Re: selective paedomorphosis

[Ronald Orenstein <ornstn@inforamp.net>]

At 02:50 PM 11/04/98 +0000, you wrote:
>Sorry gang, I'm  having trouble with the idea of massive legs and tiny
>snouts as paedmorphic traits in avians/non-avian theropods/whatever. 
>>>From what (little, admittedly) I've seen of hatchlings, etc., the head
>is HUGE (which seems very far indeed from the case in ratites), the
>beak is small only in proportion to that head.  In altricial
>hatchlings, the legs may be too puny to do more than prop up the body
>for the first couple of days after hatching, and hardly sufficient to
>do even that at first. 

I strongly suggest that you read some of Storrs Olson's papers on
flightlessness in rails and other birds, in which he makes this case very
well.  First of all, altricial birds probably are derived from birds with
precocial young, and represent a poor model for the sorts of birds in which
flightlessness occurs commonly (there is, for example, only one passerine bird
generally considered to have been flightless, the extinct Stephens Island Rock
Wren of New Zealand, though some other ground-dwelling songbirds like
tapaculos
may be pretty close to flightless.  The allometrics of the limbs of flightless
rails, for example, do indeed resemble those of precocial chicks.  The
feathers
of flightless birds lose some of the characteristics of adult contour
feathers,
and there are other similarities.  And as far as leg strength goes in chicks,
consider the megapodes, which have very strong hind limbs at birth, can
actually fly on hatching, and according to some may represent a quite
primitive
(or basal) stage in neornithine evolution.


--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
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