Re: New alvarezsaurid

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

>> Paedomorphic changes are always seen with the loss of flight . <
>
>. . . except in certain flightless maniraptorans  . . .
>
> . . . when their  non-paedomorphic-ness is taken as circular evidence 
of
>never having flown.

    It can be used as evidence toward those lines, yes.

> Paedomrphism is one way of evolving flightlessness, and a good way if 
small
>wings and a small beak suits you.  However if big toothy snouts and 
strong
>real arms are needed, some other mutation would be preferable.

    Actually, as far as is known in Recent times, it is the only way 
that has been convincably shown to work. The example of " big toothy 
snouts and a strong real arms are needed " is even not applicable for 
phorusrhacids, whose "arms" are simply modified wings. For a real 
telling example along these lines, the phorusrhacid forelimb is refined 
to a point for predation that is not seen in theropods.

>Where is it *written* that paedomorphic changes are always seen with 
the
>loss of flight ?

    Before I list the vast, vast list of publications ( doesn't it seem 
I'm making a lot of lists lately?) let me tell everyone the scoop on 
this story. Paedomorphosis is the retention of juvenile characteristics 
and is seen in all known flightless birds. The large orbit, vestigal 
forelimbs, increased robustness of the hindlimbs, degeneration of the 
furcula, loss of pygostyle, and other consistently seen characters in 
flightless birds can be linked to paedomorphosis. Now, one can site 
experiments where the development was disabled and the chicks of that 
species resembled flightless birds. So, it seems that flightlessness is 
linked with paedomorphosis very deeply. Paedomorphosis is usually taken 
to selective advantage when a bird is isolated, either geographically or 
ecologically. Isolation and paedomorphosis are usually linked closely 
together. Though I doubt that all instances of flightlessness are always 
linked with isloation, the taking of unoccupied ecological niches is 
another reason for flightlessness, though not as much as isolation. The 
problem for both of these causes is that there seems to be few cases of 
possible isolation in the Mesozoic except in the late K when there were 
more islands. And for ecological niches, the evidence has not been 
gathered yet.

 Well enough ranting, here's the list:

Dawson et al. 1994. Ratite-like neoteny induced by neonatal 
thyroiddectomy of European starlings, Sturnus vulgaris. Journal of 
Zoology 232; 633-639.

Olson, Storrs L. 1973. Evolution of the rails of the South American 
islands ( Aves: Rallidae ). Smithsonian Contributions to Zoology 152; 
1-53.

Olson, Storrs L. and James, H.F. 1991. Descriptions of thirty-two new 
species of birds from the Hawaiian Islands. Part I. Non-passeriformes. 
Ornithological Monographs. 45: 1-88.

And check out Feduccia's book for excellent review of these papers and 
expansion of these even more.


MattTroutman


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