Re: Carniadactylus paper and pterosaur ontogeny

[David Peters <davidrpeters@charter.net>]

On Aug 1, 2009, at 3:35 PM, Mike Habib wrote:

> David Peters wrote:
>
> > > None of the embryos discovered are geometrically similar to the  
> > > adults.
> >
> > Not true. Trace and reconstruct the bones. Then get back to me.  
> > We'll compare notes.
>
> I've done one better: measuring the original specimens, there are  
> notable deviations from isometry.  For example, the small  
> Santanadactylus at the AMNH is not geometrically similar to larger  
> ones, though it's close in some dimensions.  Same for Quetz.  Also  
> true of Anurognathus.

Then they are without a doubt distinct taxa. All big pterosaurs derive  
from small ones. And many small ones derive from large ones. Bennett  
and Jouve thought Ctenochasma added teeth via ontogeny forgetting that  
every other known pterosaur, including the ancestral lineage of  
Ctenochasma, has fewer teeth.
> > > It's also worth noting that for pterosaurs to be flighted at small  
> > > size and retain flight ability through growth, they cannot grow  
> > > isometrically.
> >
> > 1. Only Unwin said they were flighted at hatching.
> >
> > 2.Your statement is not backed up by the literature. Please share.
>
> It just comes from basic biomechanics (which I have checked against  
> bone strength calculations, using my own dimensions data and those  
> from the literature) - if you scale the hatchlings up isometrically  
> you end up with a wing spar that cannot handle flight loads.

Send your reconstructions. I should also ask, which hatchlings? Send  
species numbers. We may thinking of different hatchlings. The only  
ones I am aware of are Pterodaustro hatchlings.

> Same pattern appears with making comparisons among species - as body  
> size increases, there is an allometric change in wing spar dimensions.

That may be so. But the differences are phylogenetic as I can show you.

> In both cases, the trend is not at all unexpected, because the small  
> species and/or juveniles would need to be exceptionally "overbuilt"  
> for isometric growth to result in a viable adult. As it is, they  
> appear to have flown at a higher safety factor than the adults, but  
> not by the margin that would exist under isometric growth.

Let's check this out. Species numbers for a start.

David


> Cheers,
>
> --Mike
>
>
> Michael Habib, M.S.
> PhD. Candidate
> Center for Functional Anatomy and Evolution
> Johns Hopkins School of Medicine
> 1830 E. Monument Street
> Baltimore, MD 21205
> (443) 280-0181
> habib@jhmi.edu