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Re: A note on pterosaur nesting behavior

On Jul 24, 2009, at 1:59 PM, David Peters wrote:

Bats that dig? Not aware of that. Even so, the key word here is "in" as in tunneling to the surface vs. "on".

Mystacinus roots around pretty vigorously in leaf litter and soil. They have some limited digging ability. I wouldn't consider them fossorial by any means, but then again, exceptional digging ability is not required for burying eggs. To return to the original point, the presence of membrane wings is not as limiting with regards to terrestrial locomotion and rigor as it might seem at first. Especially given that pterosaur wings were likely more resilient than bat wings.

This could be the case, but why do you think that need be true?

Mike, I'm arguing AGAINST the burial. I'm arguing that it need NOT be true. All present pterosaur eggs are singletons. IF they were intentionally buried, then these three, all distinct and widely separated taxa, were buried alone. That's a lot of work for one egg. Modern analogies? I can't think of any.

Geckos do so, actually. But aside from that, your counter-evidence seems rather circumstantial to me. The authors made a morphology/ physiology argument for the likelihood of egg burial. I'm not saying it's a slam-dunk case, but if we're going to challenge the conclusion, then I think counter-evidence of a physio-structural nature is required.

Life history variables are often quite plastic;

Insert "over-generalization"  Let's stay specific.

It was general, but relevant: egg laying strategies are plastic in both archosaurs and lepidosaurs. Therefore, I would consider phylogenetic brackets for egg-laying behavior to be weaker than some other potential brackets; that's all.

I would hypothesize
that a short incubation time would be possible for many potential
phylogenetic positions.  Some birds have quite short incubation

And do they hatch ready to fly? No.

Megapodes get darn close. In fact, they get close enough that purely osteological remains of a fossil megapode chick would appear borderline flighted - it is conceivable that hatchling pterosaurs were also not quite able to fly at birth, but did so within short order, as in megapodes. There's really no way to test for the difference, so we're left with the conclusion that pterosaurs flew very early; it may or may not have been immediately.

Lepidosaurs take it even further, of course, with ovi-
viviparity and the like, but I would argue that the possible
incubation and nesting parameters has more to do with egg structure
and physiology than phylogenetic position (except to the the extent
that egg morphology happens to be phylogenetically constrained - which
is rather complicated).

Exactly my point. Egg structure is lepidosaurian. Therefore look in that direction for answers.

The egg structure is indeed very lepidosaurian. This could be homology or homoplasy, depending on which phylogenetic reconstruction one trusts. Either way, the eggs were structurally similar, it would appear, to those of living lepidosaurs that bury their eggs. Therefore, it is a reasonable conclusion that pterosaurs may have done the same, unless alternative structural evidence can be brought to bear (for example, if it turns out that the same details of egg morphology typify another life history strategy among living diapsids). Looking to lepidosaurs for answers, we find that the most robust conclusion, if the authors have done their analysis correctly, is egg burial. Personally, I don't find this very surprising, as egg burial is awfully common in living diapsids: nearly all crocodilians, several birds, and most lepidosaurs. Even in cases where a natural cavity (like a tree cavity) is utilized, the eggs are often buried inside the cavity.



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