Re: Archaeopteryx and Flight

[NCLARK@museum.gla.ac.uk]

Reply to Stan's comments,

>From: NEIL CLARK <NCLARK@museum.gla.ac.uk>
 > 
 > Why?  Why should there have been any evolutionary pressure to 
 > develop flight at all? 

> Well, to start with, flight is metabolically expensive.
> So expensive that it is often *lost* in island species.

This may be so, but 'hopeful monsters' could easily have been an extreme 
morphological varient of primitive feathered 'birds' that were able to take 
advantage of an enironment in which competition was minimal.  The 
non-flighted feathered varients may have been under greater competition from 
other terrestrial animals.  So in this sense metabolic considerations may 
have been outweighed by other factors.  The fact that flight has been *lost* 
in island species may be more to do with the lack of terrestrial based 
competition that allows the non-flighted varients (which may be genetically 
dominant) to become the sole form.  The islands may not have large enough 
populations to allow enough (if any) flighted varients from becoming 
re-established.

 > Within the range of intraspecific variation, there 
 > may have been an extreme morph that allowed for flight.  Due to the 
 > lack of competition in this area, the morph was able to alienate itself 
 > further from the non-flighted morphs especially after the demise of the 
 > pterosaurs. 

> Pterosaurs did not start to decline until *after* birds evolved.
> In fact it is reasonable to conclude that it was competition with
> birds that gradually eliminated most pterosaur groups.
> [The last pterosaur groups, in the Late Cretaceous, were very
> specialized, and invariably large - all of the small, generalized
> insectivorous types had died out by then].

Yes, birds had evolved a number of forms, some flighted and some not, before 
the demise of the pterosaurs, but it may not have been competition with 
birds that caused their demise.  The specialisation of the pterosaurs may 
hae been the cause of their downfall at a time when birds were perhaps more 
generalistic and opportunistic.


Happy New Year :-)


Neil Clark
Curator of Palaeontology
Hunterian Museum
University of Glasgow
email: NCLARK@museum.gla.ac.uk

Mountains are found in erogenous zones.
(Geological Howlers - ed. WDI Rolfe)