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Re: Impacts and ETs



John Bois (jbois@umd5.umd.edu) wrote:

<For an egg layer, the longer one tends a nest in one location, the longer
that nest is at risk.  This provides a pressure to vacate. And, after
hatching, a long period of precociality adds even more of the same
pressure.  Hatchlings that fly or run immediately must be under the same
developmental pressure as marsupials, i.e., physiological choices favoring
locomotion/coordination must be made. I think this leaves archosaurs with
only one option: develop safety and ontological leisure time _in utero_. I
know we've talked about this before...but I can't remember why--or if
there are good hypotheses--why this was not done as far as we know in
archosaurs.  The one I do remember goes like this: lizards and other
_small_ reptiles have evolved similar structures independently and
repeatedly.  But archosaurs were too big (i.e., small populations/slow
evoltionary rates) to create such a revolutionary structure (meaning, a
structure which would have to have so many physiological factors
changing).>

  Then there is this reason, which is grounded in extant biology:

  http://dml.cmnh.org/2004Jul/msg00350.html

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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