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RE: Question on glide reflections in Ediacaran biota
> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of
> Erik Boehm
> Subject: Question on glide reflections in Ediacaran biota
> I've seen that many Ediacaran biota are described as having a glide
> reflection (Spriggina, Pteridinium, Dickinsonia for example) -
> the pictures I see of the fossils are (in my opinion) inconclusive.
> Can anyone comment on this or provide clear photographs conclusively showing
> I am unsure how to interpret this. If these disparate forms all share glide
> reflections, then it seems that one should conclude
> 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
> Perhaps "glide-reflection" forms later evolved true bilateral symmetry? but
> If you have Kimberella as a Mollusk, and Arkarua as a echinoderm (assuming
> these are valid), then bilateria was already around for
> while by this point, and it seems unlikely that a creature such as Sprigginia
> with glide-reflection independently evolved true
> 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
Chances that Sprigginia is a stem-arthropod are near nil: it's wishful thinking.
And don't forget: most non-panarthropod ecydozoans are microscopic. What makes
you think that stem-ecdysozoans would be big enough
to fossilize in coarse sandstones?
> It would simplify things if this "glide reflection" stuff could be discounted
> (and also make the Cambrian explosion look like less
> Ok, its not dino related, but I assume anything Paleontology related goes,
Glide reflection is unquestionably real in some of these! I had to trace out
specimens in class in grad school!
Must read literature on Ediacaran biota (our modern understanding thereof):
http://wuos.org/content/334/6059/1091.short (especially the supplementary
Thomas R. Holtz, Jr.
Email: email@example.com Phone: 301-405-4084
Office: Centreville 1216
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Faculty Director, Science & Global Change Program, College Park Scholars
Mailing Address: Thomas R. Holtz, Jr.
Department of Geology
Building 237, Room 1117
University of Maryland
College Park, MD 20742 USA