re:pteros have lift-off

[Tim Williams <tijawi@yahoo.com>]

David Peters wrote:


> Highly derived? No intermediate forms? Intermediate between
> what and pterosaurs?


Well, if we knew that, we wouldn't need the intermediate forms.  :-)
The advantage of having basal pterosaurs is that we can use their character 
states to help clarify the sister taxon to Pterosauria.  

To use an analogy, imagine how hard it would be to find the sister taxon to 
birds if all we had were 'advanced' forms like _Hesperornis_, _Ichthyornis_, 
and neornitheans, and we had no knowledge of basal avians such as 
_Archaeopteryx_, _Jeholornis_ or confuciusornithids.  This is what we're faced 
with for the pterosaurs.

 
> Just find a diapsid taxon or two (if parts are missing)
> with a displaced naris, an antorbital fenestra, multi-cusped
> (not serrated) teeth, a keeled sternal complex
> (interclavicle+clavicle+sternum), an attenuated tail without
> descending chevrons but with elongated centra, a proximal
> deltopectoral crest, an appressed radius/ulna, metacarpals
> that elongate laterally but III equals IV, manual digits
> that elongate laterally but V is very short, an elongated
> ilium, a fused pubis/ischium, a longer tibia than femur, an
> attenuated fibula, a simple hinge ankle-joint, metatarsals
> that elongate laterally, pedal digits that elongate
> laterally, a pedal digit V with an elongated proximal
> phalanx and fiber-supported dermal membranes trailing any of
> the limbs. Shouldn't be too hard. I can think of a few
> just off the top of my head. I'm sure you can too.


I could, but it wouldn't make any difference to pterosaur relationships.  I 
glean from the above paragraph that you've already made up your mind regarding 
which taxon is closest to Pterosauria.

 
> And getting back to that arboreal theory, which theropods
> prior to Archaeopteryx and kin had long forelimbs?


One of the diagnostic characters of Coelurosauria is: "Elongate forelimb 
exceeds half the length of hindlimb and/or presacral vertebral column" (e.g., 
Gauthier, 1986).  This is apparent in forms such as _Coelurus_ and 
_Tanycolagreus_ (both possibly basal tyrannosaurs), _ornithomimosaurs, 
therizinosaurs, oviraptorosaurs, and deinonychosaurs.  These taxa, while found 
in strata not older than _Archaeopteryx_, lie outside the clade that includes 
"_Archaeopteryx_ and kin" (by which I interpret to mean Avialae).


Cheers

Tim