some reason. (By the way, what came first, autonomous larvae or insects that hatch as "mini-adults"?)

    Is this sort of thing a possibility still held in a non-pseudo-scientific manner by some, regarding the evolution of feathers? That is, the possibility that feathers evolved originally as stretched weird scales, but later on a different developmental pattern evolved, but resulting in the same final phenotype? I know that the notion of a sequential conservation of developmental stages, and of feathers as a complete evolutionary novelty is the favored one, but I recall having read a somewhat "recent" (published after Prum's and Brush's theory) paper that suggested something along these lines, if I recall. I also recall something somewhat related (maybe from Prum and Brush themselves)), that even though downy feathers would naturally be thought as something more primitive and ancestral, due to their simpler final phenotype, the're actually developmentally more "advanced", or just as advanced, and can't be seen as an ancestral form of flight or contour feathers (even if nestlings are downy first, it's not a Haeckelian recapitulation thing).

    Scientists sometimes tweak these developmental stages and things like that, like preventing feathers from forming or inducing feathers to form in place of the "ancestral" not-totally homologous scale type. Perhaps some of such tweaks results in feather-ish malformed scales (or scale-ish malformed feathers) that skip the normal feather developmental stages? I recall something along these lines, but except from a photo of an "weird" thing, malformed feather or scale, there was no explanation of how it compared with one or another, structurally or developmentally.

    I'm not trying to "defend my theory" here or anything like that, I don't really care either way, I'm just curious about the possibility, even if somewhat fringe/less favored (if still not "wacko"), of that alternative evolutionary origin. But even though that's the trigger of the question, I think it's an interesting question even in this broader sense, that may include then insects, amphibians, plants, whatever.
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  3. Buckaroo Banzai Mentat Registered Senior Member

    It seems it's too late to edit the post, so I'll put this addition by itself. From "Avian Skin Development and the Evolutionary Origin of Feathers", by

    This finding seems to put into question the regular pattern of feather development as a fundamental hierarchical constraint, even though nothing there favors a "classic" notion of feathers deriving from elongated scales either (or at least elongated scales such as those seen in other reptiles, rather than an hypothetical elongated/weird scutate).

    It's however suggested that bird scales are actually derived from feathers and not vice-versa, even though they still would be homologous to some degree with crocodillian scutate.
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  5. GeoffP Caput gerat lupinum Valued Senior Member

    The answer is: yeah, a bit. The problem - because there always is one - is that idiots unacquainted with the concept of partial variance functions claimed absolute or predominance of the phenomenon, which is absurd in either direction.
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  7. Buckaroo Banzai Mentat Registered Senior Member

    333 lost me. Can you please give examples of the reasonable instances of the phenomenon, and cite those who are are claiming predominance, specially in the "direction" of divergence of an intermediate developmental stage, followed by a "return to the original path" and "destination" at a later stage?
    Last edited: Jan 27, 2015

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