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Re: Changyuraptor, new big microraptorine theropod from Early Cretaceous of China

Thanks to Kevin for the excellent commentary on our manuscript. We declined to 
explicit support either a more arboreal/gliding or WAIR/powered model for 
exactly the reasons Kevin notes - a combination of limited forewing 
preservation (which is why we left out commentary on the matter) and polarizing 
opinions we thought best to stay clear of in this case. 

As a quick follow-up to the gliding prospects: I (and at least most of my 
co-authors) agree entirely that a sprawling mode for the hind limbs is 
extremely unlikely (at best) in microraptorines. However, this may not speak 
directly to the validity of a general gliding model (though it does speak 
strongly against the original “tetrapteryx” glider concept). The hind limb 
feather surfaces have broad, low-aspect planforms that are suitable as control 
surfaces producing both roll and yaw when held below the body (through a 
combination of high drag and high lift - it should be noted that lift can be 
oriented in any direction that is perpendicular to flow). These sorts of 
control options are advantageous in both a gliding and a WAIR/descent model, so 
I remain cautious in suggesting that the non-sprawling models necessarily speak 
to one or the other. 
[It is possible that microraptorines used the forelimbs to support their weight 
during arboreal gliding, with the hind wings providing control authority in 
roll and yaw, and the tail providing control authority in pitch (the latter 
being particularly important for animals with long torsos, since the center of 
mass tends to be somewhat caudally located relative to the wings). It is, of 
course, also quite possible that that same control authority was used with 
behaviors like WAIR and flapping descent. The latter does have the advantage of 
providing an explicit model for flight stroke evolution.]

To expand briefly on Kevin’s excellent point about thrust production: in living 
powered flyers, the wing undergoes twist during the flight stroke (both 
phases). During the downstroke phase, this twist reorients much of the lift 
from the distal wing to produce thrust instead of weight support. The trick is 
that the distal wing can also provide weight support at lower degrees of twist 
(as is the case in soaring flight, for example). One thing that might be worth 
looking at in paravians, in addition to the feather structure and location, are 
the adaptations for twisting the distal wing. If “twistiness” shows up before 
large wing areas (either ontogenetically or evolutionarily) in microraptorines, 
then it would support hypotheses such as flapping-descent and other non-gliding 
first, early flight stroke models. Unfortunately, the new Changyuraptor 
specimen doesn’t preserve the required distal wing anatomy to test this idea, 
but other specimens may be promising.

On Jul 15, 2014, at 3:45 PM, Kevin PADIAN <kpadian@berkeley.edu> wrote:

> I think what Mike says is reasonable, although because so many people
> (read:  potential reviewers) have such different views on early flight
> capabilities, it's difficult to say much of anything definitive
> without alienating your chances for a high-profile publication.
> People who think gliding has to precede flight may be comforted by the
> calculations here, although drag is likely to have been far more
> effective than lift, especially given that the legs could not
> apparently be placed in a batlike posture and hence could not have
> spread the feathers horizontally to form an effective airfoil that
> transmitted significant lift.  This, of course, depends on the
> orientation of the feathers with respect to the hindlimb parts, which
> is not clear from any of these allegedly gliding animals.  However an
> unusual configuration, such as a lateral splay of the hip joint, has
> to be demonstrated rather than assumed, and it has not been for any of
> these animals beginning with the original interpretation of
> Microraptor.
> People who think gliding is not necessary for flight may find the new
> discovery consistent with the WAIR hypothesis:  once up a tree the
> animal may have fluttered down with its forelimbs (not glided), using
> the hindlimbs and tail for drag and lift, plus dynamic stability. The
> humerus and forearm, compared to the femur and tibia, are no longer
> proportionally than in Archaeopteryx, a smaller animal.  It is
> surprising that this new animal shows so little evidence of forewings,
> about which the authors say almost nothing; if they were large one
> might have expected them to overlap the body, though they may have
> been prepared away.  However, the feathers that produce the most
> thrust, as opposed to lift for gliding, are not mostly on the inner
> wing but on the hand, which was not preserved here.  Baby birds
> develop these outer feathers first, and they are the ones that are
> effective in WAIR at early stages.  -- kp
> Kevin Padian
> Professor and Curator
> Department of Integrative Biology and Museum of Paleontology
> University of California, Berkeley CA 94720
> On Tue, Jul 15, 2014 at 3:27 PM, Mike Habib <biologyinmotion@gmail.com> wrote:
>> We don't exclude other functions in the manuscript. Rather, the focus is on 
>> the performance effects the feathers would have related to aerial locomotion 
>> (sustained or not). These effects occur regardless of the selective 
>> landscape of the feathers. Since some of the performance outcomes are 
>> potentially advantageous (control of pitch, for example) we felt that 
>> referring to these as likely aerodynamic functions was warranted. 
>> Display-related or not, they will still produce fluid forces. Furthermore, 
>> the allometry of the feathers and tail length relative to body size is 
>> consistent with a pitch control hypothesis. This does not exclude display as 
>> an additional (or even primary) function.
>> Cheers,
>> --Mike H.
>> Sent from my Cybernetic Symbiote