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Re: Carniadactylus paper and pterosaur ontogeny



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.


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

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