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RE: Deinonychus Morphological Variations within Ontogeny



What scenario do you prefer, then, logically, for the origin of flapping 
flight? At one point or another you have discounted all of the transitional 
states that have been proposed, saying all of them can only happen after the 
acquisition of the full powered flight apparatus: not arboreal perches 
(gravitational acceleration), not WAIR (impossible for the humerus to be 
elevated). Also not leaping takeoff and flapping, and not leap - gliding (just 
tonight, restricting these to ornithothoraces without any justification).

Perhaps you suggest that Iberomesornis and Archaeorhynchus (the most basal 
ornithothoraceans) were the the first to experiment with any aerodynamic 
behaviors? Such as parachuting? Then we are faced with a  scenario where 
animals had developed extremely long wings with asymmetrical feathers, tiny 
body size, fully reversed halluces, and huge sternum muscles, all BEFORE they 
made any attempts to flap.

I must repeat that pterosaurs and bats have never had any problem flapping 
without a triosseal canal or sternal keel.

In some cases you seem to venture up to the brink of logic (as in noting that 
ANY downward motion of the wing would add lift), but then you retreat to a 
strange, ex post facto position (arguing that only things that have advanced 
flying capabilities can be models for the incipient stages of flight). In fact, 
reading back, it appears that you must dispute that paravians are the ancestors 
of the birds, is that correct? Because you do not seem to see wings, 
asymmetrical feathers, hugely long arms, or tiny body size, as even remotely 
indicative of aerodynamic behaviors.

Please state your hypothesis clearly and succinctly so that we on DML may 
critique it. 

Thank You.
________________________________________
From: owner-DINOSAUR@usc.edu [owner-DINOSAUR@usc.edu] on behalf of Tim Williams 
[tijawi@gmail.com]
Sent: Tuesday, April 21, 2015 9:26 PM
To: dinosaur@usc.edu
Subject: Re: Deinonychus Morphological Variations within Ontogeny

Jason Brougham <jaseb@amnh.org> wrote:

> Agreed that non - avialan paravians did not fly like modern birds. Modern 
> birds can fly for 9 days and
> nights, over 11,000  kilometers, without stopping, eating, or resting even 
> once. (Limosa  lapponica
> baueri, Gill R. E, Jr, Tibbitts T. L, Douglas D. C, Handel C. M, Mulcahy D. 
> M, et al. Extreme endurance
> flights by landbirds crossing the Pacific Ocean: ecological corridor rather 
> than barrier? Proc R Soc B.
> 2009;276:447–457).


Yes, very impressive.  At the other extreme there are birds who have
extremely poor flight abilities, insofar as they can become airborne
but lack sustained flight: scrubbirds, lyrebirds, wattlebirds
(including the kokako), tapaculos, mesites, several rails, etc.  These
are birds that engage in short fluttering bouts of flight - such as to
escape a predator, or clear a hurdle on the ground, or reach a tree
branch.  There are also flightless birds that glide while on the
ground (kagu), or glide down to earth from trees (kakapo) - so no
powered flight, just "passive" gliding.  It may be that the incipient
stages of flight in theropods resembled one or more of these aerial
behaviors, observed in weakly-flighted or flightless-but-gliding birds
of today.


> But many of us are interested in how flight in the bird lineage began, and 
> rudimentary aerodynamic
> capabilities are of the greatest interest to us. A small theropod that could 
> leap and glide downhill away
> from danger is extremely interesting.


So do I (see above for possible modern analogs). This is the kind of
rudimentary aerial behavior that could have started flight evolution
in terrestrial theropods.  I certainly think it's a far more plausible
scenario than arboreal gliding (= gliding from tree to tree).


> (Especially considering that both quail and starlings produce 80 -
> 90% of their takeoff velocity from leaping, rather than flapping. Earls, 
> K.D.; (2000) The Journal of
> Experimental Biology 203, 725 - 739.) Personally I think that, looking at the 
> whole pool of basal
> paravians we have in Eosinopteryx, Xiaotingia, Anchiornis, Aurornis, and the 
> like, there is a great
> profusion of possibilities.


Take-off velocity was hindlimb-driven; the wings then continue the
motion initiated by the hindlimbs (including supporting the bird's
weight in the air), and sustain forward or ascending flight.

I particularly like Earls' thoughts on the origin of avian flight,
including her "jump-start" model.  As she says: "Any downward movement
of a feathered forelimb after the initiation of a leap could
potentially add height or distance to the ballistic path, regardless
of the reason for jumping."  The initial launch could be
hindlimb-driven, but the lift and thrust thereafter (required to
remain airborne) would both depend on the actions of the forelimbs and
pectoral musculature.  This could be a problem for basal (=
non-ornithothoracean) birds, irrespective of the range of excursion
the forelimbs were capable of.




Cheers

Tim