Re: NO SECONDARILY FLIGHTLESS THEROPODS

["Matthew Troutman" <m_troutman@hotmail.com>]

<<You are talking about how birds of a >modern< aspect might evolve into 
flightless forms. This is not particularly relevant to how birds of a 
very primitive< aspect--having elongate tails, hind limbs powered by 
extensive caudal musculature, and grasping forelimbs doing double duty 
as not particularly efficient wings--might have evolved into flightless 
forms. The fundamental bauplan of an avialan bird is quite different 
from the fundamental bauplan of an early dino-bird, and one may 
reasonably expect that flightlessness would evolve through a different 
mechanism in birds of a modern aspect from that in dino-birds. The only 
thing that remains relevant is that flightlessness among birds of any 
kind occurs much more frequently than the
opposite.>>

I do not see why a more " primitive " species cannot evolve 
flightlessness in the same way that modern species do. Let's look at 
phorusrhacids, they had functional forelimbs and they appear to have 
lost flight through paedomorphosis. Now, the bauplans are not that 
different, even though they had functional forelimbs does not disprove 
my point. There are few examples where a volant bird does not lose 
flight through paedomorphic characters. The bauplan of "dinobirds" such 
as dromaeosaurs is not as different as you state. There is a shift in 
the caudal and hindlimb musclature in maniraptoriformes that makes it 
rather birdlike. Varying birds of varying behaviors and morphologies all 
evolved birds through paedomorphosis. 

<<Here you are excluding from the discussion an example of the evolution 
of flightlessness that evidently does not conform to your idea that 
flightlessness appears through paedomorphosis--indeed, an example that 
contradicts your thesis that avian flightlessness evolves exclusively 
through paedomorphosis. Obviously, penguins don't fly; they have evolved 
from previously flying forms into forms that swim through water. 
Likewise, theropods didn't fly; they evolved from previously flying 
forms into forms that walked, ran, and hunted on the ground.>>

     But, my point was, these birds are essentially still fliers. They 
use their forelimbs for " flying " through water. Their forelimb and 
pectoral musclature is enlarged to a point even above flighted birds.

>What you are saying is, all birds that have become flightless through
>paedomorphosis have become flightless through paedomorphosis.
>

    Yes.


MattTroutman

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