Re: Archaeopteryx not the first bird, is the earliest known (powered) flying dinosaur

[don ohmes <d_ohmes@yahoo.com>]

>>> Tim Williams wrote: "The question I'm trying to
get 
GSP 
to think about is "How did it all get started?"  In
other words, even 
at the 
non-flyer stage the prospect of aerial locomotion must
be selectively 
advantageous, and there must be some anatomical
hardware for evolution 
to 
start moulding into a future flight apparatus.  I
don't think this 
hardware 
(= incipient flight adaptations) needs to be involved
in flight, or 
perhaps 
any kind of aerial locomotory behavior for that
matter."<<<

+++++++++++++++++++++++++++++++++++++++

Don wrote:

My primary point-- T. Williams is correct that some
pre-flight "raw material" is needed. However, in the
animals under discussion, the only raw material
logically required to catalyze flight adaptations is
the (proto) feather. See below.

Basic assumption-- 
The stages underlying the evolution of morphology are:
1. Fortuitous structure (mutation).
2. Approach to optimal morphology (directional
selection).
3. Optimal ("Goldilocks") morphology (stabilizing
selection, or selective compromise).

If you will--

Consider a generic pre-flight(Early Jurassic?)
theropod in the Goldilocks stage. Locomotion
(especially predation-related locomotion) is primarily
bipedal, but may well include non-aerodynamic use of
the arms, as in traversing shallow water, dense
vegetation or trees. The arms (whatever the length)
could advantageously be longer from the perspective of
resource acquisition, but there are counter-pressures
limiting limb length.

Enter a fortuitous structure, the proto-feather.
Pre-flight or "onramp advantages" (a term I first saw
used on DML) enlarge this structure* until selectively
significant aerodynamic properties are attained. At
this point, the entire organism is subject to
pressures relating to an aerodynamic effect on
locomotion.

In the early stage, the lengthening of limbs is
_doubly_  advantageous (both locomotive and
predatory/grabbing), altering the relationship w/
whatever counterpressure formerly limited limb length.
Eventually, however, the mouth is capable performing
the function of prey capture, and locomotive (i.e.
flight) pressures will logically determine the final
form of the limbs.

*Onramp advantages: various thermal relations
(brooding, insulation) and camoflage (I believe I can
claim camo as my personal contribution to the
discussion).  I feel camoflage is important because it
transcends climate and bodysize, and is doubly
advantageous in predatory animals (i.e., predation
avoidance and enhancement). These onramps are additive
in nature and logically could occur, relative to
_primary_ function, in time sequence (i.e.,
insulation/camoflage/aerodynamic structure).

Don

++++++++++++++++++++++++++++++++++++++++++++


--- Tim Williams <twilliams_alpha@hotmail.com> wrote:

> Gregory S. Paul wrote:
> 
> >The basic contention that small theropods must have
> had a lot of 
> >preadaptations on hand before becoming fliers is
> fundamentally absurd. 
> >Something similar to Ornitholestes already has the
> basic skeletal features 
> >needed to become an incipient glider.
> 
> It may be true that _Ornitholestes_ had sufficient
> hardware to become an 
> incipient glider.  To me an "incipient glider" is a
> parachuter: the animal 
> cannot yet produce an airfoil, but the skeletal
> proportions and integument 
> are sufficient to slow and perhaps guide its descent
> to the ground.  But 
> your hypothesis implies that the direct ancestors of
> flying theropods must 
> have evolved flight in the trees.  I don't think we
> have yet reached the 
> point where we can establish that birds did evolve
> flight with the 
> assistance of gravity every step of the way
> ('trees-down', if you will).
> 
> You may argue that _Ornitholestes_ already had the
> basic skeletal features 
> needed to become an incipient glider, but you need
> to explain (a) why 
> _Ornitholestes_ would need to glide; and (b) how
> _Ornitholestes_ arrived at 
> an elevation (e.g., a tree-branch) that allowed it
> to turn potential energy 
> into kinetic energy - and commence gliding.  I know
> you are just using 
> _Ornitholestes_ as an example, and that you are not
> implying that 
> _Ornitholestes_ gave rise to birds; but my
> counter-arguments apply to any 
> small theropod.  Every stage leading to flight has
> to be selectively 
> advantageous.  If you contend that the ancestors of
> birds were arboreal 
> gliders, then there must be a selective advantage to
> the theropod being 
> arboreal, then becoming airborne, and then staying
> airborne.
> 
> >All it has to do is evolved sufficiently long wing,
> asymmetrical wing 
> >feathers, hold the arms out to the sides and there
> you go.
> 
> But why would it need to do this?  What's missing is
> a *reason* to evolve 
> all of these features.
> 
> >All the other stuff for folding the wings
> (elbow-wrist push-pulley system), 
> >further increasing lift area (longer arms and still
> bigger wing feathers)  
> >and producing a power stroke (large sternal plate,
> bigger pectoral crest, 
> >ossified sternal ribs and uncinates) can be
> developed as flight progresses.
> 
> This may be true, but it requires that theropods
> passed through a gliding 
> stage on the way to flight.  And you do not say why
> these features could 
> *not* be pre-adaptations - like the elongated
> forelimb and manus, and 
> ossified sternum, and short tail.  I am not saying
> that these characters 
> *must* be preadaptations that evolved for a
> non-aerial purpose (like 
> predation, or maneuverability on the ground) before
> being exapted for 
> powered flight.  What I am trying to do is keep this
> question open - instead 
> of asserting that these features *must* have been
> flight-related from the 
> very beginning.  I think there is evidence that
> certain features (e.g., 
> elongated forelimb and manus, ossified sternum,
> shorter tail, maybe even 
> broad-vaned feathers) may have evolved prior to the
> advent of powered 
> flight, and were later incorporated into the flight
> apparatus.  But I'm not 
> being dogmatic on this point.
> 
> >No one has ever shown why any dinosaurian flight
> adaptation had to evolve 
> >first as a preadaptation, aside from the
> combination of long arms and 
> >bipedalism.
> 
> I don't want to get bogged down in the old
> 'ground-up' vs 'trees-down' 
> dichotomy, but if the ancestors of birds evolved
> flight in a terrestrial 
> setting then the requirements become a little
> steeper.  Unless the animal is 
> fully arboreal, then the animal's own exertions are
> needed to get it into 
> the air and keep it there.  The WAIR model, for
> example, requires an 
> incipient flight stroke, which implies that the
> expanded wing elbow-wrist 
> push-pulley system could have evolved prior to
> powered flight.  By contrast, 
> a passive gliding stage is 'easier' in the sense
> that the evolution of a 
> lift-and-thrust-generating stroke and more
> heavy-duty pectoral musculature 
> can be deferred.  But I don't think we are at the
> point where we can dismiss 
> the role of a terrestrial component in the evolution
> of avian flight, so all 
> options are still on the table.
> 
> I personally favor a gliding phase as a prelude to
> powered flight, but this 
> is just my intuition at work; and I cannot use my
> intuition alone to trump 
> the work of people like Burgers and Chiappe and Dial
> who demonstrated (both 
> theoretically and experimentally) that a 'ground-up'
> model of avian flight 
> is feasible.
> 
> >One or more flight feature may have started as a
> preadaptation, but that 
> >does not mean any or all
> >had to.
> 
> I know - that's what I've been saying all along.  In
> a nutshell.
> 
> >Nor has anyone explained why Archaeopteryx has
> expanded muscle attachments 
> >areas on its arms just to glide.
> 
> I wasn't arguing that _Archaeopteryx_ was a passive
> glider.  However, I was 
> arguing that the expansion of muscle attachments
> *might* be a preadaptation 
> to flight, and were inherited by birds from theropod
> forbears that used 
> their powerful arms for catching and holding prey.
> 
> >It is obvious that expansion of muscle attachments
> on a forewing will one 
> >way or another allow and improve the power of a
> flight stroke.
> 
> By the same token, it is obvious that these same
> adaptations might allow a 
> predator to better hold onto large prey - like a
> _Velociraptor_ trying to 
> grapple with a _Protoceratops_, for example.  Or a
> _Deinonychus_ holding 
> onto a bucking _Tenontosaurus_.
> 
> >I truly do not even begin to understand the
> arguments to the contrary. They 
> >seem part of a continuing effort to some, based on
> a historical heritage 
> >that saw dinosaurs as having nothing to do with
> birds, to keep theropods 
> >that were not full birds as nonfliers or mere
> gliders, as though nonavian 
> >dinosaurs were for some reason not allowed to be
> true fliers. Very odd.
> 
> Speaking for myself, as someone who has absolutely
> no doubt that birds 
> evolved from theropods (and so, therefore, *are*
> theropods), I can say that 
> I completely disagree with this statement.  And
> there is nothing 'mere' 
> about gliding.  Successful gliding is an aerodynamic
> feat that requires a 
> considerable anatomical investment on the part of
> the glider.
> 
> Cheers
> 
> Tim
> 
> 
>