Re: Feather Flap

[Tim Williams <twilliams_alpha@hotmail.com>]

Scott Hartman wrote:

> Right...but colugos and draco have other specializations for living in 
> trees, such as limbs that can be laterally splayed, (realitively) shorter 
> manus and pes (for better leverage while climbing), highly flexible ankle 
> and wrist joints, and flexible backs.

But colugos and dracos evolved within lineages that were already specialized 
for arboreality.  In these groups gliding evolved as a means of commuting 
from tree to tree.  The same is true for most gliding tetrapods, including 
gliding marsupials and rodents.  I'm not sure this holds for the first 
gliding theropods, who may have evolved gliding ability as means of getting 
from trees to the ground.  In this case, it would make sense to retain a 
morphology that was suited for terrestrial bipedal locomotion.  Of course, 
this scenario is a "just-so" story, and not evidence - but I don't see any 
reason to assume that you have to be specialized for arboreality in order to 
be an effective glider.

> And their gliding surface is confluent with the abdomen, like essentailly 
> any other gliding arboreal organism. Winged dinosaurs lack all of these, 
> including the fact that the phylogenetically earliest wings appear distally 
> on the limbs, and are not confluent with the abdominal  airfoil...exactly 
> the opposite of arboreal gliding animals.

This is not true for all arboreal gliders.  Some gliding amphibians have 
flaps on the distal limbs, such as "flying frogs" (_Rhacophorus_ spp.) which 
have huge webbed feet for gliding.  The "flying geckoes" (_Ptychozoon_ spp.) 
have gliding surfaces on the abdomen and feet that are not confluent.

Having said that, there is the argument that the reason why _Archaeopteryx_ 
and _Caudipteryx_ lack an "inner wing" is a preservation artefact.  The 
argument runs that these festhers are less likely to be preserved with the 
skeleton because the attachment is not as strong, given that these proximal 
feathers have a lesser role in thrust-generation.

> Again, it's not that Archaeopteryx could not have gotten in a tree...it's 
> that it shows no specializations for doing so relative to its closest 
> relatives.

Nevertheless, certain maniraptorans do show some traits that might be 
associated with arboreality - or at least scansoriality.  There's small body 
size, for one (yeah, I know this one's a stretch).  There's possible 
scansorial/arboreal traits in the manus and pes, including (for example) an 
enlarged hallux that has shifted distally on the foot compared to other 
theropods.  Still not a reversed hallux, just a longer and lower one.

Cheers

Tim

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