Re: NO SECONDARILY FLIGHTLESS THEROPODS

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

><< I do not see why a more " primitive " species cannot evolve 
> flightlessness in the same way that modern species do. >>

<<They may, or they may not; they're certainly not >obliged< to. By the 
way, I find your posts on paedomorphosis in the evolution of 
flightlessness quite interesting. Please keep them coming; you have a 
good command of the material.>> 

Thanks for your interest and the compliment.


But, there is a possibilty that they _are_ obliged to. Now among 
vertebrates that fly, as far as is known, only birds have become 
flightless. What makes them special in this regard? The answer is rather 
obvious : birds are an extremely adaptable group of vertebrates that are 
able of equal locomotion on ground, sea, or air. But, even some birds 
that live on ground or in the sea do not show progressive trends toward 
flightlessness. The factor which turns a bird flightless is 
paedomorphosis which makes the forelimbs vestigilize, feathers 
degenerate, and the bird to stay a chick the rest of its life. 
Paedomorphosis is simply the factor which makes a bird flightless and 
which may be the only factor which makes a bird flightless. Roadrunners 
are cuckoos ( Cuculiformes ), they were once arboreal as shown by their 
zygodactyl foot, now they are teresstrial cursors. They fly little 
compared to other birds but they are not flightless, they show hardly 
any trends toward flightlessness. Chickens are another good example, 
though slightly different. Chickens do not fly that much, hence their 
white breast muscles, however they are showing a few trends toward 
flightlessness that can be linked to paedomorphosis. The shortening of 
the forelimbs, increased massiveness and robustness of the vertebrae, 
and unfused tarsometatarsus ( in the Dorking fowl ), show that 
paedomorphosis is taking place. Chickens are a good example of how 
paedomorphosis and isolation can effect a bird to where it can become 
flightlessness. 

Now, it seems that paedomorphosis is the only way that birds become 
flightless. Why they become flightless by this way is somewhat easy. 
It's the easiest way to become flightless and possibly the only way. 
What other factors do we have? Not using the forelimbs is one way. The 
fault of this hypothesis is:

1) There are no other selective factors that can explain the extreme 
vestigilization of the forelimbs.

Other than that factor there are few other factors which can adequately 
explain how a volant animal will go flightless. 

Before somebody brings up the "penguins didn't go flightless through 
paedomorphosis" issue, let me adress this issue. As outlined by 
Feduccia, the evolution of penguins can be explored through a 
pseudo-phylogeny. The first stage would be be a petrel-like creature 
that would fly around water. Soon the animal would start to dive into 
water and use its wings for underwater and submarine flight as shown by 
diving petrels. Soon the animal would use its wings only for submarine 
flight. Essentially the animal would be an underwater flier, not an 
aerial flier, but essentially the same thing. ( The actual idea of the 
pseudo-phylogeny was made by Storer but I haven't read that paper yet). 

Hope this will settle this issue ( unless any other questions or 
rebuttals are in line ),

MattTroutman

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