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Re: Exaptation



>In a posting dated 12-18-95 Dr. Holtz says:
>>"Exaptation": formerly 'preadaptation'.  The adoption of a previously
>>existing evolutionary character into a new use.  For example, the
>>bones of
>>vertebrates (ancestrally for mineral storage) were exapted into
>>locomotory
>>structures by the ancestral sarcopterygians.
>
>Out of curiosity please give details about bones being exaptated for
>locomotion from storage sites.  That is if this is not tooo much of a
>divergence from dinosaurs.  :-)  TR

In the short form: "bones" in the sense of the structural units of the
skeleton are primitively cartilage, and in this form seem to do very well in
terms as support in the water.  The osteichthyes (bony fish) ossified these
cartiliginous structure, but there is no strong evidence that this is to
strenghten the skeleton of the fish.

As most of you (hopefully) known, there is more to bone than being the hard
parts of vertebrate anatomy.  There are also the storage sites in the body
for many "salts" (calcium, potassium, etc.), which are occasionally
dissolved out of the bone for use in metabolism.

It appears that this mineral storage feature is the primitive use for
bones.  As sarcopterygians began using their limbs as legs, and later when
basal tetrapods were crawlling around on the ground, the "bony" bones were
exapted for the uses we associate with them: locomotion and so on.

Hope this helps,

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084