[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Arms into wings



>We have photos of gulls, eagles, flamingos, ducks, blackbirds, and ostriches
>engaged in "under the wing" sheltering activities.
>    It's not the photo that does it. It's the identified behavior in a wide
>range of species. Perhaps this can never "establish" the trait as basal, but
>it can make it extremely uncomfortable for anyone arguing that modern birds
>developed wing feather brooding recently and independently. As we pile on more
>examples, such critics will have to say that convergent evolution happened
>separately in the great majority of modern species.

Why?  All modern birds belong to a single derived clade, the Neornithes.
That they share a behaviour may be suggestive of its function in other
clades possessing feathers, but that is all - in no way does it establish
that such behaviour is basal to feathered archosaurs or even found in other
bird clades now extinct (eg enantiornithids).

Further, as all of these living groups share other feather-related
behaviours (such as the use of feathers in display), even if not all bird
species use remiges in this way, I fail to see how establishing that
brooding with feathers is widespread in Neornithes singles it out as MORE
basal than any of these other behaviours.

On the subject of brooding vs. incubation, by the way:  The term "brooding"
as defined in A Dictionary of Birds (Campbell and Lack, eds) can be used
either for sheltering young after hatching or for incubation, though Hopp
is correct that the former use is more widespread.  Anyway, I would remind
readers that the only evidence we have for any brood-protecting behaviour
in fossils is the famous Oviraptor specimen which was sheltering eggs, not
hatchlings.  We have NO evidence that these animals sheltered their young
after hatching (living megapodes do not, so the behaviour is not even
universal among living birds).

My own feeling is that brooding, though certainly a function of feathers
once acquired, is less certain as a factor in their initial evolution.  The
absence of equivalent brooding structures in non-birds today, which may
have an equal investment in protecting their young, suggests that it might
be difficult to argue that a need to brood drove feather evolution (as does
the loss of remiges in flightless birds, as I pointed out in an earlier
post).  Further, it does not explain the one definitely feathered feature
found in both non-avian fossils with pinnate feathers: the tail fan of
Caudipteryx and Protarchaeopteryx, an unlikely brooding structure but, in
my view, a quite reasonable display ornament.
--
Ronald I. Orenstein                           Phone: (905) 820-7886
International Wildlife Coalition              Fax/Modem: (905) 569-0116
1825 Shady Creek Court                 
Mississauga, Ontario, Canada L5L 3W2          mailto:ornstn@home.com