Re: Coelurosauravus: glider? or bluffer?

[David Marjanovic <david.marjanovic@gmx.at>]

----- Original Message -----
From: "david peters" <davidrpeters@earthlink.net>
Sent: Wednesday, November 10, 2004 5:06 PM

> Without mechanical pathways (I-beams or bones) leading back to the 
> vertebral column, these membranes are going to fold up. Draco uses ribs. 
> Icarosaurus and Kuehneosaurus use ?ribs (well, weâ?Tll get into that 
> later), flying squirrels, flying lemurs, birds, bats and pterosaurs use 
> limbs. Only Coelurosauravus uses spars/rods that are dermal in origin to 
> supposedly support itself in the air. The limbs are free.

That the rods are dermal in origin is obviously less important than the fact 
that they are bone. (Most skull bones are dermal, as are the clavicles... 
ribs are not, they are endochondral like limb bones and vertebrae.) Whether 
they must be connected to the vertebral column or not depends, I'd say, on 
the wing loading... I won't risk a guess here... though, small as the animal 
is, it's probably imaginable that ligaments would suffice as connections 
between the ribs and the dermal rods.

> Frey, Sues and Munk reported that all of the spars originated in the arm 
> pit. My reconstruction indicates that about half of the 23 spars 
> originated on the first dorsal rib and the other half bore a one-to-one 
> correspondence with the remaining ribs. So there _is_ a rib connection in 
> Coelurosauravus. The only problem is each rib connection is a universal 
> joint, a single point that is capable or rotating in any direction.

This merely means that more soft tissue is needed to keep the wing stretched 
out. Is a disadvantage (weight), but doesn't necessarily destroy the 
animal's chances to fly.

> And every spar is the shape of a strand of angel-hair spaghetti. Not much 
> support here, engineering-wise.

Perhaps not more is needed.

> Maybe the ribs in Coelurosauravus simply spread out in order to make this 
> skinny little bluffer appear much bigger than it was, similar in concept 
> to the extradermal membranes in the Australian frilled lizard. Draco 
> volans also spreads its ribs to impress â?~the ladiesâ?T. And â?~the 
> ladiesâ?T spread their ribs to show disinterest. The head crest is a sign 
> that Coelurosauravus was into intimidation, whether intraspecific or 
> otherwise. It also has a pretty substantial anterior process of the ilium, 
> which permitted some form of bipedal configuration, whether running or 
> standing. So we can picture Coelurosauravus standing bipedally and 
> spreading its spars. Pretty impressive.

Please explain why you think that process is sufficient evidence 
(...especially considering the fact that the ilia _you_ find may not even 
exist). The anterior processes on your ilia are ridiculously short, while 
those on a ceratopsian ilium are extremely long...

> Maybe Icarosaurus and Kuehneosaurus are descendants of this bluffer.

Then why are they always found so far apart (*Coelurosauravus* outside crown 
Diapsida, *Icarosaurus* and *Kuehneosaurus* inside Lepidosauromorpha)?

> Previously the spars in the spreading membranes of Kuehneosauridae were 
> considered true ribs because they were reported to connect to 
> hyperelongated transverse processes. But is that the case?
>
> A closer look at Icarosaurus shows that the hyperelongated transverse 
> processes are actually laterally-oriented ribs fused to traditional 
> transverse proceses. They just look like giant transverse processes. 
> Unfused samples are in the anterior ribcage, between the scapulae.

http://www.pterosaurinfo.com/icarosaurus_recon.html confirms this 
interpretation -- except for the important point! Why should the rib of 
Colbert's vertebra 11 is homologous to any part of the giant transverse 
process of vertebra 12, and not instead to the wing-supporting rod of 
vertebra 12? Just because it's the same length? Oops -- in what you call 
vertebra 11, you show both parts separate. But you haven't put a photo 
online, and I can't get the paper from 1970 anytime soon... which probably 
contains a very bad black-and-white photo...

> One thing that hasnâ?Tt changed is the unique metapodial configuration in 
> which mtII is the longest in the set. Yes, thereâ?Ts a match.

Compare your hands to those you reconstruct for *Icarosaurus*. You're in for 
a surprise... perhaps an adaptation to arboreality.

> So, if valid, somewhere between Coelurosauravus and Icarosaurus, a sister 
> taxon with the beginnings of I-beams for spars jumped and survived the 
> fall

That would be parachuting, not gliding. :-)