Re: Exaptation

[Robert.J.Meyerson@uwrf.edu (Rob Meyerson)]

>>Here's an alternative scenario:
>>
>>Birds are the volant ancestors of nonflying coelurosaurs.
>
>What, have I converted you? :-)

Not necessarily.  One can say that the dromeys and _Archaeopterix_ both have=
 a common ancestor.

Here's another possibility: Archy is only known from Solnhofen sediments, no=
 terrestrial ones.  Now in a terrestrial sediment, only the toughest parts=
 of the animal will survive (usually teeth, which are helpful if we're=
 talking mammals, but a nightmare with reptiles).  What if there were quite=
 a few of these small theropods running around then; quite a few may have=
 been arboreal too (yes, I have been convinced on this point;-).  Now, just=
 as with all the squirell (sp) species, there is only one (relatively)=
 flying member.  What if the dromey line evolved from one of the arboreal,=
 non-flying, theropods.  I still like the idea of the enlarged claw in this=
 group used for climbing trees, and later exapted for a killing claw.

My biggest reservation for BCF is the unlikelyhood of the events. =
 Essentially, what is being said is that an animal gains the power of=
 flight, then gives it up again.  What's the adaptive value in that???  I=
 mean, no one talks about secondarily flightless pterosaurs.  Once theropods=
 learned to fly, a whole new set of niches opened up for exploitation, and=
 it seems to me that the wouldn't be able to reverse the trend until the=
 evolutionary momentum had run down.  Evolution may be random usually; but=
 once a trend has started, the group is usually committed to that trend to=
 the end.

Your turn!

Rob

***
"Don't panic!"