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Re: Question on glide reflections in Ediacaran biota



On Wed, Sep 19, 2012 at 7:41 PM, Erik Boehm <erikboehm07@yahoo.com> wrote:
> I've seen that many Ediacaran biota are described as having a glide 
> reflection (Spriggina, Pteridinium, Dickinsonia for example) - yet the 
> pictures I see of the fossils are (in my opinion) inconclusive.
> Can anyone comment on this or provide clear photographs conclusively showing 
> this?
>
> I am unsure how to interpret this. If these disparate forms all share glide 
> reflections, then it seems that one should conclude they are monophyletic.
>
> Spriggina has been compared to a proto-worm-arthropod - yet I can't see how 
> it fits in with this if it really does have a glide reflection symmetry.
> Perhaps "glide-reflection" forms later evolved true bilateral symmetry? but 
> then:
>
> If you have Kimberella as a Mollusk, and Arkarua as a echinoderm (assuming 
> these are valid), then bilateria was already around for a while by this 
> point, and it seems unlikely that a creature such as Sprigginia with 
> glide-reflection independently evolved true bilateral symmetry before leading 
> to the ecdysozoa clade. (this would also imply that bilateral symmetry in 
> Deuterostomes was independently evolved, which isn't so hard to believe, but 
> we'd also need to postulate it independently evolved in Lophotrochozoa)
> - Or we coud just write off Sprigginia as a dead end, but then we'd be 
> missing a precambrian antecedent to the arthropods in the cambrian.
>
> It would simplify things if this "glide reflection" stuff could be discounted 
> (and also make the Cambrian explosion look like less of an explosion).
>
> Ok, its not dino related, but I assume anything Paleontology related goes, 
> right?

Dinos are deuterostomes, so clearly it's dino related!

-- 
Andreas Johansson

Why can't you be a non-conformist just like everybody else?