Re: Paedomorphosis ( Re: BARYONYX' CLAWS )

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

Matt Troutman ( me ) wrote:

<< Au contaire! Many ornithologists ( Feduccia, Olson ) have speculated  
along these lines, and lets just face it, all of the flightless  
characteristics seen in flightless birds are paedomorphic 
characteristics. >>

Dinogeorge rebuttal:

>Except, as you have previously noted, in penguins and auks.

    OK. As I have said at least 3 times on and off list; penguins and 
auks never really became flightless!!! It is true that aerial flight is 
gone, but they still "fly" underwater. In both penguins and auks the 
forelimbs still have the same motions and basic functions as aerial 
fliers. Now, though they came from different ancestors, the two appear 
to have undergone their transformation in the same way. For penguins you 
can use a pseudo-phylogeny to trace the conditions of which they 
acquired their lifestyle:

1) Petrels that live near the open seas and use their wings for aerial 
flight only.
2) Diving petrels that use their wings for both aquatic and aerial 
flight.
3) Penguins which use their wings for underwater flight only.

You can do the same with auks:

1) Gulls that live near the seas and use their wings for aerial flight 
only. 
2) The razorbills use their wings for both aerial and submarine flight.
3) Auks that use their wings for submarine flight only. 

Go to your local zoo and go observe penguins "fly" underwater. They look 
like flying birds. So you can see, penguins and auks ( and the extinct 
plotopterid pelecans ) are still fliers and never really went 
flightless. Comprende?

Dinogeorge rambles on:

<<Certainly paedomorphosis--which I might describe as the "Baby Huey" 
mechanism--is doubtless the >easiest< path for a modern avian to develop 
flightlessness: the chicks simply don't develop their wings and just get 
bigger. It might even be the case that flightlessness in Triassic 
theropods developed through paedomorphosis. For example, the giant 
skulls of carnosaurs and other large theropods seems as if it might be a 
juvenile feature. Who knows? We certainly don't have enough information 
about hatchling and juvenile Triassic theropods to reject a paedomorphic 
origin for flightlessness that far back in theropod evolution.>>

     We cannot know anything about Triassic theropods because the 
evidence is too sparse. Regardless, the features would still show up: 
ratites have been flightless for at least 50 million years and they 
haven't lost their flightless characteristics. The giant skulls of the 
giant theropods are not a secondarily flightless characteristic. Now if 
they all had huge eyes, short preorbital regions ( short snouts ), 
almost complete lack of bone fusion even in fully grown adults, and 
massive, thick walled, and disproportionate hindlimbs then I would 
concede that maybe they were secondarily flightless. The features of 
flightless birds stay consistent even after long periods of times, and 
there is no reason for this to be untrue in theropods. 

Dinogeorge:

<<But to state that paedomorphosis is the >only< way that flightlessness 
>can< evolve is dogmatic, and is contradicted by your own example of 
penguins.>>

     Increasingly, it appears that paedomorphosis is the only reason 
that flightlessness did evolve in birds, because all the features that 
are seen in flightless birds ( keel-less sternum, juvenile plumage, 
atrophied forelimbs, large eyes, open ilioischiatic foramen, 
thick-walled pelvis, degeneration of the pygostyle, obtuse 
scapulacoracoid angle, complete unfusion, and lowered basal metabolic 
rate ) can be traced to paedomorphosis. Feduccia also notes that in zoo 
birds where the flight apparatus is artificially immobilized, the 
surrounding bones exhibit bizarre and extensive lesions. This type of 
pathology is not congruent with the "wings disuse" theory of secondary 
flightlessness, so paedomorphosis looks more attractive. And check above 
for why penguins never really went flightless.

MattTroutman

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