Re: A note on pterosaur nesting behavior

[Mike Habib <habib@jhmi.edu>]

On Jul 24, 2009, at 11:21 PM, David Peters wrote:

> Two words:
>
> desiccation
>
> ovoviviparity
>
>
> Mama carries the eggs until just about to hatch. Babies fly free  
> shortly thereafter. Very little down time where anything could get  
> to them.

It's an interesting scenario, but what's the evidence for it?   
Incidentally, ovoviviparous lizards and snakes tend to have very  
weakly calcified eggs; even more so than Grellet-Tinner suggest for  
pterosaur eggs based on preserved microstructure.  I also note that no  
pterosaurs have been recovered with embryos inside (as has occurred  
for mosasaurs and ichthyosaurs), but we do find a number of cases of  
pterosaur eggs preserved without bits of mom.  If they were retained  
for pseudo-livebirth, we might expect a different pattern.

> This scenario cannot happen with archosaurs. Bottom line. It's not  
> in their gene pool.

Are we certain of this?  I'm skeptical of "can't get there from here"  
arguments.  If it is correct, then there is still the issue that we  
need evidence for ovoviviparity, first.  Not sure what you were trying  
to indicate with the comment about desiccation.  Living diapsids with  
weakly calcified eggs combat desiccation through burial - so the  
Grellet-Tinner et al. hypothesis would actually deal with that  
problem, as it is.

> Megapodes have long incubation times.
> Birds with short incubation times don't fly immediately after  
> hatching.

As a general rule of thumb, this is true (though not a hard and fast  
rule).  Either way, we don't know anything about incubation times for  
pterosaurs.  I suppose you're arguing that if they were superprecocial  
then it is likely that pterosaurs had long incubation times.  It's not  
a bad concept, though I have no idea how'd we would confirm or refute  
it.  Supposing that we did, though, it really does not speak to the  
egg burial issue, anyway, because incubation times among species that  
bury eggs vary enormously.  Some are very long indeed (200+ days for  
some turtles, for example).

--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