Re: Fwd: Heavy breathing in pterosaurs

[Tim Williams <tijawi@yahoo.com>]

> Respiratory Evolution Facilitated the Origin of Pterosaur
> Flight and Aerial Gigantism
> 
> Leon P. A. M. Claessens, Patrick M. O'Connor, David M.  Unwin
> 
> And  specially for readers of the DML, a mini update:
> 
> Since the MS went to  press, Richard Butler at the
> NHM, London, has very 
> kindly pointed out that  pneumatic openings are
> present in the cervical and dorsal 
> vertebrae of  Dimorphodon (as noted by Sarah Sangster
> in her PhD thesis) and 
> in a cervical of  Raeticodactylus (see also Stecher,
> 2008: fig.5). This 
> suggests that air sacs  (and by inference the
> respiratory mechanism that we posit 
> for pterosaurs) were  present in one of the most basal
> of all known pterosaurs 
> and in at least one  Triassic  taxon.


This could mean that axial air sacs (and the associated flow-through 
respiratory system) are primitive for pterosaurs, and therefore preceded the 
origin of flight.  Just like in birds.

Putative pneumatic openings (pleurocoels) in the cervicals have also been 
reported for derived suchians such as _Effigia_, _Shuvosaurus_ and 
_Sillosuchus_.  So perhaps the inception of this flow-through breathing system 
is associated with cursorial/bipedal locomotion - which would lend credence to 
the hypothesis that the ancestors of pterosaurs were cursorial bipeds (like 
_Scleromochlus_).

For argument's sake... is it conceivable that the respiratory system of 
pterosaurs and saurischians was not analogous, but homologous?  Yeah, I know 
this is an off-the-wall idea, because basal dinosauromorphs (at least, those 
for which the cervicals are preserved) and ornithischians show no evidence of 
this system (implying it would have been secondarily lost in these taxa).

I'm not going to suggest that pterosaurs are actually saurischians, because 
there's enough wacky ideas about pterosaur ancestry circulating already.  (Then 
again, the skull of _Raeticodactylus_ is spookily theropod-like...)

That's enough blather from me.  I'll shut up before I say something REALLY 
crazy.


Cheers

Tim