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Re: Wing Feather Arrangement in Archaeopteryx and Anchiornis

Matthew Martyniuk <martyniuk@gmail.com> wrote:

> It's only in soaring birds like vultures that the humerus is held
> extended to maximize wing length and where the tertials become a
> well-developed part of the wing surface. There's no reason to think a
> sizable gap would exist in primitive birds even without any tertials.

I agree that the angle at which the humerus is held relative to the
body is critical in determining the size of the inboard gap.  However,
in _Archaeopteryx_ (and _Microraptor_) the humerus is relatively
longer than in modern birds.  Also, in many modern birds that lack
tertials on the humerus, the humerus is very short and/or the span is
filled (at least partially) by inclined secondaries (of which there is
no evidence in _Archaeopteryx_ etc).

It is possible that a sizable gap did exist between the wing and body
wall in basal avialans like _Archaeopteryx_, and that this gap was
actively selected for in these forms.  Creating a "draggy" inner wing
during humeral extension (effectively an extra wing tip) might
actually have been advantageous to these early gliders or fliers.

Longrich et al. is the latest in a long line of recent papers that
emphasize just how different the aerial styles of _Archaeopteryx_and
non-avialan maniraptorans might have been compared to modern birds.
Features that would be detrimental to modern volant birds might have
been useful to the flight behaviors of _Archaeopteryx_ etc.  We don't
even know if these early experiments in aerial behavior (exemplified
by _Anchiornis_ or _Microraptor_ or _Archaeopteryx_) actually gave
rise to modern avian flight.  They might each have been aerodynamic
dead-ends, with modern avian flight beginning at something closer to
the flight abilities of _Sapeornis_ or _Jeholornis_.