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Re: Arms into wings



Ronald Ornstein wrote:

>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.

Why do we need just one feature to push the evolution of feathers? One may
not be enough. Enlarging whatever bodily covering early theropods/birds had
may have offered multiple advantages. Protofeathers could have improved
thermal insulation for small animals. They could have added streamlining
for movement in air or even water. (An animal that lived in a
wetlands/marsh environment might have gained an evolutionary edge from
being able to move faster when in jumped in the water to catch prey. Or it
might have benefitted from a body covering that was water-resistant in some
way. We know Archaeopteryx lived in or near wetlands, although that could
be a preservational artiface.) Display could have been another advantage.
Feathers could have helped brooding as well. If multiple factors encouraged
feather growth for body protection, and enlarging wing and tail feathers
for display may have brought avian ancestors to the threshold of flight. In
short, I don't think there's a simple answer because the evoluton of
feathers wasn't simple. -- Jeff Hecht