Re: L'origine/Cosesaurus/Sharovipteryx

[Tim Williams <tijawi@yahoo.com>]

David Peters wrote:

> Exactly my point. Thank you. And--> fact check: Draco
> volans (arboreal, short limbs) vs. nearly every bipedal
> running lizard (terrestrial) in the Jayne videos. Check the
> ratios.


_Draco_ is an extant patagial glider in which the patagium is supported by 
elongated dorsal ribs.  The fossil _Sharovipteryx_ is interpreted as a patagial 
glider in which the hindlimbs and tail supported an extensive patagial 
membrane.  The patagium of _Draco_ is not supported by the hindlimbs, so a 
comparison of limb proportions between _Draco_ and _Sharovipteryx_ isn't useful 
in this respect.  


> I note the weasel word, "may," in your text. So,
> bottom line: you don't know.


This is a little unfair, David.  Of course Jaime doesn't *know*.  He's being 
careful not to phrase his own interpretations and opinions as facts.


> Wouldn't it be nice to actually demonstrate one way or
> the other through evidence and phylogenetic analysis? 


Yes, it would.  But the best we can do is erect hypotheses and refute or 
corroborate these hypotheses with available evidence.  I'm not saying your 
hypothesis of a terrestrial/bipedal cursorial _Sharovipteryx_ is wrong.  
However, no amount of emphatic assertions on your part has yet overturned the 
alternative hypothesis that _Sharovipteryx_ was an arboreal glider in which the 
hindlimbs were elongated in order to increase the patagial span.


BTW, even if a phylogenetic analysis recovers _Sharovipteryx_ as the sister 
taxon to Pterosauria, it does not *prove* that _Sharovipteryx_ was a 
terrestrial biped.  Ichnological data indicate that pterosaurs were quadrupeds 
when on the ground.  Although you yourself might interpret the pterosaurs as 
bipeds (based on anatomy), this is just circular reasoning if you use this to 
support bipedality in _Sharovipteryx_.


Cheers

Tim