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Re: Sinosauropteryx tail colors
Mike Keesey wrote:
> Of course, that's a Just-So Story until someone does the
> genetic/developmental legwork (pun intended). I will note, however,
> that something very similar happens in (apo-)pterygote insects: the
> earliest ones have six wings (the anterior ones being shorter), and
> these are winnowed down to four before the appearance of the crown
> clade. (And further down to two in dipterans.)
Yes, there are fossil insects (Palaeodictyopteroidea) that show six wings -
just like seraphim.
For this reason, palaeodictyopteroideans are often regarded as the most
primitive known pterygote (primitively winged) insects. The paranotal
hypothesis of the origin of wings goes back to Woodward (1876), and proposes
that wings arose from stiff, lateral outgrowths (paranota) of the thoracic
terga. These outgrowths became enlarged, and then later evolved a hinge to
articulate with the thorax (meso- and metathorax). Many fossil insects (both
apterygotes and pterygotes) show large paranotal lobes on the prothorax, and in
winged forms these lobes often show venation (but are never hinged, so they
couldn't move). It's thought that whereas three pairs of wings might have been
useful for attitudinal control when falling from heights (e.g., plants), two
pairs of flapping wings were optimal for powered flight.
Also, before they became exapted for wings, these paranotal lobes are thought
to have had a non-aerodynamic function in insects. There are several competing
hypotheses for the original function of paranota: (1) display; (2)
thermoregulation; (3) protection (e.g., of legs or spiracles).
So it's interesting how there are parallels between hypotheses on the origin of
insect flight and te origin of bird flight. Unfortunately, an insect
equivalent of _Archaeopteryx_ has yet to be found. The Early Devonian
_Rhyniognatha_, a possible pterygote, might turn out to be a candidate - once
the body is discovered.