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Re: A note on pterosaur nesting behavior
On Jul 24, 2009, at 11:21 PM, David Peters wrote:
Mama carries the eggs until just about to hatch. Babies fly free
shortly thereafter. Very little down time where anything could get
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
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).
Michael Habib, M.S.
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205