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Re: Exaptation



>Actually, as the central avian lineage approaches modern birds, the rate of
>appearance of flightless branches seem to decrease. There were
>hesperornithiforms, _Patagopteryx_, perhaps alvarezsaurids and avimimids.

This does not seem to fit the facts.  Post-KT flightless birds include the
various ratites (which may or may not have evolved flightlessness
independently), penguins, dromornithids, diatrymids, phorusracids, mancallid
auks, plotopterygids (or whatever these things were called, I forget), and,
in recent times (though not all at present, alas) flightless cormorants (at
least two lines), ibises (at least two or three separate lines), ducks
(several lines), megapodes (as I recall), rails (lots of lines), the Great
Auk, aptornithids, kagus, parrots (the kakapo), a probably flightless hoopoe
from St. Helena, and even passerines (the hapless Stephen Island Rockwren of
New Zealand, exterminated by the lighthouse-keeper's cat).  I see no
drop-off in the rate of appearance of flightless lineages.

>Compare this to the wealth of herrerasaurians, ceratosaurians, carnosaurs,
>dromaeosaurids, oviraptorosaurs, ornithomimosaurs, and so forth, which BCF
>asserts branched off mainly before the advent of powered flight. Your thesis
>may be more correct than you think.

Well, if they branched off before the advent of powered flight they can
hardly be secondarily flightless, can they?

>
>Regarding secondarily flightless pterosaurs and bats: it's entirely possible
>that they existed but haven't yet been found. I've heard intriguing rumors,
>but nothing concrete yet. Meanwhile, you might want to give some thought to
>how you might identify a flightless pterosaur in the fossil record.
>

We might note that some gliding mammals have close relatives that lack a
gliding membrane (eg Zenkerella among the anomalures, the New Guinea
feathertail possum and Leadbeater's possum).  Perhaps one or more of these
represents a secondary loss?
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
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