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Re: [Re: Theory on ornithoptering and could Archie do it ?]



Archosaur J wrote:

[power flight v flight snipped]

>Chris:
>
>The lack of a sternum in Archae is a bit of a red herring.  It is probable
>> that the sternum was not ossified, but still allowed muscle attachment.
>> Also, the new form has a small sternum.
>>
>> Also it is unlikely that Archae was on the direct line to power flight,
>> since it lacks a number of critical features such as ligament placement.
>>
>===============================================================================
>============================================================
>Still, didn't Archaeopteryx show signs of strong muscle attachments
>furcula wise. Sorta showing where large wing muscles started at before
>working their way down.
>
>Maybe I'm just getting this from an old source
>======================================================================

Archae is a good candidate for a flyer.  It appears to have had enough
muscle mass to keep itself airborn by flapping.  All that is needed is a
good set of wings some flight muscle and a good pair of drumsticks for
getting up some speed - Archae had a fine set of drumsticks.  Grebes are a
good analogy.  They have a very low weight% flight muscle v body mass,
close to that envisaged for Archae.  They get airborn by running
hell-for-leather across the ground or water until they get up enough speed
to get airborn.  Archae may have run across branches and launched itself.
>
>> >Now as for how powered flight in insects evolved. That's anyone's guess.
>>
>> Ah this is quite interesting.  For instance did you know that the HOX genes
>> for wing development are actually expressed in all segments, but is turned
>> OFF in all but the segment(s) carrying wings?  This suggests that the
>> ancestral insect actually carried the stuctures which were modified into
>> wings on all segments. Specimens of fossil insects tend to support this.
>===============================================================================
>=============================================================
>
>I take it that you (like myself) are one of those people who can easily
>get >caught up in subjects that they didn't intend to.
>
>That bit on insect wing segments is intrigueing. Makes paleo-insects sound
>like >Hallucinogenia. That invert has to be the weirdest of the weird.
>
>Aren't the wings of flying insects (extant forms at least) connected on
>the >thorax only ?
>======================================================================

Yep.  Tagmatization is common in the arthropods (its easy with serial
repeated segments).  Cephalization concentrated sensory apparatus up the
front end leaving the thorax relatively underdeveloped, but you can still
get the head to produce legs instead of antennae if you tweak the right HOX
gene.

>Chris:
>
>> It has been suggested that the original structures had another function,
>> probably temperature control and experiments suggest that the size at which
>> they become inefficient as temperature controllers (too big) is the size
>> that makes a difference to falling insects.  Fossil insects show a series
>> of these stucutures running along the back, but tapering so that the first
>> is the biggest and the last the smallest.  Switching off the smaller ones
>> would leave just the larger ones at the front of the body.  Also  . . .er,
>> but I digress . . .
>>
>> Chris
>===============================================================================
>=============================================================
>
>Which means that flies went one step further and turned off the second
>pair, >leaving only stubs behind.

Yep, halteres.  Very useful things halteres, keeps the buggers upright in
flight.

>Very interesting. And, unfortunately, very off subject. Perhaps this might
>do >better off list. Still very interesting discussion though.

Yep, I am surprised Mickey hasn't cut us off ye. . .

[lost connection to server]

Chris

cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
-------------------------------------------------------------------
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong.
It was all downhill from there.