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Re: Campbell's even crazier than a MANIAC? (archeopteryx climbing)



-- On Fri, 9/26/08, Michael Habib <mhabib5@jhmi.edu> wrote:

> > It (gliding+flapping) is only viable if there are no
> flappers around 
> > that can glide whenever they want to.
> 
> Why not?  Yes, clearly competitive exclusion can be
> powerful, but do we 
> really expect that the simple existence of powered flyers
> should 
> completely shut down gliders with limited powered ability? 

Yes, I do. I take the lack of "gliders with limited powered ability" as implied 
support for this assumption. It is also worth noting that the 'transitional' 
animals you describe would be unlikely to remain in such a state for long (on 
evolutionary time scales).

> And if so, then that would seem to argue against a gliding
> stage in 
> almost every group of flyers - only insects evolved flight
> in the 
> absence of other flying animals.  We might argue that
> pterosaurs had 
> sufficiently small overlap in body size with insects that
> they did the 
> same, 

Definitely. Insects did provide a ready source of food, though.

> but birds and bats certainly both appeared in the
> presence of 
> pre-existing powered flyers. 

I think it is a safe assumption that they were not faced w/ the competitive 
barriers modern-day putative transitionals would have to overcome, from the 
perspective of niche specialization. Also, mere global presence does not imply 
local competition. E.g., the feathers of basal birds could have allowed 
exploitation of thermal regimes not suited for rhamphorhynchnids.

> But many of the pure gliders alive today compete for food
> with powered 
> flyers, as it is.  

Hmmm. Might account for their relative rarity. Of course, pure gliders are MUCH 
more numerous than incipient "ground-up" animals.

> > So I continue to maintain that the obvious
> "terrestrial-ness" of 
> > Archaeopteryx, et al, is not necessarily key to the
> gravity vs muscle 
> > power debate.
> 
> That may be true.  I'm not sure I'd frame a
> separation between gravity 
> and muscle power usage, however.  Even in those groups
> where arboreal 
> stages have been critical to the origin of flight, it is
> quite likely 
> that powered leaps were involved - there is no reason to
> assume that 
> flight evolution needs to be begin with simple falls
> (especially for a 
> group such as birds, which inherited a strong leaping
> apparatus).  

My apologies, perhaps I was momentarily unclear. I define an animal leaping of 
a high place as 'gravity-driven', and do not restrict the term to animals that 
simply let go.

I think the dichotomy holds for the first step, which I define as attaining a 
'glide ratio' over 1. Certainly any number of subsequent 
lifestyles/combinations can occur, as we all have theorized.

Don