[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: pterosaurs, bats, flying theropods



Stephan Pickering (stefanpickering2002@yahoo.com) wrote:

<REPLY: actually, what we are seeking, as paleobiological scholars, are
not "miracle specimens" (a meaningless phrase), nor "the special fossil 
that will confirm everything we are preconceived about regard[ing] bat
evolution".>

  I think a lack of clarity on my part for use of "miracle" has resulted
in this confusion. I consider *Archaeopteryx* both a morphological and
historical "miracle specimen", in that it upset the natural order and
bound two different groups into an evolutionary concept. The original bat
would be one such specimen in that it would tie in the morphological
ancestry of the group.

<REPLY: this, too, is a hodge-podge of non-sequitur sentences, filler
space as newspaper editors call it.>

  I'm sorry it didn't cross the palate of some folk. This was a discussion
on the issue of bats and their morphological/molecuylar evolution and
concepts of ancestry and origins. I considered them _very_ sequituur. I am
loathe, often, to post a variety of sub-subjects in different posts,
especially given long discussions where I can cover a variety of concepts
in a single post.

<Molecular dating is an evolving technique, and the paleobiologists who
have written papers on its applicability to specific lineages have not, to
my knowledge, used dating to pinpoint evolvability of clades. A clade will
"enjoy" stasis for a period of time, and analysing this (molecular dating
will provide one with indications, parameters of deductions) can be done
with tracking of habitat (Niles Eldredge), evolutionary constraints on
subdivided populations (B.S. Lieberman), selections within clades
normalized (George Williams), etc.>

  How can you state that _lineages_ can enjoy any stasis if you, Stephan,
know of no work on the evolvability of these lineages? This seems to
contradict itself, but that is not really important. A lineage has no
absolute constraint on its evolution; constraints must be external to the
nucleotide sequence itself, if by environment, another nucleotide sequence
by ancestry, etc.

<"Gene evolution": what do you mean by this vague souvenir from an echo
chamber?.>

  Uhm, there is a healthy literature on genetic evolution by
transformations of genes and gene sequences. I suggest you, Stephan,
follow this up through the sources of _Nature_, _Science_, _Systematic
Biology_, and _Proceedings of the National Academy of Sciences,
Philadephia_. Vague souvenir ... that's funny.

<Genomic changes on fitness landscapes indeed transpire at different
rates, at different times, and molecular dating as a tool of phylogenetic
extrapolations is cognizant of this.>

  I suggest you actually look at _genetic evolution_, not on ecology or
systematic research, if you want to explore the nature of evolution. The
latest book by Ernst Mayr, _What Evolution Is_, is a wonderful discussion
from a genetic evolutionary scientist who has taut several molecular
scientists.

  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)

__________________________________________________
Do you Yahoo!?
Yahoo! Mail Plus - Powerful. Affordable. Sign up now.
http://mailplus.yahoo.com