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RE: Did dinosaur wings evolve for breeding display?/Longisquama




 
--- On Fri, 4/17/09, Jaime Headden <qi_leong@hotmail.com> wrote:

\> 
>   In the holotype specimen, the structures appear arranged
> in a radial fashion with some elements overlapping partially
> only on their "distal" extremities (for lack of a
> better term when inferring doubt as to their origin), and
> moreover the most "posterior" of these is
> positioned in such a way that it overlies where on a
> complete skeleton the posterior half of the torso, hips, and
> base of the tail might/would be. This implies at least some
> distortion/dislocation has occured on the specimen should
> these be integumental, and that some, if not most or all,
> are not in life position. But that's a LOT of
> speculation.

What you've just said is self contradictory. If everything originates in an 
orderly fashion, where the torso, hips, base of the tail would be, then you 
have no dislocation.
> 
> 
> 
>   I still have a copy of one of your speculative
> reconstructions with outline restoration. Without passing
> judgment on that image, I can argue that what the holotype
> shows 

by that do you mean Sharov's rough drawing?

are a row of irregular, semi-trapezoidal structures
> along the posterior margin of the forearm, which at least
> marginally resembles the condition in *Crocodilus*, 

by that do you mean a set of extra large scales that stick out a wee bit?

and
> therefore any referral of this structure and arm design to a
> "wing" is a fair bit close to being fanciful. 

Given those parameters: yes. But are those parameters valid? No, after careful 
observation, IMHO.

It
> takes the speculative restorations I have seen (not just by
> you, Dave) to derive a wing-like arm, 

Every arm is wing-like. They are homologs. What factors change the ordinary 
forelimb into a wing-like one in your opinion?

and that massive
> speculation is not based on the raw data that is the slab,
> the skeleton, and the associated structures. Such a short
> arm, with such short structures would be about as capable of
> flapping flight as my arms with a hoodie on, and
> *Longisquama* has a proportionately bigger body to arm
> length than I do.

Never forget Dial's studies with young birds with small wings. Also the 
previews to a new Disney movie, Earth, show a duckling 'parachuting' to the 
leaf litter. Wing length is not as important as you imply. Especially when you 
consider Longi's cousin: Sharovipteryx. Don't follow your preconconceptions. 
Follow the fossils. Flapping doesn't necessarily mean flying, either. Birds 
flap long before they fly ontogenetically.
> 
>   I prefer, of course, studying what the skeleton tells us.
> As such, my skeletal restoration is rooted on the bones as
> preserved:
> 
> http://upload.wikimedia.org/wikipedia/commons/a/a1/Longisquama_insignis_skeleton%26silhouette_small.jpg
> 
As I recall, a fine piece of art. Comments follow on another email.


>   Here I reconstructed the skeleton based only on the bones
> (although the unknown proportions and posture are based on a
> basal ornithodire, which is almost certainly wrong at this
> point) and there is a lot of doubt as to the structure of
> the bones of the snout (as the skull is crushed and
> distorted). We know VERY little about this due to the fact
> that a single crushed, incomplete specimen with poorly
> preserved surfaces makes for determination difficulties.

You and I both gotta go with what we got. I think you'll be pleasantly 
surprised when you see the skeletal tracing. It covers all the bases.
> 
>   Cheers,
> 
> Jaime A. Headden
> 
> "Innocent, unbiased observation is a myth." ---
> P.B. Medawar (1969)
> 
> 
> "Human beings, who are almost unique in having the
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> 
> 
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> 
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