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RE: Swimmin' dinos, fish milk, avian polyphyly (was RE: Sheesh)



The following message was bounced to me because listproc didn't
recognize the address.  Tony, please write to me directly if you want
me to do what I can to make sure that doesn't happen to you again...
And I hope you don't mind that I trimmed out some unnecessarily quoted
text.

-- MPR

--- Begin forwarded message

  Date: Wed, 25 Oct 2006 16:10:01 +0100
  From: Tony Canning <tony.canning@foe.co.uk>
  Subject: RE: Swimmin' dinos, fish milk, avian polyphyly (was RE: Sheesh)
  To: tholtz@umd.edu
  Cc: dinosaur@usc.edu

  At 8:55 AM -0400 10/25/06, Thomas R. Holtz, Jr. wrote:
  >
  > Here are a few thoughts on why the first group of dinosaurs to become
  > marine were hesperornithiforms:

  > 2) Mechanical constraints. The limbs of most dinosaurs were pretty 
  > tightly locked into parasagittal motions: great for striding, but not 
  > terribly good for swimming. Additionally, the major clades had 
  > mechanisms that tended to tighten up the flexibility of the dorsal
  >column (e.g., epaxial ossified tendons or hyposphene-hypantrum
  > articulations): again, great for striding, not so good for undulatory
  > locomotion.

  Are there any modern vertebrates that can't swim?  I have heard that
  camels can't swim, but I think that might be a myth.   But then again, I
  don't recall ever seeing a swimming camel.

  > 3) Physiological constraints. Okay, so this isn't really testable or
  > what have you, but just suggesting it...

  Not testable, but it may be significant that aquatic forms  have evolved
  repeatedly in both modern 'typical' endothermic and ectothermic
  amniotes; perhaps an intermediate condition such as inertial homeothermy
  simply wouldn't work as a starting point in the evolutionary return to
  water?   Not a strong argument, I know..

  > And as for fish milk: a gland that leaks liquid into another liquid 
  > might not be the best method of delivering nourishment. However, in a 
  > non-aqueous environment, glands already leaking liquid into air (e.g.,
  > sweat glands) might evolve, allowing for exaptation as a source of
  > nourishment.
  >
  > A.P. Hazen: the skin-feeding animal you are likely referring to (the 
  > one announced earlier this year) was a caecillian (a member of
  > Lissamphibia, the modern amphibians), not a fish. However, there might
  > well be skin-feeding fish for all I know.

  What about discus? See http://www.idiocentrism.com/milk.htm

  Regards
  Tony Canning
  -- 
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