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Re: Carniadactylus paper and pterosaur ontogeny
On Aug 1, 2009, at 3:35 PM, Mike Habib wrote:
David Peters wrote:
None of the embryos discovered are geometrically similar to the
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
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.
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205