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Re: New alvarezsaurid
>> 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
>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
>wings and a small beak suits you. However if big toothy snouts and
>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
>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
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;
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.
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