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Re: The "ideal" Eumaniraptoran arm motion
Early birds may have been more interested in directing lift horizontally for
thrust and maneuverability. In other words, their goal may have been to increase
the achievable zenith angle of the force vector between the ground and their
Many birds can develop enough lift ("upward thrust") to support their body
weight during the entire upstroke, and do so whenever using the 'concertina'
gait (which by the way is a term I don't especially care for). Even when using
the vortex ring gait, they will often support their body weight through the
first half of the upstroke as their hands 'go up in the air'.
John V Jackson wrote:
> The drag generated by an effective wing may not seem very significant
> compared to its lift, but for evolution to progress the design, we must
> consider the benefit to the very early forms. Lift, to a cursorial bird, is
> useless in an upward direction. Sprinters are told to keep in contact with
> the ground as much as possible, and sports cars press down as hard as they
> can. Vertical lift would not be selected for unless the predator were
> jumping up into the air.
> However, if it were jumping up into the air, to catch insects presumably,
> why would it need a sickle claw? For occasionally catching huge prey when
> it wasn't going after butterflies? Anyway, if it were grabbing at insects
> with its hands (and utilising the feathers as collectors), it would be
> throwing its hands *up* into the air, just at the moment when, for upward
> thrust, it should be pushing backwards, downwards, or anywhere in the
> basically opposite direction.
> --Original Message--From: Thomas R. Holtz, Jr. : Wednesday, March 03, 1999
> 01:32 PM
> Subject: RE: Arms into wings
> >At 05:20 PM 3/2/99 -0500, Patrick Norton wrote:
> >>I guess I'm suggesting that overall function of the arm and hand as prey
> >>capturing devices must have been compromised over time once selection
> >>began acting to improve aerodynamic performance. If you are running
> >>after a dragonfly and flapping, you can't also be grabbing for it with
> >>your hands-- at least not without breaking the flapping rhythm.
> >(I didn't just read that, did I?)
> >The "chasing a dragonfly" model is about as dead as _Archaeopteryx_. No
> >I know of considers that a likely life habit: heck, even Ostrom was only
> >partly serious when proposing it.
> Ah good. So two possibilities now remain for the use of aerodynamic wings
> in cursorial activities: forward thrust, and turning corners (that's
> assuming no-one is going to suggest they ran along and one day just took
> straight off).
> WRT forward thrust, that is what asymmetric feathers are all about. The
> vast majority of vertical lift is generated by the aerofoil shape of the
> whole wing (and a bit of vortex handling in advanced forms, certainly not
> the first in the line). The asymmetric feathers on the other hand (both
> hands actually) towards the end of the wing are used on the downstroke to
> give thrust, ie lift in a forward direction - they automatically angle
> themselves. Before this can happen, the creature has to be in a habit of
> flapping its arms up and down, it has to have arms long enough for this to
> have a worthwhile effect (and the shorter the arms, the faster they have to
> be flapped), it has to have not just feathers on its arms, but they have to
> be blade shaped with the fibres locked together, and aligned adequately...
> ...all this *before you get any beneficial effect at all* !
> Or alternatively, wings were used for changing direction. If they were used
> to give differential thrust from opposing wings, the same arguments apply as
> for purely forward thrust. If they were used as passive rudders, they would
> need some vertical component to their angle, and the animal would have to be
> running very fast indeed for any noticeable benefit to accrue. No
> particularly perfect aerodynamic shape would be necessary as a slab shape
> would still get some force off the air, though the earliest feathers would
> have had to have made a fairly air-proof screen.
> Which of these two is now the preferred BAMM scenario?
> >Archie would presumably be going after more substantial game (lizards,
> >sphenodontians, etc.), and dromaeosaurids much more substantial game (other
> >More to the point, as Padian & Gauthier showed back in 1985, the predatory
> >strike of a eumaniraptoran forelimb uses the same basic movements in the
> >same sequence as the flight stroke: it would be a synchronized movement.
> What is this predatory strike doing? Snagging prey? - Why the big muscles?
> Clubbing it? - The hand morphology is wrong - bones too spindly, claws not
> suitable for high speed heavy collisions.
> Skewering it? - The claws are not long and thin like a modern birds of
> Slicing it? - What are the teeth and foot claws for?
> We're looking for a big change in behaviour here. I'm afraid saying "It
> just happened" won't quite do.
> Patrick Norton (I think I'm right this time!) said on 2 March 99:
> >My own theory about this is that the feet may have taken over the role of
> >the hands in prey capture as the arms became more dedicated to flight. As
> >a hypothesis for this, I would suggest that the evolution of the reversed
> >hallux (development of grasping ability by the feet) and the
> >carpometacarpus (loss of grasping ability in the hands) are related
> >evolutionary innovations.
> When I read this first, I thought you were talking about the sickle claw as
> a repalcement for the now-winged hands, and I wrote:
> This is an extremely valid point, and I don't remember ever hearing anyone
> mention it before. It suggests that somewhere along the line, hands were
> just not cutting the mustard as far as direct predation use is concerned.
> This would suggest the change in hand design was probably not for the
> purpose of predation.
> Betty (presumably no relation to Jim) said (also 2 March 99)
> >Why would it reduce prey capture? Bats use their wings to capture
> >bugs-it makes a dandy scoop that funnels everything small to the mouth.
> >If the proto-wings were being used in an equivalent manner (and not
> >trying to hold a creature up in the air) I could see them being even
> >more efficient for this purpose than that of bats.
> Bats don't actually scoop them up in their wings as a steam express used to
> scoop water, they catch them in the wing-end as a lacrosse player might
> catch the ball, then flick the insect back into the.. er.. caudal patagium,
> and thence to the mouth.
> But if catching insects in the feathers is such a potentially effective use
> for feathers, why do 0 out of 3210 species of insect-eating birds do it
> today? (All right Roger - 1/3210!)
> --Original Message-- From: James R. Cunningham <firstname.lastname@example.org>To:
> email@example.com : Wednesday, March 03, 1999 09:54 AM
> >I think you guys may be slightly overestimating the amount of drag
> involved. To roughly quantify it, a 360 pound animal with a 36 foot wing,
> moving at 45 mph and carrying its full weight with its wings, would generate
> about 15 pounds of drag (half profile, half induced). This applies whether
> the wings are feathered or membraned. Were he to unload his wings, the
> induced drag component would go to zero, leaving only 7.5 pounds of profile
> drag, 3.75 pounds on each wing. This describes a big animal. A smaller or
> slower animal with shorter arms would generate much less
> >drag. At what point does the drag become inconsequential? For that matter,
> by flapping a bit, pronating on the downstroke, and supinating appropriately
> on the recovery, the animal can make net thrust exceed net drag, to the tune
> of about 1/3 g available for horizontal acceleration in the direction of
> choice. At what point does net >thrust become consequential?<
> Aren't we begging the question here? All this applies to a highly tuned
> flying entity. What would be the equivalents for structures say 1% starling
> wing and 99% witch's broomstick?