Re: pteros have lift-off

[Tim Williams <tijawi@yahoo.com>]

David Peters wrote:


> Greg Paul in dinos of the air suggested that Archaeopteryx and other
> birdy descendants of short-armed theropods gained their long arms from 
> tree-clinging and tree-climbing. Is this the general consensus?


I don't believe so.  (Are you sure Greg Paul actually said that??  
Specifically, did he actually say that _Archaeopteryx_ evolved from 
"short-armed" theropods?) 

Elongation of the forelimbs is a character that appears to be primitive for 
coelurosaurs.  Those coelurosaurs with relatively short forelimbs (e.g., 
compsognathids, alvarezsaurs, _Caudipteryx_, _Austroraptor_) appear to 
represent secondary reversals of this character.  Forelimb elongation could be 
associated with the need to grasp branches, and/or a shift to aerial 
locomotion; or it could be associated with improved reach in prey capture.


> Padian championed bipedal locomotion. Bennett followed von
> Huene who championed arboreal leaping and illustrated
> Eudimorphodon's hind limb in a leap. No one else I am
> aware of has broached the subject. If you choose dinos or
> Scleromochlus as sister taxa, you have long hindlimbs and
> short forelimbs. The same if you choose Cosesaurus and
> Sharovipteryx. No other taxa have been promoted seriously
> with matrices.


The thing is, while the above paragraph is technically correct, it omits one 
crucial detail: pterosaurs have long forelimbs and short hindlimbs.  We do not 
know what the intermembral indices were for those (as-yet-unknown) pterosaur 
ancestors that exhibited incipient flight behaviors.

Further, AFAIK, no obligately bipedal prolacertiforms or basal ornithodirans 
are known, and the Prolacertiformes and basal Dinosauromorpha plexus both 
include non-bipedal forms.  So I don't think we can assume that the first 
aerial pterosaurs (or pterosauromorphs) were bipedal.


Cheers

Tim